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diff --git a/41135.txt b/41135.txt deleted file mode 100644 index 17668a2..0000000 --- a/41135.txt +++ /dev/null @@ -1,8547 +0,0 @@ -The Project Gutenberg EBook of The Theory and Practice of Model Aeroplaning, by -V. E. Johnson - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org/license - - -Title: The Theory and Practice of Model Aeroplaning - -Author: V. E. Johnson - -Release Date: October 21, 2012 [EBook #41135] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK THE THEORY AND PRACTICE *** - - - - -Produced by Chris Curnow, Mark Young and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - - - - -[Illustration: THE MOST IMPORTANT "TOOL" IN THE BUILDING OF MODEL -AEROPLANES. - -[_Illustration by permission from_ MESSRS. A. GALLENKAMP & CO'S. -CHEMICAL CATALOGUE.]] - - - - - THE THEORY AND PRACTICE - OF - MODEL AEROPLANING - - BY - V.E. JOHNSON, M.A. - - AUTHOR OF - 'THE BEST SHAPE FOR AN AIRSHIP,' 'SOARING FLIGHT,' - 'HOW TO ADVANCE THE SCIENCE OF AERONAUTICS,' - 'HOW TO BUILD A MODEL AEROPLANE,' ETC. - - "Model Aeroplaning is an Art in itself" - - [Illustration] - - London - E. & F.N. SPON, LTD., 57 HAYMARKET - - New York - SPON & CHAMBERLAIN, 123 LIBERTY STREET - - 1910 - - - - -PREFACE - - -The object of this little book is not to describe how to construct -some particular kind of aeroplane; this has been done elsewhere: but -to narrate in plain language the general practice and principles of -model aeroplaning. - -There is a _science_ of model aeroplaning--just as there is a science -of model yachting and model steam and electric traction, and an -endeavour is made in the following pages to do in some measure for -model aeroplanes what has already been done for model yachts and -locomotives. To achieve the best results, theory and practice must go -hand in hand. - -From a series of carefully conducted experiments empirical formulae can -be obtained which, combined later with mathematical induction and -deduction, may lead, not only to a more accurate and generalized law -than that contained in the empirical formula, but to valuable -deductions of a totally new type, embodying some general law hitherto -quite unknown by experimentalists, which in its turn may serve as a -foundation or stepping stone for suggesting other experiments and -empirical formulae which may be of especial importance, to be treated -in _their_ turn like their predecessor. By "especial importance," I -mean not only to "model," but "Aeroplaning" generally. - -As to the value of experiments on or with models with respect to -full-sized machines, fifteen years ago I held the opinion that they -were a very doubtful factor. I have since considerably modified that -view, and now consider that experiments with models--if properly -carried out, and given due, not _undue_, weight--both can and will be -of as much use to the science of Aeronautics as they have already -proved themselves to be in that of marine engineering. - -The subject of model propellers and motors has been somewhat fully -dealt with, as but little has been published (in book form, at any -rate) on these all-important departments. On similar grounds the -reasons why and how a model aeroplane flies have been practically -omitted, because these have been dealt with more or less in every book -on heavier-than-air machines. - -Great care has been exercised in the selection of matter, and in the -various facts stated herein; in most cases I have personally verified -them; great pains have also been exercised to exclude not only -misleading, but also doubtful matter. I have no personal axe to grind -whatever, nor am I connected either directly or indirectly with any -firm of aeroplane builders, model or otherwise. - -The statements contained in these pages are absolutely free from bias -of any kind, and for them I am prepared to accept full responsibility. - -I have to thank Messrs. A.W. GAMAGE (Holborn) for the use of various -model parts for testing purposes, and also for the use of various -electros from their modern Aviation Catalogue; also Messrs. T.W.K. -CLARKE & CO., of Kingston-on-Thames. For the further use of electros, -and for permission to reproduce illustrations which have previously -appeared in their papers, I must express my acknowledgment and thanks -to the publishers of the "Model Engineer," "Flight," and the "Aero." -Corrections and suggestions of any kind will be gratefully received, -and duly acknowledged. - - V.E. JOHNSON. - - - - -CONTENTS - - - INTRODUCTION. - PAGE - - Sec.Sec. 1-5. The two classes of models--First requisite of a model - aeroplane. Sec. 6. An art in itself. Sec. 7. The leading principle 1 - - - CHAPTER I. - - THE QUESTION OF WEIGHT. - - Sec.Sec. 1-2. Its primary importance both in rubber and - power-driven models--Professor Langley's experiences. Sec. 3. - Theoretical aspect of the question. Sec. 4. Means whereby more - weight can be carried--How to obtain maximum strength with - minimum weight. Sec. 5. Heavy models versus light ones 4 - - - CHAPTER II. - - THE QUESTION OF RESISTANCE. - - Sec. 1. The chief function of a model in the medium in which it - travels. Sec. 2. Resistance considered as load percentage. Sec. 3. - How made up. Sec. 4. The shape of minimum resistance. Sec. 5. The - case of rubber-driven models. Sec. 6. The aerofoil - surface--Shape and material as affecting this question. Sec. 7. - Skin friction--Its coefficient. Sec. 8. Experimental proofs of - its existence and importance 7 - - - CHAPTER III. - - THE QUESTION OF BALANCE. - - Sec. 1. automatic stability essential in a flying model. Sec. 2. - theoretical researches on this question. Sec.Sec. 3-6. a brief - summary of the chief conclusions arrived at--remarks on and - deductions from the same--conditions for automatic stability. - Sec. 7. theory and practice--stringfellow--penaud--tatin--the - question of fins--clarke's models--some further - considerations. Sec. 8. longitudinal stability. Sec. 9. transverse - stability. Sec. 10. the dihedral angle. Sec. 11. different forms of - the latter. Sec. 12. the "upturned" tip. Sec. 13. the most - efficient section 13 - - - CHAPTER IV. - - THE MOTIVE POWER. - - SECTION I.--RUBBER MOTORS. - - Sec. 1. Some experiments with rubber cord. Sec. 2. Its extension - under various weights. Sec. 3. The laws of elongation - (stretching)--Permanent set. Sec. 4. Effects of elongation on - its volume. Sec. 5. "Stretched-twisted" rubber cord--Torque - experiments with rubber strands of varying length and number. - Sec. 6. Results plotted as graphs--Deductions--Various - relations--How to obtain the most efficient - results--Relations between the torque and the number of - strands, and between the length of the strands and their - number. Sec. 7. Analogy between rubber and "spring" - motors--Where it fails to hold. Sec. 8. Some further practical - deductions. Sec. 9. The number of revolutions that can be given - to rubber motors. Sec. 10. The maximum number of turns. Sec. 11. - "Lubricants" for rubber. Sec. 12. Action of copper upon rubber. - Sec. 12A. Action of water, etc. Sec. 12B. How to preserve rubber. - Sec. 13. To test rubber. Sec. 14. The shape of the section. Sec. 15. - Size of section. Sec. 16. Geared rubber motors. Sec. 17. The only - system worth consideration--Its practical difficulties. Sec. 18. - Its advantages 24 - - SECTION II.--OTHER FORMS OF MOTORS. - - Sec. 18A. _Spring motors_; their inferiority to rubber. Sec. 18B. - The most efficient form of spring motor. Sec. 18C. _Compressed - air motors_--A fascinating form of motor, "on paper." Sec. 18D. - The pneumatic drill--Application to a model aeroplane--Length - of possible flight. Sec. 18E. The pressure in motor-car tyres. - Sec. 19. Hargraves' compressed air models--The best results - compared with rubber motors. Sec. 20. The effect of heating the - air in its passage from the reservoir to the motor--The great - gain in efficiency thereby attained--Liquid air--Practical - drawbacks to the compressed-air motor. Sec. 21. Reducing - valves--Lowest working pressure. Sec. 22. The inferiority of - this motor compared with the steam engine. Sec. 22A. Tatin's - air-compressed motor. Sec. 23. _Steam engine_--Steam engine - model--Professor Langley's models--His experiment with - various forms of motive power--Conclusions arrived at. Sec. 24. - His steam engine models--Difficulties and failures--and final - success--The "boiler" the great difficulty--His model - described. Sec. 25. The use of spirit or some very volatile - hydrocarbon in the place of water. Sec. 26. Steam turbines. - Sec. 27. Relation between "difficulty in construction" and the - "size of the model." Sec. 28. Experiments in France. Sec. 29. - _Petrol motors._--But few successful models. Sec. 30. Limit to - size. Sec. 31. Stanger's successful model described and - illustrated. Sec. 32. One-cylinder petrol motors. Sec. 33. - _Electric motors_ 39 - - - CHAPTER V. - - PROPELLERS OR SCREWS. - - Sec. 1. The position of the propeller. Sec. 2. The number of - blades. Sec. 3. Fan _versus_ propeller. Sec. 4. The function of a - propeller. Sec. 5. The pitch. Sec. 6. Slip. Sec. 7. Thrust. Sec. 8. Pitch - coefficient (or ratio). Sec. 9. Diameter. Sec. 10. Theoretical - pitch. Sec. 11. Uniform pitch. Sec. 12. How to ascertain the pitch - of a propeller. Sec. 13. Hollow-faced blades. Sec. 14. Blade area. - Sec. 15. Rate of rotation. Sec. 16. Shrouding. Sec. 17. General - design. Sec. 18. The shape of the blades. Sec. 19. Their general - contour--Propeller design--How to design a propeller. Sec. 20. - Experiments with propellers--Havilland's design for - experiments--The author experiments on dynamic thrust and - model propellers generally. Sec. 21. Fabric-covered screws. - Sec. 22. Experiments with twin propellers. Sec. 23. The Fleming - Williams propeller. Sec. 24. Built-up _v._ twisted wooden - propellers 52 - - - CHAPTER VI. - - THE QUESTION OF SUSTENTATION. - THE CENTRE OF PRESSURE. - - Sec. 1. The centre of pressure--Automatic stability. Sec. 2. - Oscillations. Sec. 3. Arched surfaces and movements of the - centre of pressure--Reversal. Sec. 4. The centre of gravity and - the centre of pressure. Sec. 5. Camber. Sec. 6. Dipping front - edge--Camber--The angle of incidence and camber--Attitude of - the Wright machine. Sec. 7. The most efficient form of camber. - Sec. 8. The instability of a deeply cambered surface. Sec. 9. - Aspect ratio. Sec. 10. Constant or varying camber. Sec. 11. Centre - of pressure on arched surfaces 78 - - - CHAPTER VII. - - MATERIALS FOR AEROPLANE - CONSTRUCTION. - - Sec. 1. The choice strictly limited. Sec. 2. Bamboo. Sec. 3. - Ash--spruce-- whitewood--poplar. Sec. 4. Steel. Sec. 5. Umbrella - section steel. Sec. 6. Steel wire. Sec. 7. Silk. Sec. 8. Aluminium and - magnalium. Sec. 9. Alloys. Sec. 10. Sheet ebonite--Vulcanized - fibre--Sheet celluloid--Mica 86 - - - CHAPTER VIII. - - HINTS ON THE BUILDING OF MODEL - AEROPLANES. - - Sec. 1. The chief difficulty to overcome. Sec. 2. General - design--The principle of continuity. Sec. 3. Simple monoplane. - Sec. 4. Importance of soldering. Sec. 5. Things to avoid. Sec. 6. - Aerofoil of metal--wood--or fabric. Sec. 7. Shape of aerofoil. - Sec. 8. How to camber an aerocurve without ribs. Sec. 9. Flexible - joints. Sec. 10. Single surfaces. Sec. 11. The rod or tube carrying - the rubber motor. Sec. 12. Position of the rubber. Sec. 13. The - position of the centre of pressure. Sec. 14. Elevators and - tails. Sec. 15. Skids _versus_ wheels--Materials for skids. - Sec. 16. Shock absorbers, how to attach--Relation between the - "gap" and the "chord" 93 - - - CHAPTER IX. - - THE STEERING OF THE MODEL. - - Sec. 1. A problem of great difficulty--Effects of propeller - torque. Sec. 2. How obviated. Sec. 3. The two-propeller - solution--The reason why it is only a partial success. Sec. 4. - The _speed_ solution. Sec. 5. Vertical fins. Sec. 6. Balancing tips - or ailerons. Sec. 7. Weighting. Sec. 8. By means of transversely - canting the elevator. Sec. 9. The necessity for some form of - "keel" 105 - - - CHAPTER X. - - THE LAUNCHING OF THE MODEL. - - Sec. 1. The direction in which to launch them. Sec. 2. The - velocity--wooden aerofoils and fabric-covered - aerofoils--Poynter's launching apparatus. Sec. 3. The launching - of very light models. Sec. 4. Large size and power-driven - models. Sec. 5. Models designed to rise from the - ground--Paulhan's prize model. Sec. 6. The setting of the - elevator. Sec. 7. The most suitable propeller for this form of - model. Sec. 8. Professor Kress' method of launching. Sec. 9. How to - launch a twin screw model. Sec. 10. A prior revolution of the - propellers. Sec. 11. The best angle at which to launch a model 109 - - - CHAPTER XI. - - HELICOPTER MODELS. - - Sec. 1. Models quite easy to make. Sec. 2. Sir George Cayley's - helicopter model. Sec. 3. Phillips' successful power-driven - model. Sec. 4. Toy helicopters. Sec. 5. Incorrect and correct way - of arranging the propellers. Sec. 6. Fabric covered screws. Sec. 7. - A design to obviate weight. Sec. 8. The question of a fin or - keel. 113 - - - CHAPTER XII. - - EXPERIMENTAL RECORDS 116 - - - CHAPTER XIII. - - MODEL FLYING COMPETITIONS. - - Sec. 1. A few general details concerning such. Sec. 2. Aero Models - Association's classification, etc. Sec. 3. Various points to be - kept in mind when competing 119 - - - CHAPTER XIV. - - USEFUL NOTES, TABLES, FORMULAE, ETC. - - Sec. 1. Comparative velocities. Sec. 2. Conversions. Sec. 3. Areas of - various shaped surfaces. Sec. 4. French and English measures. - Sec. 5. Useful data. Sec. 6. Table of equivalent inclinations. Sec. 7. - Table of skin friction. Sec. 8. Table I. (metals). Sec. 9. Table - II. (wind pressures). Sec. 10. Wind pressure on various shaped - bodies. Sec. 11. Table III. (lift and drift) on a cambered - surface. Sec. 12. Table IV. (lift and drift)--On a plane - aerofoil--Deductions. Sec. 13. Table V. (timber). Sec. 14. Formula - connecting weight lifted and velocity. Sec. 15. Formula - connecting models of similar design but different weights. - Sec. 16. Formula connecting power and speed. Sec. 17. Propeller - thrust. Sec. 18. To determine experimentally the static thrust - of a propeller. Sec. 19. Horse-power and the number of - revolutions. Sec. 20. To compare one model with another. Sec. 21. - Work done by a clockwork spring motor. Sec. 22. To ascertain the - horse-power of a rubber motor. Sec. 23. Foot-pounds of energy in - a given weight of rubber--Experimental determination of. - Sec. 24. Theoretical length of flight. Sec. 25. To test different - motors. Sec. 26. Efficiency of a model. Sec. 27. Efficiency of - design. Sec. 28. Naphtha engines. Sec. 29. Horse-power and weight - of model petrol motors. Sec. 30. Formula for rating the same. - Sec. 30A. Relation between static thrust of propeller and total - weight of model. Sec. 31. How to find the height of an - inaccessible object (kite, balloon, etc.). Sec. 32. Formula for - I.H.P. of model steam engines 125 - - APPENDIX A. Some models which have won medals at open - competitions 143 - - - - -GLOSSARY OF TERMS USED IN MODEL AEROPLANING. - - -_Aeroplane._ A motor-driven flying machine which relies upon surfaces -for its support in the air. - -_Monoplane_ (single). An aeroplane with one pair of outstretched -wings. - -_Aerofoil._ These outstretched wings are often called aerofoil -surfaces. One pair of wings forming one aerofoil surface. - -_Monoplane_ (double). An aeroplane with two aerofoils, one behind the -other or two main planes, tandem-wise. - -_Biplane._ An aeroplane with two aerofoils, one below the other, or -having two main planes superposed. - -_Triplane._ An aeroplane having three such aerofoils or three such -main planes. - -_Multiplane._ Any such machine having more than three of the above. - -_Glider._ A motorless aeroplane. - -_Helicopter._ A flying machine in which propellers are employed to -raise the machine in the air by their own unaided efforts. - -_Dihedral Angle._ A dihedral angle is an angle made by two surfaces -that do not lie in the same plane, i.e. when the aerofoils are -arranged V-shaped. It is better, however, to somewhat extend this -definition, and not to consider it as necessary that the two surfaces -_do_ actually meet, but would do so if produced thus in figure. BA and -CD are still dihedrals, sometimes termed "upturned tips." - -[Illustration: Dihedrals.] - -_Span_ is the distance from tip to tip of the main supporting surface -measured transversely (across) the line of flight. - -_Camber_ (a slight arching or convexity upwards). This term denotes -that the aerofoil has such a curved transverse section. - -_Chord_ is the distance between the entering (or leading) edge of the -main supporting surface (aerofoil) and the trailing edge of the same; -also defined as the fore and aft dimension of the main planes measured -in a straight line between the leading and trailing edges. - - span - _Aspect Ratio_ is ----- - chord - -_Gap_ is the vertical distance between one aerofoil and the one which -is immediately above it. - -(The gap is usually made equal to the chord). - -_Angle of Incidence._ The angle of incidence is the angle made by the -chord with the line of flight. - -[Illustration: - - AB = chord. AB = cambered surface. - SP = line of flight. ASP = {alpha} = L of incidence.] - -_Width._ The width of an aerofoil is the distance from the front to -the rear edge, allowing for camber. - -_Length._ This term is usually applied to the machine as a whole, from -the front leading edge of elevator (or supports) to tip of tail. - -_Arched._ This term is usually applied to aerofoil surfaces which dip -downwards like the wings of a bird. The curve in this case being at -right angles to "camber." A surface can, of course, be both cambered -and arched. - -_Propeller._ A device for propelling or pushing an aeroplane forward -or for raising it vertically (lifting screw). - -_Tractor Screw._ A device for pulling the machine (used when the -propeller is placed in the front of the machine). - -_Keel._ A vertical plane or planes (usually termed "fins") arranged -longitudinally for the purposes of stability and steering. - -_Tail._ The plane, or group of planes, at the rear end of an -aeroplane for the purpose chiefly of giving longitudinal stability. In -such cases the tail is normally (approx.) horizontal, but not -unfrequently vertical tail-pieces are fitted as well for steering -(transversely) to the right or left, or the entire tail may be twisted -for the purpose of transverse stability (vide _Elevator_). Such -appendages are being used less and less with the idea of giving actual -support. - -_Rudder_ is the term used for the vertical plane, or planes, which are -used to steer the aeroplane sideways. - -_Warping._ The flexing or bending of an aerofoil out of its normal -shape. The rear edges near the tips of the aerofoil being dipped or -tilted respectively, in order to create a temporary difference in -their inclinations to the line of flight. Performed in conjunction -with rudder movements, to counteract the excessive action of the -latter. - -_Ailerons_ (also called "righting-tips," "balancing-planes," etc.). -Small aeroplanes in the vicinity of the tips of the main aerofoil for -the purpose of assisting in the maintenance of equilibrium or for -steering purposes either with or without the assistance of the rudder. - -_Elevator._ The plane, or planes, in front of the main aerofoil used -for the purpose of keeping the aeroplane on an even keel, or which -cause (by being tilted or dipped) the aeroplane to rise or fall (vide -_Tail_). - - - - -MODEL AEROPLANING - - - - -INTRODUCTION. - - -Sec. 1. Model Aeroplanes are primarily divided into two classes: first, -models intended before all else to be ones that shall _fly_; secondly, -_models_, using the word in its proper sense of full-sized machines. -Herein model aeroplanes differ from model yachts and model -locomotives. An extremely small model locomotive _built to scale_ will -still _work_, just as a very small yacht built to scale will _sail_; -but when you try to build a scale model of an "Antoinette" monoplane, -_including engine_, it cannot be made to fly unless the scale be a -very large one. If, for instance, you endeavoured to make a 1/10 scale -model, your model petrol motor would be compelled to have eight -cylinders, each 0.52 bore, and your magneto of such size as easily to -pass through a ring half an inch in diameter. Such a model could not -possibly work.[1] - - _Note._--Readers will find in the "Model Engineer" of June 16, - 1910, some really very fine working drawings of a prize-winning - Antoinette monoplane model. - -Sec. 2. Again, although the motor constitutes the _chief_, it is by no -means the sole difficulty in _scale_ model aeroplane building. To -reproduce to scale at _scale weight_, or indeed anything approaching it, -_all_ the _necessary_--in the case of a full-sized machine--framework is -not possible in a less than 1/5 scale. - -Sec. 3. Special difficulties occur in the case of any prototype taken. -For instance, in the case of model Bleriots it is extremely difficult -to get the centre of gravity sufficiently forward. - -Sec. 4. Scale models of actual flying machines _that will fly_ mean -models _at least_ 10 or 12 feet across, and every other dimension in -like proportion; and it must always be carefully borne in mind that -the smaller the scale the greater the difficulties, but not in the -same proportion--it would not be _twice_ as difficult to build a -1/4-in. scale model as a 1/2-in., but _four_, _five_ or _six_ times as -difficult. - -Sec. 5. Now, the _first_ requirement of a model aeroplane, or flying -machine, is that it shall FLY. - -As will be seen later on--unless the machine be of large size, 10 feet -and more spread--the only motor at our disposal is the motor of -twisted rubber strands, and this to be efficient requires to be long, -and is of practically uniform weight throughout; this alone alters the -entire _distribution of weight_ on the machine and makes: - -Sec. 6. "=Model Aeroplaning an Art in itself=," and as such we propose to -consider it in the following pages. - -We have said that the first requisite of a model aeroplane is that it -shall fly, but there is no necessity, nor is it indeed always to be -desired, that this should be its only one, unless it be built with the -express purpose of obtaining a record length of flight. For ordinary -flights and scientific study what is required is a machine in which -minute detail is of secondary importance, but which does along its -main lines "_approximate_ to the real thing." - -Sec. 7. Simplicity should be the first thing aimed at--simplicity means -efficiency, it means it in full-sized machines, still more does it -mean it in models--and this very question of simplicity brings us to -that most important question of all, namely, the question of _weight_. - -FOOTNOTE: - -[1] The smallest working steam engine that the writer has ever heard -of has a net weight of 4 grains. One hundred such engines would be -required to weigh one ounce. The bore being 0.03 in., and stroke 1/32 -of an inch, r.p.m. 6000 per min., h.p. developed 1/489000 ("Model -Engineer," July 7, 1910). When working it hums like a bee. - - - - -CHAPTER I. - -THE QUESTION OF WEIGHT. - - -Sec. 1. The following is an extract from a letter that appeared in the -correspondence columns of "The Aero."[2] - -"To give you some idea how slight a thing will make a model behave -badly, I fitted a skid to protect the propeller underneath the -aeroplane, and the result in retarding flight could be seen very -quickly, although the weight of the skid was almost nil.[3] To all -model makers who wish to make a success I would say, strip all that -useless and heavy chassis off, cut down the 'good, honest stick' that -you have for a backbone to half its thickness, stay it with wire if it -bends under the strain of the rubber, put light silk on the planes, -and use an aluminium[4] propeller. The result will surpass all -expectations." - -Sec. 2. The above refers, of course, to a rubber-motor driven model. Let -us turn to a steam-driven prototype. I take the best known example of -all, Professor Langley's famous model. Here is what the professor has -to say on the question[5]:-- - -"Every bit of the machinery had to be constructed with scientific -accuracy. It had to be tested again and again. The difficulty of -getting the machine light enough was such that every part of it had to -be remade several times. It would be in full working order when -something would give way, and this part would have to be strengthened. -This caused additional weight, and necessitated cutting off so much -weight from some other part of the machinery. At times the difficulty -seemed almost heartbreaking; but I went on, piece by piece and atom by -atom, until I at last succeeded in getting all the parts of the right -strength and proportion." - -How to obtain the maximum strength with the minimum of weight is one -of the, if not the most, difficult problems which the student has to -solve. - -Sec. 3. The theoretical reason why _weight_ is such an all-important item -in model aeroplaning, much more so than in the case of full-size -machines, is that, generally speaking, such models do not fly fast -enough to possess a high weight carrying capacity. If you increase the -area of the supporting surface you increase also the resistance, and -thereby diminish the speed, and are no better off than before. The -only way to increase the weight carrying capacity of a model is to -increase its speed. This point will be recurred to later on. One of -Mr. T.W.K. Clarke's well-known models, surface area 11/4 sq. ft., -weight 11/4 lb., is stated to have made a flight of 300 yards -carrying 6 oz. of lead. This works out approximately at 21 oz. per sq. -ft. - -The velocity (speed) is not stated, but some earlier models by the -same designer, weight 11/2 lb., supporting area 11/2 sq. ft., i.e., -at rate of 16 oz. per sq. ft., travelled at a rate of 37 ft. per -second, or 25 miles an hour. - -The velocity of the former, therefore, would certainly not be less -than 30 miles an hour. - -Sec. 4. Generally speaking, however, models do not travel at anything -like this velocity, or carry anything like this weight per sq. ft. - -An average assumption of 13 to 15 miles an hour does nor err on the -minimum side. Some very light fabric covered models have a speed of -less than even 10 miles an hour. Such, of course, cannot be termed -efficient models, and carry only about 3 oz. per sq. ft. Between these -two types--these two extremes--somewhere lies the "Ideal Model." - -The maximum of strength with the minimum of weight can be obtained -only:-- - -1. By a knowledge of materials. - -2. Of how to combine those materials in a most efficient and skilful -manner. - -3. By a constant use of the balance or a pair of scales, and noting -(in writing) the weight and result of every trial and every experiment -in the alteration and change of material used. WEIGH EVERYTHING. - -Sec. 5. The reader must not be misled by what has been said, and think -that a model must not weigh anything if it is to fly well. A heavy -model will fly much better against the wind than a light one, provided -that the former _will_ fly. To do this it must fly _fast_. To do this -again it must be well powered, and offer the minimum of resistance to -the medium through which it moves. This means its aerofoil -(supporting) surfaces must be of polished wood or metal. This point -brings us to the question of Resistance, which we will now consider. - -FOOTNOTES: - -[2] "Aero," May 3, 1910. - -[3] Part of this retardation was, of course, "increased resistance." - -[4] Personally I do not recommend aluminium.--V.E.J. - -[5] "Aeronautical Journal," January 1897, p. 7. - - - - -CHAPTER II. - -THE QUESTION OF RESISTANCE. - - -Sec. 1. It is, or should be, the function of an aeroplane--model or -otherwise--to pass through the medium in which it travels in such a -manner as to leave that medium in as motionless a state as possible, -since all motion of the surrounding air represents so much power -wasted. - -Every part of the machine should be so constructed as to move through -the air with the minimum of disturbance and resistance. - -Sec. 2. The resistance, considered as a percentage of the load itself, -that has to be overcome in moving a load from one place to another, -is, according to Mr. F.W. Lanchester, 121/2 per cent. in the case of -a flying machine, and 0.1 per cent. in the case of a cargo boat, and -of a solid tyre motor car 3 per cent., a locomotive 1 per cent. Four -times at least the resistance in the case of aerial locomotion has to -be overcome to that obtained from ordinary locomotion on land. The -above refer, of course, to full-sized machines; for a model the -resistance is probably nearer 14 or 15 per cent. - -Sec. 3. This resistance is made up of-- - - 1. Aerodynamic resistance. - 2. Head resistance. - 3. Skin-friction (surface resistance). - -The first results from the necessity of air supporting the model -during flight. - -The second is the resistance offered by the framework, wires, edges of -aerofoils, etc. - -The third, skin-friction or surface resistance, is very small at low -velocities, but increases as the square of the velocity. To reduce the -resistance which it sets up, all surfaces used should be as smooth as -possible. To reduce the second, contours of ichthyoid, or fish-like, -form should be used, so that the resultant stream-line flow of the -medium shall keep in touch with the surface of the body. - -Sec. 4. As long ago as 1894 a series of experiments were made by the -writer[6] to solve the following problem: given a certain length and -breadth, to find the shape which will offer the least resistance. The -experiments were made with a whirling table 40 ft. in diameter, which -could be rotated so that the extremity of the arm rotated up to a -speed of 45 miles an hour. The method of experimenting was as follows: -The bodies (diam. 4 in.) were balanced against one another at the -extremity of the arm, being so balanced that their motions forward and -backward were parallel. Provision was made for accurately balancing -the parallel scales on which the bodies were suspended without -altering the resistance offered by the apparatus to the air. Two -experiments at least (to avoid error) were made in each case, the -bodies being reversed in the second experiment, the top one being put -at the bottom, and _vice versa_. The conclusions arrived at were:-- - -For minimum (head) resistance a body should have-- - -1. Its greatest diameter two-fifths of its entire length from its -head. - -2. Its breadth and its depth in the proportion of four to three. - -3. Its length at least from five to nine times its greatest breadth -(nine being better than five). - -4. A very tapering form of stern, the actual stern only being of just -sufficient size to allow of the propeller shaft passing through. In -the case of twin propellers some slight modification of the stern -would be necessary. - -5. Every portion of the body in contact with the fluid to be made as -smooth as possible. - -6. A body of such shape gives at most only _one-twentieth_ the -resistance offered by a flat disk of similar maximum sectional area. - -_Results since fully confirmed._ - -[Illustration: FIG. 1.--SHAPE OF LEAST RESISTANCE.] - -The design in Fig. 2 is interesting, not only because of its probable -origin, but because of the shape of the body and arrangement of the -propellers; no rudder is shown, and the long steel vertical mast -extending both upwards and downwards through the centre would render -it suitable only for landing on water. - -Sec. 5. In the case of a rubber-driven model, there is no containing body -part, so to speak, a long thin stick, or tubular construction if -preferred, being all that is necessary. - -The long skein of elastic, vibrating as well as untwisting as it -travels with the machine through the air, offers some appreciable -resistance, and several experimenters have _enclosed_ it in a light -tube made of _very thin_ veneer wood rolled and glued, or paper even -may be used; such tubes can be made very light, and possess -considerable rigidity, especially longitudinally. If the model be a -biplane, then all the upright struts between the two aerofoils should -be given a shape, a vertical section of which is shown in Fig. 3. - -Sec. 6. In considering this question of resistance, the substance of -which the aerofoil surface is made plays a very important part, as -well as whether that surface be plane or curved. For some reason not -altogether easy to determine, fabric-covered planes offer -_considerably_ more resistance than wooden or metal ones. That they -should offer _more_ resistance is what common sense would lead one to -expect, but hardly to the extent met with in actual practice. - -[Illustration: FIG. 2.--DESIGN FOR AN AEROPLANE MODEL (POWER DRIVEN). - -This design is attributed to Professor Langley.] - -_Built up fabric-covered aeroplanes[7] gain in lightness, but lose in -resistance._ In the case of curved surfaces this difference is -considerably more; one reason, undoubtedly, is that in a built up -model surface there is nearly always a tendency to make this curvature -excessive, and much more than it should be. Having called attention to -this under the head of resistance, we will leave it now to recur to it -later when considering the aerofoil proper. - -[Illustration: FIG. 3.--HORIZONTAL SECTION OF VERTICAL STRUT -(ENLARGED.)] - -Sec. 7. Allusion has been made in this chapter to skin friction, but no -value given for its coefficient.