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It is a book of instructions +intended to point out the theories of flying, as given by the +pioneers, the practical application of power to the various +flying structures; how they are built, the different methods of +controlling them; the advantages and disadvantages of the types +now in use; and suggestions as to the directions in which +improvements are required. + +It distinctly points out wherein mechanical flight differs +from bird flight, and what are the relations of shape, form, size +and weight. It treats of kites, gliders and model aeroplanes, +and has an Interesting chapter on the aeroplane and its uses In +the great war. All the illustrations have been specially prepared +for the work. + + +Every Boy's Mechanical Library + +AEROPLANES + +BY +J. S. ZERBE, M. E. +Author of Automobiles--Motors + + +COPYRIGHT, 1915, BY +CUPPLES & LEON COMPANY +NY + + +CONTENTS + +INTRODUCTORY + +CHAPTER I. THEORIES AND FACTS ABOUT FLYING + +The "Science" of Aviation. Machine Types. Shape +or Form not Essential. A Stone as a Flying Machine. +Power the Great Element. Gravity as Power. Mass +and Element in Flying. Momentum a Factor. Resistance. +How Resistance Affects Shape. Mass and Resistance. +The Early Tendency to Eliminate Momentum. +Light Machines Unstable. The Application of +Power. The Supporting Surfaces. Area not the Essential +Thing. The Law of Gravity. Gravity. Indestructibility +of Gravitation. Distance Reduces Gravitational +Pull. How Motion Antagonizes Gravity. A +Tangent. Tangential Motion Represents Centrifugal +Pull. Equalizing the Two Motions. Lift and Drift. +Normal Pressure. Head Resistance. Measuring Lift +and Drift. Pressure at Different Angles. Difference +Between Lift and Drift in Motion. Tables of Lift and +Drift. Why Tables of Lift and Drift are Wrong. +Langley's Law. Moving Planes vs. Winds. Momentum +not Considered. The Flight of Birds. The +Downward Beat. The Concaved Wing. Feather Structure +Considered. Webbed Wings. The Angle of Movement. +An Initial Movement or Impulse Necessary. A +Wedging Motion. No Mystery in the Wave Motion. +How Birds Poise with Flapping Wings. Narrow- +winged Birds. Initial Movement of Soaring Birds. +Soaring Birds Move Swiftly. Muscular Energy +Exerted by Soaring Birds. Wings not Motionless. + +CHAPTER II. PRINCIPLES OF AEROPLANE FLIGHT +Speed as one of the Elements. Shape and Speed. +What "Square of the Speed" Means. Action of a +"Skipper." Angle of Incidence. Speed and Surface. +Control of the Direction of Flight. Vertical Planes. + +CHAPTER III. THE FORM OR SHAPE OF FLYING MACHINES +The Theory of Copying Nature. Hulls of Vessels. +Man Does not Copy Nature. Principles Essential, not +Forms. Nature not the Guide as to Forms. The Propeller +Type. Why Specially-designed Forms Improve +Natural Structures. Mechanism Devoid of Intelligence. +A Machine Must Have a Substitute for Intelligence. +Study of Bird Flight Useless. Shape of +Supporting Surface. The Trouble Arising From Outstretched +Wings. Density of the Atmosphere. Elasticity +of the Air. "Air Holes." Responsibility for +Accidents. The Turning Movement. Centrifugal Action: +The Warping Planes. + +CHAPTER IV. FORE AND AFT CONTROL +The Bird Type of Fore and Aft Control. Angle and +Direction of Flight. Why Should the Angle of the +Body Change. Changing Angle of Body not Safe. A +Non-changing Body. Descending Positions by Power +Control. Cutting off the Power. The Starting Movement. +The Suggested Type. The Low Center of Gravity. +Fore and Aft Oscillations. Application of the +New Principle. Low Weight not Necessary with Synchronously- +moving wings. + +CHAPTEB V. DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS +The Helicopter. Aeroplanes. The Monoplane. Its +Advantages. Its Disadvantages. The Bi-plane. Stability +in Bi-planes. The Orthopter. Nature's Type +not Uniform. Theories About Flight of Birds. Instinct. +The Mode of Motion. The Wing Structure. +The Wing Movement. The Helicopter Motion. + +CHAPTER VI. THE LIFTING SURFACES OF AEROPLANES +Relative Speed and Angle. Narrow Planes Most Effective. +Stream Lines Along a Plane. The Center of +Pressure. Air Lines on the Upper Side of a Plane. +Rarefied Area. Rarefaction Produced by Motion. The +Concaved Plane. The Center of Pressure. Utilizing +the Rarefied Area. Changing Center of Pressure. +Plane Monstrosities. The Bird Wing Structure. +Torsion. The Bat's Wing. An Abnormal Shape. The +Tail as a Monitor. + +CHAPTER VII. ABNORMAL FLYING STUNTS AND SPEEDS +Lack of Improvements in Machines. Men Exploited +and not Machines. Abnormal Flying of no Value. +The Art of Juggling. Practical Uses the Best Test. +Concaved and Convex Planes. How Momentum is a +Factor in Inverted Flying. The Turning Movement. +When Concaved Planes are Desirable. The Speed +Mania. Uses of Flying Machines. Perfection in Machines +Must Come Before Speed. The Range of its +Uses. Commercial Utility. + +CHAPTER VIII. KITES AND GLIDERS +The Dragon Kite. Its Construction. The Malay +Kite. Dihedral Angle. The Common Kite. The Bow +Kite. The Box Kite. The Voison Bi-plane. Lateral +Stability in Kites, not Conclusive as to Planes. The +Spear Kite. The Cellular Kite. Tetrahedral Kite. +The Deltoid. The Dunne Flying Machine. Rotating +Kite. Kite Principles. Lateral Stability in Kites. +Similarity of Fore and Aft Control. Gliding Flight +One of the Uses of Glider Experiments. Hints in +Gliding. + +CHAPTER IX. AEROPLANE CONSTRUCTION +Lateral and Fore and Aft. Transverse. Stability +and Stabilization. The Wright System. Controlling +the Warping Ends. The Curtiss Wings. The Farman +Ailerons. Features Well Developed. Depressing the +Rear End. Determining the Size. Rule for Placing +the Planes. Elevating Plane. Action in Alighting. +The Monoplane. The Common Fly. Stream Lines. +The Monoplane Form. + +CHAPTER X. POWER AND ITS APPLICATION +Features in Power Application. Amount of Power +Necessary. The Pull of the Propeller. Foot Pounds +Small Amount of Power Available. High Propeller +Speed Important. Width and Pitch of Blades. Effect +of Increasing Propeller Pull. Disposition of the +Planes. Different Speeds with Same Power. Increase +of Speed Adds to Resistance. How Power Decreases +with Speed. How to Calculate the Power Applied. +Pulling Against an Angle. The Horizontal and the +Vertical Pull. The Power Mounting. Securing the +Propeller to the Shaft. Vibrations. Weaknesses in +Mounting. The Gasoline Tank. Where to Locate the +Tank. The Danger to the Pilot. The Closed-in Body. +Starting the Machine. Propellers with Varying Pitch. + +CHAPTER XI. FLYING MACHINE ACCESSORIES +The Anemometer. The Anemograph. The Anemometrograph. +The Speed Indicator. Air Pressure Indicator. +Determining the Pressure From the Speed. +Calculating Pressure From Speed. How the Figures +are Determined. Converting Hours Into Minutes. +Changing Speed Hours to Seconds. Pressure as the +Square of the Speed. Gyroscopic:Balance. The Principles +Involved. The Application of the Gyroscope. +Fore and Aft Gyroscopic Control. Angle Indicator. +Pendulum Stabilizer. Steering and Controlling +Wheel. Automatic Stabilizing Wings. Barometers. +Aneroid Barometer. Hydroplanes. Sustaining Weight +of Pontoons. Shape of the Pontoon. + +CHAPTER XII. EXPERIMENTAL WORK IN FLYING +Certain Conditions in Flying. Heat in Air. Motion +When in Flight. Changing Atmosphere. "Ascending +Currents." "Aspirate Currents." Outstretched Wings. +The Starting Point. The Vital Part of the Machine. +Studying the Action of the Machine. Elevating the +Machine. How to Practice. The First Stage. Patience +the Most Difficult Thing. The Second Stage. +The Third Stage. Observations While in Flight. Flying +in a Wind. First Trials in a Quiet Atmosphere. +Making Turns. The Fourth Stage. The Figure 8. +The Vol Plane. The Landing. Flying Altitudes. + +CHAPTER XIII. THE PROPELLER +Propeller Changes. Propeller Shape. The Diameter. +Pitch. Laying Out the Pitch. Pitch Rule. Laminated +Construction. Laying up a Propeller Form. +Making Wide Blades. Propeller Outline. For High +Speeds. Increasing Propeller Efficiency. + +CHAPTER XIV. EXPERIMENTAL GLIDERS AND MODEL AEROPLANES +The Relation of Models to Flying Machines. Lessons +From Models. Flying Model Aeroplanes. An +Efficient Glider. The Deltoid Formation. Racing +Models. The Power for Model Aeroplanes. Making +the Propeller. Material for the Propeller. Rubber. +Propeller Shape and Size. Supporting Surfaces. + +CHAPTER XV. THE AEROPLANE IN THE GREAT WAR +Balloon Observations. Changed Conditions in Warfare. +The Effort to Conceal Combatants. Smokeless +Powder. Inventions to Attack Aerial Craft. Functions +of the Aeroplane in War. Bomb-throwing Tests. +Method for Determining the Movement of a Bomb. +The Great Extent of Modern Battle Lines. The Aeroplane +Detecting the Movements of Armies. The Effective +Height for Scouting. Sizes of Objects at Great +Distances. Some Daring Feats in War. The German +Taube. How Aeroplanes Report Observations. Signal +Flags. How Used. Casualties Due to Bombs +From Aeroplanes. + +GLOSSARY + + + +INTRODUCTORY + +In preparing this volume on Flying Machines +the aim has been to present the subject in such a +manner as will appeal to boys, or beginners, in +this field of human activity. + +The art of aviation is in a most primitive state. +So many curious theories have been brought out +that, while they furnish food for thought, do not, +in any way, advance or improve the structure of +the machine itself, nor are they of any service +in teaching the novice how to fly. + +The author considers it of far more importance +to teach right principles, and correct reasoning +than to furnish complete diagrams of the details +of a machine. The former teach the art, whereas +the latter merely point out the mechanical +arrangements, independently of the reasons for +making the structures in that particular way. + +Relating the history of an art, while it may be +interesting reading, does not even lay the foundations +of a knowledge of the subject, hence that +field has been left to others. + +The boy is naturally inquisitive, and he is interested +in knowing WHY certain things are +necessary, and the reasons for making structures in +particular ways. That is the void into which +these pages are placed. + +The author knows from practical experience, +while experimenting with and building aeroplanes, +how eagerly every boy inquires into details. +They want the reasons for things. + +One such instance is related to evidence this +spirit of inquiry. Some boys were discussing the +curved plane structure. One of them ventured +the opinion that birds' wings were concaved on the +lower side. "But," retorted another, "why are +birds' wings hollowed?" + +This was going back to first principles at one +leap. It was not satisfying enough to know that +man was copying nature. It was more important +to know why nature originated that type of formation, +because, it is obvious, that if such structures +are universal in the kingdom of flying creatures, +there must be some underlying principle +which accounted for it. + +It is not the aim of the book to teach the art +of flying, but rather to show how and why the +present machines fly. The making and the using +are separate and independent functions, and of +the two the more important is the knowledge how +to make a correct machine. + +Hundreds of workmen may contribute to the +building of a locomotive, but one man, not a +builder, knows better how to handle it. To +manipulate a flying machine is more difficult to +navigate than such a ponderous machine, because +it requires peculiar talents, and the building is +still more important and complicated, and requires +the exercise of a kind of skill not necessary +in the locomotive. + +The art is still very young; so much is done +which arises from speculation and theories; too +much dependence is placed on the aviator; the +desire in the present condition of the art is to exploit +the man and not the machine; dare-devil exhibitions +seem to be more important than perfecting +the mechanism; and such useless attempts as +flying upside down, looping the loop, and characteristic +displays of that kind, are of no value to +the art. + THE AUTHOR. + + + +AEROPLANES + +CHAPTER I + +THEORIES AND FACTS ABOUT FLYING + + +THE "SCIENCE" OF AVIATION.--It may be +doubted whether there is such a thing as a "science +of aviation." Since Langley, on May 6, +1896, flew a motor-propelled tandem monoplane +for a minute and an half, without a pilot, and the +Wright Brothers in 1903 succeeded in flying a +bi-plane with a pilot aboard, the universal opinion +has been, that flying machines, to be successful, +must follow the structural form of birds, and +that shape has everything to do with flying. + +We may be able to learn something by carefully +examining the different views presented by +those interested in the art, and then see how they +conform to the facts as brought out by the actual +experiments. + +MACHINE TYPES.--There is really but one type +of plane machine. While technically two forms +are known, namely, the monoplane and the +bi-plane, they are both dependent on outstretched +wings, longer transversely than fore and aft, so +far as the supporting surfaces are concerned, and +with the main weight high in the structure, thus, +in every particular, conforming to the form +pointed out by nature as the apparently correct +type of a flying structure. + +SHAPE OR FORM NOT ESSENTIAL.