[8] Lanchester's value for planes from -1/2 to 11/2 sq. ft. in area, moving about 20 to 30 ft. per second, is - - 0.009 to 0.015. - -Professor Zahm (Washington) gives 0.0026 lb. per sq. ft. at 25 ft. per -second, and at 37 ft. per second, 0.005, and the formula - - _f_ = 0.00000778_l_^{.93}_v_^{1.85} - -_f_ being the average friction in lb. per sq. in., _l_ the length in -feet, and _v_ the velocity in ft. per second. He also experimented -with various kinds of surfaces, some rough, some smooth, etc. - -His conclusion is:--"All even surfaces have approximately the same -coefficient of skin friction. Uneven surfaces have a greater -coefficient." All formulae on skin friction must at present be accepted -with reserve. - -Sec. 8. The following three experiments, however, clearly prove its -_existence_, and _that it has considerable effect_:-- - -1. A light, hollow celluloid ball, supported on a stream of air -projected upwards from a jet, rotates in one direction or the other as -the jet is inclined to the left or to the right. (F.W. Lanchester.) - -2. When a golf ball (which is rough) is hit so as to have considerable -underspin, its range is increased from 135 to 180 yards, due entirely -to the greater frictional resistance to the air on that side on which -the whirl and the progressive motion combine. (Prof. Tait.) - -3. By means of a (weak) bow a golf ball can be made to move point -blank to a mark 30 yards off, provided the string be so adjusted as to -give a good underspin; adjust the string to the centre of the ball, -instead of catching it below, and the drop will be about 8 ft. (Prof. -Tait.) - -FOOTNOTES: - -[6] _Vide_ "Invention," Feb. 15, 22, and 29, 1896. - -[7] Really aerofoils, since we are considering only the supporting -surface. - -[8] I.e., to express it as a decimal fraction of the resistance, -encountered by the same plane when moving "face" instead of "edge" on. - - - - -CHAPTER III. - -THE QUESTION OF BALANCE. - - -Sec. 1. It is perfectly obvious for successful flight that any model -flying machine (in the absence of a pilot) must possess a high degree -of automatic stability. The model must be so constructed as to be -naturally stable, _in the medium through which it is proposed to drive -it_. The last remark is of the greatest importance, as we shall see. - -Sec. 2. In connexion with this same question of automatic stability, the -question must be considered from the theoretical as well as from the -practical side, and the labours and researches of such men as -Professors Brian and Chatley, F.W. Lanchester, Captain Ferber, -Mouillard and others must receive due weight. Their work cannot yet be -fully assessed, but already results have been arrived at far more -important than are generally supposed. - -The following are a few of the results arrived at from theoretical -considerations; they cannot be too widely known. - -(A) Surfaces concave on the under side are not stable unless some form -of balancing device (such as a tail, etc.) is used. - -(B) If an aeroplane is in equilibrium and moving uniformly, it is -necessary for stability that it shall tend towards a condition of -equilibrium. - -(C) In the case of "oscillations" it is absolutely necessary for -stability that these oscillations shall decrease in amplitude, in -other words, be damped out. - -(D) In aeroplanes in which the dihedral angle is excessive or the -centre of gravity very low down, a dangerous pitching motion is quite -likely to be set up. [Analogy in shipbuilding--an increase in the -metacentre height while increasing the stability in a statical sense -causes the ship to do the same.] - -(E) The propeller shaft should pass through the centre of gravity of -the machine. - -(F) The front planes should be at a greater angle of inclination than -the rear ones. - -(G) The longitudinal stability of an aeroplane grows much less when -the aeroplane commences to rise, a monoplane becoming unstable when -the angle of ascent is greater than the inclination of the main -aerofoil to the horizon. - -(H) Head resistance increases stability. - -(I) Three planes are more stable than two. [Elevator--main -aerofoil--horizontal rudder behind.] - -(J) When an aeroplane is gliding (downwards) stability is greater than -in horizontal flight. - -(K) A large moment of inertia is inimical (opposed) to stability. - -(M) Aeroplanes (naturally) stable up to a certain velocity (speed) may -become unstable when moving beyond that speed. [Possible explanation. -The motion of the air over the edges of the aerofoil becomes -turbulent, and the form of the stream lines suddenly changes. -Aeroplane also probably becomes deformed.] - -(N) In a balanced glider for stability a separate surface at a -negative angle to the line of flight is essential. [Compare F.] - -(O) A keel surface should be situated well above and behind the centre -of gravity. - -(P) An aeroplane is a conservative system, and stability is greatest -when the kinetic energy is a maximum. [Illustration, the pendulum.] - -Sec. 3. Referring to A. Models with a plane or flat surface are not -unstable, and will fly well without a tail; such a machine is called a -simple monoplane. - -[Illustration: FIG. 4.--ONE OF MR. BURGE WEBB'S SIMPLE MONOPLANES. - -Showing balance weight A (movable), and also his winding-up gear--a -very handy device.] - - -Sec. 4. Referring to D. Many model builders make this mistake, i.e., the -mistake of getting as low a centre of gravity as possible under the -quite erroneous idea that they are thereby increasing the stability of -the machine. Theoretically the _centre of gravity should be the centre -of head resistance, as also the centre of pressure_. - -In practice some prefer to put the centre of gravity in models -_slightly_ above the centre of head resistance, the reason being that, -generally speaking, wind gusts have a "lifting" action on the machine. -It must be carefully borne in mind, however, that if the centre of -wind pressure on the aerofoil surface and the centre of gravity do not -coincide, no matter at what point propulsive action be applied, it can -be proved by quite elementary mechanics that such an arrangement, -known as "acentric," produces a couple tending to upset the machine. - -This action is the probable cause of many failures. - -[Illustration: FIG. 5.--THE STRINGFELLOW MODEL MONOPLANE OF 1848.] - -Sec. 5. Referring to E. If the propulsive action does not pass through -the centre of gravity the system again becomes "acentric." Even -supposing condition D fulfilled, and we arrive at the following most -important result, viz., that for stability:-- - -THE CENTRES OF GRAVITY, OF PRESSURE, OF HEAD RESISTANCE, SHOULD BE -COINCIDENT, AND THE PROPULSIVE ACTION OF THE PROPELLER PASS THROUGH -THIS SAME POINT. - -[Illustration: FIG. 6.--THE STRINGFELLOW MODEL TRIPLANE OF 1868.] - -Sec. 6. Referring to F and N--the problem of longitudinal stability. -There is one absolutely essential feature not mentioned in F or N, and -that is for automatic longitudinal stability _the two surfaces, the -aerofoil proper and the balancer_ (elevator or tail, or both), _must -be separated by some considerable distance, a distance not less than -four times the width of the main aerofoil_.[9] More is better. - -[Illustration: FIG. 7. _PENAUD 1871_] - -Sec. 7. With one exception (Penaud) early experimenters with model -aeroplanes had not grasped this all-important fact, and their models -would not fly, only make a series of jumps, because they failed to -balance longitudinally. In Stringfellow's and Tatin's models the main -aerofoil and balancer (tail) are practically contiguous. - -Penaud in his rubber-motored models appears to have fully realised -this (_vide_ Fig. 7), and also the necessity for using long strands of -rubber. Some of his models flew 150 ft., and showed considerable -stability. - -[Illustration: FIG. 8.--TATIN'S AEROPLANE (1879). - -Surface 0.7 sq. metres, total weight 1.75 kilogrammes, velocity of -sustentation 8 metres a second. Motor, compressed air (for description -see Sec. 23, ch. iv). Revolved round and round a track tethered to a post -at the centre. In one of its jumps it cleared the head of a -spectator.] - -With three surfaces one would set the elevator at a slight plus angle, -main aerofoil horizontal (neither positive nor negative), and the tail -at a corresponding negative angle to the positive one of the elevator. - -Referring to O.[10] One would naturally be inclined to put a keel -surface--or, in other words, vertical fins--beneath the centre of -gravity, but D shows us this may have the opposite effect to what we -might expect. - -In full-sized machines, those in which the distance between the main -aerofoil and balancers is considerable (like the Farman) show -considerable automatic longitudinal stability, and those in which it -is short (like the Wright) are purposely made so with the idea of -doing away with it, and rendering the machine quicker and more -sensitive to personal control. In the case of the Stringfellow and -Tatin models we have the extreme case--practically the bird entirely -volitional and personal--which is the opposite in every way to what we -desire on a model under no personal or volitional control at all. - -[Illustration: FIG. 9.--CLARK'S MODEL FLYER. - -Main aerofoil set at a slight negative angle. Dihedral angles on both -aerofoils.] - -The theoretical conditions stated in F and N are fully borne out in -practice. - -And since a curved aerofoil even when set at a _slight_ negative -angle has still considerable powers of sustentation, it is possible to -give the main aerofoil a slight negative angle and the elevator a -slight positive one. This fact is of the greatest importance, since it -enables us to counteract the effect of the travel of the "centre of -pressure."[11] - -[Illustration: FIG. 10.--LARGE MODEL MONOPLANE. - -Designed and constructed by the author, with vertical fin (no dihedral -angle). With a larger and more efficient propeller than the one here -shown some excellent flights were obtained. Constructed of bamboo and -nainsook. Stayed with steel wire.] - -Sec. 8. Referring to I. This, again, is of primary importance in -longitudinal stability. The Farman machine has three such -planes--elevator, main aerofoil, tail the Wright originally had _not_, -but is now being fitted with a tail, and experiments on the -Short-Wright biplane have quite proved its stabilising efficiency. - -The three plane (triple monoplane) in the case of models has been -tried, but possesses no advantage so far over the double monoplane -type. The writer has made many experiments with vertical fins, and has -found the machine very stable, even when the fin or vertical keel is -placed some distance above the centre of gravity. - -Sec. 9. The question of transverse (side to side) stability at once -brings us to the question of the dihedral angle, practically similar -in its action to a flat plane with vertical fins. - -[Illustration: FIG. 11.--SIR GEORGE CAYLEY'S FLYING MACHINE. - -Eight feathers, two corks, a thin rod, a piece of whalebone, and a -piece of thread.] - -Sec. 10. The setting up of the front surface at an angle to the rear, or -the setting of these at corresponding compensatory angles already -dealt with, is nothing more nor less than the principle of the -dihedral angle for longitudinal stability. - -[Illustration: FIG. 12.--VARIOUS FORMS OF DIHEDRALS.] - -As early as the commencement of last century Sir George Cayley (a -man more than a hundred years ahead of his times) was the first to -point out that two planes at a dihedral angle constitute a basis of -stability. For, on the machine heeling over, the side which is -required to rise gains resistance by its new position, and that which -is required to sink loses it. - -Sec. 11. The dihedral angle principle may take many forms. - -As in Fig. 12 _a_ is a monoplane, the rest biplanes. The angles and -curves are somewhat exaggerated. It is quite a mistake to make the -angle excessive, the "lift" being thereby diminished. A few degrees -should suffice. - -Whilst it is evident enough that transverse stability is promoted by -making the sustaining surface trough-shaped, it is not so evident what -form of cross section is the most efficient for sustentation and -equilibrium combined. - -[Illustration: FIG. 13.] - -It is evident that the righting moment of a unit of surface of an -aeroplane is greater at the outer edge than elsewhere, owing to the -greater lever arm. - -Sec. 12. The "upturned tip" dihedral certainly appears to have the -advantage. - -_The outer edges of the aerofoil then should be turned upward for the -purpose of transverse stability, while the inner surface should remain -flat or concave for greater support._ - -Sec. 13. The exact most favourable outline of transverse section for -stability, steadiness and buoyancy has not yet been found; but the -writer has found the section given in Fig. 13, a very efficient one. - -FOOTNOTES: - -[9] If the width be not uniform the mean width should be taken. - -[10] This refers, of course, to transverse stability. - -[11] See ch. vi. - - - - -CHAPTER IV. - -THE MOTIVE POWER. - - -SECTION I.--RUBBER MOTORS. - -Sec. 1. Some forty years have elapsed since Penaud first used elastic -(rubber) for model aeroplanes, and during that time no better -substitute (in spite of innumerable experiments) has been found. Nor -for the smaller and lighter class of models is there any likelihood of -rubber being displaced. Such being the case, a brief account of some -experiments on this substance as a motive power for the same may not -be without interest. The word _elastic_ (in science) denotes: _the -tendency which a body has when distorted to return to its original -shape_. Glass and ivory (within certain limits) are two of the most -elastic bodies known. But the limits within which most bodies can be -distorted (twisted or stretched, or both) without either fracture or a -LARGE _permanent_ alteration of shape is very small. Not so rubber--it -far surpasses in this respect even steel springs. - -Sec. 2. Let us take a piece of elastic (rubber) cord, and stretch it with -known weights and observe carefully what happens. We shall find that, -first of all: _the extension is proportional to the weight -suspended_--but soon we have an _increasing_ increase of extension. In -one experiment made by the writer, when the weights were removed the -rubber cord remained 1/8 of an inch longer, and at the end of an hour -recovered itself to the extent of 1/16, remaining finally permanently -1/16 of an inch longer. Length of elastic cord used in this experiment -8-1/8 inches, 3/16 of an inch thick. Suspended weights, 1 oz. up to 64 -oz. Extension from 1/4 inch up to 24-5/8 inches. Graph drawn in Fig. -14, No. B abscissae extension in eighths of an inch, ordinates weights -in ounces. So long as the graph is a straight line it shows the -extension is proportional to the suspended weight; afterwards in -excess. - -[Illustration: FIG. 14.--WEIGHT AND EXTENSION. - -B, rubber 3/16 in. thick; C, 2/16 in. thick; D, 1/16 in. thick. A, -theoretical line if extension were proportional to weight.] - -In this experiment we have been able to stretch (distort) a piece of -rubber to more than three times its original length, and afterwards it -finally returns to almost its original length: not only so, a piece of -rubber cord can be stretched to eight or nine times its original -length without fracture. Herein lies its supreme advantage over steel -or other springs. Weight for weight more energy can be got or more -work be done by stretched (or twisted, or, to speak more correctly, by -stretched-twisted) rubber cord than from any form of steel spring.[12] -It is true it is stretched--twisted--far beyond what is called the -"elastic limit," and its efficiency falls off, but with care not -nearly so quickly as is commonly supposed, but in spite of this and -other drawbacks its advantages far more than counterbalance these. - -Sec. 3. Experimenting with cords of varying thickness we find that: _the -extension is inversely proportional to the thickness_. If we leave a -weight hanging on a piece of rubber cord (stretched, of course, beyond -its "elastic limit") we find that: _the cord continues to elongate as -long as the weight is left on_. For example: a 1 lb. weight hung on a -piece of rubber cord, 8-1/8 inches long and 1/8 of an inch thick, -stretched it--at first--61/4 inches; after two minutes this had -increased to 6-5/8 (3/8 of an inch more). One hour later 1/8 of an -inch more, and sixteen hours later 1/8 of an inch more, i.e. a sixteen -hours' hang produced an additional extension of 3/4 of an inch. On a -thinner cord (half the thickness) same weight produced _an additional -extension_ (_after_ 14 _hours_) _of _10-3/8 _in_. - -N.B.--An elastic cord or spring balance should never have a weight -left permanently on it--or be subjected to a distorting force for a -longer time than necessary, or it will take a "permanent set," and not -return to even approximately its original length or form. - -In a rubber cord the extension is _directly proportional to the -length_ as well as _inversely proportional to the thickness and to the -weight suspended_--true only within the limits of elasticity. - -[Illustration: FIG. 15.--EXTENSION AND INCREASE IN VOLUME.] - -Sec. 4. =When a Rubber Cord is stretched there is an Increase of -Volume.=--On stretching a piece of rubber cord to _twice_ its -original (natural) length, we should perhaps expect to find that the -string would only be _half_ as thick, as would be the case if the -volume remained the same. Performing the experiment, and measuring the -cord as accurately as possible with a micrometer, measuring to the -one-thousandth of an inch, we at once perceive that this is not the -case, being about _two-thirds_ of its former volume. - -Sec. 5. In the case of rubber cord used for a motive power on model -aeroplanes, the rubber is _both_ twisted and stretched, but chiefly -the latter. - -Thirty-six strands of rubber, weight about 56 grammes, at 150 turns -give a torque of 4 oz. on a 5-in. arm, but an end thrust, or end pull, -of about 31/2 lb. (Ball bearings, or some such device, can be used to -obviate this end thrust when desirable.) A series of experiments -undertaken by the writer on the torque produced by twisted rubber -strands, varying in number, length, etc., and afterwards carefully -plotted out in graph form, have led to some very interesting and -instructive results. Ball bearings were used, and the torque, measured -in eighths of an ounce, was taken (in each case) from an arm 5 in. in -length. - -The following are the principal results arrived at. For graphs, see -Fig. 16. - -Sec. 6. A. Increasing the number of (rubber) strands by _one-half_ -(length and thickness of rubber remaining constant) increases the -torque (unwinding tendency) _twofold_, i.e., doubles the motive power. - -B. _Doubling_ the number of strands increases the torque _more than -three times_--about 3-1/3 times, 3 times up to 100 turns, 31/2 times -from 100 to 250 turns. - -C. _Trebling_ the number of strands increases the torque at least -_seven times_. - -The increased _size_ of the coils, and thereby _increased_ extension, -explains this result. As we increase the number of strands, the -_number_ of twists or turns that can be given it becomes less. - -D. _Doubling_ the number of strands (length, etc., remaining -constant) _diminishes_ the number of turns by _one-third to -one-half_. (In few strands one-third, in 30 and over one-half.) - -[Illustration: FIG. 16.--TORQUE GRAPHS OF RUBBER MOTORS. - - Abscissae = Turns. Ordinates = Torque measured in 1/16 of an oz. - Length of arm, 5 in. - - A. 38 strands of new rubber, 2 ft. 6 in. long; 58 grammes weight. - B. 36 strands, 2 ft. 6 in. long; end thrust at 150 turns, 31/2 lb. - C. 32 strands, 2 ft. 6 in. long. - D. 24 " " " - E. 18 " " " weight 28 grammes. - F. 12 " 1 ft. 3 in. long - G. 12 " 2 ft. 6 in. long.] - -E. If we halve the length of the rubber strands, keeping the _number_ -of strands the same, the torque is but slightly increased for the -first 100 turns; at 240 turns it is double. But the greater number of -turns--in ratio of about 2:1--that can be given the longer strand much -more than compensates for this. - -F. No arrangement of the strands, _per se_, gets more energy (more -motive power) out of them than any other, but there are special -reasons for making the strands-- - -G. As long and as few in number as possible. - -1. More turns can be given it. - -2. It gives a far more even torque. Twelve strands 2 ft. 6 in. long -give practically a line of small constant angle. Thirty-six strands -same length a much steeper angle, with considerable variations. - -A very good result, which the writer has verified in practice, paying -due regard to _both_ propeller and motor, is to make-- - -H. _The length of the rubber strands twice[13] in feet the number of -the strands in inches_,[14] e.g., if the number of strands is 12 their -length should be 2 ft., if 18, 3 ft., and so on. - -Sec. 7. Experiments with 32 to 38 strands 2 ft. 6 in. long give a torque -curve almost precisely similar to that obtained from experiments made -with flat spiral steel springs, similar to those used in watches and -clocks; and, as we know, the torque given by such springs is very -uneven, and has to be equalised by use of a fusee, or some such -device. In the case of such springs it must not be forgotten that the -turning moment (unwinding tendency) is NOT proportional to the amount -of winding up, this being true only in the "balance" springs of -watches, etc., where _both_ ends of the spring are rigidly fastened. - -In the case of SPRING MOTORS.[15] - -I. The turning moment (unwinding tendency) is proportional to the -difference between the angle of winding and yielding, proportional to -the moment of inertia of its section, i.e., to the breadth and the -cube of its thickness, also proportional to the modulus of elasticity -of the substance used, and inversely proportional to the length of the -strip. - -Sec. 8. Referring back to A, B, C, there are one or two practical -deductions which should be carefully noted. - -Supposing we have a model with one propeller and 36 strands of -elastic. If we decide to fit it with twin screws, then, other reasons -apart, we shall require two sets of strands of more than 18 in number -each to have the same motive power (27 if the same torque be -required).[16] This is an important point, and one not to be lost -sight of when thinking of using two propellers. - -Experiments on-- - -Sec.9. =The Number of Revolutions= (turns) =that can be given to Rubber -Motors= led to interesting results, e.g., the number of turns to -produce a double knot in the cord from end to end were, in the case of -rubber, one yard long:-- - - No. of Strands. No. of Turns. No. of Strands. No. of Turns. - 4 440 16 200 - 8 310 28 170 - 12 250 - -It will be at once noticed that the greater the number of rubber -strands used in a given length, the fewer turns will it stand in -proportion. For instance, 8 strands double knot at 310, and 4 at 440 -(and not at 620), 16 at 200, and 8 at 310 (and not 400), and so on. -The reason, of course, is the more the strands the greater the -distance they have to travel round themselves. - -Sec. 10. =The Maximum Number of Turns.=--As to the maximum number of -permissible turns, rubber has rupture stress of 330 lb. per sq. in., -_but a very high permissible stress_, as much as 80 per cent. The -resilience (power of recovery after distortion) in tension of rubber -is in considerable excess of any other substance, silk being the only -other substance which at all approaches it in this respect, the ratio -being about 11 : 9. The resilience of steel spiral spring is very -slight in comparison. - -A rubber motor in which the double knot is not exceeded by more than -100 turns (rubber one yard in length) should last a good time. When -trying for a record flight, using new elastic, as many as even 500 or -600 or even more turns have been given in the case of 32-36 strands a -yard in length; but such a severe strain soon spoils the rubber. - -Sec. 11. =On the Use of "Lubricants."=--One of the drawbacks to rubber is -that if it be excessively strained it soon begins to break up. One of -the chief causes of this is that the strands stick together--they -should always be carefully separated, if necessary, after a -flight--and an undue strain is thereby cast on certain parts. Apart -also from this the various strands are not subject to the same -tension. It has been suggested that if some means could be devised to -prevent this, and allow the strands to slip over one another, a -considerable increase of power might result. It must, however, be -carefully borne in mind that anything of an oily or greasy nature has -an injurious effect on the rubber, and must be avoided at all costs. -Benzol, petroleum, ether, volatile oils, turpentine, chloroform, -naphtha, vaseline, soap, and all kinds of oil must be carefully -avoided, as they soften the rubber, and reduce it more or less to the -consistence of a sticky mass. The only oil which is said to have no -action on rubber, or practically none, is castor oil; all the same, I -do not advise its use as a lubricant. - -There are three only which we need consider:-- - - 1. Soda and water. - 2. French chalk. - 3. Pure redistilled glycerine. - -The first is perfectly satisfactory when freshly applied, but soon -dries up and evaporates. - -The second falls off; and unless the chalk be of the softest kind, -free from all grit and hard particles, it will soon do more harm than -good. - -The third, glycerine, is for ordinary purposes by far the best, and -has a beneficial rather than a deleterious effect on the rubber; but -it must be _pure_. The redistilled kind, free from all traces of -arsenic, grease, etc., is the only kind permissible. It does not -evaporate, and a few drops, comparatively speaking, will lubricate -fifty or sixty yards of rubber. - -Being of a sticky or tacky nature it naturally gathers up dust and -particles of dirt in course of time. To prevent these grinding into -the rubber, wash it from time to time in warm soda, and warm and apply -fresh glycerine when required. - -Glycerine, unlike vaseline (a product of petroleum), is not a grease; -it is formed from fats by a process known as _saponification_, or -treatment of the oil with caustic alkali, which decomposes the -compound, forming an alkaline stearate (soap), and liberating the -glycerine which remains in solution when the soap is separated by -throwing in common salt. In order to obtain pure glycerine, the fat -can be decomposed by lead oxide, the glycerine remaining in solution, -and the lead soap or plaster being precipitated. - -By using glycerine as a lubricant the number of turns that can be -given a rubber motor is greatly increased, and the coils slip over one -another freely and easily, and prevent the throwing of undue strain on -some particular portion, and absolutely prevent the strands from -sticking together. - -Sec. 12. =The Action of Copper upon Rubber.=--Copper, whether in the form -of the metal, the oxides, or the soluble salts, has a marked injurious -action upon rubber. - -In the case of metallic copper this action has been attributed to -oxidation induced by the dissolved oxygen in the copper. In working -drawings for model aeroplanes I have noticed designs in which the -hooks on which the rubber strands were to be stretched were made of -_copper_. In no case should the strands be placed upon bare metal. I -always cover mine with a piece of valve tubing, which can easily be -renewed from time to time. - -Sec. 12A. =The Action of Water, etc., on Rubber.=--Rubber is quite -insoluble in water; but it must not be forgotten that it will absorb -about 25 per cent. into its pores after soaking for some time. - -Ether, chloroform, carbon-tetrachloride, turpentine, carbon -bi-sulphide, petroleum spirit, benzene and its homologues found in -coal-tar naphtha, dissolve rubber readily. Alcohol is absorbed by -rubber, but is not a solvent of it. - -Sec. 12B. =How to Preserve Rubber.=--In the first place, in order that it -shall be _possible_ to preserve and keep rubber in the best condition -of efficiency, it is absolutely essential that the rubber shall be, -when obtained, fresh and of the best kind. Only the best Para rubber -should be bought; to obtain it fresh it should be got in as large -quantities as possible direct from a manufacturer or reliable rubber -shop. The composition of the best Para rubber is as follows:--Carbon, -87.46 per cent.; hydrogen, 12.00 per cent.; oxygen and ash, 0.54 per -cent. - -In order to increase its elasticity the pure rubber has to be -vulcanised before being made into the sheet some sixty or eighty yards -in length, from which the rubber threads are cut; after vulcanization -the substance consists of rubber plus about 3 per cent. of sulphur. -Now, unfortunately, the presence of the sulphur makes the rubber more -prone to atmospheric oxidation. Vulcanized rubber, compared to pure -rubber, has then but a limited life. It is to this process of -oxidation that the more or less rapid deterioration of rubber is due. - -To preserve rubber it should be kept from the sun's rays, or, indeed, -any actinic rays, in a cool, airy place, and subjected to as even a -temperature as possible. Great extremes of temperature have a very -injurious effect on rubber, and it should be washed from time to time -in warm soda water. It should be subjected to no tension or -compression. - -Deteriorated rubber is absolutely useless for model aeroplanes. - -Sec. 13. =To Test Rubber.=--Good elastic thread composed of pure Para -rubber and sulphur should, if properly made, stretch to seven times -its length, and then return to its original length. It should also -possess a stretching limit at least ten times its original length. - -As already stated, the threads or strands are cut from sheets; these -threads can now be cut fifty to the inch. For rubber motors a very -great deal so far as length of life depends on the accuracy and skill -with which the strands are cut. When examined under a microscope (not -too powerful) the strands having the least ragged edge, i.e., the best -cut, are to be preferred. - -Sec. 14. =The Section--Strip or Ribbon versus Square.=--In section the -square and not the ribbon or strip should be used. The edge of the -strip I have always found more ragged under the microscope than the -square. I have also found it less efficient. Theoretically no doubt a -round section would be best, but none such (in small sizes) is on the -market. Models have been fitted with a tubular section, but such -should on no account be used. - -Sec. 15. =Size of the Section.=--One-sixteenth or one-twelfth is the best -size for ordinary models; personally, I prefer the thinner. If more -than a certain number of strands are required to provide the necessary -power, a larger size should be used. It is not easy to say _what_ this -number is, but fifty may probably be taken as an outside limit. -Remember the size increases by area section; twice the _sectional_ -height and breadth means four times the rubber. - -Sec. 16. =Geared Rubber Motors.=--It is quite a mistake to suppose that -any advantage can be obtained by using a four to one gearing, say; all -that you do obtain is one-fourth of the power minus the increased -friction, minus the added weight. This presumes, of course, you make -no alteration in your rubber strands. - -Gearing such as this means _short_ rubber strands, and such are not to -be desired; in any case, there is the difficulty of increased friction -and added weight to overcome. It is true by splitting up your rubber -motor into two sets of strands instead of one you can obtain more -turns, but, as we have seen, you must increase the number of strands -to get the same thrust, and you have this to counteract any advantage -you gain as well as added weight and friction. - -Sec. 17. The writer has tried endless experiments with all kinds of -geared rubber motors, and the only one worth a moment's consideration -is the following, viz., one in which two gear wheels--same size, -weight, and number of teeth--are made use of, the propeller being -attached to the axle of one of them, and the same number of strands -are used on each axle. The success or non-success of this motor -depends entirely on the method used in its construction. At first -sight it may appear that no great skill is required in the -construction of such a simple piece of apparatus. No greater mistake -could be made. It is absolutely necessary that _the friction and -weight be reduced to a minimum_, and the strength be a maximum. The -torque of the rubber strands on so short an arm is very great. - -Ordinary light brass cogwheels will not stand the strain. - -A. The cogwheels should be of steel[17] and accurately cut of diameter -sufficient to separate the two strands the requisite distance, _but no -more_. - -B. The weight must be a minimum. This is best attained by using solid -wheels, and lightening by drilling and turning. - -C. The friction must be a minimum. Use the lightest ball bearings -obtainable (these weigh only 0.3 gramme), adjust the wheels so that -they run with the greatest freedom, but see that the teeth overlap -sufficiently to stand the strain and slight variations in direction -without fear of slipping. Shallow teeth are useless. - -D. Use vaseline on the cogs to make them run as easily as possible. - -[Illustration: FIG. 17.--GEARED RUBBER MOTOR. - -Designed and constructed by the writer. For description of the model, -etc., see Appendix.] - -E. The material of the containing framework must be of maximum -strength and minimum lightness. Construct it of minimum size, box -shaped, use the thinnest tin (really tinned sheet-iron) procurable, -and lighten by drilling holes, not too large, all over it. Do not use -aluminium or magnalium. Steel, could it be procured thin enough, would -be better still. - -F. Use steel pianoforte wire for the spindles, and hooks for the -rubber strands, using as thin wire as will stand the strain. - -Unless these directions are carefully carried out no advantage will be -gained--the writer speaks from experience. The requisite number of -rubber strands to give the best result must be determined by -experiment. - -Sec. 18. One advantage in using such a motor as this is that the two -equal strands untwisting in opposite directions have a decided -steadying effect on the model, similar almost to the case in which two -propellers are used. - -The "best" model flights that the writer has achieved have been -obtained with a motor of this description.[18] - -In the case of twin screws two such gearings can be used, and the -rubber split up into four strands. The containing framework in this -case can be simply light pieces of tubing let into the wooden -framework, or very light iron pieces fastened thereto. - -Do not attempt to split up the rubber into more than two strands to -each propeller. - - -SECTION II.--OTHER FORMS OF MOTORS. - -Sec. 18A. =Spring Motors.=--This question has already been dealt with -more or less whilst dealing with rubber motors, and the superiority of -the latter over the former pointed out. Rubber has a much greater -superiority over steel or other springs, because in stretch-twisted -rubber far more energy can be stored up weight for weight. One pound -weight of elastic can be made to store up some 320 ft.