--It may be +stated with perfect confidence, that shape or form +has nothing to do with the mere act of flying. It +is simply a question of power. This is a broad +assertion, and its meaning may be better understood +by examining the question of flight in a +broad sense. + +A STONE AS A FLYING MACHINE.--When a stone +is propelled through space, shape is of no importance. +If it has rough and jagged sides its speed +or its distance may be limited, as compared with +a perfectly rounded form. It may be made in +such a shape as will offer less resistance to the air +in flight, but its actual propulsion through space +does not depend on how it is made, but on the +power which propelled it, and such a missile is a +true heavier-than-air machine. + +A flying object of this kind may be so constructed +that it will go a greater distance, or require +less power, or maintain itself in space at +less speed; but it is a flying machine, nevertheless, +in the sense that it moves horizontally through the +air. + +POWER THE GREAT ELEMENT.--Now, let us examine +the question of this power which is able to +set gravity at naught. The quality called energy +resides in material itself. It is something within +matter, and does not come from without. The +power derived from the explosion of a charge of +powder comes from within the substance; and so +with falling water, or the expansive force of +steam. + +GRAVITY AS POWER.--Indeed, the very act of the +ball gradually moving toward the earth, by the +force of gravity, is an illustration of a power +within the object itself. Long after Galileo +firmly established the law of falling bodies it began +to dawn on scientists that weight is force. +After Newton established the law of gravitation +the old idea, that power was a property of each +body, passed away. + +In its stead we now have the firmly established +view, that power is something which must have +at least two parts, or consist in pairs, or two elements +acting together. Thus, a stone poised on +a cliff, while it exerts no power which can be +utilized, has, nevertheless, what is called potential +energy. When it is pushed from its lodging place +kinetic energy is developed. In both cases, +gravity, acting in conjunction with the mass of +the stone, produced power. + +So in the case of gunpowder. It is the unity of +two or more substances, that causes the expansion +called power. The heat of the fuel converting +water into steam, is another illustration of the +unity of two or more elements, which are necessary +to produce energy. + +MASS AN ELEMENT IN FLYING.--The boy who +reads this will smile, as he tells us that the power +which propelled the ball through the air came +from the thrower and not from the ball itself. +Let us examine this claim, which came from a real +boy, and is another illustration how acute his mind +is on subjects of this character. + +We have two balls the same diameter, one of +iron weighing a half pound, and the other of cotton +weighing a half ounce. The weight of one +is, therefore, sixteen times greater than the other. + +Suppose these two balls are thrown with the +expenditure of the same power. What will be the +result! The iron ball will go much farther, or, +if projected against a wall will strike a harder +blow than the cotton ball. + +MOMENTUM A FACTOR.--Each had transferred +to it a motion. The initial speed was the same, +and the power set up equal in the two. Why this +difference, The answer is, that it is in the +material itself. It was the mass or density which accounted +for the difference. It was mass multiplied +by speed which gave it the power, called, in +this case, momentum. + +The iron ball weighing eight ounces, multiplied +by the assumed speed of 50 feet per second, equals +400 units of work. The cotton ball, weighing 1/2 +ounce, with the same initial speed, represents 25 +units of work. The term "unit of work" means +a measurement, or a factor which may be used to +measure force. + +It will thus be seen that it was not the thrower +which gave the power, but the article itself. A +feather ball thrown under the same conditions, +would produce a half unit of work, and the iron +ball, therefore, produced 800 times more energy. + +RESISTANCE.--Now, in the movement of any body +through space, it meets with an enemy at every +step, and that is air resistance. This is much +more effective against the cotton than the iron +ball: or, it might be expressed in another way: +The momentum, or the power, residing in the +metal ball, is so much greater than that within the +cotton ball that it travels farther, or strikes a +more effective blow on impact with the wall. + +HOW RESISTANCE AFFECTS THE SHAPE.--It is because +of this counterforce, resistance, that shape +becomes important in a flying object. The metal +ball may be flattened out into a thin disk, and now, +when the same force is applied, to project it forwardly, +it will go as much farther as the difference +in the air impact against the two forms. + +MASS AND RESISTANCE.--Owing to the fact that +resistance acts with such a retarding force on an +object of small mass, and it is difficult to set up a +rapid motion in an object of great density, lightness +in flying machine structures has been considered, +in the past, the principal thing necessary. + +THE EARLY TENDENCY TO ELIMINATE MOMENTUM.-- +Builders of flying machines, for several +years, sought to eliminate the very thing +which gives energy to a horizontally-movable +body, namely, momentum. + +Instead of momentum, something had to be +substituted. This was found in so arranging the +machine that its weight, or a portion of it, would +be sustained in space by the very element which +seeks to retard its flight, namely, the atmosphere. + +If there should be no material substance, like +air, then the only way in which a heavier-than-air +machine could ever fly, would be by propelling it +through space, like the ball was thrown, or by +some sort of impulse or reaction mechanism on +the air-ship itself. It could get no support from +the atmosphere. + +LIGHT MACHINES UNSTABLE.--Gradually the +question of weight is solving itself. Aviators are +beginning to realize that momentum is a wonderful +property, and a most important element in +flying. The safest machines are those which have +weight. The light, willowy machines are subject +to every caprice of the wind. They are notoriously +unstable in flight, and are dangerous even +in the hands of experts. + +THE APPLICATION OF POWER.--The thing now to +consider is not form, or shape, or the distribution +of the supporting surfaces, but HOW to apply +the power so that it will rapidly transfer a machine +at rest to one in motion, and thereby get +the proper support on the atmosphere to hold it +in flight. + +THE SUPPORTING SURFACES.--This brings us to +the consideration of one of the first great problems +in flying machines, namely, the supporting +surfaces,--not its form, shape or arrangement, +(which will be taken up in their proper places), but +the area, the dimensions, and the angle necessary +for flight. + +AREA NOT THE ESSENTIAL THING.--The history +of flying machines, short as it is, furnishes many +examples of one striking fact: That area has +but little to do with sustaining an aeroplane when +once in flight. The first Wright flyer weighed +741 pounds, had about 400 square feet of plane +surface, and was maintained in the air with a 12 +horse power engine. + +True, that machine was shot into the air by a +catapult. Motion having once been imparted to it, +the only thing necessary for the motor was to +maintain the speed. + +There are many instances to show that when +once in flight, one horse power will sustain over +100 pounds, and each square foot of supporting +surface will maintain 90 pounds in flight. + +THE LAW OF GRAVITY.--As the effort to fly +may be considered in the light of a struggle to +avoid the laws of nature with respect to matter, +it may be well to consider this great force as a +fitting prelude to the study of our subject. + +Proper understanding, and use of terms is very +desirable, so that we must not confuse them. +Thus, weight and mass are not the same. Weight +varies with the latitude, and it is different at various +altitudes; but mass is always the same. + +If projected through space, a certain mass +would move so as to produce momentum, which +would be equal at all places on the earth's surface, +or at any altitude. + +Gravity has been called weight, and weight +gravity. The real difference is plain if gravity +is considered as the attraction of mass for mass. +Gravity is generally known and considered as a +force which seeks to draw things to the earth. +This is too narrow. + +Gravity acts in all directions. Two balls suspended +from strings and hung in close proximity +to each other will mutually attract each other. +If one has double the mass it will have twice the +attractive power. If one is doubled and the other +tripled, the attraction would be increased six +times. But if the distance should be doubled the +attraction would be reduced to one-fourth; and +if the distance should be tripled then the pull +would be only one-ninth. + +The foregoing is the substance of the law, +namely, that all bodies attract all other bodies +with a force directly in proportion to their mass, +and inversely as the square of their distance from +one another. + +To explain this we cite the following illustration: +Two bodies, each having a mass of 4 +pounds, and one inch apart, are attracted toward +each other, so they touch. If one has twice the +mass of the other, the smaller will draw the larger +only one-quarter of an inch, and the large one +will draw the other three-quarters of an inch, +thus confirming the law that two bodies will attract +each other in proportion to their mass. + +Suppose, now, that these balls are placed two +inches apart,--that is, twice the distance. As +each is, we shall say, four pounds in weight, the +square of each would be 16. This does not mean +that there would be sixteen times the attraction, +but, as the law says, inversely as the square of +the distance, so that at two inches there is only +one-sixteenth the attraction as at one inch. + +If the cord of one of the balls should be cut, it +would fall to the earth, for the reason that the +attractive force of the great mass of the earth is +so much greater than the force of attraction in +its companion ball. + +INDESTRUCTIBILITY OF GRAVITATION.--Gravity +cannot be produced or destroyed. It acts between +all parts of bodies equally; the force being +proportioned to their mass. It is not affected by +any intervening substance; and is transmitted +instantaneously, whatever the distance may be. + +While, therefore, it is impossible to divest matter +of this property, there are two conditions +which neutralize its effect. The first of these is +position. Let us take two balls, one solid and +the other hollow, but of the same mass, or density. +If the cavity of the one is large enough to receive +the other, it is obvious that while gravity is still +present the lines of attraction being equal at +all points, and radially, there can be no pull which +moves them together. + +DISTANCE REDUCES GRAVITATIONAL PULL.--Or +the balls may be such distance apart that the attractive +force ceases. At the center of the earth +an object would not weigh anything. A pound +of iron and an ounce of wood, one sixteen times +the mass of the other, would be the same,--absolutely +without weight. + +If the object should be far away in space it +would not be influenced by the earth's gravity; +so it will be understood that position plays an +important part in the attraction of mass for mass. + +HOW MOTION ANTAGONIZES GRAVITY.--The second +way to neutralize gravity, is by motion. A +ball thrown upwardly, antagonizes the force of +gravity during the period of its ascent. In like +manner, when an object is projected horizontally, +while its mass is still the same, its weight is less. + +Motion is that which is constantly combating +the action of gravity. A body moving in a circle +must be acted upon by two forces, one which tends +to draw it inwardly, and the other which seeks to +throw it outwardly. + +The former is called centripetal, and the latter +centrifugal motion. Gravity, therefore, represents +centripetal, and motion centrifugal force. + +If the rotative speed of the earth should be retarded, +all objects on the earth would be increased +in weight, and if the motion should be accelerated +objects would become lighter, and if sufficient +speed should be attained all matter would fly off +the surface, just as dirt dies off the rim of a +wheel at certain speeds. + +A TANGENT.--When an object is thrown horizontally +the line of flight is tangential to the earth, +or at right angles to the force of gravity. Such +a course in a flying machine finds less resistance +than if it should be projected upwardly, or directly +opposite the centripetal pull. + +_Fig 1. Tangential Flight_ + +TANGENTIAL MOTION REPRESENTS CENTRIFUGAL +PULL.