-lb. of energy, -and steel only some 65 lb. And in addition to this there is the -question of gearing, involving extra weight and friction; that is, if -flat steel springs similar to those used in clockwork mechanism be -made use of, as is generally the case. The only instance in which such -springs are of use is for the purpose of studying the effects of -different distributions of weight on the model, and its effect on the -balance of the machine; but effects such as this can be brought about -without a change of motor. - -Sec. 18B. A more efficient form of spring motor, doing away with gearing -troubles, is to use a long spiral spring (as long as the rubber -strands) made of medium-sized piano wire, similar in principle to -those used in some roller-blinds, but longer and of thinner steel. - -The writer has experimented with such, as well as scores of other -forms of spring motors, but none can compare with rubber. - -The long spiral form of steel spring is, however, much the best. - -Sec. 18C. =Compressed Air Motors.=--This is a very fascinating form of -motor, on paper, and appears at first sight the ideal form. It is so -easy to write: "Its weight is negligible, and it can be provided free -of cost; all that is necessary is to work a bicycle pump for as many -minutes as the motor is desired to run. This stored-up energy can be -contained in a mere tube, of aluminium or magnalium, forming the -central rib of the machine, and the engine mechanism necessary for -conveying this stored-up energy to the revolving propeller need weigh -only a few ounces." Another writer recommends "a pressure of 300 lb." - -Sec. 18D. A pneumatic drill generally works at about 80 lb. pressure, -and when developing 1 horse-power, uses about 55 cubic ft. of free air -per minute. Now if we apply this to a model aeroplane of average size, -taking a reservoir 3 ft. long by 11/2 in. internal diameter, made of -magnalium, say--steel would, of course, be much better--the weight of -which would certainly not be less than 4 oz., we find that at 80 lb. -pressure such a motor would use - - 55/Horse Power (H.P.) - -cub. ft. per minute. - -Now 80 lb. is about 51/2 atmospheres, and the cubical contents of the -above motor some 63 cub. in. The time during which such a model would -fly depends on the H.P. necessary for flight; but a fair allowance -gives a flight of from 10 to 30 sec. I take 80 lb. pressure as a fair -practical limit. - -Sec. 18E. The pressure in a motor-car tyre runs from 40 to 80 lb., -usually about 70 lb. Now 260 strokes are required with an ordinary -inflator to obtain so low a pressure as 70 lb., and it is no easy job, -as those who have done it know. - -Sec. 19. Prior to 1893 Mr. Hargraves (of cellular kite fame) studied the -question of compressed-air motors for model flying machines. His motor -was described as a marvel of simplicity and lightness, its cylinder -was made like a common tin can, the cylinder covers cut from sheet tin -and pressed to shape, the piston and junk rings of ebonite. - -One of his receivers was 23-3/8 in. long, and 5.5 in. diameter, of -aluminium plate 0.2 in. thick, 3/8 in. by 1/8 in. riveting strips were -insufficient to make tight joints; it weighed 26 oz., and at 80 lb. -water pressure one of the ends blew out, the fracture occurring at the -bend of the flange, and not along the line of rivets. The receiver -which was successful being apparently a tin-iron one; steel tubing was -not to be had at that date in Sydney. With a receiver of this -character, and the engine referred to above, a flight of 343 ft. was -obtained, this flight being the best. (The models constructed by him -were not on the aeroplane, but ornithoptere, or wing-flapping -principle.) The time of flight was 23 _seconds_, with 541/2 double -vibrations of the engines. The efficiency of this motor was estimated -to be 29 per cent. - -Sec. 20. By using compressed air, and heating it in its passage to the -cylinder, far greater efficiency can be obtained. Steel cylinders can -be obtained containing air under the enormous pressure of 120 -atmospheres.[19] This is practically liquid air. A 20-ft. cylinder -weighs empty 23 lb. The smaller the cylinder the less the -proportionate pressure that it will stand; and supposing a small steel -cylinder, produced of suitable form and weight, and capable of -withstanding with safety a pressure of from 300 to 600 lb. per sq. -in., or from 20 to 40 atmospheres. The most economical way of working -would be to admit the air from the reservoir directly to the motor -cylinders; but this would mean a very great range in the initial -working pressure, entailing not-to-be-thought-of weight in the form of -multi-cylinder compound engines, variable expansion gear, etc. - -Sec. 21. This means relinquishing the advantages of the high initial -pressure, and the passing of the air through a reducing valve, whereby -a constant pressure, say, of 90 to 150, according to circumstances, -could be maintained. By a variation in the ratio of expansion the air -could be worked down to, say, 30 lb. - -The initial loss entailed by the use of a reducing valve may be in a -great measure restored by heating the air before using it in the motor -cylinders; by heating it to a temperature of only 320 deg.F., by means of -a suitable burner, the volume of air is increased by one half, the -consumption being reduced in the same proportion; the consumption of -air used in this way being 24 lb. per indicated horse-power per hour. -But this means extra weight in the form of fuel and burners, and what -we gain in one way we lose in another. It is, of course, desirable -that the motor should work at as low a pressure as possible, since as -the store of air is used up the pressure in the reservoir falls, until -it reaches a limit below which it cannot usefully be employed. The air -then remaining is dead and useless, adding only to the weight of the -aeroplane. - -Sec. 22. From calculations made by the writer the _entire_ weight of a -compressed-air model motor plant would be at least _one-third_ the -weight of the aeroplane, and on a small scale probably one-half, and -cannot therefore hold comparison with the _steam engine_ discussed in -the next paragraph. In concluding these remarks on compressed-air -motors, I do not wish to dissuade anyone from trying this form of -motor; but they must not embark on experiments with the idea that -anything useful or anything superior to results obtained with -infinitely less expense by means of rubber can be brought to pass with -a bicycle pump, a bit of magnalium tube, and 60 lb. pressure. - -Sec. 22A. In Tatin's air-compressed motor the reservoir weighed 700 -grammes, and had a capacity of 8 litres. It was tested to withstand a -pressure of 20 atmospheres, but was worked only up to seven. The -little engine attached thereto weighed 300 grammes, and developed a -motive power of 2 kilogram-metres per second (_see_ ch. iii.). - -Sec. 23. =Steam-Driven Motors.=--Several successful steam-engined model -aeroplanes have been constructed, the most famous being those of -Professor Langley. - -Having constructed over 30 modifications of rubber-driven models, and -experimented with compressed air, carbonic-acid gas, electricity, and -other methods of obtaining energy, he finally settled upon the steam -engine (the petrol motor was not available at that time, 1893). After -many months' work it was found that the weight could not be reduced -below 40 lb., whilst the engine would only develop 1/2 H.P., and -finally the model was condemned. A second apparatus to be worked by -compressed air was tried, but the power proved insufficient. Then came -another with a carbonic-acid gas engine. Then others with various -applications of electricity and gas, etc., but the steam engine was -found most suitable; yet it seemed to become more and more doubtful -whether it could ever be made sufficiently light, and whether the -desired end could be attained at all. The chief obstacle proved not to -be with the engines, which were made surprisingly light after -sufficient experiment. _The great difficulty was to make a boiler of -almost no weight which would give steam enough._ - -Sec. 24. At last a satisfactory boiler and engine were produced. - -The engine was of 1 to 11/2 H.P., total weight (including moving -parts) 26 oz. The cylinders, two in number, had each a diameter of -11/4 in., and piston stroke 2 in. - -The boiler, with its firegrate, weighed a little over 5 lb. It -consisted of a continuous helix of copper tubing, 3/8 in. external -diameter, the diameter of the coil being 3 in. altogether. Through the -centre of this was driven the blast from an "AElopile," a modification -of the naphtha blow-torch used by plumbers, the flame of which is -about 2000 deg. F.[20] The pressure of steam issuing into the engines -varied from 100 to 150 lb. per sq. in.; 4 lb. weight of water and -about 10 oz. of naphtha could be carried. The boiler evaporated 1 lb. -of water per minute. - -The twin propellers, 39 in. in diam., pitch 11/4, revolved from 800 -to 1000 a minute. The entire aeroplane was 15 ft. in length, the -aerofoils from tip to tip about 14 ft., and the total weight slightly -less than 30 lb., of which _one-fourth was contained in the -machinery_. Its flight was a little over half a mile in length, and of -11/2 minutes' duration. Another model flew for about three-quarters -of a mile, at a rate of about 30 miles an hour. - -It will be noted that engine, generator, etc., work out at about 7 lb. -per H.P. Considerable advance has been made in the construction of -light and powerful model steam engines since Langley's time, chiefly -in connexion with model hydroplanes, and a pressure of from 500 to 600 -lb. per sq. in. has been employed; the steam turbine has been brought -to a high state of perfection, and it is now possible to make a model -De Laval turbine of considerable power weighing almost next to -nothing,[21] the real trouble, in fact the only one, being the steam -generator. An economization of weight means a waste of steam, of which -models can easily spend their only weight in five minutes. - -Sec. 25. One way to economize without increased weight in the shape of a -condenser is to use spirit (methylated spirit, for instance) for both -fuel and boiler, and cause the exhaust from the engines to be ejected -on to the burning spirit, where it itself serves as fuel. By using -spirit, or some very volatile hydrocarbon, instead of water, we have a -further advantage from the fact that such vaporize at a much lower -temperature than water. - -Sec. 26. When experimenting with an engine of the turbine type we must -use a propeller of small diameter and pitch, owing to the very high -velocity at which such engines run. - -Anyone, however, who is not an expert on such matters would do well to -leave such motors alone, as the very highest technical skill, combined -with many preliminary disappointments and trials, are sure to be -encountered before success is attained. - -Sec. 27. And the smaller the model the more difficult the problem--halve -your aeroplane, and your difficulties increase anything from fourfold -to tenfold. - -The boiler would in any case be of the flash type of either copper or -steel tubing (the former for safety), with a magnalium container for -the spirit, and a working pressure of from 150 to 200 lb. per sq. in. -Anything less than this would not be worth consideration. - -Sec. 28. Some ten months after Professor Langley's successful model -flights (1896), experiments were made in France at Carquenez, near -Toulon. The total weight of the model aeroplane in this case was 70 -lb.; the engine power a little more than 1 H.P. Twin screws were -used--_one in front and one behind_. The maximum velocity obtained was -40 miles per hour; but the length of run only 154 yards, and duration -of flight only a few seconds. This result compares very poorly with -Langley's distance (of best flight), nearly one mile, duration 1 min. -45 sec. The maximum velocity was greater--30 to 40 miles per hour. The -total breadth of this large model was rather more than 6 metres, and -the surface a little more than 8 sq. metres. - -Sec. 29. =Petrol Motors.=--Here it would appear at first thought is the -true solution of the problem of the model aeroplane motor. Such a -motor has solved the problem of aerial locomotion, as the steam engine -solved that of terrestrial and marine travel, both full sized and -model; and if in the case of full sized machines, then why not models. - -[Illustration: FIG. 18.--MR. STANGER'S MODEL IN FULL FLIGHT.] - -[Illustration: FIG. 19.--MR. STANGER'S PETROL-DRIVEN MODEL AEROPLANE. - -(_Illustrations by permission from electros supplied by the "Aero."_)] - -Sec. 30. The exact size of the smallest _working_ model steam engine that -has been made I do not know,[22] but it is or could be surprisingly -small; not so the petrol motor--not one, that is, that would _work_. -The number of petrol motor-driven model aeroplanes that have actually -flown is very small. Personally I only know of one, viz., Mr. D. -Stanger's, exhibited at the aero exhibition at the Agricultural Hall -in 1908. - -[Illustration: FIG. 20.--MR. STANGER'S MODEL PETROL ENGINE.] - -[Illustration: FIG. 21.--MR. STANGER'S MODEL PETROL ENGINE.] - - In Fig. 21 the motor is in position on the aeroplane. Note - small carburettor. In Fig. 20 an idea of the size of engine may - be gathered by comparing it with the ordinary sparking-plug - seen by the side, whilst to the left of this is one of the - special plugs used on this motor. (_Illustrations by permission - from electros supplied by the "Aero."_) - -Sec. 31. The following are the chief particulars of this interesting -machine:--The engine is a four-cylinder one, and weighs (complete with -double carburetter and petrol tank) 51/2 lb., and develops 11/4 H.P. -at 1300 revolutions per minute. - -[Illustration: FIG. 22.--ONE-CYLINDER PETROL MOTOR. - -(_Electro from Messrs. A.W. Gamage's Aviation Catalogue._)] - -The propeller, 29 in. in diam. and 36 in. in pitch, gives a static -thrust of about 7 lb. The machine has a spread of 8 ft. 2 in., and is -6 ft. 10 in. in length. Total weight 21 lb. Rises from the ground when -a speed of about 16 miles an hour is attained. A clockwork -arrangement automatically stops the engine. The engine air-cooled. The -cylinder of steel, cast-iron heads, aluminium crank-case, double float -feed carburetter, ignition by single coil and distributor. The -aeroplane being 7 ft. 6 in. long, and having a span 8 ft. - -Sec. 32. =One-cylinder Petrol Motors.=--So far as the writer is aware no -success has as yet attended the use of a single-cylinder petrol motor -on a model aeroplane. Undoubtedly the vibration is excessive; but this -should not be an insuperable difficulty. It is true it is heavier in -proportion than a two-cylinder one, and not so efficient; and so far -has not proved successful. The question of vibration on a model -aeroplane is one of considerable importance. A badly balanced -propeller even will seriously interfere with and often greatly curtail -the length of flight. - -Sec. 33. =Electric Motors.=--No attempt should on any account be made to -use electric motors for model aeroplanes. They are altogether too -heavy, apart even from the accumulator or source of electric energy, -for the power derivable from them. To take an extreme case, and -supposing we use a 2-oz. electric motor capable of driving a propeller -giving a static thrust of 3 oz.,[23] on weighing one of the smallest -size accumulators without case, etc., I find its weight is 41/2 oz. -One would, of course, be of no use; at least three would be required, -and they would require practically short circuiting to give sufficient -amperage (running them down, that is, in some 10 to 15 seconds). Total -weight, 1 lb. nearly. Now from a _pound_ weight of rubber one could -obtain a thrust of _pounds_, not ounces. For scale models not intended -for actual flight, of course, electric motors have their uses. - -FOOTNOTES: - -[12] Also there is no necessity for gearing. - -[13] In his latest models the writer uses strands even three times and -not twice as long, viz. fourteen strands 43 in. long. - -[14] This refers to 1/16 in. square sectioned rubber. - -[15] Of uniform breadth and thickness. - -[16] In practice I find not quite so high a proportion as this is -always necessary. - -[17] Steel pinion wire is very suitable. - -[18] See Appendix. - -[19] As high a pressure as 250 atmospheres has been used. - -[20] There was a special pump keeping the water circulating rapidly -through the boiler, the intense heat converting some of it into steam -as it flowed. The making of this boiler alone consumed months of work; -the entire machine taking a year to construct, with the best -mechanical help available. - -[21] Model Steam Turbines. "Model Engineer" Series, No. 13, price -6_d._ - -[22] See Introduction, note to Sec. 1. - -[23] The voltage, etc., is not stated. - - - - -CHAPTER V. - -PROPELLERS OR SCREWS. - - -Sec. 1. The design and construction of propellers, more especially the -former, is without doubt one of the most difficult parts of model -aeroplaning. - -With elastic or spring driven models the problem is more complicated -than for models driven by petrol or some vaporized form of liquid -fuel; and less reliable information is to hand. The problem of -_weight_, unfortunately, is of primary importance. - -We will deal with these points in due course; to begin with let us -take:-- - - -THE POSITION OF THE PROPELLER. - -In model aeroplanes the propeller is usually situated either in front -or in the rear of the model; in the former case it is called a TRACTOR -SCREW, i.e., it pulls instead of pushes. - -As to the merits of the two systems with respect to the tractor, there -is, we know, in the case of models moving through water a distinct -advantage in placing the propeller behind, and using a pushing or -propulsive action, on account of the frictional "wake" created behind -the boat, and which causes the water to flow after the vessel, but at -a lesser velocity. - -In placing the propeller behind, we place it in such a position as to -act upon and make use of this phenomenon, the effect of the propeller -being to bring this following wake to rest. Theoretically a boat, -model or otherwise, can be propelled with less horse-power than it can -be towed. But with respect to aeroplanes, apart altogether from the -difference of medium, there is _at present_ a very considerable -difference of _form_, an aeroplane, model or otherwise, bearing at -present but little resemblance to the hull of a boat. - -Undoubtedly there is a frictional wake in the case of aeroplanes, -possibly quite as much in proportion as in the case of a boat, -allowing for difference of medium. Admitting, then, that this wake -does exist, it follows that a propulsive screw is better than a -tractor. In a matter of this kind constructional considerations, or -"ease of launching," and "ability to land without damage," must be -given due weight. - -In the case of model aeroplanes constructional details incline the -balance neither one way nor the other; but "ease in launching" and -"ability to land without damage" weigh the balance down most decidedly -in favour of a driving or propulsive screw. - -In the case of full-sized monoplanes constructional details had most -to do with the use of tractors; but monoplanes are now being built -with propulsive screws.[24] - -In the case of models, not models of full-sized machines, but actual -model flyers, the writer considers propulsive screws much the -best.[25] - -In no case should the propeller be placed in the centre of the model, -or in such a position as to _shorten the strands of the elastic -motor_, if good flights are desired. - -In the case of petrol or similar driven models the position of the -propeller can be safely copied from actual well-recognised and -successful full-sized machines. - -Sec. 2. =The Number of Blades.=--Theoretically the number of blades does -not enter into consideration. The mass of air dealt with by the -propeller is represented by a cylinder of indefinite length, whose -diameter is the same as that of the screw, and the rate at which this -cylinder is projected to the rear depends theoretically upon the pitch -and revolutions (per minute, say) of the propeller and not the number -of blades. Theoretically one blade (helix incomplete) would be -sufficient, but such a screw would not "balance," and balance is of -primary importance; the minimum number of blades which can be used is -therefore _two_. - -In marine models three blades are considered best, as giving a better -balance. - -In the case of their aerial prototypes the question of _weight_ has -again to be considered, and two blades is practically the invariable -custom.[26] Here, again, constructional considerations again come to -the fore, and in the case of wooden propellers one of two blades is of -far more easy construction than one of three. - -By increasing the number of blades the "thrust" is, of course, more -evenly distributed over a larger area, but the weight is considerably -increased, and in models a greater advantage is gained by keeping down -the weight than might follow from the use of more blades. - -Sec. 3. =Fan versus Propeller.=--It must always be most carefully borne -in mind that a fan (ventilating) and a propeller are not the same -thing. Because many blades are found in practice to be efficient in -the case of the former, it is quite wrong to assume that the same -conclusion holds in the case of the latter. - -By increasing the number of blades the skin friction due to the -resistance that has to be overcome in rotating the propeller through -the air is added to. - -Moreover a fan is stationary, whilst a propeller is constantly -_advancing_ as well as _rotating_ through the air. - -The action of a fan blower is to move a small quantity of air at a -high velocity; whereas the action of a propeller is, or should be, to -move _a large quantity of air at a small velocity_, for the function -of a screw is to create thrust. Operating on a yielding fluid medium -this thrust will evidently be in proportion to the mass of fluid -moved, and also to the velocity at which it is put in motion. - -But the power consumed in putting this mass of fluid in motion is -proportional to the mass and to the _square_ of the velocity at which -it moves. From this it follows, as stated above, that in order to -obtain a given thrust with the least loss of power, the mass of fluid -acted on should be as large as possible, and the velocity imparted to -it as little as possible. - -A fan requires to be so designed as to create a thrust when stationary -(static thrust), and a propeller whilst moving through the air -(dynamic thrust). - -Sec. 4. =The Function of a Propeller= is to produce dynamic thrust; and -the great advantage of the use of a propeller as a thrusting or -propulsive agent is that its surface is always active. It has no -_dead_ points, and its motion is continuous and not reciprocating, and -it requires no special machinery or moving parts in its construction -and operation. - -Sec. 5. =The Pitch= of a propeller or screw is the linear distance a -screw moves, backwards or forwards, in one complete revolution. This -distance is purely a theoretical one. When, for instance, a screw is -said to have a pitch of 1 ft., or 12 in., it means that the model -would advance 1 ft. through the air for each revolution of the screw, -provided that the propeller blade were mounted in _solid_ guides, like -a nut on a bolt with one thread per foot. In a yielding fluid such as -water or air it does not practically advance this distance, and hence -occurs what is known as-- - -Sec. 6. =Slip=, which may be defined as the distance which ought to be -traversed, but which is lost through imperfections in the propelling -mechanism; or it may be considered as power which should have been -used in driving the model forward. In the case of a locomotive running -on dry rails nothing is lost in slip, there being none. In the case of -a steamer moored and her engines set going, or of an aeroplane held -back prior to starting, all the power is used in slip, i.e. in putting -the fluid in motion, and none is used in propulsion. - -Supposing the propeller on our model has a pitch of 1 ft., and we give -the elastic motor 100 turns, theoretically the model should travel 100 -ft. in calm air before the propeller is run down; no propeller yet -designed will do this. Supposing the actual length 77 ft., 23 per -cent. has been lost in "slip." For this to be actually correct the -propeller must stop at the precise instant when the machine comes to -ground. - -Taking "slip" into account, then-- - -_The speed of the model in feet per minute = pitch (in feet) x -revolutions per minute -- slip (feet per minute)._ - -This slip wants to be made small--just how small is not yet known. - -If made too small then the propeller will not be so efficient, or, at -any rate, such is the conclusion come to in marine propulsion, where -it is found for the most economical results to be obtained that the -slip should be from 10 to 20 per cent. - -In the case of aerial propellers a slip of 25 per cent. is quite good, -40 per cent. bad; and there are certain reasons for assuming that -possibly about 15 per cent. may be the best. - -Sec. 7. It is true that slip represents energy lost; but some slip is -essential, because without slip there could be no "thrust," this same -thrust being derived from the reaction of the volume of air driven -backwards. - -The thrust is equal to-- - -_Weight of mass of air acted on per second x slip velocity in feet per -second._ - -In the case of an aeroplane advancing through the air it might be -thought that the thrust would be less. Sir Hiram Maxim found, however, -as the result of his experiments that the thrust with a propeller -travelling through the air at a velocity of 40 miles an hour was the -same as when stationary, the r.p.m. remaining constant throughout. The -explanation is that when travelling the propeller is continually -advancing on to "undisturbed" air, the "slip" velocity is reduced, but -the undisturbed air is equivalent to acting upon a greater mass of -air. - -Sec. 8. =Pitch Coefficient or Pitch Ratio.=--If we divide the pitch of a -screw by its diameter we obtain what is known as pitch coefficient or -ratio. - -The mean value of eighteen pitch coefficients of well-known full-sized -machines works out at 0.62, which, as it so happens, is exactly the -same as the case of the Farman machine propeller considered alone, -this ratio varying from 0.4 to 1.2; in the case of the Wright's -machine it is (probably) 1. The efficiency of their propeller is -admitted on all hands. Their propeller is, of course, a slow-speed -propeller, 450 r.p.m. The one on the Bleriot monoplane (Bleriot XI.) -pitch ratio 0.4, r.p.m. 1350. - -In marine propulsion the pitch ratio is generally 1.3 for a slow-speed -propeller, decreasing to 0.9 for a high-speed one. In the case of -rubber-driven model aeroplanes the pitch ratio is often carried much -higher, even to over 3. - -Mr. T.W.K. Clarke recommends a pitch angle of 45 deg., or less, at the -tips, and a pitch ratio of 3-1/7 (with an angle of 45 deg.). Within limits -the higher the pitch ratio the better the efficiency. The higher the -pitch ratio the slower may be the rate of revolution. Now in a rubber -motor we do not want the rubber to untwist (run out) too quickly; with -too fine a pitch the propeller "races," or does something remarkably -like it. It certainly revolves with an abnormally high percentage of -slip. And for efficiency it is certainly desirable to push this ratio -to its limit; but there is also the question of the - -Sec. 9. =Diameter.=--"The diameter (says Mr. T.W.K. Clarke) should be -equal to one-quarter the span of the machine." - -If we increase the diameter we shall decrease the pitch ratio. From -experiments which the writer has made he prefers a lower pitch ratio -and increased diameter, viz. a pitch ratio of 1.5, and a diameter of -one-third to even one-half the span, or even more.[27] Certainly not -less than one-third. Some model makers indulge in a large pitch ratio, -angle, diameter, and blade area as well, but such a course is not to -be recommended. - -Sec. 10. =Theoretical Pitch.=--Theoretically the pitch (from boss to -tip) should at all points be the same; the boss or centre of the blade -at right angles to the plane of rotation, and the angle decreasing as -one approaches the tips. This is obvious when one considers that the -whole blade has to move forward the same amount. In the diagrams Figs. -23 and 24 the tip A of the propeller travels a distance = 2 {pi} R every -revolution. At a point D on the blade, distant _r_ from the centre, -the distance is 2 {pi} _r_. In both instances the two points must advance -a distance equal to the pitch, i.e. the distance represented by P O. - -[Illustration: FIG. 23.] - -[Illustration: FIG. 24. - -A O = 2 {pi} R; D O = 2 {pi} _r_.] - -A will move along A P, B along B P, and so on. The angles at the -points A, B, C ... (Fig. 24), showing the angles at which the -corresponding parts of the blade at A, B, C ... in Fig. 23 must be set -in order that a uniform pitch may be obtained. - -Sec. 11. If the pitch be not uniform then there will be some portions of -the blade which will drag through the air instead of affording useful -thrust, and others which will be doing more than they ought, putting -air in motion which had better be left quiet. This uniform total pitch -for all parts of the propeller is (as already stated) a decreasing -rate of pitch from the centre to the edge. With a total pitch of 5 -ft., and a radius of 4 ft., and an angle at the circumference of 6 deg., -then the angle of pitch at a point midway between centre and -circumference should be 12 deg., in order that the total pitch may be the -same at all parts. - -Sec. 12. =To Ascertain the Pitch of a Propeller.=--Take any point on one -of the blades, and carefully measure the inclination of the blade at -that point to the plane of rotation. - -If the angle so formed be about 19 deg. (19.45),[28] i.e., 1 in 3, and the -point 5 in. from the centre, then every revolution this point will -travel a distance - - 2 {pi} _r_ = 2 x 22/7 x 5 = 31.34. - -Now since the inclination is 1 in 3,[29] the propeller will travel -forward theoretically one-third of this distance, or - - 31.43/3 = 10.48 = 101/2 in. approx. - -Similarly any other case may be dealt with. If the propeller have a -uniform _constant angle_ instead of a uniform pitch, then the pitch -may be calculated at a point about one-third the length of the blade -from the tip. - -Sec. 13. =Hollow-Faced Blades.=[30]--It must always be carefully borne -in mind that a propeller is nothing more nor less than a particular -form of aeroplane specially designed to travel a helical path. It -should, therefore, be hollow faced and partake of the "stream line" -form, a condition not fulfilled if the face of the blade be flat--such -a surface cutting into the air with considerable shock, and by no -means creating as little undesirable motion in the surrounding medium -as possible. - -It must not be forgotten that a curved face blade has of necessity an -increasing pitch from the cutting to the trailing edge (considering, -of course, any particular section). In such a case the pitch is the -_mean effective pitch_. - -Sec. 14. =Blade Area.=--We have already referred to the fact that the -function of a propeller is to produce dynamic thrust--to drive the -aeroplane forward by driving the air backwards. At the same time it is -most desirable for efficiency that the air should be set in motion as -little as possible, this being so much power wasted; to obtain the -greatest reaction or thrust the greatest possible volume of air should -be accelerated to the smallest velocity. - -In marine engineering in slow-speed propellers (where cavitation[31] -does not come in) narrow blades are usually used. In high-speed marine -propellers (where cavitation is liable to occur) the projected area of -the blades is sometimes as much as 0.6 of the total disk area. In the -case of aerial propellers, where cavitation does not occur, or not -unless the velocity be a very high one (1500 or more a minute), narrow -blades are the best. Experiments in marine propulsion also show that -the thrust depends more on the disk area than on the width of the -blades. All the facts tend to show that for efficiency the blades of -the propeller should be narrow, in order that the air may not be acted -on for too long a time, and so put too much in motion, and the blades -be so separated that one blade does not disturb the molecules of air -upon which the next following one must act. Both in the case of marine -and aerial propellers multiplicity of blades (i.e. increased blade -area) tends to inefficiency of action, apart altogether from the -question of weight and constructional difficulties. The question of -increasing pitch in the case of hollow-faced blades, considered in the -last paragraph, has a very important bearing on the point we are -considering. To make a wide blade under such circumstances would be to -soon obtain an excessive angle. - -In the case of a flat blade the same result holds, because the air has -by the contact of its molecules with the "initial minimum width" been -already accelerated up to its final velocity, and further area is not -only wasted, but inimical to good flights, being our old bugbear -"weight in excess." - -Requisite strength and stiffness, of course, set a limit on the final -narrowness of the blades, apart from other considerations. - -Sec. 15. The velocity with which the propeller is rotated has also an -important bearing on this point; but a higher speed than 900 r.p.m. -does not appear desirable, and even 700 or less is generally -preferable.[32] In case of twin-screw propellers, with an angle at the -tips of 40 deg. to 45 deg., as low a velocity of 500 or even less would be -still better.[33] - -Sec. 16. =Shrouding.=--No improvement whatever is obtained by the use of -any kind of shrouding or ring round the propeller tips, or by -corrugating the surface of the propeller, or by using cylindrical or -cone-shaped propeller chamber or any kind of air guide either before -or after the propeller; allow it to revolve in as free an air-feed as -possible, the air does not fly off under centrifugal force, but is -powerfully sucked inwards in a well-designed propeller. - -[Illustration: FIG. 25. - -A TUBE OF AIR.] - -[Illustration: FIG. 26. - -A CYLINDER OF AIR.] - -Sec. 17. =General Design.=--The propeller should be so constructed as to -act upon a tube and not a "cylinder" of air. Many flying toys -(especially the French ones) are constructed with propellers of the -cylinder type. Ease of manufacture and the contention that those -portions of the blades adjacent to the boss do little work, and a -slight saving in weight, are arguments that can be urged in their -favour. But all the central cut away part offers resistance in the -line of travel, instead of exerting its proportionate propulsive -power, and their efficiency is affected by such a practice. - -Sec. 18. A good =Shape= for the blades[34] is rectangular with rounded -corners; the radius of the circle for rounding off the corners may be -taken as about one-quarter of the width of the blade. The shape is not -_truly rectangular, for the width of this rectangular at (near) the -boss should be one-half the width at the tip_. - -The thickness should diminish uniformly from the boss to the tip. (In -models the thickness should be as little as is consistent with -strength to keep down the weight). _The pitch uniform and large._ - -[Illustration: FIG. 27.--O T = 1/3 O P.] - -Sec. 19. =The Blades, two in number=, and hollow faced--the maximum -concavity being one-third the distance from the entering to the -trailing edge; the ratio of A T to O P (the width) being 0.048 or 1 : -21, these latter considerations being founded on the analogy between a -propeller and the aerofoil surface. (If the thickness be varied from -the entering to the trailing edge the greatest thickness should be -towards the former.) The convex surface of the propeller must be taken -into account, in fact, it is no less important than the concave, and -the entire surface must be given a true "stream line" form. - -[Illustration: FIG. 28.] - -[Illustration: FIG. 29.] - -If the entering and trailing edge be not both straight, but one be -curved as in Fig. 28, then the straight edge must be made the -_trailing_ edge. And if both be curved as in Fig. 29, then the -_concave_ edge must be the trailing edge. - -Sec. 19. =Propeller Design.=--To design a propeller, proceed as follows. -Suppose the diameter 14 in. and the pitch three times the diameter, -i.e. 52 in. (See Fig. 30.) - -Take one-quarter scale, say. Draw a centre line A B of convenient -length, set of half the pitch 52 in. -- 1/4 scale = 51/4 in. = C - D. -Draw lines through C and D at right angles to C D. - -With a radius equal to half the diameter (i.e. in this case 13/4 in.) -of the propeller, describe a semicircle E B F and complete the -parallelogram F H G E. Divide the semicircle into a number of equal -parts; twelve is a convenient number to take, then each division -subtends an angle of 15 deg. at the centre D. - -Divide one of the sides E G into the same number of equal parts -(twelve) as shown. Through these points draw lines parallel to F E or -H G. - -And through the twelve points of division on the semicircle draw lines -parallel to F H or E G as shown. The line drawn through the successive -intersections of these lines is the path of the tip of the blade -through half a revolution, viz. the line H S O T E. - -S O T X gives the angle at the tip of the blades = 44 deg.. - -Let the shape of the blade be rectangular with rounded corners, and -let the breadth at the tip be twice that at the boss. - -Then the area (neglecting the rounded off corners) is 101/2 sq. in. - -[Illustration: FIG. 30.--PROPELLER DESIGN. - -One quarter scale. Diameter 14 in. Pitch 52 in. Angle at tip 44 deg..] - -The area being that of a rectangle 7 in. x 1 in. = 7 sq. in. plus area -of two triangles, base 1/2 in., height 7 in. Now area of triangle = -half base x height. Therefore area of both triangles = 1/2 in. x 7 -in. = 31/2 sq. in. Now the area of the disc swept out by the -propeller is - - {pi}/4 x (diam.) squared ({pi} = 22/7) - -[Illustration: FIG. 31.--PROPELLER DESIGN. - -Scale one-eighth for A B and B C; but sections of blade are -full-sized.] - -And if _d_ A _r_ = the "disc area ratio" we have - - (_d_ A _r_) x {pi}/4 x (14) squared = area of blade = 101/2, - -whence _d_ A _r_ = 0.07 about. - -[Illustration: FIG. 32.] - -[Illustration: FIG. 33.] - -In Fig. 31 set off A B equal to the pitch of the propeller (42 in.), -one-eighth scale. Set off B C at right angles to A B and equal to - - {pi} x diameter = 22/7 x 14 = 44 in. to scale 51/2 in. - -Divide B C into a convenient number of equal parts in the figure; five -only are taken, D, E, F, G, H; join A D, A E, A F, A G, A H and -produce them; mark off distances P O, S R, Y T ... equal to the width -of the blade at these points (H P = H O; G S = G R ...) and sketch in -the sections of blade as desired. In the figure the greatest concavity -of the blade is supposed to be one-third the distances P O, S R ... -from PS.... The concavity is somewhat exaggerated. The angles A H B, A -G B, A F B ... represent the pitch angle at the points H, G, F ... of -the blade. - -Similarly any other design may be dealt with; in a propeller of 14 in. -diameter the diameter of the "boss" should not be more than 10/16 in. - -Sec. 20. =Experiments with Propellers.=--The propeller design shown in -Figs. 32 and 33, due to Mr. G. de Havilland,[35] is one very suitable -for experimental purposes. A single tube passing through a T-shaped -boss forms the arms. On the back of the metal blade are riveted four -metallic clips; these clips being tightened round the arm by -countersunk screws in the face of the blade. - -The tube and clips, etc., are all contained with the back covering of -the blade, as shown in Fig. 35, if desired, the blade then practically -resembling a wooden propeller. The construction, it will be noticed, -allows of the blade being set at any angle, constant or otherwise; -also the pitch can be constant or variable as desired, and any "shape" -of propeller can be fitted. - -The advantage of being able to _twist_ the blade (within limits) on -the axis is one not to be underestimated in experimental work. - -[Illustration: FIG. 34.--THE AUTHOR'S PROPELLER TESTING APPARATUS.] - -With a view to ascertain some practical and reliable data with respect -to the _dynamic_, or actual thrust given when moving through free air -at the velocity of actual travel, the author experimented with the -apparatus illustrated in Figs. 34 and 35, which is so simple and -obvious as to require scarcely any explanation. - -The wires were of steel, length not quite 150 ft., fitted with wire -strainers for equalising tension, and absolutely free from "kinks." -As shown most plainly in Fig. 35, there were two parallel wires -sufficiently far apart for the action of one propeller not to affect -the other. Calling these two wires A and B, and two propellers _x_ and -_y_, then _x_ is first tried on A and _y_ on B. Results carefully -noted. - -[Illustration: FIG. 35.--PROPELLER TESTING. - -Showing distance separating the two wires.] - -Then _x_ is tried on B and _y_ on A, and the results again carefully -noted. If the results confirm one another, the power used in both -cases being the same, well and good; if not, adjustments, etc., are -made in the apparatus until satisfactory results are obtained. This -was done when the propellers "raced" one against the other. At other -times one wire only was made use of, and the time and distance -traversed was noted in each case. Propellers were driven through -smoke, and with silk threads tied to a light framework slightly larger -than their disc area circumference. Results of great interest were -arrived at. These results have been assumed in much that has been said -in the foregoing paragraphs. - -[Illustration: FIG. 36.--ONE GROUP OF PROPELLERS TESTED BY THE AUTHOR.] - -Briefly put, these results showed:-- - -1. The inefficiency of a propeller of the fan blower or of the static -thrust type. - -2. The advantage of using propellers having hollow-faced blades and -large diameter. - -3. That diameter was more useful than blade area, i.e. given a certain -quantity (weight) of wood, make a long thin blade and not a shorter -one of more blade area--blade area, i.e., as proportionate to its -corresponding disc area. - -4. That the propeller surface should be of true stream-line form. - -5. That it should act on a cylinder and not tubes of air. - -6. That a correctly designed and proportioned propeller was just as -efficacious in a small size of 9 in. to 28 in. as a full-sized -propeller on a full-sized machine. - -[Illustration: FIG. 37.--AN EFFICIENT PROPELLER, BUT RATHER HEAVY. - -Ball bearings, old and new. Note difference in sizes and weights. -Propeller, 14 in. diam.; weight 36 grammes.] - -A propeller of the static-thrust type was, of course, "first off," -sometimes 10 ft. or 12 ft. ahead, or even more; but the correctly -designed propeller gradually gathered up speed and acceleration, just -as the other fell off and lost it, and finally the "dynamic" finished -along its corresponding wire far ahead of the "static," sometimes -twice as far, sometimes six times. "Freak" propellers were simply not -in it. - -[Illustration: FIG. 38.--"VENNA" PROPELLER. - -A 20 per cent. more efficient propeller than that shown in Fig. 41; 14 -per cent. lighter; 6 per cent. better in dynamic thrust--14 in. diam.; -weight 31 grammes.] - -Metal propellers of constant angle, as well as wooden ones of uniform -(constant) pitch, were tested; the former gave good results, but not -so good as the latter. - -The best angle of pitch (at the tip) was found to be from 20 deg. to 30 deg.. - -In all cases when the slip was as low as 25 per cent., or even -somewhat less, nearly 20 per cent., a distinct "back current" of air -was given out by the screw. This "slip stream," as it is caused, is -absolutely necessary for efficiency. - -Sec. 21. =Fabric-covered= screws did not give very efficient results; the -only point in their use on model aeroplanes is their extreme -lightness. Two such propellers of 6 in. diameter can be made to weigh -less than 1/5 oz. the pair; but wooden propellers (built-up principle) -have been made 5 in. diameter and 1/12 oz. in weight. - -Sec. 22. Further experiments were made with twin screws mounted on model -aeroplanes. In one case two propellers, both turning in the _same_ -direction, were mounted (without any compensatory adjustment for -torque) on a model, total weight 11/2 lb. Diameter of each propeller -14 in.; angle of blade at tip 25 deg.. The result was several good -flights--the model (_see_ Fig. 49c) was slightly unsteady across the -wind, that was all. - -In another experiment two propellers of same diameter, pitch, etc., -but of shape similar to those shown in Figs. 28 and 29, were tried as -twin propellers on the same machine. The rubber motors were of equal -weight and strength. - -The model described circled to the right or left according to the -position of the curved-shaped propeller, whether on the left or right -hand, thereby showing its superiority in dynamic thrust. Various -alterations were made, but always with the same result. These -experiments have since been confirmed, and there seems no doubt that -the double-curved shaped blade _is_ superior. (See Fig. 39.) - -Sec. 23. =The Fleming-Williams Propeller.=--A chapter on propellers would -scarcely be complete without a reference to the propeller used on a -machine claiming a record of over a quarter of a mile. This form of -propeller, shown in the group in Fig. 36 (top right hand), was found -by the writer to be extremely deficient in dynamic thrust, giving the -worst result of any shown there. - -[Illustration: FIG. 39.--CURVED DOUBLE PROPELLER. - -The most efficient type yet tested by the writer, when the blade is -made hollow-faced. When given to the writer to test it was flat-faced -on one side.] - -[Illustration: FIG. 40.--THE FLEMING-WILLIAMS MODEL.] - -It possesses large blade area, large pitch angle--more than 45 deg. at the -tip--and large diameter. These do not combine to propeller efficiency -or to efficient dynamic thrust; but they do, of course, combine to -give the propeller a very slow rotational velocity. Provided they give -_sufficient_ thrust to cause the model to move through the air at a -velocity capable of sustaining it, a long flight may result, not -really owing to true efficiency on the part of the propellers,[36] but -owing to the check placed on their revolutions per minute by their -abnormal pitch angle, etc. The amount of rubber used is very great for -a 10 oz. model, namely, 34 strands of 1/16 in. square rubber to each -propeller, i.e. 68 strands in all. - -[Illustration: FIG. 41.--THE SAME IN FLIGHT. - -(_Reproduced by permission from "The Aero."_)] - -On the score of efficiency, when it is desired to make a limited -number of turns give the longest flight (which is the problem one -always has to face when using a rubber motor) it is better to make use -of an abnormal diameter, say, more than half the span, and using a tip -pitch angle of 25 deg., than to make use of an abnormal tip pitch 45 deg. and -more, and large blade area. In a large pitch angle so much energy is -wasted, not in dynamic thrust, but in transverse upsetting torque. On -no propeller out of dozens and dozens that I have tested have I ever -found a tip-pitch of more than 35 deg. give a good dynamic thrust; and for -length of flight velocity due to dynamic thrust must be given due -weight, as well as the duration of running down of the rubber motor. - -Sec. 24. Of built up or carved out and twisted wooden propellers, the -former give the better result; the latter have an advantage, however, -in sometimes weighing less. - -FOOTNOTES: - -[24] _Note._--Since the above was written some really remarkable -flights have been obtained with a 1 oz. model having two screws, one -in front and the other behind. Equally good flights have also been -obtained with the two propellers behind, one revolving in the -immediate rear of the other. Flying, of course, with the wind, -_weight_ is of paramount importance in these little models, and in -both these cases the "single stick" can be made use of. _See also_ ch. -iv., Sec. 28. - -[25] _See also_ ch. viii., Sec. 5. - -[26] Save in case of some models with fabric-covered propellers. Some -dirigibles are now being fitted with four-bladed wooden screws. - -[27] Vide Appendix. - -[28] Vide Equivalent Inclinations--Table of. - -[29] One in 3 or 0.333 is the _sine_ of the angle; similarly if the -angle were 30 deg. the sine would be 0.5 or 1/2, and the theoretical -distance travelled one-half. - -[30] _Flat-Faced Blades._--If the blade be not hollow-faced--and we -consider the screw as an inclined plane and apply the Duchemin formula -to it--the velocity remaining the same, the angle of maximum thrust is -351/4 deg.. Experiments made with such screws confirm this. - -[31] Cavitation is when the high speed of the screw causes it to carry -round a certain amount of the medium with it, so that the blades -strike no undisturbed, or "solid," air at all, with a proportionate -decrease in thrust. - -[32] In the Wright machine r.p.m. = 450; in Bleriot XI. r.p.m. = 1350. - -[33] Such propellers, however, require a considerable amount of -rubber. - -[34] But _see also_ Sec. 22. - -[35] "Flight," March 10, 1910. (Illustration reproduced by -permission.) - -[36] According to the author's views on the subject. - - - - -CHAPTER VI. - -THE QUESTION OF SUSTENTATION THE CENTRE OF PRESSURE. - - -Sec. 1. Passing on now to the study of an aeroplane actually in the air, -there are two forces acting on it, the upward lift due to the air -(i.e. to the movement of the aeroplane supposed to be continually -advancing on to fresh, undisturbed _virgin_ air), and the force due to -the weight acting vertically downwards. We can consider the resultant -of all the upward sustaining forces as acting at a single point--that -point is called the "Centre of Pressure." - -Suppose A B a vertical section of a flat aerofoil, inclined at a small -angle _a_ to the horizon C, the point of application of the resultant -upward 'lift,' D the point through which the weight acts vertically -downwards. Omitting for the moment the action of propulsion, if these -two forces balance there will be equilibrium; but to do this they must -pass through the same point, but as the angle of inclination varies, -so does the centre of pressure, and some means must be employed -whereby if C and D coincide at a certain angle the aeroplane will come -back to the correct angle of balance if the latter be altered. - -In a model the means must be automatic. Automatic stability depends -for its action upon the movement of the centre of pressure when the -angle of incidence varies. When the angle of incidence increases the -centre of pressure moves backwards towards the rear of the aerofoil, -and vice versa. - -Let us take the case when steady flight is in progress and C and D are -coincident, suppose the velocity of the wind suddenly to -increase--increased lifting effect is at once the result, and the fore -part of the machine rises, i.e. the angle of incidence increases and -the centre of pressure moves back to some point in the rear of C D. -The weight is now clearly trying to pull the nose of the aeroplane -down, and the "lift" tending to raise the tail. The result being an -alteration of the angle of incidence, or angle of attack as it is -called, until it resumes its original position of equilibrium. A drop -in the wind causes exactly an opposite effect. - -[Illustration: FIG. 42.] - -Sec. 2. The danger lies in "oscillations" being set up in the line of -flight due to changes in the position of the centre of pressure. Hence -the device of an elevator or horizontal tail for the purpose of -damping out such oscillations. - -Sec. 3. But the aerofoil surface is not flat, owing to the increased -"lift" given by arched surfaces, and a much more complicated set of -phenomena then takes place, the centre of pressure moving forward -until a certain critical angle of incidence is reached, and after -this a reversal takes place, the centre of pressure then actually -moving backwards. - -The problem then consists in ascertaining the most efficient aerocurve -to give the greatest "lift" with the least "drift," and, having found -it, to investigate again experimentally the movements of the centre of -pressure at varying angles, and especially to determine at what angle -(about) this "reversal" takes place. - -[Illustration: FIG. 43.] - -Sec. 4. Natural automatic stability (the only one possible so far as -models are concerned) necessitates permanent or a permanently -recurring coincidence (to coin a phrase) of the centre of gravity and -the centre of pressure: the former is, of course, totally unaffected -by the vagaries of the latter, any shifting of which produces a couple -tending to destroy equilibrium. - -Sec. 5. As to the best form of camber (for full sized machine) possibly -more is known on this point than on any other in the whole of -aeronautics. - -In Figs. 44 and 45 are given two very efficient forms of cambered -surfaces for models. - -[Illustration: FIG. 44.--AN EFFICIENT FORM OF CAMBER. - - B D Maximum Altitude. A C Chord. - Ratio of B D: A C :: 1:17. A D 1/3 of A C.] - -[Illustration: FIG. 45.--ANOTHER EFFICIENT FORM. - -Ratio of B D to A C 1 to 17. AD rather more than 1/4 of A C.] - -The next question, after having decided the question of aerocurve, or -curvature of the planes, is at what angle to set the cambered surface -to the line of flight. This brings us to the question of the-- - -Sec. 6. =Dipping Front Edge.=--The leading or front edge is not -tangential to the line of flight, but to a relative upward wind. It is -what is known as the "cyclic up-current," which exists in the -neighbourhood of the entering edge. Now, as we have stated before, it -is of paramount importance that the aerofoil should receive the air -with as little shock as possible, and since this up-current does -really exist to do this, it must travel through the air with a dipping -front edge. The "relative wind" (the only one with which we are -concerned) _is_ thereby met tangentially, and as it moves onward -through the air the cambered surface (or aerocurve) gradually -transforms this upward trend into a downward wake, and since by -Newton's law, "Action and reaction are equal and opposite," we have -an equal and opposite upward reaction. - -We now know that the top (or convex side) of the cambered surface is -practically almost as important as the underneath or concave side in -bringing this result about. - -The exact amount of "dipping edge," and the exact angle at which the -chord of the aerocurve, or cambered surface, should be set to the line -of flight--whether at a positive angle, at no angle, or at a negative -angle--is one best determined by experiment on the model in question. - -[Illustration: FIG. 46.] - -But _if at any angle, that angle either way should be a very small -one_. If you wish to be very scientific you can give the underside of -the front edge a negative angle of 5 deg. to 7 deg. for about one-eighth of -the total length of the section, after that a positive angle, -gradually increasing until you finally finish up at the trailing edge -with one of 4 deg.. Also, the form of cambered surface should be a -paraboloid--not arc or arc of circles. The writer does not recommend -such an angle, but prefers an attitude similar to that adopted in the -Wright machine, as in Fig. 47. - -Sec. 7. Apart from the attitude of the aerocurve: _the greatest depth of -the camber should be at one-third of the length of the section from -the front edge, and the total depth measured from the top surface to -the chord at this point should not be more than one-seventeenth of the -length of section_. - -Sec. 8. It is the greatest mistake in model aeroplanes to make the camber -otherwise than very slight (in the case of surfaced aerofoils the -resistance is much increased), and aerofoils with anything but a _very -slight_ arch are liable to be very unstable, for the aerocurve has -always a decided tendency to "follow its own curve." - -[Illustration: FIG. 47.--ATTITUDE OF WRIGHT MACHINE.] - -The nature of the aerocurve, its area, the angle of inclination of its -chord to the line of flight, its altitude, etc., are not the only -important matters one must consider in the case of the aerofoil, we -must also consider-- - -Sec. 9. Its =Aspect Ratio=, i.e. the ratio of the span (length) of the -aerofoil to the chord--usually expressed by span/chord. In the Farman -machine this ratio is 5.4; Bleriot, 4.3; Short, 6 to 7.5; Roe -triplane, 7.5; a Clark flyer, 9.6. - -Now the higher the aspect ratio the greater should be the efficiency. -Air escaping by the sides represents loss, and the length of the sides -should be kept short. A broader aerofoil means a steeper angle of -inclination, less stability, unnecessary waste of power, and is -totally unsuited for a model--to say nothing of a full-sized machine. - -In models this aspect ratio may with advantage be given a higher value -than in full-sized machines, where it is well known a practical safe -constructional limit is reached long before theory suggests the -limit. The difficulty consists in constructing models having a very -high aspect ratio, and yet possessing sufficient strength and -lightness for successful flight. It is in such a case as this where -the skill and ingenuity of the designer and builder come in. - -It is this very question of aspect ratio which has given us the -monoplane, the biplane, and the triplane. A biplane has a higher -aspect ratio than a monoplane, and a triplane (see above) a higher -ratio still. - -It will be noticed the Clark model given has a considerably higher -aspect ratio, viz. 9.6. And even this can be exceeded. - -_An aspect ratio of_ 10:1 _or even_ 12:1 _should be used if -possible._[37] - -Sec. 10. =Constant or Varying Camber.=--Some model makers vary the camber -of their aerofoils, making them almost flat in some parts, with -considerable camber in others; the tendency in some cases being to -flatten the central portions of the aerofoil, and with increasing -camber towards the tips. In others the opposite is done. The writer -has made a number of experiments on this subject, but cannot say he -has arrived at any very decisive results, save that the camber should -in all cases be (as stated before) very slight, and so far as his -experiments do show anything, they incline towards the further -flattening of the camber in the end portions of the aerofoil. It must -not be forgotten that a flat-surfaced aerofoil, constructed as it is -of more or less elastic materials, assumes a natural camber, more or -less, when driven horizontally through the air. Reference has been -made to a reversal of the-- - -Sec. 11. =Centre of Pressure on Arched Surfaces.=--Wilbur Wright in his -explanation of this reversal says: "This phenomenon is due to the fact -that at small angles the wind strikes the forward part of the aerofoil -surface on the upper side instead of the lower, and thus this part -altogether ceases to lift, instead of being the most effective part of -all." The whole question hangs on the value of the critical angle at -which this reversal takes place; some experiments made by Mr. M.B. -Sellers in 1906 (published in "Flight," May 14, 1910) place this angle -between 16 deg. and 20 deg.. This angle is much above that used in model -aeroplanes, as well as in actual full-sized machines. But the -equilibrium of the model might be upset, not by a change of attitude -on its part, but on that of the wind, or both combined. By giving (as -already advised) the aerofoil a high aspect ratio we limit the travel -of the centre of pressure, for a high aspect ratio means, as we have -seen, a short chord; and this is an additional reason for making the -aspect ratio as high as practically possible. The question is, is the -critical angle really as high as Mr. Seller's experiments would show. -Further experiments are much needed. - -FOOTNOTES: - -[37] Nevertheless some models with a very low aspect ratio make good -flyers, owing to their extreme lightness. - - - - -CHAPTER VII. - -MATERIALS FOR AEROPLANE CONSTRUCTION. - - -Sec. 1. The choice of materials for model aeroplane construction is more -or less limited, if the best results are to be obtained. The lightness -absolutely essential to success necessitates--in addition to skilful -building and best disposition of the materials--materials of no undue -weight relative to their strength, of great elasticity, and especially -of great resilience (capacity to absorb shock without injury). - -Sec. 2. =Bamboo.=--Bamboo has per pound weight a greater resilience than -any other suitable substance (silk and rubber are obviously useless as -parts of the _framework_ of an aeroplane). On full-sized machines the -difficulty of making sufficiently strong connections and a liability -to split, in the larger sizes, are sufficient reasons for its not -being made more use of; but it makes an almost ideal material for -model construction. The best part to use (split out from the -centrepiece) is the strip of tough wood immediately below the hard -glazed surface. For struts, spars, and ribs it can be used in this -manner, and for the long strut supporting the rubber motor an entire -tube piece should be used of the requisite strength required; for an -ordinary rubber motor (one yard long), 30 to 50 strands, this should -be a piece 3/8 in. in diameter, and weight about 5/8 oz. per ft. -_Bamboo may be bent_ by either the "dry" heat from a spirit lamp or -stove, or it may be steamed, the latter for preference, as there is -no danger of "scorching" the fibres on the inside of the bend. When -bent (as in the case of other woods) it should be bound on to a -"former" having a somewhat greater curvature than the curve required, -because when cool and dry it will be sure to "go back" slightly. It -must be left on the former till quite dry. When bending the "tube" -entire, and not split portions thereof, it should be immersed in very -hot, or even boiling, water for some time before steaming. The really -successful bending of the tube _en bloc_ requires considerable -patience and care. - -Bamboo is inclined to split at the ends, and some care is required in -making "joints." The ribs can be attached to the spars by lashing them -to thin T strips of light metal, such as aluminium. Thin thread, or -silk, is preferable to very thin wire for lashing purpose, as the -latter "gives" too much, and cuts into the fibres of the wood as well. - -Sec. 3. =Ash=, =Spruce=, =Whitewood= are woods that are also much used by -model makers. Many prefer the last named owing to its uniform freedom -from knots and ease with which it can be worked. It is stated 15 per -cent. additional strength can be imparted by using hot size and -allowing it to soak into the wood at an increase only of 3.7 per cent. -of weight. It is less than half the weight of bamboo, but has a -transverse rupture of only 7,900 lb. per sq. in. compared to 22,500 in -the case of bamboo tubing (thickness one-eighth diameter) and a -resilience per lb. weight of slightly more than one half. Some model -makers advocate the use of =poplar= owing to its extreme lightness -(about the same as whitewood), but its strength is less in the ratio -of about 4:3; its resilience is very slightly more. It must be -remembered that wood of the same kind can differ much as to its -strength, etc., owing to what part of the tree it may have been cut -from, the manner in which it may have been seasoned, etc. For model -aeroplanes all wood used should have been at least a year in -seasoning, and should be so treated when in the structure that it -cannot absorb moisture. - -If we take the resilience of ash as 1, then (according to Haswell) -relative resilience of beech is 0.86, and spruce 0.64. - -The strongest of woods has a weight when well seasoned of about 40 lb. -per cub. ft. and a tenacity of about 10,000 lb. per sq. in. - -[Illustration: FIG. 47A.--"AEROPLANE ALMA." - -A very effective French Toy Monoplane.] - -Sec. 4. =Steel.=--Ash has a transverse rupture of 14,300 lb. per sq. in., -steel tubing (thickness = 1/30 its diameter) 100,000 lb. per sq. in. -Ash weighs per cub. ft. 47 lb., steel 490. Steel being more than ten -times as heavy as ash--but a transverse rupture stress seven times as -high. - -Bamboo in tube form, thickness one-third of diameter, has a -transverse rupture of 22,500 lb. per sq. in., and a weight of 55 lb. -per cub. ft. - -Steel then is nine times as heavy as bamboo--and has a transverse -rupture stress 4.4 times as great. In comparing these three substances -it must be carefully borne in mind that lightness and strength are not -the only things that have to be provided for in model aeroplane -building; there is the question of _resistance_--we must offer as -small a cross-section to moving through the air as possible. - -Now while ash or bamboo and certain other timbers may carry a higher -load per unit of weight than steel, they will present about three to -three and a half times the cross-section, and this produces a serious -obstacle, while otherwise meeting certain requirements that are most -desirable. Steel tubing of sufficiently small bore is not, so far as -the writer knows, yet on the market in England. In France very thin -steel tubes are made of round, oval, hexagon, etc., shape, and of -accurate thickness throughout, the price being about 18s. a lb. - -Although suitable steel tubing is not yet procurable under ordinary -circumstances, umbrella steel is. - -Sec. 5. =Umbrella Section Steel= is a section 5/32 in. by 1/8 in. deep, 6 -ft. long weighing 2.1 oz., and a section 3/32 in. across the base by -1/8 in. deep, 6 ft. long weighing 1.95 oz. - -It is often stated that umbrella ribs are too heavy--but this entirely -depends on the length you make use of, in lengths of 25 in. for small -aerofoils made from such lengths it is so; but in lengths of 48 in. -(two such lengths joined together) the writer has used it with great -success; often making use of it now in his larger models; the -particular size used by him weighs 131/2 grammes, to a length of 25 -in. He has never had one of these aerofoils break or become -kinked--thin piano wire is used to stay them and also for spars when -employed--the front and ends of the aerofoil are of umbrella steel, -the trailing edge of steel wire, comparatively thin, kept taut by -steel wire stays. - -Sec. 6. =Steel Wire.=--Tensile strength about 300,000 lb. per sq. in. For -the aerofoil framework of small models and for all purposes of -staying, or where a very strong and light tension is required, this -substance is invaluable. Also for framework of light fabric covered -propellers as well as for skids and shock absorber--also for hooks to -hold the rubber motor strands, etc. No model is complete without it in -some form or another. - -Sec. 7. =Silk.=--This again is a _sine qua non_. Silk is the strongest of -all organic substances for certain parts of aeroplane construction. It -has, in its best form, a specific gravity of 1.3, and is three times -as strong as linen, and twice as strong in the thread as hemp. Its -finest fibres have a section of from 0.0010 to 0.0015 in diameter. It -will sustain about 35,000 lb. per sq. in. of its cross section; and -its suspended fibre should carry about 150,000 ft. of its own -material. This is six times the same figure for aluminium, and equals -about 75,000 lb. steel tenacity, and 50 more than is obtained with -steel in the form of watch springs or wire. For aerofoil surface no -substance can compare with it. But it must be used in the form of an -"oiled" or specially treated silk. Several such are on the market. -Hart's "fabric" and "radium" silk are perhaps the best known. Silk -weighs 62 lb. per cub. ft., steel has, we have seen, 490 lb., thus -paying due regard to this and to its very high tensile strength it is -superior to even steel wire stays. - -Sec. 8. =Aluminium and Magnalium.=--Two substances about which a great -deal has been heard in connection with model aeroplaning; but the -writer does not recommend their use save in the case of fittings for -scale models, not actual flyers, unless especially light ones meant -to fly with the wind. Neither can compare with steel. Steel, it is -true, is three times as heavy as aluminium, but it has four or five -times its strength; and whereas aluminium and magnalium may with -safety be given a permissible breaking strength of 60 per cent. and 80 -per cent. respectively, steel can easily be given 80 per cent. Being -also less in section, resistance to air travel is again less as in the -case of wood. In fact, steel scores all round. Weight of magnalium : -weight of aluminium :: 8:9. - -Sec. 9. =Alloys.