--A tangential motion, or a horizontal +movement, seeks to move matter away from the +center of the earth, and any force which imparts +a horizontal motion to an object exerts a centrifugal +pull for that reason. + +In Fig. 1, let A represent the surface of the +earth, B the starting point of the flight of an object, +and C the line of flight. That represents a +tangential line. For the purpose of explaining +the phenomena of tangential flight, we will assume +that the missile was projected with a sufficient +force to reach the vertical point D, which +is 4000 miles from the starting point B. + +In such a case it would now be over 5500 miles +from the center of the earth, and the centrifugal +pull would be decreased to such an extent that the +ball would go on and on until it came within the +sphere of influence from some other celestial +body. + +EQUALIZING THE TWO MOTIONS.--But now let us +assume that the line of flight is like that shown +at E, in Fig. 2, where it travels along parallel +with the surface of the earth. In this case the +force of the ball equals the centripetal pull,--or, +to put it differently, the centrifugal equals the +gravitational pull. + +The constant tendency of the ball to fly off at +a tangent, and the equally powerful pull of +gravity acting against each other, produce a +motion which is like that of the earth, revolving +around the sun once every three hundred and +sixty-five days. + +It is a curious thing that neither Langley, nor +any of the scientists, in treating of the matter of +flight, have taken into consideration this quality +of momentum, in their calculations of the elements +of flight. + +_Fig. 2 Horizontal Flight_ + +All have treated the subject as though the +whole problem rested on the angle at which the +planes were placed. At 45 degrees the lift and +drift are assumed to be equal. + +LIFT AND DRIFT.--The terms should be explained, +in view of the frequent allusion which +will be made to the terms hereinafter. Lift +is the word employed to indicate the amount +which a plane surface will support while in flight. +Drift is the term used to indicate the resistance +which is offered to a plane moving forwardly +against the atmosphere. + +_Fig. 3. Lift and Drift_ + +In Fig. 3 the plane A is assumed to be moving +forwardly in the direction of the arrow B. This +indicates the resistance. The vertical arrow C +shows the direction of lift, which is the weight +held up by the plane. + +NORMAL PRESSURE.--Now there is another term +much used which needs explanation, and that is +normal pressure. A pressure of this kind +against a plane is where the wind strikes it at +right angles. This is illustrated in Fig. 4, in +which the plane is shown with the wind striking +it squarely. + +It is obvious that the wind will exert a greater +force against a plane when at its normal. On the +other hand, the least pressure against a plane is +when it is in a horizontal position, because then +the wind has no force against the surfaces, and +the only effect on the drift is that which takes +place when the wind strikes its forward edge. + +_Fig. 4. Normal Air Pressure_ + +_Fig. 5. Edge Resistance_ + + +HEAD RESISTANCE.--Fig. 5 shows such a plane, +the only resistance being the thickness of the +plane as at A. This is called head resistance, +and on this subject there has been much controversy, +and many theories, which will be considered +under the proper headings. + +If a plane is placed at an angle of 45 degrees +the lift and the drift are the same, assumedly, because, +if we were to measure the power required +to drive it forwardly, it would be found to equal +the weight necessary to lift it. That is, suppose +we should hold a plane at that angle with a heavy +wind blowing against it, and attach two pairs of +scales to the plane, both would show the same +pull. + +_Fig. 6. Measuring Lift and Drift_ + +MEASURING LIFT AND DRIFT.--In Fig. 6, A is the +plane, B the horizontal line which attaches the +plane to a scale C, and D the line attaching it to +the scale E. When the wind is of sufficient force +to hold up the plane, the scales will show the same +pull, neglecting, of course, the weight of the +plane itself. + +PRESSURE AT DIFFERENT ANGLES.--What every +one wants to know, and a subject on which a +great deal of experiment and time have been expended, +is to determine what the pressures are at +the different angles between the horizontal, and +laws have been formulated which enable the pressures +to be calculated. + +DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION.--The +first observation is directed to the differences +that exist between the lift and drift, +when the plane is placed at an angle of less than +45 degrees. A machine weighing 1000 pounds +has always the same lift. Its mass does not +change. Remember, now, we allude to its mass, +or density. + +We are not now referring to weight, because +that must be taken into consideration, in the +problem. As heretofore stated, when an object +moves horizontally, it has less weight than when +at rest. If it had the same weight it would not +move forwardly, but come to rest. + +When in motion, therefore, while the lift, so +far as its mass is concerned, does not change, the +drift does decrease, or the forward pull is less +than when at 45 degrees, and the decrease is less +and less until the plane assumes a horizontal position, +where it is absolutely nil, if we do not consider +head resistance. + +TABLES OF LIFT AND DRIFT.--All tables of Lift +and Drift consider only the air pressures. They +do not take into account the fact that momentum +takes an important part in the translation of an +object, like a flying machine. + +A mass of material, weighing 1000 pounds while +at rest, sets up an enormous energy when moving +through the air at fifty, seventy-five, or one hundred +miles an hour. At the latter speed the movement +is about 160 feet per second, a motion which +is nearly sufficient to maintain it in horizontal +flight, independently of any plane surface. + +Such being the case, why take into account only +the angle of the plane? It is no wonder that +aviators have not been able to make the theoretical +considerations and the practical demonstrations +agree. + +WHY TABLES OF LIFT AND DRIFT ARE WRONG.-- +A little reflection will show why such tables are +wrong. They were prepared by using a plane +surface at rest, and forcing a blast of air against +the plane placed at different angles; and for determining +air pressures, this is, no doubt, correct. +But it does not represent actual flying conditions. +It does not show the conditions existing +in an aeroplane while in flight. + +To determine this, short of actual experiments +with a machine in horizontal translation, is impossible, +unless it is done by taking into account +the factor due to momentum and the element +attributable to the lift of the plane itself due to its +impact against the atmosphere. + +LANGLEY'S LAW.--The law enunciated by +Langley is, that the greater the speed the less the +power required to propel it. Water as a propelling +medium has over seven hundred times +more force than air. A vessel having, for instance, +twenty horse power, and a speed of ten +miles per hour, would require four times that +power to drive it through the water at double the +speed. The power is as the square of the speed. + +With air the conditions are entirely different. +The boat submergence in the water is practically +the same, whether going ten or twenty miles an +hour. The head resistance is the same, substantially, +at all times in the case of the boat; with the +flying machine the resistance of its sustaining +surfaces decreases. + +Without going into a too technical description +of the reasoning which led to the discovery of the +law of air pressures, let us try and understand +it by examining the diagram, Fig. 7. + +A represents a plane at an angle of 45 degrees, +moving forwardly into the atmosphere in the +direction of the arrows B. The measurement +across the plane vertically, along the line B, +which is called the sine of the angle, represents +the surface impact of air against the plane. + +In Fig. 8 the plane is at an angle of 27 degrees, +which makes the distance in height across the line +C just one-half the length of the line B of Fig. 7, +hence the surface impact of the air is one-half that +of Fig. 7, and the drift is correspondingly decreased. + +_Fig. 7. Equal Lift and Drift in Flight._ + +_Fig. 8. Unequal Lift and Drift._ + + +MOVING PLANES VS. WINDS.--In this way Boisset, +Duchemin, Langley, and others, determined +the comparative drift, and those results have been +largely relied upon by aviators, and assumed to +be correct when applied to flying machines. + +That they are not correct has been proven by +the Wrights and others, the only explanation being +that some errors had been made in the calculations, +or that aviators were liable to commit errors +in observing the true angle of the planes +while in flight. + +MOMENTUM NOT CONSIDERED.--The great factor +of momentum has been entirely ignored, and it is +our desire to press the important point on those +who begin to study the question of flying machines. + +THE FLIGHT OF BIRDS.--Volumes have been +written concerning observations on the flight of +birds. The marvel has been why do soaring birds +maintain themselves in space without flapping +their wings. In fact, it is a much more remarkable +thing to contemplate why birds which depend +on flapping wings can fly. + +THE DOWNWARD BEAT.--It is argued that the +downward beat of the wings is so much more +rapid than the upward motion, that it gets an action +on the air so as to force the body upwardly. +This is disposed of by the wing motion of many +birds, notoriously the crow, whose lazily-flapping +wings can be readily followed by the eye, and the +difference in movement, if any, is not perceptible. + +THE CONCAVED WING.--It is also urged that the +concave on the under side of the wing gives the +quality of lift. Certain kinds of beetles, and particularly +the common house fly, disprove that theory, +as their wings are perfectly flat. + +FEATHER STRUCTURE CONSIDERED.--Then the +feather argument is advanced, which seeks to +show that as each wing is made up of a plurality +of feathers, overlapping each other, they form a +sort of a valved surface, opening so as to permit +air to pass through them during the period of +their upward movement, and closing up as the +wing descends. + +It is difficult to perform this experiment with +wings, so as to show such an individual feather +movement. It is certain that there is nothing in +the structure of the wing bone and the feather +connection which points to any individual feather +movement, and our observation is, that each +feather is entirely too rigid to permit of such an +opening up between them. + +It is obvious that the wing is built up in that +way for an entirely different reason. Soaring +birds, which do not depend on the flapping motion, +have the same overlapping feather formation. + +WEBBED WINGS.--Furthermore, there are numerous +flying creatures which do not have +feathered wings, but web-like structures, or like the +house fly, in one continuous and unbroken +plane. + +That birds which fly with flapping wings derive +their support from the air, is undoubtedly true, +and that the lift produced is due, not to the form, +or shape, or area of the wing, is also beyond question. +The records show that every conceivable +type of outlined structure is used by nature; the +material and texture of the wings themselves differ +to such a degree that there is absolutely no +similarity; some have concaved under surfaces, +and others have not; some fly with rapidly beating +wings, and others with slow and measured +movements; many of them fly with equal facility +without flapping movements; and the proportions +of weight to wing surface vary to such an extent +that it is utterly impossible to use such data as a +guide in calculating what the proper surface +should be for a correct flying machine. + +THE ANGLE OF MOVEMENT.--How, then, it may +be asked, do they get their support? There must +be something, in all this variety and diversity of +form, of motion, and of characteristics, which +supplies the true answer. The answer lies in the +angle of movement of every wing motion, which +is at the control of the bird, and if this is examined +it will be found that it supplies the correct +answer to every type of wing which nature has +made. + +AN INITIAL IMPULSE OR MOVEMENT NECESSARY.-- +Let A, Fig. 9, represent the section of a bird's +wing. All birds, whether of the soaring or the +flapping kind, must have an initial forward movement +in order to attain flight. This impulse is +acquired either by running along the ground, or +by a leap, or in dropping from a perch. Soaring +birds cannot, by any possibility, begin flight, +unless there is such a movement to change from a +position of rest to one of motion. + +_Fig. 9. Wing Movement in Flight._ + +In the diagram, therefore, the bird, in moving +forwardly, while raising the wing upwardly, depresses +the rear edge of the wing, as in position +1, and when the wing beats downwardly the rear +margin is raised, in relation to its front margin, +as shown in position 2. + +A WEDGING MOTION.--Thus the bird, by a +wedge-like motion, gives a forwardly-propelling +action, and as the rear margin has more or less +flexure, its action against the air is less during its +upward beat, and this also adds to the upward lift +of the body of the bird. + +NO MYSTERY IN THE WAVE MOTION.--There is +no mystery in the effect of such a wave-like motion, +and it must be obvious that the humming +bird, and like flyers, which poise at one spot, are +able to do so because, instead of moving forwardly, +or changing the position of its body horizontally, +in performing the undulatory motion of +the wing, it causes the body to rock, so that at the +point where the wing joins the body, an elliptical +motion is produced. + +_Fig. 10. Evolution of Humming-Bird's Wing._ + + +HOW BIRDS POISE WITH FLAPPING WINGS.--This +is shown in Fig. 10, in which eight successive positions +of the wing are shown, and wherein four +of the position, namely, 1, 2, 3, and 4, represent +the downward movement, and 6, 7, 8, and 9, the +upward beat. + +All the wing angles are such that whether the +suspension point of each wing is moving downwardly, +or upwardly, a support is found in some +part of the wing. + +NARROW-WINGED BIRDS.--Birds with rapid flapping +motions have comparatively narrow wings, +fore and aft. Those which flap slowly, and are +not swift flyers, have correspondingly broader +wings. The broad wing is also typical of the +soaring birds. + +But how do the latter overcome gravitation +without exercising some sort of wing movement? + +INITIAL MOVEMENT OF SOARING BIRDS.--Acute +observations show that during the early stages +of flight, before speed is acquired, they depend +on the undulating movement of the wings, and +some of them acquire the initial motion by flapping. +When speed is finally attained it is difficult +for the eye to note the motion of the wings. + +SOARING BIRDS MOVE SWIFTLY.--Now, the first +observation is, that soaring birds are swiftly- +moving creatures. As they sail overhead +majestically they seem to be moving slowly. But +distance is deceptive. The soaring bird travels +at great speeds, and this in itself should be sufficient +to enable us to cease wondering, when it is +remembered that swift translation decreases +weight, so that this factor does not, under those +conditions, operate against flight. + +MUSCULAR ENERGY EXERTED BY SOARING BIRDS. +--It is not conceivable that the mere will of the +bird would impel it forwardly, without it exerted +some muscular energy to keep up its speed. The +distance at which the bird performs this wonderful +evolution is at such heights from the observer +that the eye cannot detect a movement. + +WINGS NOT MOTIONLESS.--While the wings appear +to be absolutely motionless, it is more reasonable +to assume that a slight sinuous movement, +or a rocking motion is constantly kept up, which +wedges forwardly with sufficient speed to compel +momentum to maintain it in flight. To do so requires +but a small amount of energy. The head +resistance of the bird formation is reduced to a +minimum, and at such high speeds the angle of +incidence of the wings is very small, requiring but +little aid to maintain it in horizontal flight. + + + +CHAPTER II + +PRINCIPLES OF AEROPLANE FLIGHT + + +FROM the foregoing chapter, while it may be +rightly inferred that power is the true secret of +aeroplane flight, it is desirable to point out certain +other things which must be considered. + +SPEED AS ONE OF THE ELEMENTS--Every boy, +probably, has at some time or other thrown small +flat stones, called "skippers." He has noticed +that if they are particularly thin, and large in +diameter, that there is a peculiar sailing motion, +and that they move through the air in an undulating +or wave-like path. + +Two things contribute to this motion; one is the +size of the skipper, relative to its weight, and the +other is its speed. If the speed is slow it will +quickly wend its way to the earth in a gradual +curve. This curved line is called its trajectory. +If it is not very large diametrically, in proportion +to its weight, it will also make a gradual curve in +descending, without "skimming" up and down +in its flight. + +SHAPE AND SPEED.--It has been observed, also, +that a round ball, or an object not flattened out, +will make a regular curved path, whatever the +speed may be. + +It may be assumed, therefore, that the shape +alone does not account for this sinuous motion; +but that speed is the element which accounts for +it. Such being the case it may be well to inquire +into the peculiar action which causes a skipper +to dart up and down, and why the path thus +formed grows more and more accentuated as the +speed increases. + +As will be more fully described in a later chapter, +the impact of air against a moving body does +not increase in proportion to its speed, but in the +ratio of the square of the speed. + +WHAT SQUARE OF THE SPEED MEANS.--In mathematics +a figure is squared when it is multiplied +by itself. Thus, 4 X 4= 16; 5 X 5 = 25; and so +on, so that 16 is the square of 4, and 25 the square +of 5. It has been found that a wind moving at the +speed of 20 miles an hour has a striking or pushing +force of 2 pounds on every square foot of surface. + +If the wind travels twice as fast, or 40 miles +an hour, the pushing force is not 4 pounds, but +8 pounds. If the speed is 60 miles an hour the +pushing force increases to 18 pounds. + +ACTION OF A SKIPPER.--When the skipper leaves +the hands of the thrower it goes through the air +in such a way that its fiat surface is absolutely +on a line with the direction in which it is projected. + +At first it moves through the air solely by force +of the power which impels it, and does not in any +way depend on the air to hold it up. See Fig. +1, in which A represents the line of projection, +and B the disk in its flight. + +_Fig. 11. A Skipper in Flight._ + +After it has traveled a certain distance, and +the force decreases, it begins to descend, thus describing +the line C, Fig. 1, the disk B, in this case +descending, without changing its position, which +might be described by saying that it merely settles +down to the earth without changing its plane. + +The skipper still remains horizontal, so that as +it moves toward the earth its flat surface, which +is now exposed to the action of the air, meets +with a resistance, and this changes the angle of +the disk, so that it will not be horizontal. Instead +it assumes the position as indicated at D, +and this impinging effect against the air causes +the skipper to move upwardly along the line E, +and having reached a certain limit, as at, say E, +it automatically again changes its angle and moves +downwardly along the path F, and thus continues +to undulate, more or less, dependent on the combined +action of the power and weight, or momentum, +until it reaches the earth. + +It is, therefore, clear that the atmosphere has +an action on a plane surface, and that the extent +of the action, to sustain it in flight, depends on two +things, surface and speed. + +Furthermore, the greater the speed the less the +necessity for surface, and that for gliding purposes +speed may be sacrificed, in a large measure, +where there is a large surface. + +This very action of the skipper is utilized by +the aviator in volplaning,--that is, where the +power of the engine is cut off, either by accident, +or designedly, and the machine descends to the +earth, whether in a long straight glide, or in a +great circle. + +As the machine nears the earth it is caused to +change the angle of flight by the control mechanism +so that it will dart upwardly at an angle, or downwardly, +and thus enable the pilot to sail to another +point beyond where he may safely land. +This changing the course of the machine so that +it will glide upwardly, means that the incidence +of the planes has been changed to a positive +angle. + +ANGLE OF INCIDENCE.--In aviation this is a term +given to the position of a plane, relative to the +air against which it impinges. If, for instance, +an aeroplane is moving through the air with the +front margin of the planes higher than their rear +margins, it is said to have the planes at a positive +angle of incidence. If the rear margins are +higher than the front, then the planes have a negative +angle of incidence. + +The word incidence really means, a falling +upon, or against; and it will be seen, therefore, +that the angle of incidence means the tilt of the +planes in relation to the air which strikes it. + +Having in view, therefore, that the two qualities, +namely, speed and surface, bear an intimate +relation with each other, it may be understood +wherein mechanical flight is supposed to be analogous +to bird flight. + +SPEED AND SURFACE.--Birds which poise in the +air, like the humming bird, do so because they +beat their wings with great rapidity. Those +which soar, as stated, can do so only by moving +through the atmosphere rapidly, or by having a +large wing spread relative to the weight. It will +thus be seen that speed and surface become the +controlling factors in flight, and that while the +latter may be entirely eliminated from the problem, +speed is absolutely necessary under any and +all conditions. + +By speed in this connection is not meant high +velocity, but that a movement, produced by power +expressed in some form, is the sole and most necessary +requisite to movement through the air with +all heavier-than-air machines. + +If sufficient power can be applied to an aeroplane, +surface is of no consequence; shape need +not be considered, and any sort of contrivance +will move through the air horizontally. + +CONTROL OF THE DIRECTION OF FLIGHT.--But the +control of such a body, when propelled through +space by force alone, is a different matter. To +change the machine from a straight path to a +curved one, means that it must be acted upon by +some external force. + +We have explained that power is something +which is inherent in the thing itself. Now, in order +that there may be a change imparted to a +moving mass, advantage must be taken of the medium +through which it moves,--the atmosphere. + +VERTICAL CONTROL PLANES.--If vertically-arranged +planes are provided, either fore or aft of +the machine, or at both ends, the angles of incidence +may be such as to cause the machine to +turn from its straight course. + +In practice, therefore, since it is difficult to supply +sufficient power to a machine to keep it in motion +horizontally, at all times, aeroplanes are provided +with supporting surfaces, and this aid in +holding it up grows less and less as its speed increases. + +But, however strong the power, or great the +speed, its control from side to side is not dependent +on the power of the engine, or the speed +at which it travels through the air. + +Here the size of the vertical planes, and their +angles, are the only factors to be considered, and +these questions will be considered in their proper +places. + + + + +CHAPTER III + +THE FORM OR SHAPE OF FLYING MACHINES + + +EVERY investigator, experimenter, and scientist, +who has given the subject of flight study, proceeds +on the theory that in order to fly man must +copy nature, and make the machine similar to the +type so provided. + +THE THEORY OF COPYING NATURE.--If such is the +case then it is pertinent to inquire which bird is +the proper example to use for mechanical flight. +We have shown that they differ so radically in +every essential, that what would be correct in one +thing would be entirely wrong in another. + +The bi-plane is certainly not a true copy. The +only thing in the Wright machine which in any +way resembles the bird's wing, is the rounded end +of the planes, and judging from other machines, +which have square ends, this slight similarity does +not contribute to its stability or otherwise help +the structure. + +The monoplane, which is much nearer the bird +type, has also sounded wing ends, made not so +much for the purpose of imitating the wing of the +bird, as for structural reasons. + +HULLS OF VESSELS.--If some marine architect +should come forward and assert that he intended +to follow nature by making a boat with a hull of +the shape or outline of a duck, or other swimming +fowl, he would be laughed at, and justly so, because +the lines of vessels which are most efficient +are not made like those of a duck or other swimming +creatures. + +MAN DOES NOT COPY NATURE.--Look about you, +and see how many mechanical devices follow the +forms laid down by nature, or in what respect +man uses the types which nature provides in devising +the many inventions which ingenuity has +brought forth. + +PRINCIPLES ESSENTIAL, NOT FORMS.--It is essential +that man shall follow nature's laws. He cannot +evade the principles on which the operations +of mechanism depend; but in doing so he has, in +nearly every instance, departed from the form +which nature has suggested, and made the machine +irrespective of nature's type. + +Let us consider some of these striking differences +to illustrate this fact. Originally pins were +stuck upon a paper web by hand, and placed in +rows, equidistant from each other. This necessitates +the cooperative function of the fingers and +the eye. An expert pin sticker could thus assemble +from four to five thousand pins a day. + +The first mechanical pinsticker placed over +500,000 pins a day on the web, rejecting every bent +or headless pin, and did the work with greater +accuracy than it was possible to do it by hand. +There was not the suggestion of an eye, or a finger +in the entire machine, to show that nature furnished +the type. + +NATURE NOT THE GUIDE AS TO FORMS.