=--During recent years scores, hundreds, possibly -thousands of different alloys have been tried and experimented on, but -steel still easily holds its own. It is no use a substance being -lighter than another volume for volume, it must be _lighter and -stronger weight for weight_, to be superior for aeronautical purpose, -and if the difference be but slight, question of _bulk_ may decide it -as offering _less resistance_. - -Sec. 10. =Sheet Ebonite.=--This substance is sometimes useful for -experiments with small propellers, for it can be bent and moulded in -hot water, and when cold sets and keeps its shape. _Vulcanized fibre_ -can be used for same purpose. _Sheet celluloid_ can be used in the -same way, but in time it becomes brittle and shrinks. _Mica_ should be -avoided. _Jointless cane_ in various sizes is a very useful -material--the main aerofoil can be built of it, and it is useful for -skids, and might be made more use of than it is.[38] _Three ply wood_, -from 1/50 in. in thickness, is now on the market. Four or five ply -wood can also be obtained. To those desiring to build models having -wooden aerofoils such woods offer the advantage of great strength and -extreme lightness. - -Referring to Table V. (Timber) at the end of the book, apparently the -most suitable wood is Lombardy poplar; but its light weight means -increased bulk, i.e. additional air resistance. Honduras mahogany is -really a better all-round wood, and beech is not far behind. - -Resilience is an important factor. Ash heads the list; but mahogany's -factor is also good, and in other respects superior. - -Lombardy poplar ought to be a very good wood for propellers, owing to -its lightness and the ease with which it can be worked. - -_Hollow reeds_, and even _porcupine quills_, have been pressed into -the service of the model maker, and owing to their great strength and -extreme lightness, more especially the latter, are not without their -uses. - -FOOTNOTES: - -[38] The chief advantage of cane--its want of stiffness, or facility -in bending--is for some parts of the machine its chief disadvantage, -where stiffness with resilience is most required. - - - - -CHAPTER VIII. - -HINTS ON THE BUILDING OF MODEL AEROPLANES. - - -Sec. 1. The chief difficulty in the designing and building of model -aeroplanes is to successfully combat the conflicting interests -contained therein. Weight gives stability, but requires extra -supporting surface or a higher speed, i.e. more power, i.e. more -weight. Inefficiency in one part has a terrible manner of repeating -itself; for instance, suppose the aerofoil surface inefficient--badly -designed--this means more resistance; more resistance means more -power, i.e. weight, i.e. more surface, and so on _ad infinitum_. - -It is because of circumstances like the above that it is so difficult -to _design_ really good and efficient flying models; the actual -building of them is not so difficult, but few tools are required, none -that are expensive or difficult to use. - -In the making of any particular model there are special points that -require special attention; but there are certain general rules and -features which if not adhered to and carefully carried out, or as -carefully avoided, will cause endless trouble and failure. - -Sec. 2. In constructing a model aeroplane, or, indeed, any piece of -aerial apparatus, it is very important not to interrupt the continuity -of any rib, tube, spar, etc., by drilling holes or making too thinned -down holding places; if such be done, additional strength by binding -(with thread, not wire), or by slipping a small piece of slightly -larger tube over the other, must be imparted to the apparatus. - -Sec. 3. Begin by making a simple monoplane, and afterwards as you gain -skill and experience proceed to construct more elaborate and -scientific models. - -Sec. 4. Learn to solder--if you do not know how to--it is absolutely -essential. - -Sec. 5. Do not construct models (intended for actual flight) with a -tractor screw-main plane in front and tail (behind). Avoid them as you -would the plague. Allusion has already been made in the Introduction -to the difficulty of getting the centre of gravity sufficiently -forward in the case of Bleriot models; again with the main aerofoil in -front, it is this aerofoil and not the balancing elevator, or tail, -that _first_ encounters the upsetting gust, and the effect of such a -gust acting first on the larger surface is often more than the -balancer can rectify in time to avert disaster. The proper place for -the propeller is behind, in the wake of the machine. If the screw be -in front the backwash from it strikes the machine and has a decidedly -retarding action. It is often contended that it drives the air at an -increased velocity under (and over) the main aerofoil, and so gives a -greater lifting effect. But for proper lifting effect which it can -turn without effort into air columns of proper stream line form what -the aerofoil requires is undisturbed air--not propeller backwash. - -The rear of the model is the proper place for the propeller, in the -centre of greatest air disturbance; in such a position it will recover -a portion of the energy lost in imparting a forward movement to the -air, caused by the resistance, the model generally running in such -air--the slip of the screw is reduced to a corresponding degree--may -even vanish altogether, and what is known as negative slip occur. - -Sec. 6. Wooden or metal aerofoils are more efficient than fabric covered -ones. But they are only satisfactory in the smaller sizes, owing, for -one thing, to the smash with which they come to the ground. This being -due to the high speed necessary to sustain their weight. For -larger-sized models fabric covered aerofoils should be used. - -Sec. 7. As to the shape of such, only three need be considered--the (_a_) -rectangular, (_b_) the elongated ellipse, (_c_) the chamfered rear -edge. - -[Illustration: FIG. 48.--(_a_), (_b_), (_c_).] - -Sec. 8. The stretching of the fabric on the aerofoil framework requires -considerable care, especially when using silk. It is quite possible, -even in models of 3 ft. to 4 ft. spread, to do without "ribs," and -still obtain a fairly correct aerocurve, if the material be stretched -on in a certain way. It consists in getting a correct longitudinal and -transverse tension. We will illustrate it by a simple case. Take a -piece of thickish steel pianoforte wire, say, 18 in. long, bend it -round into a circle, allowing 1/2 in. to 1 in. to overlap, tin and -solder, bind this with soft very thin iron wire, and again solder -(always use as little solder as possible). Now stitch on to this a -piece of nainsook or silk, deforming the circle as you do so until it -has the accompanying elliptical shape. The result is one of double -curvature; the transverse curve (dihedral angle) can be regulated by -cross threads or wires going from A to B and C to D. - -[Illustration: FIG. 49.] - -[Illustration: FIG. 49A.--MR. T.W.K. CLARKE'S 1 OZ. MODEL.] - -The longitudinal curve on the camber can be regulated by the original -tension given to it, and by the manner of its fixing to the main -framework. Suitable wire projections or loops should be bound to it by -wire, and these fastened to the main framework by binding with _thin_ -rubber cord, a very useful method of fastening, since it acts as an -excellent shock absorber, and "gives" when required, and yet -possesses quite sufficient practical rigidity. - -Sec. 9. Flexible joints are an advantage in a biplane; these can be made -by fixing wire hooks and eyes to the ends of the "struts," and holding -them in position by binding with silk or thread. Rigidity is obtained -by use of steel wire stays or thin silk cord. - -[Illustration: FIG. 49B.--MR. T.W.K. CLARKE'S 1 OZ. MODEL. - -Showing the position of C. of G., or point of support.] - -Sec. 10. Owing to the extra weight and difficulties of construction on so -small a scale it is not desirable to use "double surface" aerofoils -except on large size power-driven models. - -Sec. 11. It is a good plan not to have the rod or tube carrying the -rubber motor connected with the outrigger carrying the elevator, -because the torque of the rubber tends to twist the carrying -framework, and interferes with the proper and correct action of the -elevator. If it be so connected the rod must be stayed with piano -wire, both longitudinally (to overcome the pull which we know is very -great), and also laterally, to overcome the torque. - -[Illustration: FIG. 49C.--A LARGE MODEL AEROPLANE. - -Shown without rubber or propellers. Designed and constructed by the -writer. As a test it was fitted with two 14 in. propellers revolving -in the _same_ direction, and made some excellent flights under these -conditions, rolling slightly across the wind, but otherwise keeping -quite steady. Total weight, 11/2 lb.; length, 6 ft.; span of main -aerofoil, 5 ft. Constructed of bamboo, cane, and steel wire. Front -skids steel wire. Back skids cane. Aerofoil covering nainsook.] - - -Sec. 12. Some builders place the rubber motor above the rod, or bow frame -carrying the aerofoils, etc., the idea being that the pull of the -rubber distorts the frame in such a manner as to "lift" the elevator, -and so cause the machine to rise rapidly in the air. This it does; but -the model naturally drops badly at the finish and spoils the effect. -It is not a principle that should be copied. - -[Illustration: FIG. 49D.--A VERY LIGHT WEIGHT MODEL. - -Constructed by the author. Provided with twin propellers of a modified -Fleming-Williams type. This machine flew well when provided with an -abnormal amount of rubber, owing to the poor dynamic thrust given by -the propellers.] - -Sec. 13. In the Clarke models with the small front plane, the centre of -pressure is slightly in front of the main plane. - -The balancing point of most models is generally slightly in front, or -just within the front edge of the main aerofoil. The best plan is to -adjust the rod carrying the rubber motor and propeller until the best -balance is obtained, then hang up the machine to ascertain the centre -of gravity, and you will have (approximately) the centre of pressure. - -[Illustration: FIG. 49E.--USEFUL FITTINGS FOR MODELS. - -1. Rubber tyred wheels. 2. Ball-bearing steel axle shafts. 3. Brass wire -strainers with steel screws; breaking strain 200 lb. 4. Magnalium -tubing. 5. Steel eyebolt. 6. Aluminium "T" joint. 7. Aluminium "L" -piece. 8. Brass brazed fittings. 9. Ball-bearing thrust. 10. Flat -aluminium "L" piece. (_The above illustrations taken (by permission) -from Messrs. Gamage's catalogue on Model Aviation._)] - -Sec. 14. The elevator (or tail) should be of the non-lifting type--in -other words, the entire weight should be carried by the main aerofoil -or aerofoils; the elevator being used simply as a balancer.[39] If the -machine be so constructed that part of the weight be carried by the -elevator, then either it must be large (in proportion) or set up at a -large angle to carry it. Both mean considerably more resistance--which -is to be avoided. In practice this means the propeller being some -little distance in rear of the main supporting surface. - -[Illustration: FIG. 49F.--USEFUL FITTINGS FOR MODELS. - -11. Aluminium ball thrust and racket. 12. Ball-bearing propeller, -thrust, and stay. - -(_The above illustrations taken (by permission) from Messrs. Gamage's -catalogue on Model Aviation._)] - -Sec. 15. In actual flying models "skids" should be used and not "wheels"; -the latter to be of any real use must be of large diameter, and the -weight is prohibitive. Skids can be constructed of cane, imitation -whalebone, steel watch or clock-spring, steel pianoforte wire. Steel -mainsprings are better than imitation whalebone, but steel pianoforte -wire best of all. For larger sized models bamboo is also suitable, as -also ash or strong cane. - -Sec. 16. Apart from or in conjunction with skids we have what are termed -"shock absorbers" to lessen the shock on landing--the same substances -can be used--steel wire in the form of a loop is very effectual; -whalebone and steel springs have a knack of snapping. These shock -absorbers should be so attached as to "give all ways" for a part side -and part front landing as well as a direct front landing. For this -purpose they should be lashed to the main frame by thin indiarubber -cord. - -Sec. 17. In the case of a biplane model the "gap" must not be less than -the "chord"--preferably greater. - -In a double monoplane (of the Langley type) there is considerable -"interference," i.e. the rear plane is moving in air already acted on -by the front one, and therefore moving in a downward direction. This -means decreased efficiency. It can be overcome, more or less, by -varying the dihedral angle at which the two planes are set; but cannot -be got rid of altogether, or by placing them far apart. In biplanes -not possessing a dihedral angle--the propeller can be placed -_slightly_ to one side--in order to neutralise the torque of the -propeller--the best portion should be found by experiment--unless the -pitch be very large; with a well designed propeller this is not by any -means essential. If the propeller revolve clockwise, place it towards -the right hand of the machine, and vice versa. - -Sec. 18. In designing a model to fly the longest possible distance the -monoplane type should be chosen, and when desiring to build one that -shall remain the longest time in the air the biplane or triplane type -should be adopted.[40] For the longest possible flight twin propellers -revolving in opposite directions[41] are essential. To take a concrete -case--one of the writer's models weighed complete with a single -propeller 81/2 oz. It was then altered and fitted with two propellers -(same diameter and weight); this complete with double rubber weighed -101/4 oz. The advantage double the power. Weight increased only 20 -per cent., resistance about 10 per cent., total 30 per cent. Gain 70 -per cent. Or if the method of gearing advocated (see Geared Motors) be -adopted then we shall have four bunches of rubber instead of two, and -can thereby obtain so many more turns.[42] The length of the strands -should be such as to render possible at least a thousand turns. - -The propellers should be of large diameter and pitch (not less than -35 deg. at the tips), of curved shape, as advocated in Sec. 22 ch. v.; the -aerofoil surface of as high an aspect ratio as possible, and but -slight camber if any; this is a very difficult question, the question -of camber, and the writer feels bound to admit he has obtained as long -flights with surfaces practically flat, but which do, of course, -camber slightly in a suitable wind, as with stiffer cambered surfaces. - -Wind cambered surfaces are, however, totally unsuitable in gusty -weather, when the wind has frequently a downward trend, which has the -effect of cambering the surface the wrong way about, and placing the -machine flat on the ground. Oiled or specially prepared silk of the -lightest kind should be used for surfacing the aerofoils. Some form of -keel, or fin, is essential to assist in keeping the machine in a -straight course, combined with a rudder and universally jointed -elevator. - -The manner of winding up the propellers has already been referred to -(_see_ chap. iii., Sec. 9). A winder is essential. - -Another form of aerofoil is one of wood (as in Clarke's flyers) or -metal, such a machine relying more on the swiftness of its flight than -on its duration. In this the gearing would possibly not be so -advantageous--but experiment alone could decide. - -The weight of the machine would require to be an absolute minimum, and -everything not absolutely essential omitted. - -It is quite possible to build a twin-screw model on one central stick -alone; but the isosceles triangular form of framework, with two -propellers at the base corners, and the rubber motors running along -the two sides and terminating at the vertex, is preferred by most -model makers. It entails, of course, extra weight. A light form of -skid, made of steel pianoforte wire, should be used. As to the weight -and size of the model, the now famous "one-ouncers" have made some -long flights of over 300 yards[43]; but the machine claiming the -record, half a mile,[44] weighs about 10 oz. And apart from this -latter consideration altogether the writer is inclined to think that -from 5 oz. to 10 oz. is likely to prove the most suitable. It is not -too large to experiment with without difficulty, nor is it so small as -to require the skill of a jeweller almost to build the necessary -mechanism. The propeller speed has already been discussed (_see_ ch. -v., Sec. 15). The model will, of course, be flown with the wind. The -_total_ length of the model should be at least twice the span of the -main aerofoil. - -FOOTNOTES: - -[39] This is a good plan--not a rule. Good flying models can, of -course, be made in which this does not hold. - -[40] This is in theory only: in practice the monoplane holds both -records. - -[41] The best position for the propellers appears to be one in front -and one behind, when extreme lightness is the chief thing desired. - -[42] Because the number of strands of rubber in each bunch will be -much less. - -[43] Mr. Burge Webb claims a record of 500 yards for one of his. - -[44] Flying, of course, with the wind. _Note._--In the "Model -Engineer" of July 7, 1910, will be found an interesting account (with -illustrations) of Mr. W.G. Aston's 1 oz. model, which has remained in -the air for over a minute. - - - - -CHAPTER IX. - -THE STEERING OF THE MODEL. - - -Sec. 1. Of all the various sections of model aeroplaning that which is -the least satisfactory is the above. - -The torque of the propeller naturally exerts a twisting or tilting -effect upon the model as a whole, the effect of which is to cause it -to fly in (roughly speaking) a circular course, the direction -depending on whether the pitch of the screw be a right or left handed -one. There are various devices by which the torque may be -(approximately) got rid of. - -Sec. 2. In the case of a monoplane, by not placing the rod carrying the -rubber motor in the exact centre of the main aerofoil, but slightly to -one side, the exact position to be determined by experiment. - -In a biplane the same result is obtained by keeping the rod in the -centre, but placing the bracket carrying the bearing in which the -propeller shaft runs at right angles horizontally to the rod to obtain -the same effect. - -Sec. 3. The most obvious solution of the problem is to use _two_ equal -propellers (as in the Wright biplane) of equal and opposite pitch, -driven by two rubber motors of equal strength. - -Theoretically this idea is perfect. In practice it is not so. It is -quite possible, of course, to use two rubber motors of an equal number -of strands (equality should be first tested by _weighing_). It should -be possible to obtain two propellers of equal and opposite pitch, -etc., and it is also possible to give the rubber motors the same -number of turns. In practice one is always wound up before the other. -This is the first mistake. They should be wound up _at the same time_, -using a double winder made for the purpose. - -The fact that this is _not_ done is quite sufficient to give an -unequal torsion. The friction in both cases must also be exactly -equal. Both propellers must be released at exactly the same instant. - -Supposing _all_ these conditions fulfilled (in practice they never -are), supposing also the propellers connected by gearing (prohibitive -on account of the weight), and the air quite calm (which it never is), -then the machine should and undoubtedly would _fly straight_. - -For steering purposes by winding up one propeller _many more times_ -than the other, the aeroplane can generally speaking be steered to the -right or left; but from what I have both seen and tried twin-screw -model aeroplanes are _not_ the success they are often made out to be, -and they are much more troublesome to deal with, in spite of what some -say to the contrary. - -The solution of the problem of steering by the use of two propellers -is only partially satisfactory and reliable, in fact, it is no -solution at all.[45] The torque of the propeller and consequent -tilting of the aeroplane is not the only cause at work diverting the -machine from its course. - -Sec. 4. As it progresses through the air it is constantly meeting air -currents of varying velocity and direction, all tending to make the -model deviate more or less from its course; the best way, in fact, the -only way, to successfully overcome such is by means of _speed_, by -giving the aeroplane a high velocity, not of ten or twelve to fifteen -miles an hour, as is usual in built up fabric-covered aerofoils, but a -velocity of twenty to thirty miles an hour, attainable only in models -(petrol or steam driven) or by means of wooden or metal aerofoils. - -Sec. 5. Amongst devices used for horizontal steering are vertical "FINS." -These should be placed in the rear above the centre of gravity. They -should not be large, and can be made of fabric tightly stretched over -a wire frame, or of a piece of sheet magnalium or aluminium, turning -on a pivot at the front edge, adjustment being made by simply twisting -the fin round to the desired angle. As to the size, think of rudder -and the size of a boat, but allow for the difference of medium. The -frame carrying the pivot and fin should be made to slide along the rod -or backbone of the model in order to find the most efficient position. - -Sec. 6. Steering may also be attempted by means of little balancing tips, -or ailerons, fixed to or near the main aerofoil, and pivoted (either -centrally or otherwise) in such a manner that they can be rotated one -in one direction (tilted) and the other in the other (dipped), so as -to raise one side and depress the other. - -Sec. 7. The model can also be steered by giving it a cant to one side by -weighting the tip of the aerofoil on that side on which it is desired -it should turn, but this method is both clumsy and "weighty." - -Sec. 8. Another way is by means of the elevator; and this method, since -it entails no additional surfaces entailing extra resistance and -weight, is perhaps the most satisfactory of all. - -It is necessary that the elevator be mounted on some kind of universal -joint, in order that it may not only be "tipped" or "dipped," but also -canted sideways for horizontal steering. - -Sec. 9. A vertical fin in the rear, or something in the nature of a -"keel," i.e. a vertical fin running down the backbone of the machine, -greatly assists this movement. - -If the model be of the tractor screw and tail (Bleriot) type, then the -above remarks _re_ elevator apply _mutatis mutandis_ to the tail. - -Sec. 10. It is of the most vital importance that the propeller torque -should be, as far as possible, correctly balanced. This can be tested -by balancing the model transversely on a knife edge, winding up the -propeller, and allowing it to run down, and adjusting matters until -the torque and compensatory apparatus balance. As the torque varies -the mean should be used. - -In the case of twin propellers, suspend the model by its centre of -gravity, wind up the propellers, and when running down if the model is -drawn forward without rotation the thrust is equal; if not adjustment -must be made till it does. The easiest way to do this _may_ be by -placing one propeller, the one giving the greater thrust, slightly -nearer the centre. - -In the case of two propellers rotating in opposite directions (by -suitable gearing) on the common centre of two axes, one of the axes -being, of course, hollow, and turning on the other--the rear propeller -working in air already driven back by the other will require a coarser -pitch or larger diameter to be equally efficient. - -FOOTNOTE: - -[45] These remarks apply to rubber driven motors. In the case of -two-power driven propellers in which the power was automatically -adjusted, say, by a gyroscope as in the case of a torpedo--and the -_speed_ of each propeller varied accordingly--the machine could, of -course, be easily steered by such means; but the model to carry such -power and appliances would certainly weigh from 40 lb. to 60 lb. - - - - -CHAPTER X. - -THE LAUNCHING OF THE MODEL. - - -Sec. 1. Generally speaking, the model should be launched into the air -_against the wind_. - -Sec. 2. It should (theoretically) be launched into the air with a -velocity equal to that with which it flies. If it launch with a -velocity in excess of that it becomes at once unstable and has to -"settle down" before assuming its normal line of flight. If the -velocity be insufficient, it may be unable to "pick up" its requisite -velocity in time to prevent its falling to the ground. Models with -wooden aerofoils and a high aspect ratio designed for swift flying, -such as the well-known Clarke flyers, require to be practically -"hurled" into the air. - -Other fabric-covered models capable of sustentation at a velocity of 8 -to 10 miles an hour, may just be "released." - -Sec. 3. Light "featherweight" models designed for long flights when -travelling with the wind should be launched with it. They will not -advance into it--if there be anything of a breeze--but, if well -designed, just "hover," finally sinking to earth on an even keel. Many -ingenious pieces of apparatus have been designed to mechanically -launch the model into the air. Fig. 50 is an illustration of a very -simple but effective one. - -Sec. 4. For large size power-driven models, unless provided with a -chassis and wheels to enable them to run along and rise from the -ground under their own power, the launching is a problem of -considerable difficulty. - -Sec. 5. In the case of rubber-driven models desired to run along and rise -from the ground under their own power, this rising must be -accomplished quickly and in a short space. A model requiring a 50 ft. -run is useless, as the motor would be practically run out by that -time. Ten or twelve feet is the limit; now, in order to rise quickly -the machine must be light and carry considerable surface, or, in other -words, its velocity of sustentation must be a low one. - -[Illustration: FIG. 50.--MR. POYNTER'S LAUNCHING APPARATUS. - -(_Reproduced by permission from the "Model Engineer."_)] - -Sec. 6. It will not do to tip up the elevator to a large angle to make it -rise quickly, because when once off the ground the angle of the -elevator is wrong for actual flight and the model will probably turn a -somersault and land on its back. I have often seen this happen. If the -elevator be set at an increased angle to get it to rise quickly, then -what is required is a little mechanical device which sets the elevator -at its proper flight angle when it leaves the ground. Such a device -does not present any great mechanical difficulties; and I leave it to -the mechanical ingenuity of my readers to devise a simple little -device which shall maintain the elevator at a comparatively large -angle while the model is on the ground, but allowing of this angle -being reduced when free flight is commenced. - -Sec. 7. The propeller most suitable to "get the machine off the ground" -is one giving considerable statical thrust. A small propeller of fine -pitch quickly starts a machine, but is not, of course, so efficient -when the model is in actual flight. A rubber motor is not at all well -adapted for the purpose just discussed. - -Sec. 8. Professor Kress uses a polished plank (down which the models slip -on cane skids) to launch his models. - -Sec. 9. When launching a twin-screw model the model should be held by -each propeller, or to speak more correctly, the two brackets holding -the bearings in which the propeller shafts run should be held one in -each hand in such a way, of course, as to prevent the propellers from -revolving. Hold the machine vertically downwards, or, if too large for -this, allow the nose to rest slightly on the ground; raise (or swing) -the machine up into the air until a little more than horizontal -position is attained, and boldly push the machine into the air (moving -forward if necessary) and release both brackets and screws -simultaneously.[46] - -Sec. 10. In launching a model some prefer to allow the propellers to -revolve for a few moments (a second, say) _before_ actually launching, -contending that this gives a steadier initial flight. This is -undoubtedly the case, see note on page 111. - -Sec. 11. In any case, unless trying for a height prize, do not point the -nose of the machine right up into the air with the idea that you will -thereby obtain a better flight. - -Launch it horizontally, or at a very small angle of inclination. When -requiring a model to run along a field or a lawn and rise therefrom -this is much facilitated by using a little strip of smooth oilcloth on -which it can run. Remember that swift flying wooden and metal models -require a high initial velocity, particularly if of large size and -weight. If thrown steadily and at the proper angle they can scarcely -be overthrown. - -FOOTNOTE: - -[46] Another and better way--supposing the model constructed with a -central rod, or some suitable holdfast (this should be situated at the -centre of gravity of the machine) by which it can be held in one -hand--is to hold the machine with both hands above the head, the right -hand grasping it ready to launch it, and the left holding the two -propellers. Release the propellers and allow them a brief interval -(about half a second) to start. Then launch boldly into the air. The -writer has easily launched 11/2 lb. models by this means, even in a -high wind. Never launch a model by one hand only. - - - - -CHAPTER XI. - -HELICOPTER MODELS. - - -Sec. 1. There is no difficulty whatever about making successful model -helicopters, whatever there may be about full-sized machines. - -Sec. 2. The earliest flying models were helicopters. As early as 1796 Sir -George Cayley constructed a perfectly successful helicopter model (see -ch. iii.); it should be noticed the screws were superimposed and -rotated in opposite directions. - -Sec. 3. In 1842 a Mr. Phillips constructed a successful power-driven -model helicopter. The model was made entirely of metal, and when -complete and charged weighed 2 lb. It consisted of a boiler or steam -generator and four fans supported between eight arms. The fans had an -inclination to the horizon of 20 deg., and through the arms the steam -rushed on the principle of Hero's engines (Barker's Mill Principle -probably). By the escape of steam from the arms the fans were caused -to revolve with immense energy, so much so that the model rose to an -immense altitude and flew across two fields before it alighted. The -motive power employed was obtained from the combustion of charcoal, -nitre and gypsum, as used in the original fire annihilator; the -products of combustion mixing with water in the boiler and forming -gas-charged steam, which was delivered at high pressure from the -extremities of the eight arms.[47] This model and its flight (fully -authenticated) is full of interest and should not be lost sight of, as -in all probability being the first model actuated by steam which -actually flew. - -The helicopter is but a particular phase of the aeroplane. - -Sec. 4. The simplest form of helicopter is that in which the torque of -the propeller is resisted by a vertical loose fabric plane, so -designed as itself to form a propeller, rotating in the opposite -direction. These little toys can be bought at any good toy shop from -about 6_d._ to 1_s._ Supposing we desire to construct a helicopter of -a more ambitious and scientific character, possessing a vertically -rotating propeller or propellers for horizontal propulsion, as well as -horizontally rotating propellers for lifting purposes. - -[Illustration: FIG. 51.--INCORRECT WAY OF ARRANGING SCREWS.] - -Sec. 5. There is one essential point that must be carefully attended to, -and that is, _that the horizontal propulsive thrust must be in the -same plane as the vertical lift_, or the only effect will be to cause -our model to turn somersaults. I speak from experience. - -When the horizontally revolving propellers are driven in a horizontal -direction their "lifting" powers will be materially increased, as they -will (like an ordinary aeroplane) be advancing on to fresh undisturbed -air. - -Sec. 6. I have not for ordinary purposes advocated very light weight wire -framework fabric-covered screws, but in a case like this where the -thrust from the propeller has to be more than the total weight of the -machine, these might possibly be used with advantage. - -Sec. 7. Instead of using two long vertical rods as well as one long -horizontal one for the rubber strands, we might dispense with the two -vertical ones altogether and use light gearing to turn the torque -action through a right angle for the lifting screws, and use three -separate horizontal rubber strands for the three propellers on a -suitable light horizontal framework. Such should result in a -considerable saving of weight. - -[Illustration: FIG. 52.--CORRECT MANNER. A, B, C = Screws.] - -Sec. 8. The model would require something in the nature of a vertical fin -or keel to give the sense of direction. Four propellers, two for -"lift" and two for "drift," would undoubtedly be a better -arrangement. - -FOOTNOTE: - -[47] Report on First Exhibition of Aeronautical Society of Great -Britain, held at Crystal Palace, June 1868. - - - - -CHAPTER XII. - -EXPERIMENTAL RECORDS. - - -A model flying machine being a scientific invention and not a toy, -every devotee to the science should make it his or her business to -keep, as far as they are able, accurate and scientific records. For by -such means as this, and the making known of the same, can a _science_ -of model aeroplaning be finally evolved. The following experimental -entry forms, left purposely blank to be filled in by the reader, are -intended as suggestions only, and can, of course, be varied at the -reader's discretion. When you _have_ obtained carefully established -data, do not keep them to yourself, send them along to one of the -aeronautical journals. Do not think them valueless; if carefully -arranged they cannot be that, and may be very valuable. - - -EXPERIMENTAL DATA. - - FORM I. - - Column Headings: - - A: Model - B: Weight - C: Area of Supporting Surface - D: Aspect Ratio - E: Average Length of Flight in Feet - F: Maximum Flight - G: Time of Flight, A. average - H: M. maximum - I: Kind and Direction of Wind - J: Camber - K: Angle of Inclination of Main Aerofoil to Line of Flight - - -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- - A | B | C | D | E | F | G | H | I | J | K - -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- - | | | | | | A | M | | | - 1 | | | | | | | | | | - 2 | | | | | | | | | | - 3 | | | | | | | | | | - 4 | | | | | | | | | | - 5 | | | | | | | | | | - 6 | | | | | | | | | | - 7 | | | | | | | | | | - 8 | | | | | | | | | | - 9 | | | | | | | | | | - 10 | | | | | | | | | | - 11 | | | | | | | | | | - 12 | | | | | | | | | | - | | | | | | | | | | - -----+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- - - FORM I.--_continued_. - - Column Headings: - - A: Model - B: Weight of (Rubber) Motor - C: Kind of Rubber, Flat, Square or Round - D: Lenght in Inches and Number of Strands - E: Number of Turns - F: Condition at End of Flight - G: Number of Propellers (No.) and Diameter (Diam.) - H: Number of Blades - I: Disc Area (DiscA.) and Pitch (Pitch) - J: Percentage of Slip - K: Thrust - L: Torque in Inche-Ounces - - ----+----+----+-----+----+----+-----+----+-----+----+----+----+ - A | B | C | D | E | F | G | H | I | J | K | L | - ----+----+----+-----+----+----+-----+----+-----+----+----+----+ - | | | | | | | | | | | | | | | - 1 | | | | | | | | | | | | | | | - 2 | | | | | | | | | | | | | | | - 3 | | | | | | | | | | | | | | | - 4 | | | | | | | | | | | | | | | - 5 | | | | | | | | | | | | | | | - 6 | | | | | | | | | | | | | | | - 7 | | | | | | | | | | | | | | | - 8 | | | | | | | | | | | | | | | - 9 | | | | | | | | | | | | | | | - 10 | | | | | | | | | | | | | | | - 11 | | | | | | | | | | | | | | | - 12 | | | | | | | | | | | | | | | - | | | | | | | | | | | | | | | - ----+----+----+-----+----+----+-----+----+-----+----+----+----+ - - - - -CHAPTER XIII. - -MODEL FLYING COMPETITIONS. - - -Sec. 1. From time to time flying competitions are arranged for model -aeroplanes. Sometimes these competitions are entirely open, but more -generally they are arranged by local clubs with both closed and open -events. - -No two programmes are probably exactly alike, but the following may be -taken as fairly representative:-- - -1. Longest flight measured in a straight line (sometimes both with and -against the wind).[48] - -2. Stability (both longitudinal and transverse). - -3. Longest glide when launched from a given height without power, but -with motor and propeller attached. - -4. Steering. - -5. Greatest height. - -6. The best all-round model, including, in addition to the above, -excellence in building. - -Generally so many "points" or marks are given for each test, and the -model whose aggregate of points makes the largest total wins the -prize; or more than one prize may be offered-- - -One for the longest flight. - -One for the swiftest flight over a measured distance. - -One for the greatest height. - -One for stability and steering. - -And one for the best all-round model. - -The models are divided into classes:-- - -Sec. 2. _Aero Models Association's Classification, etc._ - - A. Models of 1 sq. ft. surface and under. - B. " 2 sq. ft. " " - C. " 4 sq. ft. " " - D. " 8 sq. ft. " " - E. " over 8 sq. ft. - -All surfaces, whether vertical, horizontal, or otherwise, to be -calculated together for the above classification. - -All round efficiency--marks or points as percentages:-- - - Distance 40 per cent. - Stability 35 " - Directional control 15 " - Gliding angle 10 "[49] - -Two prizes:-- - -One for length of flight. - -One for all-round efficiency (marked as above). - -Every competitor to be allowed three trials in each competition, the -best only to count. - -All flights to be measured in a straight line from the starting to the -landing point. - -Repairs may be made during the competition at the direction of the -judges.[50] - -There are one or two other points where flights are _not_ made with -and against the wind. The competitors are usually requested to start -their models from within a given circle of (say) six feet diameter, -and fly them _in any direction_ they please. - -"Gliding angle" means that the model is allowed to fall from a height -(say) of 20 ft. - -[Illustration: FIG. 53.--MODEL DESIGNED AND CONSTRUCTED BY THE AUTHOR -FOR "GREATEST HEIGHT." - -A very lightly built model with a very low aspect ratio, and screw -giving a very powerful dynamic thrust, and carrying rather a large -amount of rubber. Climbs in left-handed spirals.] - -"Directional control," that the model is launched in some specified -direction, and must pass as near as possible over some indicated -point. - -The models are practically always launched by hand. - -Sec. 3. Those who desire to win prizes at such competitions would do well -to keep the following points well in mind. - -1. The distance is always measured in a straight line. It is -absolutely essential that your model should be capable of flying -(approximately) straight. To see, as I have done, model after model -fly quite 150 to 200 yards and finish within 50 yards of the -starting-point (credited flight 50 yards) is useless, and a severe -strain on one's temper and patience. - -[Illustration: FIG. 54.--THE GAMAGE CHALLENGE CUP. - -Open Competition for longest flight. Crystal Palace, July 27. Won by -Mr. E.W. Twining.] - -[Illustration: FIG. 55.--MEDAL WON BY THE AUTHOR IN THE SAME -COMPETITION.] - -2. Always enter more than one model, there nearly always is an -entrance fee; never mind the extra shilling or so. Go in to win. - -3. It is not necessary that these models should be replicas of one -another. On some days a light fabric-covered model might stand the -best chance; on another day, a swift flying wooden or metal aerofoil. - -Against the wind the latter have an immense advantage; also if the day -be a "gusty" one.[51] - -4. Always make it a point of arriving early on the ground, so that you -can make some trial flights beforehand. Every ground has its local -peculiarities of air currents, etc. - -5. Always be ready in time, or you may be disqualified. If you are -flying a twin-screw model use a special winder, so that both -propellers are wound up at the same time, and take a competent friend -with you as assistant. - -6. For all-round efficiency nothing but a good all-round model, which -can be absolutely relied on to make a dozen (approximately) equivalent -flights, is any good. - -7. In an open distance competition, unless you have a model which you -can rely on to make a _minimum_ flight of 200 yards, do not enter -unless you know for certain that none of the "crack" flyers will be -present. - -8. Do not neglect the smallest detail likely to lead to success; be -prepared with spare parts, extra rubber, one or two handy tools, wire, -thread, etc. Before a lecture, that prince of experimentalists, -Faraday, was always careful to see that the stoppers of all the -bottles were loose, so that there should be no delay or mishap. - -9. If the rating of the model be by "weight" (1 oz., 2 oz., 4 oz., -etc.) and not area, use a model weighing from 10 oz. to a pound. - -10. If there is a greatest height prize, a helicopter model should win -it.[52] (The writer has attained an altitude of between three and four -hundred feet with such.) The altitude was arrived at by observation, -not guesswork. - -11. It is most important that your model should be able to "land" -without damage, and, as far as possible, on an even keel; do not omit -some form of "skid" or "shock-absorber" with the idea of saving -weight, more especially if your model be a biplane, or the number of -flights may be restricted to the number "one." - -12. Since the best "gliding" angle and "flying" angle are not the -same, being, say, 7 deg. in the former case and 1 deg.-3 deg., say, in the latter, -an adjustable angle might in some cases be advantageous. - -13. Never turn up at a competition with a model only just finished and -practically untested which you have flown only on the morning of the -competition, using old rubber and winding to 500 turns; result, a -flight of 250 yards, say. Arrived on the competition ground you put on -new rubber and wind to 750 turns, and expect a flight of a quarter of -a mile at least; result 70 yards, _measured in a straight line_ from -the starting-point. - -14. Directional control is the most difficult problem to overcome with -any degree of success under all adverse conditions, and 15 per cent., -in the writer's opinion, is far too low a percentage; by directional I -include flying in a straight line; personally I would mark for -all-round efficiency: (A) distance and stability, 50 per cent.; (B) -directional control, 30 per cent.; (C) duration of flight, 20 per -cent. In A the competitor would launch his model _in any direction_; -in B as directed by the judges. No separate flights required for C. - -FOOTNOTES: - -[48] The better way, undoubtedly, is to allow the competitor to choose -his direction, the starting "circle" only to be fixed. - -[49] Or 10 per cent. for duration of flight. - -[50] In another competition, held under the rules and regulations of -the Kite and Model Aeroplane Association for the best all-round model, -open to the world, for machines not under 2 sq. ft. of surface, the -tests (50 marks for each) were:--A. Longest flight in a straight line. -B. Circular flight to the right. C. Circular flight to the left. D. -Stability and landing after a flight. E. Excellence in building of the -model. - -[51] On the assumption that the model will fly straight. - -[52] If permitted to enter; if not see Fig. 53. - - - - -CHAPTER XIV. - -USEFUL NOTES, TABLES, FORMULAE, ETC. - - -Sec. 1. COMPARATIVE VELOCITIES. - - Miles per hr. Feet per sec. Metres per sec. - 10 = 14.7 = 4.470 - 15 = 22 = 6.705 - 20 = 29.4 = 8.940 - 25 = 36.7 = 11.176 - 30 = 44 = 13.411 - 35 = 51.3 = 15.646 - -Sec. 2. A metre = 39.37079 inches. - - _In order to convert_:-- - Metres into inches multiply by 39.37 - " feet " 3.28 - " yards " 1.09 - " miles " 0.0006214 - Miles per hour into ft. per min. multiply by 88.0 - " min. " sec. " 88.0 - " hr. into kilometres per hr. " 1.6093 - " " metres per sec. " 0.44702 - Pounds into grammes multiply by 453.593 - " kilogrammes " 0.4536 - -Sec. 8. Total surface of a cylinder = circumference of base x height + 2 -area of base. - -Area of a circle = square of diameter x 0.7854. - -Area of a circle = square of rad. x 3.14159. - -Area of an ellipse = product of axes x 0.7854. - -Circumference of a circle = diameter x 3.14159. - -Solidity of a cylinder = height x area of base. - -Area of a circular ring = sum of diameters x difference of diameters x -0.7854. - -For the area of a sector of a circle the rule is:--As 360 : number of -degrees in the angle of the sector :: area of the sector : area of -circle. - -To find the area of a segment less than a semicircle:--Find the area -of the sector which has the same arc, and subtract the area of the -triangle formed by the radii and the chord. - -The areas of corresponding figures are as the squares of corresponding -lengths. - - Sec. 4. 1 mile = 1.609 kilometres. - 1 kilometre = 1093 yards. - 1 oz. = 28.35 grammes. - 1 lb. = 453.59 " - 1 lb. = 0.453 kilogrammes. - 28 lb. = 12.7 " - 112 lb. = 50.8 " - 2240 lb. = 1016 " - 1 kilogram = 2.2046 lb. - 1 gram = 0.0022 lb. - 1 sq. in. = 645 sq. millimetres. - 1 sq. ft. = 0.0929 sq. metres. - 1 sq. yard = 0.836 " - 1 sq. metre = 10.764 sq. ft. - -Sec. 5. One atmosphere = 14.7 lb. per sq. in. = 2116 lb. per sq. ft. = -760 millimetres of mercury. - -A column of water 2.3 ft. high corresponds to a pressure of 1 lb. per -sq. in. - -1 H.P. = 33,000 ft.-lb. per min. = 746 watts. - -Volts x amperes = watts. - -{pi} = 3.1416. _g_ = 32.182 ft. per sec. at London. - -Sec. 6. TABLE OF EQUIVALENT INCLINATIONS. - - Rise. Angle in Degs. - 1 in 30 1.91 - 1 " 25 2.29 - 1 " 20 2.87 - 1 " 18 3.18 - 1 " 16 3.58 - 1 " 14 4.09 - 1 " 12 4.78 - 1 " 10 5.73 - 1 " 9 6.38 - 1 " 8 7.18 - 1 " 7 8.22 - 1 " 6 9.6 - 1 " 5 11.53 - 1 " 4 14.48 - 1 " 3 19.45 - 1 " 2 30.00 - 1 " {square root}2 45.00 - -Sec. 7. TABLE OF SKIN FRICTION. - -Per sq. ft. for various speeds and surface lengths. - - -----------------+-------------+-------------+-------------+------------ - Velocity of Wind | 1 ft. Plane | 2 ft. Plane | 4 ft. Plane | 8 ft. Plane - -----------------+-------------+-------------+-------------+------------ - 10 | .00112 | .00105 | .00101 | .000967 - 15 | .00237 | .00226 | .00215 | .00205 - 20 | .00402 | .00384 | .00365 | .00349 - 25 | .00606 | .00579 | .00551 | .00527 - 30 | .00850 | .00810 | .00772 | .00736 - 35 | .01130 | .0108 | .0103 | .0098 - -----------------+-------------+-------------+-------------+------------ - -This table is based on Dr. Zahm's experiments and the equation - - _f_ = 0.00000778_l_^{-0.07}_v_^{1.85} - -Where _f_ = skin friction per sq. ft.; _l_ = length of surface; _v_ = -velocity in feet per second. - -In a biplane model the head resistance is probably from twelve to -fourteen times the skin friction; in a racing monoplane from six to -eight times. - -Sec. 8. TABLE I.--(METALS). - - --------------+------------+-----------------+------------- - Material | Specific | Elasticity E[A] | Tenacity - | Gravity | | per sq. in. - --------------+------------+-----------------+------------- - Magnesium | 1.74 | | {22,000- - | | | {32,000 - Magnalium[B] | 2.4-2.57 | 10.2 | - Aluminium- } | | | - Copper[C]} | 2.82 | | 54,773 - Aluminium | 2.6 | 11.1 | 26,535 - Iron | 7.7 (about)| 29 | 54,000 - Steel | 7.8 (about)| 32 | 100,000 - Brass | 7.8-8.4 | 15 | 17,500 - Copper | 8.8 | 36 | 33,000 - Mild Steel | 7.8 | 30 | 60,000 - | | | - --------------+------------+-----------------+------------- - [A] E in millions of lb. per sq. in. - [B] Magnalium is an alloy of magnesium and aluminium. - [C] Aluminium 94 per cent., copper 6 per cent. (the best - percentage), a 6 per cent. alloy thereby doubles the - tenacity of pure aluminium with but 5 per cent. - increase of density. - --------------+------------+-----------------+------------- - -Sec. 9. TABLE II.--WIND PRESSURES. - - _p_ = _kv squared_. - -_k_ coefficient (mean value taken) .003 (miles per hour) = 0.0016 ft. -per second. _p_ = pressure in lb. per sq. ft. _v_ = velocity of wind. - - Miles per hr. Ft. per sec. Lb. per sq. ft. - 10 14.7 0.300 - 12 17.6 0.432 - 14 20.5 0.588 - 16 23.5 0.768 - 18 26.4 0.972 - 20 29.35 1.200 - 25 36.7 1.875 - 30 43.9 2.700 - 35 51.3 3.675 - -Sec. 10. Representing normal pressure on a plane surface by 1; pressure -on a rod (round section) is 0.6; on a symmetrical elliptic cross -section (axes 2:1) is 0.2 (approx.). Similar shape, but axes 6:1, and -edges sharpened (_see_ ch. ii., Sec. 5), is only 0.05, or 1/20, and for -the body of minimum resistance (_see_ ch. ii., Sec. 4) about 1/24. - -Sec. 11. TABLE III.--LIFT AND DRIFT. - -On a well shaped aerocurve or correctly designed cambered surface. -Aspect ratio 4.5. - - Inclination. Ratio Lift to Drift. - 0 deg. 19:1 - 2.87 deg. 15:1 - 3.58 deg. 16:1 - 4.09 deg. 14:1 - 4.78 deg. 12:1 - 5.73 deg. 9.6:1 - 7.18 deg. 7.9:1 - -Wind velocity 40 miles per hour. (The above deduced from some -experiments of Sir Hiram Maxim.) - -At a velocity of 30 miles an hour a good aerocurve should lift 21 oz. -to 24 oz. per sq. ft. - - -Sec. 12. TABLE IV.--LIFT AND DRIFT. - -On a plane aerofoil. - - N = P(2 sin {alpha}/1 + sin squared {alpha}) - - Inclination. Ratio Lift to Drift. - 1 deg. 58.3:1 - 2 deg. 29.2:1 - 3 deg. 19.3:1 - 4 deg. 14.3:1 - 5 deg. 11.4:1 - 6 deg. 9.5:1 - 7 deg. 8.0:1 - 8 deg. 7.0:1 - 9 deg. 6.3:1 - 10 deg. 5.7:1 - - P = 2_kd_ AV squared sin {alpha}. - -A useful formula for a single plane surface. P = pressure supporting -the plane in pounds per square foot, _k_ a constant = 0.003 in miles -per hour, _d_ = the density of the air. - -A = the area of the plane, V relative velocity of translation through -the air, and {alpha} the angle of flight. - -Transposing we have - - AV squared = P/(2_kd_ sin {alpha}) - -If P and {alpha} are constants; then AV squared = a constant or area is -inversely as velocity squared. Increase of velocity meaning diminished -supporting surface (_and so far as supporting surface goes_), diminished -resistance and skin friction. It must be remembered, however, that while -the work of sustentation diminishes with the speed, the work of -penetration varies as the cube of the speed. - - -Sec. 13. TABLE V.--TIMBER. - - Column Headings: - - A. Material - B. Specific Gravity - C. Weight per Cub. Ft. in Lb. - D. Strength per Sq. In. in Lb. - E. Ultimate Breaking Load (Lb.) span 1' x 1" x 1" - F. Relative Resilience in Bending - G. Modulus of Elasticity in millions of Lb. per Sq. In. for Bending - H. Relative Value. Bending Strength compared with Weight - - ---------------+-----+-------+-------------+-------+-----+-----+---- - A |B | C | D |E |F |G | H - ---------------+-----+-------+-------------+-------+-----+-----+---- - Ash | .79 | 43-52 |14,000-17,000| 622 |4.69 |1.55 |13.0 - Bamboo | | 25[A]| 6300[53] | |3.07 |3.20 | - Beech | .69 | 43 |10,000-12,000| 850 | |1.65 |19.8 - Birch | .71 | 45 | 15,000 | 550 | |3.28 |12.2 - Box |1.28 | 80 |20,000-23,000| 815 | | |10.2 - Cork | .24 | 15 | | | | | - Fir (Norway | | | | | | | - Spruce) | .51 | 32 | 9,000-11,000| 450 |3.01 |1.70 |14.0 - American | | | | | | | - Hickory | | 49 | 11,000 | 800 |3.47 |2.40 |16.3 - Honduras | | | | | | | - Mahogany | .56 | 35 | 20,000 | 750 |3.40 |1.60 |21.4 - Maple | .68 | 44 | 10,600 | 750 | | |17.0 - American White | | | | | | | - Pine | .42 | 25 | 11,800 | 450 |2.37 |1.39 |18.0 - Lombardy Poplar| | 24 | 7,000 | 550 |2.89 | 0.77|22.9 - American Yellow| | | | | | | - Poplar | | 44 | 10,000 | |3.63 |1.40 | - Satinwood | .96 | 60 | |1,033 | | |17.2 - Spruce | .50 | 31 | 12,400 | 450 | | |14.5 - Tubular Ash, | | | | | | | - _t_ = 1/8 _d_ | | 47 | | |3.50 |1.55 | - ---------------+-----+-------+-------------+-------+-----+-----+---- - - _t_ = thickness: _d_ = diameter. - - [A] Given elsewhere as 55 and 22,500 (_t_ = 1/3_d_), evidently - regarded as solid. - -Sec. 14.--=Formula connecting the Weight Lifted in Pounds per Square Foot -and the Velocity.=--The empirical formula - - W = (V squaredC)/_g_ - - Where W = weight lifted in lb. per sq. ft. - V = velocity in ft. per sec. - C = a constant = 0.025. - _g_ = 32.2, or 32 approx. - -may be used for a thoroughly efficient model. This gives -(approximately) - - 1 lb. per sq. ft. lift at 25 miles an hour. - 21 oz. " " 30 " - 6 oz. " " 15 " - 4 oz. " " 12 " - 2.7 oz. " " 10 " - -Remember the results work out in feet per second. To convert -(approximately) into miles per hour multiply by 2/3. - -Sec. 15. =Formula connecting Models of Similar Design, but Different -Weights.= - - D {proportional to} {square root}W. - -or in models of _similar design_ the distances flown are proportional -to the square roots of the weights. (Derived from data obtained from -Clarke's flyers.) - -For models from 1 oz. to 24-30 oz. the formula appears to hold very -well. For heavier models it appears to give the heavier model rather -too great a distance. - -Since this was deduced a 1 oz. Clarke model of somewhat similar design -but longer rubber motor has flown 750 ft. at least; it is true the -design is not, strictly speaking, similar, but not too much reliance -must be placed on the above. The record for a 1 oz. model to date is -over 300 yards (with the wind, of course), say 750 ft. in calm air. - -Sec. 16. =Power and Speed.=--The following formula, given by Mr. L. Blin -Desbleds, between these is-- - - W/W{0} = (3_v{0}_)/(4_v_) + 1/4(_v_/_v{0}_) cubed. - - Where _v{0}_ = speed of minimum power - W{0} = work done at speed _v{0}_. - W = work done at speed _v_. - -Making _v_ = 2_v{0}_, i.e. doubling the speed of minimum power, and -substituting, we have finally - - W = (2-3/8)W{0} - -i.e. the speed of an aeroplane can be doubled by using a power 2-3/8 -times as great as the original one. The "speed of minimum power" being -the speed at which the aeroplane must travel for the minimum -expenditure of power. - -Sec. 17. The thrust of the propeller has evidently to balance the - - Aerodynamic resistance = R - The head resistance (including skin friction) = S - -Now according to Renard's theorem, the power absorbed by R + S is a -minimum when - - S = R/3. - -Having built a model, then, in which the total resistance - - = (4/3)R. - -This is the thrust which the propeller should be designed to give. Now -supposing the propeller's efficiency to be 80 per cent., then P--the -minimum propulsion power - - = (4/3)R x 100/80 x 100/75 x _v_. - -Where 25 per cent. is the slip of the screw, _v_ the velocity of the -aeroplane. - -Sec. 18. =To determine experimentally the Static Thrust of a -Propeller.=--Useful for models intended to raise themselves from the -ground under their own power, and for helicopters. - -The easiest way to do this is as follows: Mount the propeller on the -shaft of an electric motor, of sufficient power to give the propeller -1000 to 1500 revolutions per minute; a suitable accumulator or other -source of electric energy will be required, a speedometer or speed -counter, also a voltmeter and ammeter. - -Place the motor in a pair of scales or on a suitable spring balance -(the former is preferable), the axis of the motor vertical, with the -propeller attached. Rotate the propeller so that the air current is -driven _upwards_. When the correct speed (as indicated by the speed -counter) has been attained, notice the difference in the readings if a -spring balance be used, or, if a pair of scales, place weights in the -scale pan until the downward thrust of the propeller is exactly -balanced. This gives you the thrust in ounces or pounds. - -Note carefully the voltage and amperage, supposing it is 8 volts and -10 amperes = 80 watts. - -Remove the propeller and note the volts and amperes consumed to run -the motor alone, i.e. to excite itself, and overcome friction and air -resistance; suppose this to be 8 volts and 2 amperes = 16; the -increased load when the propeller is on is therefore - - 80 - 16 = 64 watts. - -All this increased power is not, however, expended on the propeller. - -The lost power in the motor increases as C squaredR. - -R = resistance of armature and C = current. If we deduct 10 per cent. -for this then the propeller is actually driven by 56 watts. - -Now 746 watts = 1 h.p. - - {therefore} 56/746 = 1/13 h.p. approx. - -at the observed number of revolutions per minute. - -Sec. 19. N.B.--The h.p. required to drive a propeller varies as the cube -of the revolutions. - -_Proof._--Double the speed of the screw, then it strikes the air twice -as hard; it also strikes twice as much air, and the motor has to go -twice as fast to do it. - -Sec. 20. To compare one model with another the formula - - Weight x velocity (in ft. per sec.)/horse-power - -is sometimes useful. - -Sec. 21. =A Horse-power= is 33,000 lb. raised one foot in one minute, or -550 lb. one foot in one second. - -A clockwork spring raised 1 lb. through 41/2 ft. in 3 seconds. What -is its h.p.? - - 1 lb. through 41/2 ft. in 3 seconds - is 1 lb. " 90 ft. " 1 minute. - - {therefore} Work done is 90 ft.-lb. - = 90/33000 = 0.002727 h.p. - -The weight of the spring was 63/4 oz. (this is taken from an actual -experiment), i.e. this motor develops power at the rate of 0.002727 -h.p. for 31/2 seconds only. - -Sec. 22. =To Ascertain the H.P. of a Rubber Motor.= Supposing a propeller -wound up to 250 turns to run down in 15 seconds, i.e. at a mean speed -of 1200 revolutions per minute or 20 per second. Suppose the mean -thrust to be 2 oz., and let the pitch of the propeller be 1 foot. Then -the number of foot-pounds of energy developed - - = (2 oz. x 1200 revols. x 1 ft. (pitch)) / 16 oz. - -= 150 ft.-lb. per minute. - -But the rubber motor runs down in 15 seconds. - - {therefore} Energy really developed is - - = (150 x 15) / 60 = 37.5 ft.-lb. - -The motor develops power at rate of 150/33000 = 0.004545 h.p., but for -15 seconds only. - -Sec. 23. =Foot-pounds of Energy in a Given Weight of Rubber= -(experimental determination of). - - Length of rubber 36 yds. - Weight " 2-7/16 oz. - Number of turns = 200. - - 12 oz. were raised 19 ft. in 5 seconds. - i.e. 3/4 lb. was raised 19 x 12 ft. in 1 minute. - i.e. 1 lb. was raised 19 x 3 x 3 ft. in 1 minute. - = 171 ft. in 1 minute. - -i.e. 171 ft.-lb. of energy per minute. But actual time was 5 seconds. - -{therefore} Actual energy developed by 2-7/16 oz. of rubber of 36 -yards, i.e. 36 strands 1 yard each at 200 turns is - - = 171/12 ft.-lb. - - = 141/4 ft.-lb. - -This allows nothing for friction or turning the axle on which the cord -was wound. Ball bearings were used; but the rubber was not new and -twenty turns were still unwound at the end of the experiment. Now -allowing for friction, etc. being the same as on an actual model, we -can take 3/4 of a ft.-lb. for the unwound amount and estimate the -total energy as 15 ft.-lb. as a minimum. The energy actually developed -being at the rate of 0.0055 h.p., or 1/200 of a h.p. if supposed -uniform. - -Sec. 24. The actual energy derivable from 1 lb. weight of rubber is -stated to be 300 ft.-lb. On this basis 2-7/16 oz. should be capable of -giving 45.7 ft.-lb. of energy, i.e. three times the amount given -above. Now the motor-rubber not lubricated was only given 200 -turns--lubricated 400 could have been given it, 600 probably before -rupture--and the energy then derivable would certainly have been -approximating to 45 ft.-lb., i.e. 36.25. Now on the basis of 300 -ft.-lb. per lb. a weight of 1/2 oz. (the amount of rubber carried in -"one-ouncers") gives 9 ft.-lb. of energy. Now assuming the gliding -angle (including weight of propellers) to be 1 in 8; a perfectly -efficient model should be capable of flying eight times as great a -distance in a horizontal direction as the energy in the rubber motor -would lift it vertically. Now 9 ft.-lb. of energy will lift 1 oz. 154 -ft. Therefore theoretically it will drive it a distance (in yards) of - - (8 x 154)/3 = 410.6 yards. - -Now the greatest distance that a 1 oz. model has flown in perfectly -calm air (which never exists) is not known. Flying with the wind 500 -yards is claimed. Admitting this what allowance shall we make for the -wind; supposing we deduct half this, viz. 250 yards. Then, on this -assumption, the efficiency of this "one ouncer" works out (in -perfectly still air) at 61 per cent. - -The gliding angle assumption of 1 in 8 is rather a high one, possibly -too high; all the writer desires to show is the method of working out. - -Mr. T.W.K. Clarke informs me that in his one-ouncers the gliding -angle is about 1 in 5. - -Sec. 25. =To Test Different Motors or Different Powers of the Same Kind -of Motor.=--Test them on the same machine, and do not use different -motors or different powers on different machines. - -Sec. 26. =Efficiency of a Model.=--The efficiency of a model depends on -the weight carried per h.p. - -Sec. 27. =Efficiency of Design.=--The efficiency of some particular -design depends on the amount of supporting surface necessary at a -given speed. - -Sec. 28. =Naphtha Engines=, that is, engines made on the principle of the -steam engine, but which use a light spirit of petrol or similar agent -in their generator instead of water with the same amount of heat, will -develop twice as much energy as in the case of the ordinary steam -engine. - -Sec. 29.=Petrol Motors.= - - Horse-power. No. of Cylinders. Weight. - 1/4 Single 41/2 lb. - 1/2 to 3/4 " 61/2 " - 11/2 Double 9 " - -Sec. 30. =The Horse-power of Model Petrol Motors.=--Formula for rating of -the above. - - (R.P.M. = revolutions per minute.) - - H.P. = ((Bore) squared x stroke x no. of cylinders x R.P.M.)/12,000 - -If the right-hand side of the equation gives a less h.p. than that -stated for some particular motor, then it follows that the h.p. of the -motor has been over-estimated. - -[Illustration: FIG. 56.] - -Sec. 30A. =Relation between Static Thrust of Propeller and Total Weight -of Model.=--The thrust should be approx. = 1/4 of the weight. - -Sec. 31. =How to find the Height of an Inaccessible Object by Means of -Three Observations taken on the Ground (supposed flat) in the same -Straight Line.=--Let A, C, B be the angular elevations of the object -D, as seen from these points, taken in the same straight line. Let the -distances B C, C A and A B be _a_, _b_, _c_ respectively. And let -required height P D = _h_; then by trigonometry we have (see Fig. 56) - - _h squared_ = _abc_/(_a_ cot squaredA - _c_ cot squaredC + _b_ cot squaredB). - -Sec. 32. =Formula= for calculating the I.H.P. (indicated horse-power) of -a single-cylinder double-acting steam-engine. - -Indicated h.p. means the h.p. actually exerted by the steam in the -cylinder without taking into account engine friction. Brake h.p. or -effective h.p. is the actual h.p. delivered by the crank shaft of the -engine. - - I.H.P. = (2 x S x R x A x P)/33,000. - - Where S = stroke in feet. - R = revolutions per minute. - A = area of piston in inches. - P = mean pressure in lb. exerted per sq. in. on the piston. - -The only difficulty is the mean effective pressure; this can be found -approximately by the following rule and accompanying table. - - -TABLE VI. - - ---------+----------+---------+----------+---------+--------- - Cut-off | Constant | Cut-off | Constant | Cut-off | Constant - ---------+----------+---------+----------+---------+--------- - 1/6 | .566 | 3/8 | .771 | 2/3 | .917 - 1/5 | .603 | .4 | .789 | .7 | .926 - 1/4 | .659 | 1/2 | .847 | 3/4 | .937 - .3 | .708 | .6 | .895 | .8 | .944 - 1/3 | .743 | 5/8 | .904 | 7/8 | .951 - ---------+----------+---------+----------+---------+--------- - -Rule.--"Add 14.7 to gauge pressure of boiler, this giving 'absolute -steam pressure,' multiply this sum by the number opposite the fraction -representing the point of cut-off in the cylinder in accompanying -table. Subtract 17 from the product and multiply the remainder by 0.9. -The result will be very nearly the M.E.P." (R.M. de Vignier.) - - -FOOTNOTE: - -[53] Given elsewhere as 55 and 22,500 (_t_ = 1/3 _d_), evidently -regarded as solid. - - - - -APPENDIX A. - -SOME MODELS WHICH HAVE WON MEDALS AT OPEN COMPETITIONS. - - -[Illustration: FIG. 57.--THE G.P.B. SMITH MODEL.] - -The model shown in Fig. 57 has won more competition medals than any -other. It is a thoroughly well designed[54] and well constructed -model. Originally a very slow flyer, the design has been simplified, -and although by no means a fast flyer, its speed has been much -accelerated. Originally a one-propeller machine, it has latterly been -fitted with twin propellers, with the idea of obtaining more -directional control; but in the writer's opinion, speaking from -personal observation, with but little, if any, success. The steering -of the model is effected by canting the elevator. Originally the -machine had ailerons for the purpose, but these were removed owing, I -understand, to their retarding the speed of the machine. - -In every competition in which this machine has been entered it has -always gained very high marks for stability. - -[Illustration: FIG. 58.--THE GORDON-JONES DIHEDRAL BIPLANE.] - -Up to the time of writing it has not been provided with anything in -the nature of fins or rudder. - -Fig. 58 is a biplane very much after the type of the model just -alluded to, but the one straight and one curved aerofoil surfaces are -here replaced by two parallel aerofoils set on a dihedral angle. The -large size of the propeller should be noted; with this the writer is -in complete agreement. He has not unfortunately seen this model in -actual flight. - -The scientifically designed and beautifully made models illustrated in -Fig. 59 are so well known that any remarks on them appear -superfluous. Their efficiency, so far as their supporting area goes, -is of the highest, as much as 21 oz. per square foot having been -carried. - -[Illustration: FIG. 59.--MESSRS. T.W.K. CLARKE AND CO.'S MODEL -FLYERS.] - -For illustrations, etc., of the Fleming-Williams model, _see_ ch. v., -Sec. 23. - -(Fig. 60.) This is another well-constructed and efficient model, the -shape and character of the aerofoil surfaces much resembling those of -the French toy monoplane AL-MA (see Sec. 4, ch. vii.), but they are -supported and held in position by quite a different method, a neat -little device enabling the front plane to become partly detached on -collision with any obstacle. The model is provided with a keel (below -the centre of gravity), and rudder for steering; in fact, this machine -especially claims certainty of directional control. The writer has -seen a number of flights by this model, but it experiences, like other -models, the greatest difficulty in keeping straight if the conditions -be adverse. - -The model which will do this is, in his opinion, yet to be evolved. -The small size of the propellers is, of course, in total disagreement -with the author's ideas. All the same, the model is in many respects -an excellent one, and has flown over 300 yards at the time of writing. - -[Illustration: FIG. 60.--THE DING SAYERS MONOPLANE.] - -More than a year ago the author made a number of models with -triangular-shaped aerofoils, using umbrella ribs for the leading edge -and steel piano wire for the trailing, but has latterly used aerofoils -of the elongated ellipse shape. - -Fig. 61 is an illustration of one of the author's latest models which -won a Bronze Medal at the Long Distance Open Competition, held at the -Crystal Palace on July 27, 1910, the largest and most keenly contested -competition held up to that date. - -The best and straightest flight against the wind was made by this -model. - -On the morning of the competition a flight of about 320 yards -(measured in a straight line) was made on Mitcham Common, the model -being launched against the wind so as to gain altitude, and then -flying away with the breeze behind the writer. Duration of flight 50 -seconds. The following are the chief particulars of the -model:--Weight, 71/2 oz. Area of supporting surface, 1-1/3 sq. ft. -Total length, 4 ft. Span of main aerofoil, 25 in. Aspect ratio, 4 : 1. -Diameter of propeller, 14 in. Two strand geared rubber motor, carrying -altogether 28 strands of 1/16 square rubber cord 43 in. long. The -propeller was originally a Venna, but with the weight reduced by -one-third, and considerable alteration made in its central contours. -The front skid of steel pianoforte wire, the rear of jointless cane -wire tipped; the rear skid was a necessity in order to protect the -delicate gearing mechanism, the weight of which was reduced to a -minimum. - -[Illustration: FIG. 61.