--Nature +does not furnish a wheel in any of its mechanical +expressions. If man followed nature's form +in the building of the locomotive, it would move +along on four legs like an elephant. Curiously +enough, one of the first road wagons had "push +legs,"--an instance where the mechanic tried to +copy nature,--and failed. + +THE PROPELLER TYPE.--The well known propeller +is a type of wheel which has no prototype in +nature. It is maintained that the tail of a fish +in its movement suggested the propeller, but the +latter is a long departure from it. + +The Venetian rower, who stands at the stern, +and with a long-bladed oar, fulcrumed to the +boat's extremity, in making his graceful lateral +oscillations, simulates the propelling motion of +the tail in an absolutely perfect manner, but it is +not a propeller, by any means comparable to the +kind mounted on a shaft, and revoluble. + +How much more efficient are the spirally-formed +blades of the propeller than any wing or fin movement, +in air or sea. There is no comparison between +the two forms in utility or value. + +Again, the connecting points of the arms and +legs with the trunk of a human body afford the +most perfect types of universal joints which nature +has produced. The man-made universal +joint has a wider range of movement, possesses +greater strength, and is more perfect mechanically. +A universal joint is a piece of mechanism +between two elements, which enables them to be +turned, or moved, at any angle relative to each +other. + +But why multiply these instances. Like samples +will be found on every hand, and in all directions, +and man, the greatest of all of nature's +products, while imperfect in himself, is improving +and adapting the things he sees about him. + +WHY SPECIALLY-DESIGNED FORMS IMPROVE NATURAL +STRUCTURES.--The reason for this is, primarily, +that the inventor must design the article +for its special work, and in doing so makes it better +adapted to do that particular thing. The +hands and fingers can do a multiplicity of things, +but it cannot do any particular work with the facility +or the degree of perfection that is possible +with the machine made for that purpose. + +The hands and fingers will bind a sheaf of +wheat, but it cannot compete with the special machine +made for that purpose. On the other hand +the binder has no capacity to do anything else than +what it was specially made for. + +In applying the same sort of reasoning to the +building of flying machines we must be led to the +conclusion that the inventor can, and will, eventually, +bring out a form which is as far superior to +the form which nature has taught us to use as +the wonderful machines we see all about us are +superior to carry out the special work they were +designed to do. + +On land, man has shown this superiority over +matter, and so on the sea. Singularly, the submarines, +which go beneath the sea, are very far +from that perfected state which have been attained +by vessels sailing on the surface; and while +the means of transportation on land are arriving +at points where the developments are swift and +remarkable, the space above the earth has not yet +been conquered, but is going through that same +period of development which precedes the production +of the true form itself. + +MECHANISM DEVOID OF INTELLIGENCE.--The great +error, however, in seeking to copy nature's form +in a flying machine is, that we cannot invest the +mechanism with that which the bird has, namely, +a guiding intelligence to direct it instinctively, as +the flying creature does. + +A MACHINE MUST HAVE A SUBSTITUTE FOR INTELLIGENCE. +--Such being the case it must be endowed +with something which is a substitute. A +bird is a supple, pliant organism; a machine is a +rigid structure. One is capable of being directed +by a mind which is a part of the thing itself; while +the other must depend on an intelligence which is +separate from it, and not responsive in feeling or +movement. + +For the foregoing reasons success can never +be attained until some structural form is devised +which will consider the flying machine independently +of the prototypes pointed out as the correct +things to follow. It does not, necessarily, have to +be unlike the bird form, but we do know that the +present structures have been made and insisted +upon blindly, because of this wrong insistence on +forms. + +STUDY OF BIRD FLIGHT USELESS.--The study of +the flight of birds has never been of any special +value to the art. Volumes have been written on +the subject. The Seventh Duke of Argyle, and +later, Pettigrew, an Englishman, contributed a +vast amount of written matter on the subject of +bird flight, in which it was sought to show that +soaring birds did not exert any power in flying. + +Writers and experimenters do not agree on the +question of the propulsive power, or on the form +or shape of the wing which is most effective, or +in the matter of the relation of surface to weight, +nor do they agree in any particular as to the effect +and action of matter in the soaring principle. + +Only a small percentage of flying creatures use +motionless wings as in soaring. By far, the +greater majority use beating wings, a method of +translation in air which has not met with success +in any attempts on the part of the inventor. + +Nevertheless, experimenting has proceeded on +lines which seek to recognize nature's form only, +while avoiding the best known and most persistent +type. + +SHAPE OF SUPPORTING SURFACES.--When we examine +the prevailing type of supporting surfaces +we cannot fail to be impressed with one feature, +namely, the determination to insist on a broad +spread of plane surface, in imitation of the bird +with outstretched wings. + +THE TROUBLE ARISING FROM OUTSTRETCHED +WINGS.--This form of construction is what brings +all the troubles in its train. The literature on +aviation is full of arguments on this subject, all +declaring that a wide spread is essential, because, +--birds fly that way. + +These assertions are made notwithstanding the +fact that only a few years ago, in the great exhibit +of aeroplanes in Paris, many unique forms of machines +were shown, all of them capable of flying, +as proven by numerous experiments, and among +them were a half dozen types whose length fore +and aft were much greater than transversely, and +it was particularly noted that they had most wonderful +stability. + +DENSITY OF THE ATMOSPHERE.--Experts declare +that the density of the atmosphere varies throughout, +--that it has spots here and there which are, +apparently, like holes, so that one side or the +other of the machine will, unaccountably, tilt, and +sometimes the entire machine will suddenly drop +for many feet, while in flight. + +ELASTICITY OF THE AIR.--Air is the most elastic +substance known. The particles constituting it +are constantly in motion. When heat or cold penetrate +the mass it does so, in a general way, so as +to permeate the entire body, but the conductivity +of the atmospheric gases is such that the heat +does not reach all parts at the same time. + +AIR HOLES.--The result is that varying strata +of heat and cold seem to be superposed, and also +distributed along the route taken by a machine, +causing air currents which vary in direction and +intensity. When, therefore, a rapidly-moving +machine passes through an atmosphere so disturbed, +the surfaces of the planes strike a mass of +air moving, we may say, first toward the plane, +and the next instant the current is reversed, and +the machine drops, because its support is temporarily +gone, and the aviator experiences the sensation +of going into a "hole." + +RESPONSIBILITY FOR ACCIDENTS.--These so-called +"holes" are responsible for many accidents. The +outstretched wings, many of them over forty feet +from tip to tip, offer opportunities for a tilt at one +end or the other, which has sent so many machines +to destruction. + +The high center of gravity in all machines makes +the weight useless to counterbalance the rising +end or to hold up the depressed wing. + +All aviators agree that these unequal areas of +density extend over small spaces, and it is, therefore, +obvious that a machine which is of such a +structure that it moves through the air broadside +on, will be more liable to meet these inequalities +than one which is narrow and does not take in such +a wide path. + +Why, therefore, persist in making a form which, +by its very nature, invites danger? Because birds +fly that way! + +THE TURNING MOVEMENT.--This structural arrangement +accentuates the difficulty when the machine +turns. The air pressure against the wing +surface is dependent on the speed. The broad +outstretched surfaces compel the wing at the outer +side of the circle to travel faster than the inner +one. As a result, the outer end of the aeroplane +is elevated. + +CENTRIFUGAL ACTION.--At the same time the +running gear, and the frame which carries it and +supports the machine while at rest, being below +the planes, a centrifugal force is exerted, when +turning a circle, which tends to swing the wheels +and frame outwardly, and thereby still further +elevating the outer end of the plane. + +THE WARPING PLANES.--The only remedy to +meet this condition is expressed in the mechanism +which wraps or twists the outer ends of the planes, +as constructed in the Wright machine, or the +ailerons, or small wings at the rear margins of the +planes, as illustrated by the Farman machine. +The object of this arrangement is to decrease the +angle of incidence at the rising end, and increase +the angle at the depressed end, and thus, by manually- +operated means keep the machine on an even +keel. + + + +CHAPTER IV + +FORE AND AFT CONTROL + + +THERE is no phase of the art of flying more important +than the fore and aft control of an airship. +Lateral stability is secondary to this feature, for +reasons which will appear as we develop the +subject. + +THE BIRD TYPE OF FORE AND AFT CONTROL.-- +Every aeroplane follows the type set by nature +in the particular that the body is caused to oscillate +on a vertical fore and aft plane while in +flight. The bird has one important advantage, +however, in structure. Its wing has a flexure at +the joint, so that its body can so oscillate independently +of the angle of the wings. + +The aeroplane has the wing firmly fixed to the +body, hence the only way in which it is possible +to effect a change in the angle of the wing is by +changing the angle of the body. To be consistent +the aeroplane should be so constructed that the +angle of the supporting surfaces should be movable, +and not controllable by the body. + +The bird, in initiating flight from a perch, darts +downwardly, and changes the angle of the body to +correspond with the direction of the flying start. +When it alights the body is thrown so that its +breast banks against the air, but in ordinary flight +its wings only are used to change the angle of +flight. + +ANGLE AND DIRECTION OF FLIGHT.--In order to +become familiar with terms which will be frequently +used throughout the book, care should be +taken to distinguish between the terms angle and +direction of flight. The former has reference to +the up and down movement of an aeroplane, +whereas the latter is used to designate a turning +movement to the right or to the left. + +WHY SHOULD THE ANGLE OF THE BODY CHANGE? +--The first question that presents itself is, why +should the angle of the aeroplane body change? +Why should it be made to dart up and down and +produce a sinuous motion? Why should its nose +tilt toward the earth, when it is descending, and +raise the forward part of the structure while ascending? + +The ready answer on the part of the bird-form +advocate is, that nature has so designed a flying +structure. The argument is not consistent, because +in this respect, as in every other, it is not +made to conform to the structure which they seek +to copy. + +CHANGING ANGLE OF BODY NOT SAFE.--Furthermore, +there is not a single argument which can be +advanced in behalf of that method of building, +which proves it to be correct. Contrariwise, an +analysis of the flying movement will show that it is +the one feature which has militated against safety, +and that machines will never be safe so long as +the angle of the body must be depended upon to +control the angle of flying. + +_Fig. 11a Monoplane in Flight._ + +In Fig. 11a three positions of a monoplane are +shown, each in horizontal flight. Let us say that +the first figure A is going at 40 miles per hour, +the second, B, at 50, and the third, C, at 60 miles. +The body in A is nearly horizontal, the angle of +the plane D being such that, with the tail E also +horizontal, an even flight is maintained. + +When the speed increases to 50 miles an hour, +the angle of incidence in the plane D must be +decreased, so that the rear end of the frame must +be raised, which is done by giving the tail an angle +of incidence, otherwise, as the upper side of the +tail should meet the air it would drive the rear +end of the frame down, and thus defeat the attempt +to elevate that part. + +_Fig. 12. Angles of Flight._ + +As the speed increases ten miles more, the tail +is swung down still further and the rear end of +the frame is now actually above the plane of flight. +In order, now, to change the angle of flight, without +altering the speed of the machine, the tail is +used to effect the control. + +Examine the first diagram in Fig. 12. This +shows the tail E still further depressed, and the +air striking its lower side, causes an upward movement +of the frame at that end, which so much decreases +the angle of incidence that the aeroplane +darts downwardly. + +In order to ascend, the tail, as shown in the second +diagram, is elevated so as to depress the rear +end, and now the sustaining surface shoots upwardly. + +Suppose that in either of the positions 1 or 2, +thus described, the aviator should lose control of +the mechanism, or it should become deranged or +"stick," conditions which have existed in the history +of the art, what is there to prevent an accident? + +In the first case, if there is room, the machine +will loop the loop, and in the second case the machine +will move upwardly until it is vertical, and +then, in all probability, as its propelling power is +not sufficient to hold it in that position, like a +helicopter, and having absolutely no wing supporting +surface when in that position, it will dart +down tail foremost. + +A NON-CHANGING BODY.--We may contrast the +foregoing instances of flight with a machine having +the sustaining planes hinged to the body in +such a manner as to make the disposition of its +angles synchronous with the tail. In other words, +see how a machine acts that has the angle of flight +controllable by both planes,--that is, the sustaining +planes, as well as the tail. + +_Fig. 13. Planes on Non-changing Body._ + +In Fig. 13 let the body of the aeroplane be horizontal, +and the sustaining planes B disposed at +the same angle, which we will assume to be 15 +degrees, this being the imaginary angle for illustrative +purposes, with the power of the machine +to drive it along horizontally, as shown in position +1. + +In position 2 the angles of both planes are now +at 10 degrees, and the speed 60 miles an hour, +which still drives the machine forward horizontally. + +In position 3 the angle is still less, being now +only 5 degrees but the speed is increased to 80 +miles per hour, but in each instance the body of +the machine is horizontal. + +Now it is obvious that in order to ascend, in +either case, the changing of the planes to a greater +angle would raise the machine, but at the same +time keep the body on an even keel. + +_Fig. 14. Descent with Non-changing Body._ + +DESCENDING POSITIONS BY POWER CONTROL.--In +Fig. 14 the planes are the same angles in the three +positions respectively, as in Fig. 13, but now the +power has been reduced, and the speeds are 30, +25, and 20 miles per hour, in positions A, B and C. + +Suppose that in either position the power should +cease, and the control broken, so that it would be +impossible to move the planes. When the machine +begins to lose its momentum it will descend on a +curve shown, for instance, in Fig. 15, where position +1 of Fig. 14 is taken as the speed and angles +of the plane when the power ceased. + +_Fig. 15. Utilizing Momentum._ + +CUTTING OFF THE POWER.--This curve, A, may +reach that point where momentum has ceased as +a forwardly-propelling factor, and the machine +now begins to travel rearwardly. (Fig. 16.) It +has still the entire supporting surfaces of the +planes. It cannot loop-the-loop, as in the instance +where the planes are fixed immovably to the body. + +Carefully study the foregoing arrangement, and +it will be seen that it is more nearly in accord with +the true flying principle as given by nature than +the vaunted theories and practices now indulged +in and so persistently adhered to. + +The body of a flying machine should not be oscillated +like a lever. The support of the aeroplane +should never be taken from it. While it may be +impossible to prevent a machine from coming +down, it can be prevented from overturning, and +this can be done without in the least detracting +from it structurally. + +_Fig. 16. Reversing Motion._ + +The plan suggested has one great fault, however. +It will be impossible with such a structure +to cause it to fly upside down. It does not present +any means whereby dare-devil stunts can be performed +to edify the grandstand. In this respect +it is not in the same class with the present types. + +THE STARTING MOVEMENT.--Examine this plan +from the position of starting, and see the advantages +it possesses. In these illustrations we +have used, for convenience only, the monoplane +type, and it is obvious that the same remarks apply +to the bi-plane. + +Fig. 17 shows the starting position of the stock +monoplane, in position 1, while it is being initially +run over the ground, preparatory to launching. +Position 2 represents the negative angle at which +the tail is thrown, which movement depresses the +rear end of the frame and thus gives the supporting +planes the proper angle to raise the machine, +through a positive angle of incidence, of the plane. + +_Fig. 17. Showing changing angle of body._ + +THE SUGGESTED TYPE.--In Fig. 18 the suggested +type is shown with the body normally in a horizontal +position, and the planes in a neutral position, +as represented in position 1. When sufficient +speed had been attained both planes are +turned to the same angle, as in position 2, and +flight is initiated without the abnormal oscillating +motion of the body. + +But now let us see what takes place the moment +the present type is launched. If, by any error on +the part of the aviator, he should fail to readjust +the tail to a neutral or to a proper angle of incidence, +after leaving the ground, the machine would +try to perform an over-head loop. + +The suggested plan does not require this caution. +The machine may rise too rapidly, or its +planes may be at too great an angle for the power +or the speed, or the planes may be at too small an +angle, but in either case, neglect would not turn +the machine to a dangerous position. + +These suggestions are offered to the novice, because +they go to the very foundation of a correct +understanding of the principles involved in the +building and in the manipulation of flying machines +and while they are counter to the beliefs of +aviators, as is shown by the persistency in adhering +to the old methods, are believed to be mechanically +correct, and worthy of consideration. + +THE LOW CENTER OF GRAVITY.--But we have still +to examine another feature which shows the wrong +principle in the fixed planes. The question is +often asked, why do the builders of aeroplanes +place most of the weight up close to the planes? +It must be obvious to the novice that the lower +the weight the less liability of overturning. + +FORE AND AFT OSCILLATIONS.--The answer is, +that when the weight is placed below the planes it +acts like a pendulum. When the machine is traveling +forward, and the propeller ceases its motion, +as it usually does instantaneously, the weight, being +below, and having a certain momentum, continues +to move on, and the plane surface meeting +the resistance just the same, and having no means +to push it forward, a greater angle of resistance is +formed. + +In Fig. 19 this action of the two forces is illustrated. The +plane at the speed of 30 miles is at +an angle of 15 degrees, the body B of the machine +being horizontal, and the weight C suspended directly +below the supporting surfaces. + +The moment the power ceases the weight continues +moving forwardly, and it swings the forward +end of the frame upwardly, Fig. 20, and we now +have, as in the second figure, a new angle of incidence, +which is 30 degrees, instead of 12. It will +be understood that in order to effect a change in +the position of the machine, the forward end ascends, +as shown by the dotted line A. + +_Fig. 20. Action when Propeller ceases to pull._ + +The weight a having now ascended as far as +possible forward in its swing, and its motion +checked by the banking action of the plan it will +again swing back, and again carry with it the +frame, thus setting up an oscillation, which is extremely +dangerous. + +The tail E, with its unchanged angle, does not, +in any degree, aid in maintaining the frame on +an even keel. Being nearly horizontal while in +flight, if not at a negative angle, it actually assists +the forward end of the frame to ascend. + +APPLICATION OF THE NEW PRINCIPLE.--Extending +the application of the suggested form, let us see +wherein it will prevent this pendulous motion at +the moment the power ceases to exert a forwardly- +propelling force. + +_Fig. 21. Synchronously moving Planes._ + +In Fig. 21 the body A is shown to be equipped +with the supporting plane B and the tail a, so +they are adjustable simultaneously at the same +angle, and the weight D is placed below, similar to +the other structure. + +At every moment during the forward movement +of this type of structure, the rear end of +the machine has a tendency to move upwardly, +the same as the forward end, hence, when the +weight seeks, in this case to go on, it acts on the +rear plane, or tail, and causes that end to raise, +and thus by mutual action, prevents any pendulous +swing. + +LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY-MOVING WINGS. +--A little reflection will convince +any one that if the two wings move in harmony, +the weight does not have to be placed low, +and thus still further aid in making a compact +machine. By increasing the area of the tail, and +making that a true supporting surface, instead of +a mere idler, the weight can be moved further +back, the distance transversely across the planes +may be shortened, and in that way still further +increase the lateral stability. + + + +CHAPTER V + +DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS + + +THERE are three distinct types of heavier-than- +air machines, which are widely separated in all +their characteristics, so that there is scarcely a +single feature in common. + +Two of them, the aeroplane, and the orthopter, +have prototypes in nature, and are distinguished +by their respective similarities to the soaring +birds, and those with flapping wings. + +The Helicopter, on the other hand, has no antecedent +type, but is dependent for its raising +powers on the pull of a propeller, or a plurality +of them, constructed, as will be pointed out hereinafter. + +AEROPLANES.--The only form which has met +with any success is the aeroplane, which, in +practice, is made in two distinct forms, one with +a single set of supporting planes, in imitation of +birds, and called a monoplane; and the other having +two wings, one above the other, and called +the bi-plane, or two-planes. + +All machines now on the market which do not +depend on wing oscillations come under those +types. + +THE MONOPLANE.--The single plane type has +some strong claims for support. First of these +is the comparatively small head resistance, due +to the entire absence of vertical supporting posts, +which latter are necessary with the biplane type. +The bracing supports which hold the outer ends +of the planes are composed of wires, which offer +but little resistance, comparatively, in flight. + +ITS ADVANTAGES.--Then the vertical height of +the machine is much less than in the biplane. As +a result the weight, which is farther below the +supporting surface than in the biplane, aids in +maintaining the lateral stability, particularly +since the supporting frame is higher. + +Usually, for the same wing spread, the monoplane +is narrower, laterally, which is a further +aid to prevent tilting. + +ITS DISADVANTAGES.--But it also has disadvantages +which must be apparent from its structure. +As all the supporting surface is concentrated +in half the number of planes, they must +be made of greater width fore and aft, and this, +as we shall see, later on, proves to be a disadvantage. + +It is also doubted whether the monoplane can +be made as strong structurally as the other form, +owing to the lack of the truss formation which is +the strong point with the superposed frame. A +truss is a form of construction where braces can +be used from one member to the next, so as to +brace and stiffen the whole. + +THE BIPLANE.--Nature does not furnish a type +of creature which has superposed wings. In this +particular the inventor surely did not follow nature. +The reasons which led man to employ this +type may be summarized as follows: + +In experimenting with planes it is found that +a broad fore and aft surface will not lift as much +as a narrow plane. This subject is fully explained +in the chapter on The Lifting Surfaces of +Planes. In view of that the technical descriptions +of the operation will not be touched upon +at this place, except so far as it may be necessary +to set forth the present subject. + +This peculiarity is due to the accumulation of +a mass of moving air at the rear end of the plane, +which detracts from its lifting power. As it +would be a point of structural weakness to make +the wings narrow and very long, Wenham many +years ago suggested the idea of placing one plane +above the other, and later on Chanute, an +engineer, used that form almost exclusively, in +experimenting with his gliders. + +It was due to his influence that the Wrights +adopted that form in their gliding experiments, +and later on constructed their successful flyers +in that manner. Originally the monoplane was +the type generally employed by experimenters, +such as Lilienthal, and others. + +STABILITY IN BIPLANES.