--THE AUTHOR'S "GRASSHOPPER" MODEL.] - -The very large diameter of the propeller should be noted, being 56 -per cent. of the span. The fin, high above the centre of gravity, was -so placed for transverse stability and direction. At the rear of the -fin was a rudder. The small amount of rubber carried (for a long -distance machine) should also be noted, especially when allowing for -friction in gearing, etc. - -The central rod was a penny bamboo cane, the large aerofoil of -jointless cane and Hart's fabric, and the front aerofoil of steel wire -surfaced with the same material. - - -LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, GREAT WINDMILL -STREET, W., AND DUKE STREET, STAMFORD STREET, S.E. - -FOOTNOTE: - -[54] The design is patented. - - - - - _October, 1910_ - -A SHORT LIST OF - -SCIENTIFIC BOOKS - -PUBLISHED AND SOLD BY - -E. & F.N. SPON, Limited, - -57 Haymarket, London, S.W. - -SOLE ENGLISH AGENTS for the Books of-- - - MYRON C. CLARK, NEW YORK - THE BUSINESS CODE COMPANY, CHICAGO - SPON & CHAMBERLAIN, NEW YORK - - - PAGE - AERONAUTICS 2 - AGRICULTURE 2 - ARCHITECTURE 3 - ARTILLERY 5 - BRIDGES AND ROOFS 5 - BUILDING 3 - CEMENT AND CONCRETE 7 - CIVIL ENGINEERING 8 - DICTIONARIES 11 - DOMESTIC ECONOMY 12 - DRAWING 13 - ELECTRICAL ENGINEERING 14 - FOREIGN EXCHANGE 19 - GAS AND OIL ENGINES 20 - GAS LIGHTING 20 - HISTORICAL; BIOGRAPHICAL 21 - HOROLOGY 22 - HYDRAULICS 22 - INDUSTRIAL CHEMISTRY 24 - IRRIGATION 27 - LOGARITHM TABLES 28 - MANUFACTURES 24 - MARINE ENGINEERING 28 - MATERIALS 30 - MATHEMATICS 31 - MECHANICAL ENGINEERING 33 - METALLURGY 36 - METRIC TABLES 38 - MINERALOGY AND MINING 38 - MUNICIPAL ENGINEERING 45 - NAVAL ARCHITECTURE 28 - ORGANISATION 40 - PHYSICS 41 - PRICE BOOKS 42 - RAILWAY ENGINEERING 43 - SANITATION 45 - STRUCTURAL DESIGN 45 - TELEGRAPH CODES 47 - WARMING; VENTILATION 47 - WATER SUPPLY 48 - WORKSHOP PRACTICE 49 - USEFUL TABLES 52 - MISCELLANEOUS 53 - - - _Full particulars post free on application. - All books are bound in cloth unless otherwise stated._ - - _NOTE: The Prices in this Catalogue apply to books sold in - the United Kingdom only._ - - - AERONAUTICS - - =The Atmosphere=: its characteristics and dynamics. By F.J.B. - CORDEIRO. With 35 illus. 129 pp. medium 8vo. (_New York, 1910_) - - _net_ 10 6 - - =Theory and Practice of Model Aeroplaning.= By V.E. JOHNSON. 61 - illus. 150 pp. crown 8vo. (_1910_) - - _net_ 3 6 - - =How to Build a 20-ft. Biplane Glider.= By A.P. MORGAN. 31 - illus. 60 pp. crown 8vo, limp. (S. & C. SERIES, NO. 14.) (_New - York, 1909_) - - _net_ 1 6 - - =Flight-Velocity.= By A. SAMUELSON. 4 plates, 42 pp. 8vo, - sewed. (_1906_) - - _net_ 2 0 - - =Resistance of Air and the Question of Flying.= By A. - SAMUELSON. 23 illus. 36 pp. 8vo, sewed. (_1905_) - - _net_ 2 0 - - - AGRICULTURE. - - =Hemp.= A Practical Treatise on the Culture for Seed and Fibre. - By S.S. BOYCE. 13 illus. 112 pp. crown 8vo. (_New York, 1900_) - - _net_ 2 0 - - =The Fertilisation of Tea.= By G.A. COWIE. With 17 illus. 68 - pp. crown 8vo, sewed. (_1908_) - - _net_ 2 6 - - =Farm Drainage.= By H.F. FRENCH. 100 illus. 284 pp. crown 8vo. - (_New York, 1904_) - - _net_ 4 6 - - =Talks on Manures.= By J. HARRIS. New edition, 366 pp. crown - 8vo. (_New York, 1893_) - - _net_ 6 6 - - =Coffee=, its Culture and Commerce in all Countries. By C.G.W. - LOCK. 11 plates, 274 pp. crown 8vo. (_1888_) - - 12 6 - - =Sugar, a Handbook for Planters and Refiners.= By the late J.A. - R. NEWLANDS and B.E.R. NEWLANDS. 236 illus. 876 pp. demy 8vo. - (_London, 1909_) - - _net_ 1 5 0 - - =Hops=, their Cultivation, Commerce and Uses. By P.L. SIMMONDS. - 143 pp. crown 8vo. (_1877_) - - 4 6 - - =The Future of Cocoa-Planting=. By H. HAMEL SMITH. With - illustrations, 95 pp. crown 8vo, sewed. (_1908_) - - _net_ 1 0 - - =Estate Fences=, their Choice, Construction and Cost. By A. - VERNON. Re-issue, 150 illus. 420 pp. 8vo. (_1909_) - - _net_ 8 6 - - - ARCHITECTURE AND BUILDING. - - =The Hydropathic Establishment and its Baths.= By R.O. ALLSOP. - 8 plates, 107 pp. demy 8vo. (_1891_) - - 5 0 - - =The Turkish Bath=, its Design and Construction. By R.O. - ALLSOP. 27 illus. 152 pp. demy 8vo. (_1890_) - - 6 0 - - =Public Abattoirs=, their Planning, Design and Equipment. By - R.S. AYLING. 33 plates, 100 pp. demy 4to. (_1908_) - - _net_ 8 6 - - =The Builder's Clerk.= By T. BALES. Second edition, 92 pp. - fcap. 8vo. (_1904_) - - 1 6 - - =Glossary of Technical Terms= used in Architecture and the - Building Trades. By G.J. BURNS. 136 pp. crown 8vo. (_1895_) - - 3 6 - - =Chimney Design and Theory.= By W.W. CHRISTIE. Second edition, - 54 illus. 200 pp. crown 8vo. (_New York, 1902_) - - _net_ 12 6 - - =Approximate Estimates.= By T.E. COLEMAN. Third edition, 481 - pp. oblong 32mo, leather. (_1907_) - - _net_ 5 0 - - =Stable Sanitation and Construction.= By T.E. COLEMAN. 183 - illus. 226 pp. crown 8vo. (_1897_) - - _net_ 6 0 - - =Architectural Examples= in Brick, Stone, Wood and Iron. By W. - FULLERTON. Third edition, 245 plates, 254 pp. demy 4to. - (_1908_) - - _net_ 15 0 - - =Bricklaying System.= By F.B. GILBRETH. Fully illustrated, 321 - pp. 8vo. (_New York, 1909_) - - _net_ 12 6 - - =Field System.= By F.B. GILBRETH. 194 pp. 12mo leather. (_New - York, 1908_) - - _net_ 12 6 - - =The Building Trades Pocket Book.= Compiled by R. HALL. 12mo. - With interchangeable diary - - _net_ 1 6 - - Ditto ditto, in leather - - _net_ 2 6 - - =The Clerk of Works' Vade Mecum.= By G.G. HOSKINS. Seventh - edition, 52 pp. fcap. 8vo. (_1901_) - - 1 6 - - =A Handbook of Formulae, Tables, and Memoranda=, for - Architectural Surveyors and others engaged in Building. By J.T. - HURST. Fifteenth edition, 512 pp. royal 32mo, roan. (_1905_) - - _net_ 5 0 - - =Quantity Surveying=, for the Use of Surveyors, Architects, - Engineers and Builders. By J. LEANING. Fifth edition, 936 pp. - demy 8vo. (_1904_) - - _net_ 1 5 0 - - =Obstruction to Light.= A Graphic Method of determining - Problems of Ancient Lights. By H.B. MOLESWORTH. 9 folding - plates, 4to. (_1902_) - - _net_ 6 0 - - =Suburban Houses.= A series of practical plans. By J.H. - PEARSON. 46 plates and 12 pp. text, crown 4to. (_1905_) - - _net_ 7 6 - - =Solid Bitumens=, their Physical and Chemical Properties and - Chemical Analysis. By S.F. PECKHAM. 23 illus. 324 pp. 8vo. - (_New York, 1909_) - - _net_ 1 1 0 - - =Roman Architecture, Sculpture and Ornament.= By G.B. PIRANESI. - 200 plates, reproduced in facsimile from the original. 2 vols. - Imperial folio, in wrappers. (_1900_) - - _net_ 2 2 0 - - =The Seven Periods of English Architecture=, defined and - illustrated. By E. SHARPE. Third edition, 20 steel plates, - royal 8vo. (_1888_) - - 12 6 - - =Our Factories, Workshops and Warehouses=, their Sanitary and - Fire-Resisting Arrangements. By B.H. THWAITE. 183 illus. 282 - pp. crown 8vo. (_1882_) - - 9 0 - - =Elementary Principles of Carpentry.= By T. TREDGOLD and J.T. - HURST. Eleventh edition, 48 plates, 517 pp. crown 8vo. (_1904_) - - 12 6 - - =Practical Stair Building and Handrailing.= By W.H. WOOD. 32 - plates, 91 pp. crown 4to. (_1894_) - - 10 6 - - =Spons' Architects' and Builders' Pocket Price-Book=, - Memoranda, Tables and Prices. Edited by CLYDE YOUNG. Revised by - STANFORD M. BROOKS. Illustrated, 552 pp. 16mo, leather cloth - (size 61/2 in. by 33/4 in. by 1/2 in. thick). Issued annually - - _net_ 3 0 - - =Heating Engineers' Quantities.= By W.L. WHITE and G.M. WHITE. - 4 plates, 33 pp. folio. (_1910_) - - _net_ 10 6 - - - ARTILLERY. - - =Guns and Gun Making Material.= By G. EDE. Crown 8vo. (_1889_) - - 6 0 - - =Treatise on Application of Wire to Construction of Ordnance.= - By J.A. LONGRIDGE. 180 pp. 8vo. (_1884_) - - 1 5 0 - - =The Progress of Artillery: Naval Guns.= By J.A. LONGRIDGE. - 8vo, sewed. (_1896_) - - 2 0 - - =The Field Gun of the Future.= By J.A. LONGRIDGE. 8vo, sewed. - (_1892_) - - 2 6 - - - BRIDGES, ARCHES, ROOFS, AND STRUCTURAL DESIGN. - - =Strains in Ironwork.= By HENRY ADAMS. Fourth edition, 8 plates, 65 - pp. crown 8vo. (_1904_) - - 5 0 - - =The Practical Designing of Structural Ironwork.= By HENRY ADAMS. 13 - plates, 194 pp. 8vo. (_1894_) - - 8 6 - - =Designing Ironwork.= By HENRY ADAMS. Second series. 8vo, sewed. - - Part I. A Steel Box Girder. (_1894_) - - _net_ 0 9 - - " II. Built-up Steel Stanchions. (_1901_) - - _net_ 1 3 - - " III. Cisterns and Tanks. (_1902_) - - _net_ 1 0 - - " IV. A Fireproof Floor. (_1903_) - - _net_ 1 0 - - =A Practical Treatise on Segmental and Elliptical Oblique or Skew - Arches.= By G.J. BELL. Second edition, 17 plates, 125 pp. royal 8vo. - (_1906_) - - _net_ 1 1 0 - - =Economics of Construction in relation to Framed Structures.= By R.H. - Bow. Third thousand, 16 plates, 88 pp. 8vo. (1873) - - 5 0 - - =Theory of Voussoir Arches.= By Prof. W. CAIN. Third edition, 201 pp. - 18mo, boards. (_New York, 1905_) - - _net_ 2 0 - - =New Formulae for the Loads and Deflections= of Solid Beams and - Girders. By W. DONALDSON. Second edition, 8vo. (_1872_) - - 4 6 - - =Plate Girder Railway Bridges.= By M. FITZMAURICE. 4 plates, 104 pp. - 8vo. (_1895_) - - 6 0 - - =Pocket Book of Calculations in Stresses.= By E.M. GEORGE. 66 illus. - 140 pp. royal 32mo, half roan. (_1895_) - - 3 6 - - =Strains on Braced Iron Arches= and Arched Iron Bridges. By A.S. - HEAFORD. 39 pp. 8vo. (_1883_) - - 6 0 - - =Tables for Roof Framing.= By G.D. INSKIP. Second edition, 451 pp. - 8vo, leather. (_New York, 1905_) - - _net_ 12 6 - - =Stresses in Girder and Roof Frames,= for both dead and live loads, - by simple Multiplication, etc. By F.R. JOHNSON. 28 plates, 215 pp. - crown 8vo. (_1894_) - - 6 0 - - =A Graphical Method for Swing Bridges.= By B.F. LA RUE. 4 plates, 104 - pp. 18mo, boards. (_New York, 1892_) - - _net_ 2 0 - - =Notes on Cylinder Bridge Piers= and the Well System of Foundations. - By J. NEWMAN. 144 pp. 8vo. (_1893_) - - 6 0 - - =A New Method of Graphic Statics= applied in the Construction of - Wrought Iron Girders. By E. OLANDER. 16 plates, small folio. (_1887_) - - 10 6 - - =Reference Book for Statical Calculations.= By F. RUFF. With diagrams, - 140 pp. crown 8vo. (_1906_) - - _net_ 5 0 - - =The Strength and Proportion of Riveted Joints.= By B.B. STONEY. 87 - pp. 8vo. (_1885_) - - 5 0 - - =The Anatomy of Bridgework.= By W.H. THORPE. 103 illus. 190 pp. crown - 8vo. (_1906_) - - _net_ 6 0 - - - CEMENT AND CONCRETE. - - =Portland Cement:= its Manufacture, Testing and Use. By D.B. BUTLER. - Second edition, 97 illus. 396 pp. demy 8vo. (_1905_) - - _net_ 16 0 - - =Theory of Steel-Concrete Arches= and of Vaulted Structures. By W. - CAIN. Fourth edition, 27 illus. 212 pp. 18mo, boards. (_New York, - 1906_) - - _net_ 2 0 - - =Cement Users' and Buyers' Guide.= By CALCARE. 115 pp. 32mo, cloth. - (_1901_) - - _net_ 1 6 - - =Diagrams for Designing Reinforced Concrete Structures.= By G.F. - DODGE. 31 illus. 104 pp. oblong folio. (_New York, 1910_) - - _net_ 17 0 - - =Cements, Mortars, and Concretes;= their Physical properties. By M.S. - FALK. 78 illus. 176 pp. 8vo. (_New York, 1904_) - - _net_ 10 6 - - =Concrete Construction, Methods and Cost.= By H.P. GILLETTE and C.S. - HILL. 310 illus. 690 pp. 8vo. (_New York, 1908_) - - _net_ 1 1 0 - - =Engineers' Pocket-Book of Reinforced Concrete.= By E.L. HEIDENREICH. - 164 illus. 364 pp. crown 8vo, leather, gilt edges. (_New York, 1909_) - - _net_ 12 6 - - =Concrete Inspection.= By C.S. HILL. Illustrated, 179 pp. 12mo. (_New - York, 1909_) - - _net_ 4 6 - - =Reinforced Concrete.= By E. MCCULLOCH. 28 illus. 128 pp. crown 8vo. - (_New York, 1908_) - - _net_ 6 6 - - =Concrete and Reinforced Concrete.= By H.A. REID. 715 illus. 884 pp. - royal 8vo. (_New York, 1907_) - - _net_ 21 0 - - =Theory and Design of Reinforced Concrete Arches.= By A. REUTERDAHL. - 41 illus. 126 pp. 8vo. (_New York, 1908_) - - _net_ 8 6 - - =Practical Cement Testing.= By W.P. TAYLOR. With 142 illus. 329 pp. - demy 8vo. (New York, 1906) - - _net_ 12 6 - - =Concrete Bridges and Culverts.= By H.G. TYRRELL. 66 illus. 251 pp. - crown 8vo, leather - - _net_ 12 6 - - - CIVIL ENGINEERING. - - CANALS, SURVEYING. - - (_See also_ IRRIGATION _and_ WATER SUPPLY.) - - =Practical Hints to Young Engineers Employed on Indian Railways.= By - A.W.C. ADDIS. With 14 illus. 154 pp. 12mo. (_1910_) - - _net_ 3 6 - - =Levelling,= Barometric, Trigonometric and Spirit. By I.O. BAKER. - Second edition, 15 illus. 145 pp. 18mo, boards. (_New York, 1903_) .. - - _net_ 2 0 - - =Notes on Instruments= best suited for Engineering Field Work in India - and the Colonies. By W.G. BLIGH. 65 illus. 218 pp. 8vo. (_1899_) - - 7 6 - - =The Sextant and other Reflecting Mathematical Instruments.= By - F.R. BRAINARD. 33 illus. 120 pp. 18mo, boards. (_New York, 1891_) - - _net_ 2 0 - - =Practical Designing of Retaining Walls.= By Prof. W. CAIN. Fifth - edition, 14 illus. 172 pp. 18mo, boards. (_New York, 1908_) - - _net_ 2 0 - - =The Maintenance of Macadamised Roads.= By T. CODRINGTON. Second - edition, 186 pp. 8vo. (_1892_) - - 7 6 - - =Retaining Walls in Theory and Practice.= By T.E. COLEMAN. 104 illus. - 160 pp. crown 8vo. (_1909_) - - _net_ 5 0 - - =The Barometrical Determination of Heights.= By F.J.B. CORDEIRO. - Crown 8vo, limp leather. (_New York, 1898_) - - _net_ 4 6 - - =On Curved Masonry Dams.= By W.B. COVENTRY. 8vo, sewed. (_1894_) - - 2 0 - - =A Practical Method of Determining the Profile of a Masonry Dam.= By - W.B. COVENTRY. 8vo, sewed. (_1894_) - - 2 6 - - =The Stresses on Masonry Dams= (oblique sections). By W.B. COVENTRY. - 8vo, sewed. (_1894_) - - 2 0 - - =Tables for facilitating the Calculation of Earthworks.= By D. - CUNNINGHAM. 120 pp. royal 8vo - 10 6 - - =Handbook of Cost Data for Contractors and Engineers.= By H.P. - GILLETTE. 1854 pp. crown 8vo, leather, gilt edges. (_New York, 1910_) - - _net_ 1 1 0 - - =Rock Excavation, Methods and Cost.= By H.P. GILLETTE. 56 illus. 376 - pp. crown 8vo. (_New York, 1904_) - - _net_ 12 6 - - =High Masonry Dams.= By E.S. GOULD. With illus. 88 pp. 18mo, boards. - (_New York, 1897_) - - _net_ 2 0 - - =Grace's Tables for Curves,= with hints to young engineers. 8 figures, - 43 pp. oblong 8vo. (_1908_) - - _net_ 5 0 - - =Grace's Earthwork Tables.= 36 double-page tables, 4to. (_1907_) - - _net_ 12 6 - - =Railway Tunnelling= in Heavy Ground. By C. GRIPPER. 3 plates, 66 pp. - royal 8vo. (_1879_) - - 7 6 - - =Levelling and its General Application.= By T. HOLLOWAY. Second - edition, 53 illus. 147 pp. 8vo. (_1895_) - - 5 0 - - =Waterways and Water Transport= in different Countries. By J.S. JEANS. - 55 illus. 520 pp. 8vo. (_1890_) - - _net_ 9 0 - - =Table of Barometrical Heights to 20,000 Feet.= By W.H. MACKESY, with - some practical suggestions by Sir Guildford Molesworth. 1 plate, 24 - pp. royal 32mo. (_1882_) - - 3 0 - - =Aid Book to Engineering Enterprise.= By E. MATHESON. Third edition, - illustrated, 916 pp. medium 8vo, buckram. (_1898_) - - 1 4 0 - - =A Treatise on Surveying.= By R.E. MIDDLETON and O. CHADWICK. Second - edition, royal 8vo. - - Part I. 11 plates, 296 pp. (_1904_) - - 10 6 - - " II. Fully illustrated, 334 pp. (_1906_) - - 10 6 - - =A Pocket Book of Useful Formulae and Memoranda,= for Civil and - Mechanical Engineers. By Sir G.L. MOLESWORTH and H.B. MOLESWORTH. With - an Electrical Supplement by W.H. MOLESWORTH. Twenty-sixth edition, 760 - illus. 901 pp. royal 32mo, French morocco, gilt edges. (_1908_) - - _net_ 5 0 - - =The Pocket Books of Sir G.L. Molesworth and J.T. Hurst,= printed on - India paper and bound in one vol. Royal 32mo, russia, gilt edges. - - _net_ 10 6 - - =Metallic Structures: Corrosion and Fouling and their Prevention.= By - J. NEWMAN. Illustrated, 385 pp. crown 8vo. (_1896_) - - 9 0 - - =Scamping Tricks and Odd Knowledge= occasionally practised upon Public - Works. By J. NEWMAN. New impression, 129 pp. crown 8vo. (_1908_) - - _net_ 2 0 - - =Earthwork Slips and Subsidences= on Public Works. By J. NEWMAN. - 240 pp. crown 8vo. (_1890_) - - 7 6 - - =Co-ordinate Geometry= as applied to Land Surveying. By W. PILKINGTON. - 5 illus. 44 pp. 12mo. (_1909_) - - _net_ 1 6 - - =Diagrams for the Graphic Calculation of Earthwork Quantities.= By - A.H. ROBERTS. Ten cards, fcap. in cloth case - - _net_ 10 6 - - =Pioneering.= By F. SHELFORD, illustrated. 88 pp. crown 8vo. (_1909_) - - _net_ 3 0 - - =Topographical Surveying.= By G.J. SPECHT. Second edition, 2 plates - and 28 illus. 210 pp. 18mo, boards. (_New York, 1898_) - - _net_ 2 0 - - =Spons' Dictionary of Engineering,= Civil, Mechanical, Military and - Naval. 10,000 illus. 4300 pp. super royal 8vo. (_1874, Supplement - issued in 1881_). Complete with Supplement, in 11 divisions - - _net_ 3 10 0 - - Ditto ditto in 4 vols. - - _net_ 3 3 0 - - =Surveying and Levelling Instruments.= By W.F. STANLEY. Third edition, - 372 illus. 562 pp. crown 8vo. (_1901_) - - 7 6 - - =Surveyor's Handbook.= By T.U. TAYLOR. 116 illus. 310 pp. crown 8vo, - leather, gilt edges. (_New York, 1908_) - - _net_ 8 6 - - =Logarithmic Land Measurement.= By J. WALLACE. 32 pp. royal 8vo. - (_1910_) - - _net_ 5 0 - - =Hints on Levelling Operations.= By W.H. WELLS. Second edition, 8vo, - sewed. (_1890_) - - _net_ 1 0 - - =The Drainage of Fens and Low Lands= by Gravitation and Steam Power. - By W.H. WHEELER. 8 plates, 175 pp. 8vo. (_1888_) - - 12 6 - - =Stadia Surveying,= the theory of Stadia Measurements. By A. WINSLOW. - Fifth edition, 148 pp. 18mo, boards. (_New York, 1902_) - - _net_ 2 0 - - =Handbook on Tacheometrical Surveying.= By C. XYDIS. 55 illus. 3 - plates, 63 pp. 8vo. (_1909_) - - _net_ 6 0 - - - DICTIONARIES. - - =Technological Dictionary in the English, Spanish, German and French - Languages.= By D. CARLOS HUELIN Y ARSSU. Crown 8vo. - - Vol. I. ENGLISH-SPANISH-GERMAN-FRENCH. - 609 pp. (_1906_) - - _net_ 10 6 - - Vol. II. GERMAN-ENGLISH-FRENCH-SPANISH. - 720 pp. (_1908_) - - _net_ 10 6 - - Vol. III. FRENCH-GERMAN-SPANISH-ENGLISH. - In preparation. - - Vol. IV. SPANISH-FRENCH-ENGLISH-GERMAN. - 750 pp. (_1910_) - - _net_ 10 6 - - =English-French and French-English Dictionary of the Motor-Car, Cycle - and Boat.= By F. LUCAS. 171 pp. crown 8vo. (_1905_) - - _net_ 5 0 - - =Spanish-English Dictionary of Mining Terms.= By F. LUCAS. 78 pp. 8vo. - (_1905_) - - _net_ 5 0 - - =English-Russian and Russian-English Engineering Dictionary.= By L. - MEYCLIAR. 100 pp. 16mo. (_1909_) - - _net_ 2 6 - - =Reed's Polyglot Guide to the Marine Engine,= in English, French, - German and Norsk. Second edition, oblong 8vo. (_1900_). - - _net_ 6 0 - - - DOMESTIC ECONOMY. - - =Food Adulteration and its Detection.= By J.P. BATTERSHALL. 12 plates, - 328 pp. demy 8vo. (_New York, 1887_) - - 15 0 - - =How to Check Electricity Bills.= By S.W. BORDEN. 41 illus. 54 pp. - crown 8vo. (_New York, 1907_) - - _net_ 2 0 - - =Practical Hints on Taking a House.= By H.P. BOULNOIS. 71 pp. 18mo. - (_1885_) - - 1 6 - - =The Cooking Range,= its Failings and Remedies. By F. DYE. 52 pp. - fcap. 8vo, sewed. (_1888_) - - 0 6 - - =The Kitchen Boiler and Water Pipes.= By H. GRIMSHAW. 8vo, sewed. - (_1887_) - - _net_ 1 0 - - =Cookery and Domestic Management,= including economic and middle class - Practical Cookery. By K. MELLISH. 56 coloured plates and 441 illus. - 987 pp. super-royal 8vo. (_1901_) - - _net_ 16 0 - - =Spons' Household Manual.= 250 illus. 1043 pp. demy 8vo. (_1902_) - - 7 6 - - Ditto ditto half-bound French morocco - - 9 0 - - =Handbook of Sanitary Information= for Householders. By R.S. TRACY. 33 - illus. 114 pp. 18mo. (_New York, 1900_) - - 2 6 - - - DRAWING. - - =The Ornamental Penman's,= Engraver's and Sign Writer's Pocket Book of - Alphabets. By B. ALEXANDER. Oblong 12mo, sewed - - 0 6 - - =The Draughtsman's Handbook= of Plan and Map Drawing. By G.G. ANDRE. - 87 illus. and 34 plain and coloured plates, 162 pp. crown 4to. - (_1891_) - - 9 0 - - =Slide Valve Diagrams:= a French Method for their Construction. By L. - BANKSON. 18mo, boards. (_New York, 1892_) . . . - - _net_ 2 0 - - =A System of Easy Lettering.= By J.H. CROMWELL. With Supplement by G. - MARTIN. Sixth thousand, oblong 8vo. (_New York, 1900_) - - _net_ 2 0 - - =Plane Geometrical Drawing.= BY R.C. FAWDRY. Illustrated, 185 pp. - crown 8vo. (_1901_) - - _net_ 3 0 - - =Twelve Plates on Projection Drawing.= By O. GUETH. Oblong 4to. (_New - York, 1903_) - - _net_ 3 0 - - =Hints on Architectural Draughtsmanship.= By G.W.T. HALLATT. Fourth - edition, 80 pp. 18mo. (_1906_) - - _net_ 1 6 - - =A First Course of Mechanical Drawing= (Tracing). By G. HALLIDAY. - Oblong 4to, sewed - - 2 0 - - =Drawings for Medium-sized Repetition Work.= By R.D. SPINNEY. With 47 - illus. 130 pp. 8vo. (_1909_) - - _net_ 3 6 - - =Mathematical Drawing Instruments.= By W.F. STANLEY. Seventh edition, - 265 illus. 370 pp. crown 8vo. (_1900_) - - 5 0 - - - ELECTRICAL ENGINEERING. - - =Practical Electric Bell Fitting.= By F.C. ALLSOP. Tenth edition, 186 - illus. including 8 folding plates, 185 pp. crown 8vo. (_1903_) - - 3 6 - - =Telephones:= their Construction and Fitting. By F.C. ALLSOP. Eighth - edition, 184 illus. 222 pp. crown 8vo. (_1909_) - - 3 6 - - =Thermo-electric Reactions= and Currents between Metals in Fused - Salts. By T. ANDREWS. 8vo, sewed. (_1896_) - - 1 0 - - =Auto-Transformer Design.= By A.H. AVERY. 25 illus. 60 pp. 8vo. - (_1909_) - - _net_ 3 6 - - =Principles of Electric Power= (Continuous Current) for Mechanical - Engineers. By A.H. BATE. 63 illus. 204 pp. crown 8vo. (_1905_) - (FINSBURY TECHNICAL MANUAL) - - _net_ 4 6 - - =Practical Construction of Electric Tramways.= By WILLIAM R. BOWKER. - 93 illus. 119 pp. 8vo. (_1903_) - - _net_ 6 0 - - =Design and Construction of Induction Coils.= By A.F. COLLINS. 155 - illus. 272 pp. demy 8vo. (_New York, 1909_) - - _net_ 12 6 - - =Switchboard Measuring Instruments= for Continuous and Polyphase - Currents. By J.C. CONNAN. 117 illus. 150 pp. 8vo, cloth. (_1908_) - - _net_ 5 0 - - =Electric Cables, their Construction and Cost.= By D. COYLE and F.J. - O. HOWE. With many diagrams and 216 tables, 467 pp. crown 8vo, - leather. (_1909_) - - _net_ 15 0 - - =Management of Electrical Machinery.= By F.B. CROCKER and S.S. - WHEELER. Eighth edition, 131 illus. 223 pp. crown 8vo. (_New York, - 1909_) - - _net_ 4 6 - - =Electric Lighting:= A Practical Exposition of the Art. By F.B. - CROCKER. Royal 8vo. (_New York._) - - Vol. I. =The Generating Plant.= Sixth edition, 213 illus. 470 - pp. (_1904_) - - _net_ 12 6 - - Vol. II. =Distributing Systems and Lamps.= Second edition, 391 - illus. 505 pp. (_1905_) - - _net_ 12 6 - - =The Care and Management of Ignition Accumulators.= By H.H.U. CROSS. - 12 illus. 74 pp. crown 8vo, limp. (S. & C. SERIES, NO. 19.) (_1910_) - - _net_ 1 6 - - =Elementary Telegraphy and Telephony.= By ARTHUR CROTCH. 238 illus. - 223 pp. 8vo. (_1903._) (FINSBURY TECHNICAL MANUAL) - - _net_ 4 6 - - =Electricity and Magnetism in Telephone Maintenance.= By G.W. - CUMMINGS. 45 illus. 137 pp. 8vo. (_New York, 1908_) . .. - - _net_ 6 6 - - =Grouping of Electric Cells.= By W.F. DUNTON. 4 illus. 50 pp. fcap. - 8vo. (1906) - - _net_ 1 6 - - MAGNETS AND ELECTRIC CURRENTS. By Prof. J.A. FLEMING. Second edition, - 136 illus. 417 pp. crown 8vo (_1902_) - - _net_ 5 0 - - =Notes on Design of Small Dynamo.= By GEORGE HALLIDAY. Second edition, - 8 plates, 8vo. (_1895_) 2 6 =Practical Alternating Currents and Power - Transmission.= By N. HARRISON. 172 illus. 375 pp. - crown 8vo. (_New York, 1906_) - - 10 6 - - =Making Wireless Outfits.= By N. HARRISON. 27 illus. 61 pp. crown 8vo, - limp. (S. & C. SERIES, NO. 11.) (_New York, 1909_) - - _net_ 1 6 - - =Wireless Telephone Construction.= By N. HARRISON. 43 illus. 73 pp. - crown 8vo, limp. (S. & C. Series, No. 12.) (_New York, 1909_) - - _net_ 1 6 - - =The Phoenix Fire Office Rules= for Electric Light and Electrical - Power Installations. By M. HEAPHY. Thirty-seventh edition, 8vo, sewed. - (_1908_) - - 0 6 - - =Testing Telegraph Cables.= By Colonel V. HOSKIOER. Third edition, - crown 8vo. (_1889_) - - 4 6 - - =Long Distance Electric Power Transmission.= By R.W. HUTCHINSON. 136 - illus. 345 pp. crown 8vo. (_New York, 1907_) - - _net_ 12 6 - - =Theory and Practice of Electric Wiring.= By W.S. IBBETSON. 119 illus. - 366 pp. crown 8vo. (_1909_) - - _net_ 5 0 - - =Practical Electrical Engineering for Elementary Students.= By W.S. - IBBETSON. With 61 illus. 155 pp. crown 8vo. (_1910_) - - _net_ 3 0 - - =General Rules recommended for Wiring= for the Supply of Electrical - Energy. Issued by THE INSTITUTION OF ELECTRICAL ENGINEERS. 8vo, sewed. - (_Revised, April 1907_) - - _net_ 0 6 - - =Form of Model General Conditions= recommended by THE INSTITUTION OF - ELECTRICAL ENGINEERS for use in connection with Electrical Contracts. - 8vo, sewed. (_1906_) - - _net_ 1 0 - - =A Handbook of Electrical Testing.= By H.R. KEMPE. Seventh edition, - 285 illus. 706 pp. demy 8vo. (_1908_) - - _net_ 18 0 - - =Application of Electricity to Railway Working.= By W.E. LANGDON. - 142 illus. and 5 plates, 347 pp. 8vo. (_1897_) - - 10 6 - - =How to Become a Competent Motorman.= By V.B. LIVERMORE and J. - WILLIAMS. 45 illus. 252 pp. 12mo. (_New York, 1903_) - - _net_ 4 6 - - =Electromagnets,= their design and construction. By A.N. MANSFIELD. 36 - illus. 155 pp. 18mo, boards. (_New York, 1901_) - - _net_ 2 0 - - =Telephone Construction, Methods and Cost.= By C. MAYER. With - Appendices on the cost of materials and labour by J.C. SLIPPY. 103 - illus. 284 pp. crown 8vo. (_New York, 1908_) - - _net_ 12 6 - - =Induction Coils.= By N.H. SCHNEIDER. Second edition, 79 illus. 285 - pp. crown 8vo. (_New York, 1901_) - - _net_ 4 6 - - =Electric Gas Lighting.= By N.H. SCHNEIDER. 57 illus. 101 pp. 12mo. - (S. & C. SERIES, NO. 8.) (_New York, 1901_) - - _net_ 2 0 - - =How to Install Electric Bells, Annunciators and Alarms.= By N.H. - SCHNEIDER. 59 illus. 63 pp. crown 8vo, limp. (S. & C. SERIES, NO. 2.) - (_New York, 1905_) - - _net_ 1 6 - - =Modern Primary Batteries,= their construction, use and maintenance. - By N.H. SCHNEIDER. 54 illus. 94 pp. crown 8vo, limp. (S. & C. SERIES, - NO. 1.) (_New York, 1905_) - - _net_ 1 6 - - =Practical Engineers' Handbook on the Care and Management of Electric - Power Plants.= By N.H. SCHNEIDER. 203 illus. 274 pp. crown 8vo. (_New - York, 1906_) - - _net_ 5 0 - - =Electrical Circuits and Diagrams,= illustrated and explained. By N.H. - SCHNEIDER. 8vo, limp. (S. & C. SERIES, NOS. 3 AND 4.) (_New York_) - - Part 1. 217 illus. 72 pp. (_1905_) - - _net_ 1 6 - - Part 2. 73 pp. (_1909_) - - _net_ 1 6 - - =Electrical Instruments and Testing.= By N.H. SCHNEIDER. Third - edition. 133 illus. 239 pp. crown 8vo. (_New York, 1907_) - - _net_ 4 6 - - =Experimenting with Induction Coils.= By N.H. SCHNEIDER. 26 illus. 73 - pp. crown 8vo, limp. (S. & C. SERIES, NO. 5.) (_New York, 1906_) - - _net_ 1 6 - - =Study of Electricity for Beginners.= By N.H. SCHNEIDER. 54 illus. 88 - pp. crown 8vo, limp. (S. & C. SERIES, NO. 6.) (_New York, 1905_) - - _net_ 1 6 - - =Practical Electrics:= a Universal Handybook on Every Day Electrical - Matters. Seventh edition, 126 illus. 135 pp. 8vo. (S. & C. SERIES, NO. - 13.) (_New York, 1902_) - - _net_ 1 6 - - =The Voltaic Accumulator:= an elementary treatise. By E. REYNIER. - Translated from the French by J.A. BERLY. 62 illus. 202 pp. 8vo - - 9 0 - - =Dry Batteries:= how to Make and Use them. By a DRY BATTERY EXPERT. - With additional notes by N.H. SCHNEIDER. 30 illus. 59 pp. crown 8vo, - sewed. (S. & C. SERIES, NO. 7.) (_New York, 1905_) - - _net_ 1 6 - - =The Diseases of Electrical Machinery.= By E. SCHULZ. Edited, with a - Preface, by Prof. S.P. THOMPSON. 42 illus. 84 pp. crown 8vo - - _net_ 2 0 - - =Electric Toy-Making.= By T.O. SLOANE. Fifteenth edition, 70 illus. - 183 pp. crown 8vo. (_New York, 1903_) - - _net_ 4 6 - - =Electricity Simplified.= By T.O. SLOANE. Tenth edition, 29 illus. 158 - pp. crown 8vo. (_New York, 1901_) - - _net_ 4 6 - - =How to become a Successful Electrician.= By T.O. SLOANE. Third - edition, illustrated, crown 8vo. (_New York, 1899_) - - _net_ 4 6 - - =Electricity:= its Theory, Sources and Applications. By J.T. SPRAGUE. - Third edition, 109 illus. 658 pp. crown 8vo. (_1892_) - - _net_ 7 6 - - =Telegraphic Connections.= By C. THOM and W.H. JONES. 20 plates, 59 - pp. oblong 8vo. (_New York, 1892_) - - _net_ 3 6 - - =Roentgen Rays= and Phenomena of the Anode and Cathode. By E.P. - THOMPSON and W.A. ANTHONY. 105 illus. 204 pp. 8vo. (_New York, 1896_) - - _net_ 4 6 - - =Dynamo Electric Machinery.= By Prof. S.P. THOMPSON. Seventh edition, - demy 8vo. (FINSBURY TECHNICAL MANUAL.) - - Vol. I. =Continuous-Current Machinery.= With 4 coloured and 30 - folding plates, 573 illus. 984 pp. (_1904_) - - _net_ 1 10 0 - - Vol. II. =Alternating Current Machinery.= 15 coloured and 24 - folding plates, 546 illus. 900 pp. (_1905_) - - _net_ 1 10 0 - - =Design of Dynamos= (Continuous Currents). By Prof. S.P. THOMPSON. 4 - coloured and 8 folding plates, 243 pp. demy 8vo. (_1903_) - - _net_ 12 0 - - =Schedule for Dynamo Design,= issued with the above. 6_d_. each, 4_s_. - per doz., or 18_s_. per 100 _net_ - - =Curves of Magnetic Data for Various Materials.= A reprint on - transparent paper for office use of Plate L from Dynamo Electric - Machinery, and measuring 25 in. by 16 in. - - _net_ 0 7 - - =The Electromagnet.= By C.R. UNDERHILL. 67 illus. 159 pp. crown 8vo. - (_New York, 1903_) - - _net_ 6 6 - - =Practical Guide to the Testing of Insulated Wires and Cables.= By - H.L. WEBB. Fifth edition, 38 illus. 118 pp. crown 8vo. (_New York, - 1902_) - - _net_ 4 6 - - - FOREIGN EXCHANGE. - - =English Prices with Russian Equivalents= (at Fourteen Rates of - Exchange). English prices per lb., with equivalents in roubles and - kopecks per pood. By A. ADIASSEWICH. 182 pp. fcap. 32mo, roan. - (_1908_) - - _net_ 1 0 - - =English Prices with German Equivalents= (at Seven Rates of Exchange). - English prices per lb., with equivalents in marks per kilogramme. By - St. KOCZOROWSKI. 95 pp. fcap. 32mo, roan. (_1909_) - - _net_ 1 0 - - =English Prices with Spanish Equivalents.= At Seven Rates of Exchange. - English prices per lb., with equivalents in pesetas per kilogramme. By - S. LAMBERT. 95 pp. 32mo, roan. (_1910_) - - _net_ 1 0 - - =English Prices with French Equivalents= (at Seven Rates of Exchange). - English prices per lb. to francs per kilogramme. By H.P. MCCARTNEY. 97 - pp. 32mo, roan. (_1907_) - - _net_ 1 0 - - =Principles of Foreign Exchange.= By E. MATHESON. Fourth edition, 54 - pp. 8vo, sewed. (_1905_) - - _net_ 0 3 - - - GAS AND OIL ENGINES. - - =The Theory of the Gas Engine.= By D. CLERK. Edited by F.E. IDELL. - Third edition, 19 illus. 180 pp. 18mo, boards. (_New York, 1903_) - - _net_ 2 0 - - =The Design and Construction of Oil Engines.= By A.H. GOLDINGHAM. - Third edition, 112 illus. 260 pp. crown 8vo. (_New York, 1910_) - - _net_ 10 6 - - =Gas Engine in Principle and Practice.= By A.H. GOLDINGHAM. 107 illus. - 195 pp. 8vo, cloth. (_New York, 1907_) - - _net_ 6 6 - - =Practical Hand-Book on the Care and Management of Gas Engines.= By - G. LIECKFELD. Third edition, square 16mo. (_New York, 1896_) - - 3 6 - - =Elements of Gas Engine Design.= By S.A. MOSS. 197 pp. 18mo, boards. - (_New York, 1907_) - - _net_ 2 0 - - =Gas and Petroleum Engines.= A Manual for Students and Engineers. - (FINSBURY TECHNICAL MANUAL.) By Prof. W. ROBINSON. _Third edition in - preparation_ - - - GAS LIGHTING. - - =Gas Analyst's Manual= (incorporating Hartley's "Gas Analyst's Manual" - and "Gas Measurement"). By J. ABADY. 102 illustrations, 576 pp. demy - 8vo. (_1902_) - - _net_ 18 0 - - =Gas Works:= their Arrangement, Construction, Plant and Machinery. By - F. COLYER. 31 folding plates, 134 pp. 8vo. (_1884_) - - _net_ 8 6 - - =Transactions of the Institution of Gas Engineers.= Edited by WALTER - T. DUNN, _Secretary_. Published annually. 8vo - - _net_ 10 6 - - =Lighting by Acetylene.= By F. DYE. 75 illus. 200 pp. crown 8vo. - (_1902_) - - _net_ 6 0 - - =A Comparison of the English and French Methods of Ascertaining the - Illuminating Power of Coal Gas.= By A.J. VAN EIJNDHOVEN. Illustrated, - crown 8vo. (_1897_) - - 4 0 - - =Gas Lighting and Gas Fitting.= By W.P. GERHARD. Second edition, 190 - pp. 18mo, boards. (_New York, 1894_) - - _net_ 2 0 - - =A Treatise on the Comparative Commercial Values of Gas Coals and - Cannels.= By D.A. GRAHAM. 3 plates, 100 pp. 8vo. (_1882_) - - 4 6 - - =The Gas Engineer's Laboratory Handbook.= By J. HORNBY. Third edition, - revised, 70 illus. 330 pp. crown 8vo. (_1910_) - - _net_ 6 0 - - - HISTORICAL AND BIOGRAPHICAL. - - =Extracts from the Private Letters of the late Sir William Fothergill - Cooke,= 1836-9, relating to the Invention and Development of the - Electric Telegraph; also a Memoir by LATIMER CLARK. Edited by F.H. - WEBB. Sec. Inst.E.E. 8vo. (_1895_) - - 3 0 - - =A Chronology of Inland Navigation= in Great Britain. By H.R. DE - SALIS. Crown 8vo. (1897) - - 4 6 - - =A History of Electric Telegraphy= to the year 1837. By J.J. FAHIE. 35 - illus. 542 pp. crown 8vo. (_1889_) - - 2 0 - - =History and Development of Steam Locomotion on Common Roads.= By W. - FLETCHER. 109 illus. 288 pp. 8vo - - 5 0 - - =Life as an Engineer:= its Lights, Shades, and Prospects. By J.W.C. - HALDANE. 23 plates, 338 pp. crown 8vo. (_1905_) - - _net_ 5 0 - - =Philipp Reis,= Inventor of the Telephone: a Biographical Sketch. By - Prof. S.P. THOMPSON. 8vo, cloth. (_1883_) - - 7 6 - - =The Development of the Mercurial Air Pump.= By Prof. S.P. THOMPSON. - Illustrated, royal 8vo, sewed. (_1888_) - - 1 6 - - - HOROLOGY. - - =Watch and Clock Maker's Handbook,= Dictionary and Guide. By F.J. - BRITTEN. Tenth edition, 450 illus. 492 pp. crown 8vo. (_1902_) - - _net_ 5 0 - - =The Springing and Adjusting of Watches.= By F.J. BRITTEN. 75 illus. - 152 pp. crown 8vo. (_1898_) - - _net_ 3 0 - - =Prize Essay on the Balance Spring= and its Isochronal Adjustments. By - M. IMMISCH. 7 illus. 50 pp. crown 8vo. (_1872_) - - 2 6 - - - HYDRAULICS AND HYDRAULIC MACHINERY. - - (_See also_ WATER SUPPLY.) - - =Pumps:= Historically, Theoretically and Practically Considered. By - P.R. BJOeRLING. Second edition, 156 illus. 234 pp. crown 8vo. (_1895_) - - 7 6 - - =Pump Details.= By P.R. BJOeRLING. 278 illus. 211 pp. crown 8vo. - (_1892_) - - 7 6 - - =Pumps and Pump Motors:= A Manual for the use of Hydraulic Engineers. - By P.R. BJOeRLING. Two vols. 261 plates, 369 pp. royal 4to. (_1895_). - - _net_ 1 10 0 - - =Practical Handbook on Pump Construction.= By P.R. BJOeRLING. Second - edition, 9 plates, 90 pp. crown 8vo. (_1904_) - - 5 0 - - =Water or Hydraulic Motors.