--Biplanes are not naturally +as stable laterally as the monoplane. +The reason is, that a downward tilt has the benefit +of only a narrow surface, comparable with the +monoplane, which has broadness of wing. + +To illustrate this, let us assume that we have +a biplane with planes five feet from front to rear, +and thirty-six feet in length. This would give +two planes with a sustaining surface of 360 square +feet. The monoplane would, probably, divide +this area into one plane eight and a half feet from +front to rear, and 42 feet in length. + +In the monoplane each wing would project out +about three feet more on each side, but it would +have eight and a half feet fore and aft spread +to the biplane's five feet, and thus act as a greater +support. + +THE ORTHOPTER.--The term orthopter, or ornithopter, +meaning bird wing, is applied to such +flying machines as depend on wing motion to support +them in the air. + +Unquestionably, a support can be obtained by +beating on the air but to do so it is necessary to +adopt the principle employed by nature to secure +an upward propulsion. As pointed out elsewhere, +it cannot be the concaved type of wing, +or its shape, or relative size to the weight it must +carry. + +As nature has furnished such a variety of data +on these points, all varying to such a remarkable +degree, we must look elsewhere to find the secret. +Only one other direction offers any opportunity, +and that is in the individual wing movement. + +NATURE'S TYPE NOT UNIFORM.--When this is +examined, the same obscurity surrounds the issue. +Even the speeds vary to such an extent that when +it is tried to differentiate them, in comparison +with form, shape, and construction, the experimenter +finds himself wrapt in doubt and perplexity. + +But birds do fly, notwithstanding this wonderful +array of contradictory exhibitions. Observation +has not enabled us to learn why these things +are so. High authorities, and men who are expert +aviators, tell us that the bird flies because +it is able to pick out ascending air currents. + +THEORIES ABOUT FLIGHT OF BIRDS.--Then we +are offered the theory that the bird has an instinct +which tells it just how to balance in the +air when its wings are once set in motion. +Frequently, what is taken for instinct, is something +entirely different. + +It has been assumed, for instance, that a cyclist +making a turn at a rapid speed, and a bird flying +around a circle will throw the upper part of the +body inwardly to counteract the centrifugal force +which tends to throw it outwardly. + +Experiments with the monorail car, which is +equipped with a gyroscope to hold it in a vertical +position, show that when the car approaches a +curve the car will lean inwardly, exactly the same +as a bird, or a cyclist, and when a straight stretch +is reached, it will again straighten up. + +INSTINCT.--Now, either the car, so equipped +possesses instinct, or there must be a principle +in the laws of nature which produces the similarity +of action. + +In like manner there must be some principle +that is entirely independent of the form of matter, +or its arrangement, which enables the bird +to perform its evolutions. We are led to believe +from all the foregoing considerations that it is +the manner or the form of the motion. + +MODE OF MOTION.--In this respect it seems to +be comparable in every respect to the great and +universal law of the motions in the universe. +Thus, light, heat and electricity are the same, the +manifestations being unlike only because they +have different modes of motion. + +Everything in nature manifests itself by motion. +It is the only way in which nature acts. +Every transformation from one thing to another, +is by way of a movement which is characteristic +in itself. + +Why, then, should this great mystery of nature, +act unlike the other portions of which it is +a part? + +THE WING STRUCTURE.--The wing structure of +every flying creature that man has examined, has +one universal point of similarity, and that is the +manner of its connection with the body. It is a +sort of universal joint, which permits the wing +to swing up and down, perform a gyratory movement +while doing so, and folds to the rear when +at rest. + +Some have these movements in a greater or +less degree, or capable of a greater range; but +the joint is the same, with scarcely an exception. +When the stroke of the wing is downwardly the +rear margin is higher than the front edge, so +that the downward beat not only raises the body +upwardly, but also propels it forwardly. + +THE WING MOVEMENT.--The moment the wing +starts to swing upwardly the rear end is +depressed, and now, as the bird is moving forwardly, +the wing surface has a positive angle of +incidence, and as the wing rises while the forward +motion is taking place, there is no resistance +which is effective enough to counteract the +momentum which has been set up. + +The great problem is to put this motion into a +mechanical form. The trouble is not ascribable +to the inability of the mechanic to describe this +movement. It is an exceedingly simple one. +The first difficulty is in the material that must +be used. Lightness and strength for the wing +itself are the first requirements. Then rigidity +in the joint and in the main rib of the wing, are +the next considerations. + +In these respects the ability of man is limited. +The wing ligatures of flying creatures is exceedingly +strong, and flexible; the hollow bone formation +and the feathers are extremely light, compared +with their sustaining powers. + +THE HELICOPTER MOTION.--The helicopter, or +helix-wing, is a form of flying machine which depends +on revolving screws to maintain it in the +air. Many propellers are now made, six feet in +length, which have a pull of from 400 to 500 +pounds. If these are placed on vertically-disposed +shafts they would exert a like power to +raise a machine from the earth. + +Obviously, it is difficult to equip such a machine +with planes for sustaining it in flight, after it is +once in the air, and unless such means are provided +the propellers themselves must be the +mechanism to propel it horizontally. + +This means a change of direction of the shafts +which support the propellers, and the construction +is necessarily more complicated than if they +were held within non-changeable bearings. + +This principle, however, affords a safer means +of navigating than the orthopter type, because +the blades of such an instrument can be forced +through the air with infinitely greater speed than +beating wings, and it devolves on the inventor to +devise some form of apparatus which will permit +the change of pull from a vertical to a horizontal +direction while in flight. + + + +CHAPTER VI + +THE LIFTING SURFACES OF AEROPLANES + + +THIS subject includes the form, shape and angle +of planes, used in flight. It is the direction in +which most of the energy has been expended in +developing machines, and the true form is still +involved in doubt and uncertainty. + +RELATIVE SPEED AND ANGLE.--The relative +speed and angle, and the camber, or the curved +formation of the plane, have been considered in +all their aspects, so that the art in this respect has +advanced with rapid strides. + +NARROW PLATES MOST EFFECTIVE.--It was +learned, in the early stages of the development +by practical experiments, that a narrow plane, +fore and aft, produces a greater lift than a wide +one, so that, assuming the plane has 100 square +feet of sustaining surface, it is far better to make +the shape five feet by twenty than ten by ten. + +However, it must be observed, that to use the +narrow blade effectively, it must be projected +through the air with the long margin forwardly. +Its sustaining power per square foot of surface +is much less if forced through the air lengthwise. + +Experiments have shown why a narrow blade +has proportionally a greater lift, and this may +be more clearly understood by examining the +illustrations which show the movement of planes +through the air at appropriate angles. + +_Fig. 22. Stream lines along a plane._ + +STREAM LINES ALONG A PLANE.--In Fig. 22, A +is a flat plane, which we will assume is 10 feet +from the front to the rear margin. For convenience +seven stream lines of air are shown, +which contact with this inclined surface. The first +line 1, after the contact at the forward end, is +driven downwardly along the surface, so that it +forms what we might term a moving film. + +The second air stream 2, strikes the first stream, +followed successively by the other streams, 3, 4, +and so on, each succeeding stream being compelled +to ride over, or along on the preceding mass of +cushioned air, the last lines, near the lower end, +being, therefore, at such angles, and contacting +with such a rapidly-moving column, that it produces +but little lift in comparison with the 1st, +2d and 3d stream lines. These stream lines are +taken by imagining that the air approaches and +contacts with the plane only along the lines indicated +in the sketch, although they also in practice +are active against every part of the plane. + +THE CENTER OF PRESSURE.--In such a plane the +center of pressure is near its upper end, probably +near the line 3, so that the greater portion of the +lift is exerted by that part of the plane above +line 3. + +AIR LINES ON THE UPPER SIDE OF THE PLANE.-- +Now, another factor must be considered, namely, +the effect produced on the upper side of the plane, +over which a rarefied area is formed at certain +points, and, in practice, this also produces, or +should be utilized to effect a lift. + +RAREFIED AREA.--What is called a rarefied area, +has reference to a state or condition of the atmosphere +which has less than the normal pressure or +quantity of air. Thus, the pressure at sea level, +is about 14 3/4 per square inch + +As we ascend the pressure grows less, and the +air is thus rarer, or, there is less of it. This is a +condition which is normally found in the atmosphere. +Several things tend to make a rarefied +condition. One is altitude, to which we have just +referred. + +Then heat will expand air, making it less dense, +or lighter, so that it will move upwardly, to be +replaced by a colder body of air. In aeronautics +neither of these conditions is of any importance +in considering the lifting power of aeroplane surfaces. + +RAREFACTION PRODUCED BY MOTION.--The third +rarefied condition is produced by motion, and generally +the area is very limited when brought about +by this means. If, for instance, a plane is held +horizontally and allowed to fall toward the earth, +it will be retarded by two forces, namely, compression +and rarefaction, the former acting on the +under side of the plane, and the latter on the upper +side. + +Of the two rarefaction is the most effectual, +and produces a greater effect than compression. +This may be proven by compressing air in a long +pipe, and noting the difference in gauge pressure +between the ends, and then using a suction pump +on the same pipe. + +When a plane is forced through the air at any +angle, a rarefied area is formed on the side which +is opposite the one having the positive angle of +incidence. + +If the plane can be so formed as to make a large +and effective area it will add greatly to the value +of the sustaining surface. + +Unfortunately, the long fiat plane does not lend +any aid in this particular, as the stream line flows +down along the top, as shown in Fig. 23, without +being of any service. + +_Fig. 23. Air lines on the upper side of a Plane._ + +THE CONCAVED PLANE.--These considerations +led to the adoption of the concaved plane formation, +and for purposes of comparison the diagram, +Fig. 24, shows the plane B of the same length and +angle as the straight planes. + +In examining the successive stream lines it will +be found that while the 1st, 2d and 3d lines have +a little less angle of impact than the corresponding +lines in the straight plane, the last lines, 5, 6 +and 7, have much greater angles, so that only line +4 strikes the plane at the same angle. + +Such a plane structure would, therefore, have +its center of pressure somewhere between the +lines 3 and 4, and the lift being thus, practically, +uniform over the surface, would be more effective. + +THE CENTER OF PRESSURE.--This is a term used +to indicate the place on the plane where the air +acts with the greatest force. It has reference to +a point between the front and rear margins only +of the plane. + +_Fig. 24. Air lines below a concaved Plane._ + +UTILIZING THE RAREFIED AREA.