= By P.R. BJOeRLING. 206 illus. 287 pp. - crown 8vo. (_1903_) - - 9 0 - - =Hydraulic Machinery,= with an Introduction to Hydraulics. By R.G. - BLAINE. Second edition with 307 illus. 468 pp. 8vo. (FINSBURY - TECHNICAL MANUAL). (_1905_) - - _net_ 14 0 - - =Practical Hydraulics.= By T. BOX. Fifteenth edition, 8 plates, 88 pp. - crown 8vo. (_1909_) - - _net_ 5 0 - - =Hydraulic, Steam, and Hand Power Lifting and Pressing Machinery.= By - F. COLYER. Second edition, 88 plates, 211 pp. imperial 8vo. (_1892_) - - _net_ 10 6 - - =Pumps and Pumping Machinery.= By F. COLYER. - - Vol. I. Second edition, 53 plates, 212 pp. 8vo (_1892_) - - _net_ 10 6 - - Vol. II. Second edition, 48 plates, 169 pp. 8vo. (_1900_) - - _net_ 10 6 - - =Construction of Horizontal and Vertical Water-wheels.= By W. CULLEN. - Second edition, small 4to. (_1871_) - - 5 0 - - =Donaldson's Poncelet Turbine= and Water Pressure Engine and Pump. - By W. DONALDSON. 4to. (_1883_) - - 5 0 - - =Principles of Construction and Efficiency of Water-wheels.= By W. - DONALDSON. 13 illus. 94 pp. 8vo. (_1876_) - - 5 0 - - =Practical Hydrostatics and Hydrostatic Formulae.= By E.S. GOULD. 27 - illus. 114 pp. 18mo, boards. (_New York, 1903_) - - _net_ 2 0 - - =Hydraulic and other Tables= for purposes of Sewerage and Water - Supply. By T. HENNELL. Third edition, 70 pp. crown 8vo. (_1908_) - - _net_ 4 6 - - =Hydraulic Tables= for finding the Mean Velocity and Discharge in Open - Channels. By T. HIGHAM. Second edition, 90 pp. super-royal 8vo. - (_1898_) - - 7 6 - - =Tables for Calculating the Discharge of Water= in Pipes for Water and - Power Supplies. Indexed at side for ready reference. By A.E. SILK. 63 - pp. crown 8vo. (_1899_) - - 5 0 - - =Simple Hydraulic Formulae.= By T.W. STONE. 9 plates, 98 pp. crown 8vo. - (_1881_) - - 4 0 - - - INDUSTRIAL CHEMISTRY AND MANUFACTURES. - - =Perfumes and their Preparation.= By G.W. ASKINSON. Translated from - the Third German Edition by I. FUEST. Third edition, 32 illus. 312 pp. - 8vo. (_New York, 1907_) - - _net_ 12 6 - - =Brewing Calculations,= Gauging and Tabulation. By C.H. BATER. 340 pp. - 64mo, roan, gilt edges. (_1897_) - - _net_ 1 6 - - =A Pocket Book for Chemists,= Chemical Manufacturers, Metallurgists, - Dyers, Distillers, etc. By T. BAYLEY. 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(_1900_) - - 9 0 - - =Ice-Making Machines.= By M. Ledoux and others. Sixth edition. 190 pp. - 18mo, boards. (_New York, 1906_) - - _net_ 2 0 - - =Brewing with Raw Grain.= By T.W. Lovibond. 75 pp. crown 8vo. (1883) - - 5 0 - - =Sugar, a Handbook for Planters and Refiners.= By the late J.A.R. - NEWLANDS and B.E.R. NEWLANDS. 236 illus. 876 pp. demy 8vo. (_London, - 1909_) - - _net_ 1 5 0 - - =Principles of Leather Manufacture.= By Prof. H.R. PROCTER. 101 illus. - 520 pp. medium 8vo. (_1908_) - - _net_ 18 0 - - =Leather Industries Laboratory Handbook= of Analytical and - Experimental methods. By H.R. PROCTER. Second edition, 4 plates, 46 - illus. 450 pp. demy 8vo. (_1908_) - - _net_ 18 0 - - =Theoretical and Practical Ammonia Refrigeration.= By I.I. REDWOOD. - Sixth thousand, 15 illus. 146 pp. square 16mo. (_New York, 1909_) - - _net_ 4 6 - - =Breweries and Maltings.= By G. SCAMMELL and F. COLYER. Second - edition, 20 plates, 178 pp. 8vo. 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ATKINSON. - Revised by MAJOR B.R. WARD, R.E. Second edition, 17 plates, 8vo. - (_1901_) - - 7 6 - - =Quick and Easy Methods of Calculating,= and the Theory and Use of the - Slide Rule. By R.G. BLAINE. Third edition, 6 illus. 152 pp. 16mo, - leather cloth. (_1907_) - - 2 6 - - =Symbolic Algebra,= or the Algebra of Algebraic Numbers. By W. CAIN. - 18mo, boards. (_New York_) - - _net_ 2 0 - - =Nautical Astronomy.= By J.H. COLVIN. 127 pp. crown, 8vo. (_1901_) - - _net_ 2 6 - - =Chemical Problems.= By J.C. FOYE. Fourth edition, 141 pp. 18mo, - boards. (_New York, 1898_) - - _net_ 2 0 - - =Primer of the Calculus.= By E.S. GOULD. Second edition, 24 illus. 122 - pp. 18mo, boards. (_New York, 1899_) - - _net_ 2 0 - - =Elementary Treatise on the Calculus= for Engineering Students. By J. - GRAHAM. Third edition, 276 pp. crown 8vo. (_1905_). (FINSBURY - TECHNICAL MANUAL) - - 7 6 - - =Manual of the Slide Rule.= By F.A. HALSEY. Second edition, 31 illus. - 84 pp. 18mo, boards. (_New York, 1901_) - - _net_ 2 0 - - =Reform in Chemical and Physical Calculations.= By C.J.T. HANSSEN. - 4to. (_1897_) - - _net_ 6 6 - - =Algebra Self-Taught.= By P. HIGGS. Third edition, 104 pp. crown 8vo. - (_1903_) - - 2 6 - - =Galvanic Circuit investigated Mathematically.= By G.S. OHM. - Translated by WILLIAM FRANCIS. 269 pp. 18mo, boards. (_New York, - 1891_) - - _net_ 2 0 - - =Elementary Practical Mathematics.= By M.T. ORMSBY. 420 pp. demy 8vo. - (_1900_) - - _net_ 7 6 - - =Elements of Graphic Statics.= By K. VON OTT. Translated by G.S. - CLARKE. 93 illus. 128 pp. crown 8vo. (_1901_) - - 5 0 - - =Figure of the Earth.= By F.C. ROBERTS. 18mo, boards. (_New York_) - - _net_ 2 0 - - =Arithmetic of Electricity.= By T. O'C. SLOANE. Thirteenth edition, - crown 8vo. (_New York, 1901_) - - _net_ 4 6 - - =Graphic Method for Solving certain Questions in Arithmetic or - Algebra.= By G.L. VOSE. Second edition with 28 illus. 62 pp. 18mo, - boards. (_New York, 1902_) - - _net_ 2 0 - - =Problems in Electricity.= A Graduated Collection comprising all - branches of Electrical Science. By R. WEBER. Translated from the - French by E.A. O'KEEFE. 34 illus. 366 pp. crown 8vo. (_1902_). - - _net_ 7 6 - - - MECHANICAL ENGINEERING. - - STEAM ENGINES AND BOILERS, ETC. - - =Handbook for Mechanical Engineers.= By HY. ADAMS. Fourth edition, 426 - pp. crown 8vo. (_1897_) - - _net_ 4 6 - - =Appleby's Handbooks of Machinery.= Many illustrations, 8vo. Sections - 2, 3, 4 and 6 - - _each_ 3 6 - - Section 5 - - 5 0 - - Section 1.--Prime Movers. _Out of Print._ - Section 2.--Hoisting Machinery, Winding Engines, etc. - Section 3.--_Out of print._ - Section 4.--Machine Tools and Accessories. - Section 5.--Contractors' Plant and Railway Materials. - Section 6.--Mining, Colonial and Manufacturing Machinery. - - =Engineers' Sketch Book of Mechanical Movements.= By T.W. BARBER. - Fifth edition, 3000 illus. 355 pp. 8vo. (_1906_) - - _net_ 10 6 - - =The Repair and Maintenance of Machinery.= By T.W. BARBER. 417 illus. - 476 pp. 8vo. (_1895_) - - 10 6 - - =Slide Valve and its Functions=, with special reference to Modern - Practice in the United States. By J. BEGTRUP. 90 diagrams, 146 pp. - medium 8vo. (_New York, 1902_) - - _net_ 8 0 - - =Practical Treatise on Mill Gearing.= By T. BOX. Fifth edition, 11 - plates, 128 pp. crown 8vo. (_1892_) - - 7 6 - - =Safety Valves.= By R.H. BUELL. Third edition, 20 illus. 100 pp. 18mo, - boards. (_New York, 1898_) - - _net_ 2 0 - - =Machine Design.= By Prof. W.L. CATHCART. Part I. FASTENINGS. 123 - illus. 291 pp. demy 8vo. (_New York, 1903_) - - _net_ 12 6 - - =Chimney Design and Theory.= By W.W. CHRISTIE. Second edition, 54 - illus. 192 pp. crown 8vo. (_New York, 1902_) - - _net_ 12 6 - - =Furnace Draft:= its Production by Mechanical Methods. By W.W. - CHRISTIE. 5 illus. 80 pp. 18mo, boards. (_New York, 1906_) - - _net_ 2 0 - - =Working and Management of Steam Boilers and Engines.= By F. COLYER. - Second edition, 108 pp. crown 8vo. (_1902_) - - 3 6 - - =The Stokers' Catechism.= By W.J. CONNOR. 63 pp. limp cloth. (_1906_) - - _net_ 1 0 - - =Treatise on the use of Belting for the Transmission of Power.= By - J.H. COOPER. Fifth edition, 94 illus. 399 pp. demy 8vo. (_New York, - 1901_) - - _net_ 12 6 - - =The Steam Engine considered as a Thermodynamic Machine.= By J.H. - COTTERILL. Third edition, 39 diagrams, 444 pp. 8vo. (_1896_) - - 15 0 - - =Fireman's Guide=, a Handbook on the Care of Boilers. By K.P. - DAHLSTROM. Ninth edition fcap. 8vo. (_New York, 1902_) - - _net_ 1 6 - - =Heat for Engineers.= By C.R. DARLING. 110 illus. 430 pp. 8vo. - (_1908._) (FINSBURY TECHNICAL MANUAL.) - - _net_ 12 6 - - =Diseases of a Gasolene Automobile=, and How to Cure Them. By A.L. - DYKE and G.P. DORRIS. 127 illus. 201 pp. crown 8vo. (_New York, 1903_) - - _net_ 6 6 - - =Belt Driving.= By G. HALLIDAY. 3 folding plates, 100 pp. 8vo. - (_1894_) - - 3 6 - - =Worm and Spiral Gearing.= By F.A. HALSEY. 13 plates, 85 pp. 18mo, - boards. (_New York, 1903_) - - _net_ 2 0 - - =Commercial Efficiency of Steam Boilers.= By A. HANSSEN. Large 8vo, - sewed. (1898) - - 0 6 - - =Corliss Engine.= By J.T. HENTHORN. Third edition, 23 illus. 95 pp. - square 16mo. (S. & C. SERIES, No. 20.) (_New York, 1910_) - - _net_ 1 6 - - =Liquid Fuel= for Mechanical and Industrial Purposes. By E.A. - BRAYLEY HODGETTS. 106 illus. 129 pp. 8vo. (_1890_) - - 5 0 - - =Elementary Text-Book on Steam Engines and Boilers.= By J.H. - KINEALY. Fourth edition, 106 illus. 259 pp. 8vo. (_New York, - 1903_) - - _net_ 8 6 - - =Centrifugal Fans.= By J.H. KINEALY. 33 illus. 206 pp. fcap. - 8vo, leather. (_New York, 1905_) - - _net_ 12 6 - - =Mechanical Draft.= By J.H. KINEALY. 27 original tables and 13 - plates, 142 pp. crown 8vo. (_New York, 1906_) - - _net_ 8 6 - - =The A.B.C. of the Steam Engine=, with a description of the - Automatic Governor. By J.P. LISK. 6 plates, 12mo. (S. & C. - SERIES, No. 17.) (_New York, 1910_) - - _net_ 1 6 - - =Valve Setting Record Book.= By P.A. LOW. 8vo, boards. - - 1 6 - - =The Lay-out of Corliss Valve Gears.= By S.A. MOSS. Second - edition, 3 plates, 108 pp. 18mo, boards. (_New York, 1906_) - - _net_ 2 0 - - =Steam Boilers=, their Management and Working. By J. PEATTIE. - Fifth edition, 35 illus. 230 pp. crown 8vo. (_1906_) - - _net_ 4 6 - - =Treatise on the Richards Steam Engine Indicator.= By C.T. - PORTER. Sixth edition, 3 plates and 73 diagrams, 285 pp. 8vo. - (_1902_) - - 9 0 - - =Practical Treatise on the Steam Engine.= By A. RIGG. Second - edition, 103 plates, 378 pp. demy 4to. (_1894_) - - 1 5 0 - - =Power and its Transmission.= A Practical Handbook for the - Factory and Works Manager. By T.A. SMITH. 76 pp. fcap. 8vo. - (_1910_) - - _net_ 2 0 - - =Drawings for Medium Sized Repetition Work.= By R.D. SPINNEY. - With 47 illus. 130 pp. 8vo. (_1909_) - - _net_ 3 6 - - =Slide Valve Simply Explained.= By W.J. TENNANT. Revised by - J.H. KINEALY. 41 illus. 83 pp. crown 8vo. (_New York, 1899_) - - _net_ 4 6 - - =Shaft Governors.= By W. TRINKS and C. HOOSUM. 27 illus. 97 pp. - 18mo, boards. (_New York, 1905_) - - _net_ 2 0 - - =Slide and Piston Valve Geared Steam Engines.= By W.H. UHLAND. - 47 plates and 314 illus. 155 pp. Two vols. folio, half morocco. - (_1882_) - - 1 16 0 - - =How to run Engines and Boilers.= By E.P. WATSON. Fifth - edition, 31 illus. 160 pp. crown 8vo. (_New York, 1904_) - - 3 6 - - =Position Diagram of Cylinder with Meyer Cut-off.= By W.H. - WEIGHTMAN. On card. (_New York_) - - _net_ 1 0 - - =Practical Method of Designing Slide Valve Gearing.= By E.J. - WELCH. 69 diagrams, 283 pp. Crown 8vo. (_1890_) - - 6 0 - - =Elements of Mechanics.= By T.W. WRIGHT. Eighth edition, - illustrated, 382 pp. 8vo. (_New York, 1909_) - - _net_ 10 6 - - - METALLURGY. - - IRON AND STEEL MANUFACTURE. - - =Life of Railway Axles.= By T. ANDREWS. 8vo, sewed. (_1895_) - - 1 0 - - =Microscopic Internal Flaws in Steel Rails and Propeller - Shafts.= By T. ANDREWS. 8vo, sewed. (_1896_) - - 1 0 - - =Microscopic Internal Flaws, Inducing Fracture in Steel.= By T. - ANDREWS. 8vo, sewed. (_1896_) - - 2 0 - - =Relations between the Effects of Stresses= slowly applied and - of Stresses suddenly applied in the case of Iron and Steel: - Comparative Tests with Notched and Plain Bars. By P. BREUIL. 23 - plates and 60 illus. 151 pp. 8vo. (_1904_) - - _net_ 8 0 - - =Brassfounders' Alloys.= By J.F. BUCHANAN. Illustrated, 129 pp. - crown 8vo. (_1905_) - - _net_ 4 6 - - =Foundry Nomenclature.= The Moulder's Pocket Dictionary and - concise guide to Foundry Practice. By JOHN F. BUCHANAN. - Illustrated, 225 pp. crown 8vo. (_1903_) - - _net_ 5 0 - - =American Standard Specifications for Steel.= By A.L. COLBY. - Second edition, revised, 103 pp. crown 8vo. (_New York, 1902_) - - _net_ 5 0 - - =Galvanised Iron=: its Manufacture and Uses. By J. DAVIES. 139 - pp. 8vo. (_1899_) - - _net_ 5 0 - - =Management of Steel.= By G. EDE. Seventh edition, 216 pp. - crown 8vo. (_1903_) - - 5 0 - - =Galvanising and Tinning=, with a special Chapter on Tinning - Grey Iron Castings. By W.T. FLANDERS. 8vo. (_New York_) - - _net_ 8 6 - - =Cupola Furnace.= A practical treatise on the Construction and - Management of Foundry Cupolas. By E. KIRK. Third edition, 78 - illus. 450 pp. demy 8vo. (_New York, 1910_) - - _net_ 15 0 - - =Practical Notes on Pipe Founding.= By J.W. MACFARLANE. 15 - plates, 148 pp. 8vo - - 12 6 - - =Atlas of Designs concerning Blast Furnace Practice.= By M.A. - PAVLOFF. 127 plates, 14 in. by 101/2 in. oblong, sewed. - (_1902_) - - _net_ 1 1 0 - - =Album of Drawings relating to the Manufacture of Open Hearth - Steel.= By M.A. PAVLOFF. - - Part I. Open Hearth Furnaces. 52 plates, 14 in. by 101/2 in. - oblong folio in portfolio. (_1904_) - - _net_ 12 0 - - =Metallography Applied to Siderurgic Products.= By H. SAVOIA. - Translated by R.G. CORBET. With 94 illus. 180 pp. crown 8vo. - (_1910_) - - _net_ 4 6 - - =Modern Foundry Practice.= Including revised subject matter and - tables from SPRETSON'S "Casting and Founding." By J. SHARP. - Second edition, 272 illus. 759 pp. 8vo. (_1905_) - - _net_ 1 1 0 - - =Roll Turning for Sections in Steel and Iron.= By A. SPENCER. - Second edition, 78 plates, 4to. (_1894_) - - 1 10 0 - - - METRIC TABLES. - - =French Measure and English Equivalents.= By J. BROOK. Second - edition, 80 pp. fcap. 32mo, roan. (_1906_) - - _net_ 1 0 - - =A Dictionary of Metric and other useful Measures.= By L. - CLARK. 113 pp. 8vo. (_1891_) - - 6 0 - - =English Weights, with their Equivalents in kilogrammes per - cent.= By F.W.A. LOGAN. 96 pp. fcap. 32mo, roan. (_1906_) - - _net_ 1 0 - - =Metric Weights with English Equivalents.= By H.P. MCCARTNEY. - 84 pp. fcap. 32mo. (_1907_) - - _net_ 1 0 - - =Metric Tables.= By Sir G.L. MOLESWORTH. Fourth edition, 95 pp. - royal 32mo. (_1909_) - - _net_ 2 0 - - =Tables for Setting out Curves= from 200 metres to 4000 metres - by tangential angles. By H. WILLIAMSON. 4 illus. 60 pp. 18mo. - (_1908_) - - _net_ 2 0 - - - MINERALOGY AND MINING. - - =Rock Blasting.= By G.G. ANDRE. 12 plates and 56 illus. in - text, 202 pp. 8vo. (_1878_) - - 5 0 - - =Winding Plants for Great Depth.= By H.C. BEHR. In two parts. - 8vo, sewed. (_1902_) - - _net_ 2 2 0 - - =Practical Treatise on Hydraulic Mining in California.= By A.J. - BOWIE, Jun. Tenth edition, 73 illus. 313 pp. royal 8vo. (_New - York, 1905_) - - _net_ 1 1 0 - - =Manual of Assaying Gold, Silver, Copper and Lead Ores.= By - W.L. BROWN. Twelfth edition, 132 illus. 589 pp. crown 8vo. - (_New York, 1907_) - - _net_ 10 6 - - =Fire Assaying.= By E.W. BUSKETT. 69 illus. 105 pp. crown 8vo. - (_New York, 1907_) - - _net_ 4 6 - - =Tin=: Describing the Chief Methods of Mining, Dressing, etc. - By A.G. CHARLETON. 15 plates, 83 pp. crown 8vo. (_1884_) - - 12 6 - - =Gold Mining and Milling= in Western Australia, with Notes upon - Telluride Treatment, Costs and Mining Practice in other Fields. - By A.G. CHARLETON. 82 illus. and numerous plans and tables, 648 - pp. super-royal 8vo. (_1903_) - - _net_ 1 5 0 - - =Miners' Geology and Prospectors' Guide.= By G.A. CORDER. 29 - plates, 224 pp. crown 8vo. (_1907_) - - _net_ 5 0 - - =Blasting of Rock in Mines, Quarries, Tunnels, etc.= By A.W. - and Z.W. DAW. Second edition, 90 illus. 316 pp. demy 8vo. - (_1909_) - - _net_ 15 0 - - =Handbook of Mineralogy=; determination and description of - Minerals found in the United States. By J.C. FOYE. 18mo, - boards. (_New York, 1886_) - - _net_ 2 0 - - =Conversations on Mines.= By W. HOPTON. Ninth edition, 33 - illus. 356 pp. crown 8vo. (_1891_) - - 4 6 - - =Our Coal Resources= at the End of the Nineteenth Century. By - Prof. E. HULL. 157 pp. demy 8vo. (_1897_) - - 6 0 - - =Hydraulic Gold Miners' Manual.= By T.S.G. KIRKPATRICK. Second - edition, 12 illus. 46 pp. crown 8vo. (_1897_) - - 4 0 - - =Economic Mining.= By C.G.W. LOCK. 175 illus. 680 pp. 8vo. - (_1895_) - - _net_ 10 6 - - =Gold Milling=: Principles and Practice. By C.G.W. LOCK. 200 - illus. 850 pp. demy 8vo. (_1901_) - - _net_ 1 1 0 - - =Mining and Ore-Dressing Machinery.= By C.G.W. LOCK. 639 - illus. 466 pp. super-royal 4to. (_1890_) - - 1 5 0 - - =Miners' Pocket Book.= By C.G.W. LOCK. Fifth edition, 233 - illus. 624 pp. fcap. 8vo, roan, gilt edges. (_1908_) - - _net_ 10 6 - - =Tests for Ores, Minerals and Metals of Commercial Value.= By - R.L. MCMECHEN. 152 pp. 12mo. (_New York, 1907_) - - _net_ 5 6 - - =Practical Handbook for the Working Miner and Prospector=, and - the Mining Investor. By J.A. MILLER. 34 illus. 234 pp. crown - 8vo. (_1897_) - - 7 6 - - =Theory and Practice of Centrifugal Ventilating Machines.= By - D. MURGUE. 7 illus. 81 pp. 8vo. (_1883_) - - 5 0 - - =Examples of Coal Mining Plant.= By J. POVEY-HARPER. Second - edition, 40 plates, 26 in. by 20 in. (_1895_) - - _net_ 4 4 0 - - =Examples of Coal Mining Plant, Second Series.= By J. - POVEY-HARPER. 10 plates, 26 in. by 20 in. (_1902_) - - _net_ 1 12 6 - - - ORGANISATION. - - ACCOUNTS, CONTRACTS AND MANAGEMENT. - - =Organisation of Gold Mining Business=, with Specimens of the - Departmental Report Books and the Account Books. By NICOL - BROWN. Second edition, 220 pp. fcap. folio. (_1903_) - - _net_ 1 5 0 - - =Manual of Engineering Specifications= and Contracts. By L.M. - HAUPT. Eighth edition, 338 pp. 8vo. (_New York, 1900_) - - _net_ 12 6 - - =Depreciation of Factories=, Municipal, and Industrial - Undertakings, and their Valuation. By E. MATHESON. Fourth - edition, 230 pp. 8vo, cloth. (_1910_) - - _net_ 10 6 - - =Aid Book to Engineering Enterprise.= By E. MATHESON. Third - edition, 916 pp. 8vo, buckram. (_1898_) - - 1 4 0 - - =Office Management.= A handbook for Architects and Civil - Engineers. By W. KAYE PARRY. New impression, 187 pp. medium - 8vo. (_1908_) - - _net_ 5 0 - - =Commercial Organisation of Engineering Factories.= By H. - SPENCER. 92 illus. 221 pp. 8vo. (_1907_) - - _net_ 10 6 - - - PHYSICS. - - COLOUR, HEAT AND EXPERIMENTAL SCIENCE. - - =The Entropy Diagram= and its Applications. By M.J. BOULVIN. 38 - illus. 82 pp. demy 8vo. (_1898_) - - 5 0 - - =Physical Problems and their Solution.= By A. BOURGOUGNON. 224 - pp. 18mo, boards. (_New York, 1897_) - - _net_ 2 0 - - =Heat for Engineers.= By C.R. DARLING. 110 illus. 430 pp. 8vo. - (_1908_) (FINSBURY TECHNICAL MANUAL) - - _net_ 12 6 - - =The Colourist.= A method of determining colour harmony. By - J.A.H. HATT. 2 coloured plates, 80 pp. 8vo. (_New York, 1908_) - - _net_ 6 6 - - =Engineering Thermodynamics.= By C.F. HIRSCHFELD. 22 illus. 157 - pp. 18mo, boards. (_New York, 1907_) - - _net_ 2 0 - - =Experimental Science=: Elementary, Practical and Experimental - Physics. By G.M. HOPKINS. Twenty-third edition, 920 illus. 1100 - pp. large 8vo. (_New York, 1902_) - - _net_ 1 1 0 - - =Reform in Chemical and Physical Calculations.= By C.J.T. - HANSSEN. Demy 4to. (_1897_) - - _net_ 6 6 - - =Introduction to the Study of Colour Phenomena.= By J.W. - LOVIBOND. 10 hand coloured plates, 48 pp. 8vo. (_1905_) - - _net_ 5 0 - - =Practical Laws and Data on the Condensation of Steam in Bare - Pipes=; to which is added a Translation of PECLET'S Theory and - Experiments on the Transmission of Heat through Insulating - Materials. By C.P. PAULDING. 184 illus. 102 pp. demy 8vo. (_New - York, 1904_) - - _net_ 8 6 - - =The Energy Chart.= Practical application to reciprocating - steam-engines. By Captain H.R. SANKEY. 157 illus. 170 pp. 8vo. - (_1907_) - - _net_ 7 6 - - - PRICE BOOKS. - - =Approximate Estimates.= By T.E. COLEMAN. Third edition, 481 - pp. oblong 32mo, leather. (_1907_) - - _net_ 5 0 - - =Railway Stores Price Book.= By W.O. KEMPTHORNE. 500 pp. demy - 8vo. (_1909_) - - _net_ 10 6 - - =Spons' Engineers' Price Book.= A Synopsis of Current Prices - and Rates for Engineering Materials and Products. Edited by - T.G. MARLOW. 650 pp. folio. (_1904_) - - _net_ 7 6 - - =Spons' Architects' and Builders' Pocket Price Book=, - Memoranda, Tables and Prices. Edited by CLYDE YOUNG. Revised by - STANFORD M. BROOKS. Illustrated, 552 pp. 16mo, leather cloth - (size 61/2 in. by 33/4 in. by 1/2 in. thick). Issued annually - - _net_ 3 0 - - - RAILWAY ENGINEERING. - - =Practical Hints to Young Engineers Employed on Indian - Railways.= By A.W.C. ADDIS. With 14 illus. 154 pp. 12mo. - (_1910_) - - _net_ 3 6 - - =Railroad Curves and Earthwork.= By C.F. ALLEN. Third edition, - 4 plates, 198 pp. 12mo, leather, gilt edges. (_New York, 1903_) - - _net_ 8 6 - - =Field and Office Tables=, specially applicable to Railroads. - By C.F. ALLEN. 293 pp. 16mo, leather. (_New York, 1903_) - - _net_ 8 6 - - _The two above combined in one vol. limp leather_ - - _net_ 12 6 - - =Up-to-date Air Brake Catechism.= By R.H. BLACKALL. - Twenty-third edit. 5 coloured plates, 96 illus. 305 pp. crown - 8vo. (_New York, 1908_) - - _net_ 8 6 - - =Simple and Automatic Vacuum Brakes.= By C. BRIGGS, G.N.R. 11 - plates, 8vo. 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(_1907_) - - _net_ 10 6 - - =Railway Engineering, Mechanical and Electrical.= By J.W.C. - HALDANE, 141 illus. 563 pp. 8vo. (_1897_) - - 15 0 - - =Tables for setting-out Railway Curves.= By C.P. HOGG. A series - of cards in neat cloth case - - 4 6 - - =The Construction of the Modern Locomotive.= By G. HUGHES. 300 - illus. 261 pp. 8vo. (_1894_) - - 9 0 - - =Practical Hints for Light Railways= at Home and Abroad. By - F.R. JOHNSON. 6 plates, 31 pp. crown 8vo. (_1896_) - - 2 6 - - =Handbook on Railway Stores Management.= By W.O. KEMPTHORNE. - 268 pp. demy 8vo. (_1907_) - - _net_ 10 6 - - =Railway Stores Price Book.= By W.O. KEMPTHORNE. 487 pp. demy - 8vo. (_1909_) - - _net_ 10 6 - - =Tables for setting out Curves= for Railways, Roads, Canals, - etc. By A. KENNEDY and R.W. HACKWOOD. 32mo - - _net_ 2 0 - - =Railroad Location Surveys and Estimates.= By F. LAVIS. 68 - illus. 270 pp. 8vo. (_New York, 1906_) - - _net_ 12 6 - - =Tables for Computing the Contents of Earthwork= in the - Cuttings and Embankments of Railways. By W. MACGREGOR. Royal - 8vo - - 6 0 - - =Bridge and Tunnel Centres.= By J.B. MCMASTERS. Illustrated, - 106 pp. 18mo, boards. (_New York, 1893_) - - _net_ 2 0 - - =Pioneering.= By F. SHELFORD. Illustrated, 88 pp. crown 8vo. - (_1909_) - - _net_ 3 0 - - =Handbook on Railway Surveying= for Students and Junior - Engineers. By B. STEWART. 55 illus. 98 pp. crown 8vo. (_1909_) - - _net_ 2 6 - - =Spiral Tables.= By J.G. SULLIVAN. 47 pp. 12mo, leather. (_New - York, 1908_) - - _net_ 6 6 - - =Modern British Locomotives.= By A.T. TAYLOR. 100 diagrams of - principal dimensions, 118 pp. oblong 8vo. (_1907_) - - _net_ 4 6 - - =Locomotive Slide Valve Setting.= By C.E. TULLY. Illustrated, - 18mo - - _net_ 1 0 - - =The Walschaert Locomotive Valve Gear.= By W.W. WOOD. 4 plates - and set of movable cardboard working models of the valves, 193 - pp. crown 8vo. (_New York, 1907_) - - _net_ 6 6 - - =The Westinghouse E.T. Air-Brake Instruction Pocket Book.= By - W.W. WOOD. 48 illus. including many coloured plates, 242 pp. - crown 8vo. (_New York, 1909_) - - _net_ 8 6 - - - SANITATION, PUBLIC HEALTH AND MUNICIPAL ENGINEERING. - - =Sewers and Drains for Populous Districts.= By J.W. ADAMS. - Ninth edition, 81 illus. 236 pp. 8vo. (_New York, 1902_) - - _net_ 10 6 - - =Public Abattoirs=, their Planning, Design and Equipment. By - R.S. AYLING. 33 plates, 100 pp. demy 4to. (_1908_) - - _net_ 8 6 - - =Sewage Purification.= By E. BAILEY-DENTON. 8 plates, 44 pp. - 8vo. (_1896_) - - 5 0 - - =Water Supply and Sewerage of Country Mansions= and Estates. By - E. BAILEY-DENTON. 76 pp. crown 8vo. (_1901_) - - _net_ 2 6 - - =Sewerage and Sewage Purification.= By M.N. BAKER. Second - edition, 144 pp. 18mo, boards. (_New York, 1905_) - - _net_ 2 0 - - =Sewage Irrigation by Farmers.= By R.W.P. BIRCH. 8vo, sewed. - (_1878_) - - 2 6 - - =Sanitary House Drainage=, its Principles and Practice. By T.E. - COLEMAN. 98 illus. 206 pp. crown 8vo. (_1896_) - - 6 0 - - =Stable Sanitation and Construction.= By T.E. COLEMAN. 183 - illus. 226 pp. crown 8vo. (_1897_) - - 6 0 - - =Public Institutions=, their Engineering, Sanitary and other - Appliances. By F. COLYER. 231 pp. 8vo. (_1889_) - - _net_ 2 0 - - =Discharge of Pipes and Culverts.= By P.M. CROSTHWAITE. Large - folding sheet in case. - - _net_ 2 6 - - =A Complete and Practical Treatise on Plumbing and Sanitation: - Hot Water Supply, Warming and Ventilation=, Steam Cooking, Gas, - Electric Light, Bells, etc., with a complete Schedule of Prices - of Plumber's Work. By G.B. DAVIS and F. DYE. 2 vols. 637 illus. - and 21 folding plates, 830 pp. 4to, cloth. (_1899_) - - _net_ 1 10 0 - - =Standard Practical Plumbing.= By P.J. DAVIES. - - Vol. I. Fourth edition, 768 illus. 355 pp. royal 8vo. (_1905_) - - _net_ 7 6 - - Vol. II. Second edition, 953 illus. 805 pp. (_1905_) - - _net_ 10 6 - - Vol. III. 313 illus. 204 pp. (_1905_) - - _net_ 5 0 - - =Conservancy, or Dry Sanitation versus Water Carriage.= By J. - DONKIN. 7 plates, 33 pp. 8vo, sewed. (_1906_) - - _net_ 1 0 - - =Sewage Disposal Works=, their Design and Construction. By W.C. - EASDALE. With 160 illus. 264 pp. demy 8vo. (_1910_) - - _net_ 10 6 - - =House Drainage and Sanitary Plumbing.= By W.P. GERHARD. Tenth - edition, 6 illus. 231 pp. 18mo, boards. (_New York, 1902_) - - _net_ 2 0 - - =Engineering Work in Towns and Cities.= By E. MCCULLOCH. 44 - illus. 502 pp. crown 8vo. (_New York, 1908_) - - _net_ 12 6 - - =The Treatment of Septic Sewage.= By G.W. RAFTER. 137 pp. 18mo, - boards. (_New York, 1904_) - - _net_ 2 0 - - =Reports and Investigations on Sewer Air= and Sewer - Ventilation. By R.H. REEVES. 8vo, sewed. (_1894_) - - 1 0 - - =The Law and Practice of Paving= Private Street Works. By W. - SPINKS. Fourth edition, 256 pp. 8vo. (_1904_) - - _net_ 12 6 - - - STRUCTURAL DESIGN. - - (_See_ BRIDGES AND ROOFS.) - - - TELEGRAPH CODES. - - =New Business Code.= 320 pp. narrow 8vo. (Size 43/4 in. by - 73/4 in. and 1/2 in. thick, and weight 10 oz.) (_New York, - 1909_) - - _net_ 1 10 0 - - =Miners' and Smelters' Code= (formerly issued as the =Master - Telegraph Code=). 448 pp. 8vo, limp leather, weight 14 oz. - (_New York, 1899_) - - _net_ 2 10 0 - - =Billionaire Phrase Code=, containing over two million - sentences coded in single words. 56 pp. 8vo, leather. (_New - York, 1908_) - - _net_ 6 6 - - - WARMING AND VENTILATION. - - =Hot Water Supply.= By F. DYE. Fifth edition, 48 illus. 86 pp. - crown 8vo. (_1902_) - - _net_ 3 0 - - =A Practical Treatise upon Steam Heating.= By F. DYE. 129 - illus. 246 pp. demy 8vo. (_1901_) - - _net_ 10 0 - - =Practical Treatise on Warming Buildings by Hot Water.= By F. - DYE. 192 illus. 319 pp. 8vo. cloth. (_1905_) - - _net_ 8 6 - - =Charts for Low Pressure Steam Heating.= By J.H. KINEALY. Small - folio. (_New York_) - - 4 6 - - =Formulae and Tables for Heating.= By J.H. KINEALY. 18 illus. 53 - pp. 8vo. (_New York, 1899_) - - 3 6 - - =Mechanics of Ventilation.= By G.W. RAFTER. Second edition, - 18mo, boards. (_New York, 1896_) - - _net_ 2 0 - - =Principles of Heating.= By W.G. SNOW. 62 illus. 161 pp. 8vo. - (_New York, 1907_) - - _net_ 8 6 - - =Furnace Heating.= By W.G. SNOW. Fourth edition, 52 illus. 216 - pp. 8vo. (_New York, 1909_) - - _net_ 6 6 - - =Ventilation of Buildings.= By W.G. SNOW and T. NOLAN. 83 pp. - 18mo, boards. (_New York, 1906_) - - _net_ 2 0 - - =Heating Engineers' Quantities.= By W.L. WHITE and G.M. WHITE. - 4 plates, 33 pp. folio. (_1910_) - - _net_ 10 6 - - - WATER SUPPLY. - - (_See also_ HYDRAULICS.) - - =Potable Water and Methods of Testing Impurities.= By M.N. - BAKER. 97 pp. 18mo, boards. (_New York, 1905_) - - _net_ 2 0 - - =Manual of Hydrology.= By N. BEARDMORE. New impression, 18 - plates, 384 pp. 8vo. (_1906_) - - _net_ 10 6 - - =Boiler Waters=, Scale, Corrosion and Fouling. By W.W. - CHRISTIE. 77 illus. 235 pp. 8vo, cloth. (_New York, 1907_) - - _net_ 12 6 - - =Water Softening and Purification.= By H. COLLET. Second - edition, 6 illus. 170 pp. crown 8vo. (_1908_) - - _net_ 5 0 - - =Treatise on Water Supply=, Drainage and Sanitary Appliances of - Residences. By F. COLYER. 100 pp. crown 8vo. (_1899_) - - _net_ 1 6 - - =Report on the Investigations into the Purification of the Ohio - River Water= at Louisville, Kentucky. By G.W. FULLER. 8 plates, - 4to, cloth. (_New York, 1898_) - - _net_ 2 2 0 - - =Purification of Public Water Supplies.= By J.W. HILL. 314 pp. - 8vo. (_New York, 1898_) - - 10 6 - - =Well Boring for Water, Brine and Oil.= By C. ISLER. _New - edition in the Press._ - - =Method of Measuring Liquids Flowing through Pipes by means of - Meters of Small Calibre.= By Prof. G. LANGE. 1 plate, 16 pp. - 8vo, sewed - - _net_ 0 6 - - =On Artificial Underground Water.= By G. RICHERT. 16 illus. 33 - pp. 8vo, sewed. (_1900_) - - _net_ 1 6 - - =Notes on Water Supply= in new Countries. By F.W. STONE. 18 - plates, 42 pp. crown 8vo. (_1888_) - - 5 0 - - =The Principles of Waterworks Engineering.= By J.H.T. TUDSBERY - and A.W. BRIGHTMORE. Third edition, 13 folding plates, 130 - illus. 447 pp. demy 8vo. (_1905_) - - _net_ 1 1 0 - - - WORKSHOP PRACTICE. - - =A Handbook for Apprenticed Machinists.= By O.J. BEALE. Second - edition, 89 illus., 141 pp. 16mo. (_New York, 1901_) - - _net_ 2 6 - - =Bicycle Repairing.= By S.D.V. BURR. Sixth edition, 200 illus. - 208 pp. 8vo. (_New York, 1903_) - - _net_ 4 6 - - =Practice of Hand Turning.= By F. CAMPIN. Third edition, 99 - illus. 307 pp. crown 8vo. (_1883_) - - 3 6 - - =Calculation of Change Wheels for Screw Cutting on Lathes.= By - D. DE VRIES. 46 illus. 83 pp. 8vo. (_1908_) - - _net_ 3 0 - - =Milling Machines and Milling Practice.= By D. DE VRIES. With - 536 illus. 464 pp. medium 8vo. (_1910_) - - _net_ 14 0 - - =French-Polishers' Manual.= By a French-Polisher. 31 pp. royal - 32mo, sewed. (_1902_) - - _net_ 0 6 - - =Art of Copper Smithing.= By J. FULLER. Third edition, 475 - illus. 325 pp. royal 8vo. (_New York, 1901_) - - _net_ 12 6 - - =Saw Filing and Management of Saws.= By R. GRIMSHAW. New - edition, 81 illus. 16mo. (_New York, 1906_) - - _net_ 3 6 - - =Paint and Colour Mixing.= By A.S. JENNINGS. Fourth edition. 14 - coloured plates, 190 pp. 8vo. (_1910_) - - _net_ 5 0 - - =The Mechanician=: a Treatise on the Construction and - Manipulation of Tools. By C. KNIGHT. Fifth edition, 96 plates, - 397 pp. 4to. (_1897_) - - 18 0 - - =Turner's and Fitter's Pocket Book.= By J. LA NICCA. 18mo, - sewed - - 0 6 - - =Tables for Engineers and Mechanics=, giving the values of the - different trains of wheels required to produce Screws of any - pitch. By LORD LINDSAY. Second edition, royal 8vo, oblong - - 2 0 - - =Screw-cutting Tables.= By W.A. MARTIN. Seventh edition, royal - 8vo, oblong - - 1 0 - - =Metal Plate Work=, its Patterns and their Geometry, for the - use of Tin, Iron and Zinc Plate Workers. By C.T. MILLIS. Fourth - edition, 280 diagrams, 470 pp. crown 8vo. (_1906_) - - 9 0 - - =Engineers' and General Smiths' Work.= The smith and forgeman's - handbook of practical smithing and forging. By T. MOORE. 401 - illus. 248 pp. crown 8vo. (_1906_) - - _net_ 5 0 - - =Modern Machine Shop Construction=, equipment and management. - By O.E. PERRIGO. 208 illus. 343 pp. crown 4to. (_New York, - 1906_) - - _net_ 21 0 - - =Turner's Handbook on Screw-cutting=, Coning, etc. By W. PRICE. - Fcap. 8vo - - 1 0 - - =Introduction to Eccentric Spiral Turning.= By H.C. ROBINSON. - 12 plates, 23 illus. 48 pp. 8vo. (_1906_) - - _net_ 4 6 - - =Manual of Instruction in Hard Soldering.= By H. ROWELL. Sixth - edition, 7 illus. 66 pp. crown 8vo. 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SPON, Ltd., 57 Haymarket, London, S.W. - - -LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED. - - - - - JUST OUT THE LATEST - -The - -Aeroplane Portfolio - -By D. 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In paper, postpaid, 25c. - -In handsome cloth binding, postpaid, 55c. - - =Flying Machines, Past, Present and Future.= A popular account - of flying machines, dirigible balloons and aeroplanes. - Describing many different kinds of machines, and their chief - feature. By A.W. Marshall and Henry Greenly. 138 pages 23 - illustrations and many plates, 12 mo. boards. By mail 55c. - - =Model Flying Machines.= Their design and construction by W.G. - Aston. A first rate little book showing numerous methods of - propelling models, making propellors, construction of different - kinds of models, etc., etc. 130 pages, 94 illustrations. 12 mo. - boards, by mail 55c. - -=Model Aeroplanes.= How to Build and Fly Them, by E.W. Twining. A set -of 5 full-size scale drawings for three different models with -descriptive illustrated book explaining how to make and fly them. - - Postpaid : : : : 55c - -=No. 2 Model.= Complete set of parts in the rough to make up this -model. (Without drawings), - - Postpaid : : 65c - -[Illustration: No. 3 Model] - -=No. 3 Model.= Complete set of parts in the rough (without drawings). -This makes up into a beautiful little model. - - Postpaid : : : : $1.15 - - -=Model Gliders, Birds, Butterflies and Aeroplanes.= - -How to make and fly them, by E.W. Twining. Consisting of one large -sheet of 12 butterflies and two birds printed in bright colors. One -small cardboard Model Glider with descriptive illustrated book showing -how to make and fly them. - - Postpaid : : : : 55c - - - - - * * * * * - - - Transcriber's Notes - - Obvious punctuation and spelling errors and inconsistent hyphenation - have been corrected. - - Italic text is denoted by _underscores_ and bold text by =equal signs=. - - The OE ligature has been replaced by the separate characters. - - The fractions 1/4, 1/2 and 3/4 are represented using the Latin-1 characters, - but other fractions use the / and - symbols, e.g. 3/8 or 2-5/8. - - The exponents 2 and 3 are represented using squared and cubed respectively, but - other exponents are indicated by the caret character, for example, - v^{1.85} - - Subscripts are simply enclosed in braces, e.g. W{0}. - - Other symbols that cannot be represented have been replaced by words - in braces: {alpha}, {pi}, {therefore}, {square root} and - {proportional to}. - - The skin friction formulae given on pages 11 and 128 have been corrected - by comparison with other sources. Respectively, the formulae were - originally printed as - _f_ = 0.00000778_l_^{9.3}_v_^{1.85} - and - _f_ = 0.00000778_l_ - ^{00.7}_v_^{1.85} - - In ambiguous cases, the text has been left as it appears in the - original book. - - - - - -End of the Project Gutenberg EBook of The Theory and Practice of Model -Aeroplaning, by V. E. 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