--This structure, +however, has another important advantage, as it +utilizes the rarefied area which is produced, and +which may be understood by reference to Fig. 25. + +The plane B, with its upward curve, and at the +same angle as the straight plane, has its lower +end so curved, with relation to the forward movement, +that the air, in rushing past the upper end, +cannot follow the curve rapidly enough to maintain +the same density along C, hence this exerts + +an upward pull, due to the rarefied area, which +serves as a lifting force, as well as the compressed +mass beneath the plane. + +CHANGING CENTER OF PRESSURE.--The center of +pressure is not constant. It changes with the +angle of the plane, but the range is considerably +less on a concave surface than on a flat plane. + +_Fig. 25. Air lines above a convex Plane._ + +In a plane disposed at a small angle, A, as in +Fig. 26, the center of pressure is nearer the forward +end of the plane than with a greater positive +angle of incidence, as in Fig. 27, and when +the plane is in a normal flying angle, it is at the +center, or at a point midway between the margins. + +PLANE MONSTROSITIES.--Growing out of the idea +that the wing in nature must be faithfully copied, +it is believed by many that a plane with a +pronounced thickness at its forward margin is one +of the secrets of bird flight. + +Accordingly certain inventors have designed +types of wings which are shown in Figs. 28 and +29. + +_Fig. 28 Changing centers of Pressures._ + +_Fig 29. Bird-wing structures._ + +Both of these types have pronounced bulges, +designed to "split" the air, forgetting, apparently, +that in other parts of the machine every effort is +made to prevent head resistance. + +THE BIRD WING STRUCTURE.--The advocates of +such construction maintain that the forward edge +of the plane must forcibly drive the air column +apart, because the bird wing is so made, and that +while it may not appear exactly logical, still there +is something about it which seems to do the work, +and for that reason it is largely adopted. + +WHY THE BIRD'S WING HAS A PRONOUNCED +BULGE.--Let us examine this claim. The bone +which supports the entire wing surface, called the +(pectoral), has a heavy duty to perform. It is so +constructed that it must withstand an extraordinary +torsional strain, being located at the forward +portion of the wing surface. Torsion has +reference to a twisting motion. + +In some cases, as in the bat, this primary bone +has an attachment to the rear of the main joint, +where the rear margin of the wing is attached to +the leg of the animal, thus giving it a support +and the main bone is, therefore, relieved of this +torsional stress. + +THE BAT'S WING.--An examination of the bat's +wing shows that the pectoral bone is very small +and thin, thus proving that when the entire wing +support is thrown upon the primary bone it must +be large enough to enable it to carry out its functions. +It is certainly not so made because it is a +necessary shape which best adapts it for flying. + +If such were the case then nature erred in the +case of the bat, and it made a mistake in the +housefly's wing which has no such anterior enlargement +to assist (?) it in flying. + +AN ABNORMAL SHAPE.--Another illustration is +shown in Fig. 30, which has a deep concave directly +behind the forward margin, as at A, so +that when the plane is at an angle of about 22 +degrees, a horizontal line, as B, passing back from +the nose, touches the incurved surface of the plane +at a point about one-third of its measurement +back across the plane. + +_Fig. 30. One of the Monstrosities_ + +This form is an exact copy of the wing of an +actual bird, but it belongs, not to the soaring, +but to the class which depends on flapping wings, +and as such it cannot be understood why it should +be used for soaring machines, as all aeroplanes +are. + +The foregoing instances of construction are +cited to show how wildly the imagination will +roam when it follows wrong ideals. + +THE TAIL AS A MONITOR.--The tendency of the +center of pressure to change necessitates a correctional +means, which is supplied in the tail of +the machine, just as the tail of a kite serves to +hold it at a correct angle with respect to the wind +and the pull of the supporting string. + + + + +CHAPTER VII + +ABNORMAL FLYING STUNTS AND SPEEDS + + +"PEQUOD, a Frenchman, yesterday repeatedly +performed the remarkable feat of flying with the +machine upside down. This exhibition shows +that the age of perfection has arrived in flying +machines, and that stability is an accomplished +fact."--News item. + + +This is quoted to show how little the general +public knows of the subject of aviation. It correctly +represents the achievement of the aviator, +and it probably voiced the sentiment of many +scientific men, as well as of the great majority of +aviators. + +A few days afterwards, the same newspaper +published the following: + + +"Lieutenant ----, while experimenting yesterday +morning, met his death by the overturning +of his machine at an altitude of 300 meters. +Death was instantaneous, and the machine was +completely destroyed." + +The machines used by the two men were of the +same manufacture, as Pequod used a stock machine +which was strongly braced to support the +inverted weight, but otherwise it was not unlike +the well known type of monoplane. + +Beachy has since repeated the experiment with +a bi-plane, and it is a feat which has many imitators, +and while those remarkable exhibitions +are going on, one catastrophe follows the other +with the same regularity as in the past. + +Let us consider this phase of flying. Are they +of any value, and wherein do they teach anything +that may be utilized, + +LACK OF IMPROVEMENTS IN MACHINES.--It is remarkable +that not one single forward step has +been taken to improve the type of flying machines +for the past five years. They possess the same +shape, their stabilizing qualities and mechanism +for assuring stability are still the same. + +MEN EXPEDITED, AND NOT THE MACHINE.--The +fact is, that during this period the man has been +exploited and not the machine. Men have learned, +some few of them, to perform peculiar stunts, +such as looping the loop, the side glide, the drop, +and other features, which look, and are, hazardous, +all of which pander to the sentiments of the spectators. + +ABNORMAL FLYING OF NO VALUE.--It would be +too broad an assertion to say that it has absolutely +no value, because everything has its use +in a certain sense, but if we are to judge from +the progress of inventions in other directions, +such exhibitions will not improve the art of building +the device, or make a fool-proof machine. + +Indeed, it is the very thing which serves as a +deterrent, rather than an incentive. If machines +can be handled in such a remarkable manner, they +must be, indeed, perfect! Nothing more is +needed! They must represent the highest structural +type of mechanism! + +That is the idea sought to be conveyed in the +first paragraph quoted. It is pernicious, instead +of praiseworthy, because it gives a false impression, +and it is remarkable that even certain scientific +journals have gravely discussed the perfected +(?) type of flying machine as demonstrated +by the experiments alluded to. + +THE ART OF JUGGLING.--We may, occasionally, +see a cyclist who understands the art of balancing +so well that he can, with ease, ride a machine +which has only a single wheel; or he can, with a +stock bicycle, ride it in every conceivable attitude, +and make it perform all sorts of feats. + +It merely shows that man has become an +expert at juggling with a machine, the same as he +manipulates balls, and wheels, and other artifices, +by his dexterity. + +PRACTICAL USES THE BEST TEST.--The bicycle +did not require such displays to bring it to perfection. +It has been the history of every invention +that improvements were brought about, not +by abnormal experiments, but by practical uses +and by normal developments. + +The ability of an aviator to fly with the machine +in an inverted position is no test of the machine's +stability, nor does it in any manner prove that +it is correctly built. It is simply and solely a +juggling feat--something in the capacity of a certain +man to perform, and attract attention because +they are out of the ordinary. + +CONCAVED AND COXVEX PLANES:--They were performed +as exhibition features, and intended as +such, and none of the exponents of that kind of +flying have the effrontery to claim that they prove +anything of value in the machine itself, except +that it incidentally has destroyed the largely +vaunted claim that concaved wings for supporting +surfaces are necessary. + +HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.-- +When flying "upside down," the convex +side of the plane takes the pressure of the air, +and maintains, so it is asserted, the weight of the +machine. This is true during that period when +the loop is being made. The evolution is made +by first darting down, as shown in Fig. 31, from +the horizontal position, 1, to the position 2, where +the turn begins. + +_Fig. 31. Flying upside down._ + +TURNING MOVEMENT.--Now note the characteristic +angles of the tail, which is the controlling +factor. In position 1 the tail is practically +horizontal. In fact, in all machines, at +high flight, the tail is elevated so as to give little +positive angle of incidence to the supporting +planes. + +In position No. 2, the tail is turned to an angle +of incidence to make the downward plunge, and +when the machine has assumed the vertical, as in +position 3, the tail is again reversed to assume +the angle, as in 1, when flying horizontally. + +At the lower turn, position 4, the tail is turned +similar to the angle of position 2, which throws +the rear end of the machine down, and as the +horizontal line of flight is resumed, in an inverted +position, as in position 4, the tail has the same +angle, with relation to the frame, as the supporting +planes. + +During this evolution the engine is running, and +the downward plunge develops a tremendous +speed, and the great momentum thus acquired, +together with the pulling power of the propeller +while thus in flight, is sufficient to propel it along +horizontally, whatever the plane surface curve, or +formation may be. + +It is the momentum which sustains it in space, +not the air pressure beneath the wings, for +reasons which we have heretofore explained. +Flights of sufficient duration have thus been made +to prove that convex, as well as concave surfaces +are efficient; nevertheless, in its proper place we +have given an exposition of the reasoning which +led to the adoption of the concaved supporting +surfaces. + +WHEN CONCAVED PLANES ARE DESIRABLE.-- +Unquestionably, for slow speeds the concaved wing +is desirable, as will be explained, but for high +speeds, surface formation has no value. That is +shown by Pequod's feat. + +THE SPEED MANIA.--This is a type of mania +which pervades every field of activity in the building +of aeroplanes. Speed contests are of more +importance to the spectators on exhibition +grounds than stability or durability. Builders +pander to this, hence machines are built on lines +which disregard every consideration of safety +while at normal flight. + +USES OF FLYING MACHINES.--The machine as +now constructed is of little use commercially. +Within certain limitations it is valuable for scouting +purposes, and attempts have been made to +use it commercially. But the unreliable character +of its performances, due to the many elements +which are necessary to its proper working, have +operated against it. + +PERFECTION IN MACHINES MUST COME BEFORE +SPEED.--Contrary to every precept in the building +of a new article, the attempt is made to make +a machine with high speed, which, in the very +nature of things, operates against its improvement. +The opposite lack of speed--is of far +greater utility at this stage of its development. + +THE RANGE OF ITS USE.--The subject might be +illustrated by assuming that we have a line running +from A to Z, which indicates the range of +speeds in aeroplanes. The limits of speeds are +fairly stated as being within thirty and eighty- +five miles per hour. Less than thirty miles are +impossible with any type of plane, and while some +have made higher speeds than eighty-five miles it +may be safe to assume that such flights took place +under conditions where the wind contributed to +the movement. + +_Fig. 32. Chart showing Range of Uses_ + +COMMERCIAL UTILITY.--Before machines can be +used successfully they must be able to attain +slower speeds. Alighting is the danger factor. +Speed machines are dangerous, not in flight or +at high speeds, but when attempting to land. A +large plane surface is incompatible with speed, +which is another illustration that at high velocities +supporting surfaces are not necessary. + +Commercial uses require safety as the first element, +and reliability as the next essential. For +passenger service there must be an assurance that +it will not overturn, or that in landing danger is +not ever-present. For the carrying of freight interrupted +service will militate against it. + +How few are the attempts to solve the problem +of decreased speed, and what an eager, restless +campaign is being waged to go faster and faster, +and the addition of every mile above the record +is hailed as another illustration of the perfection +(?) of the flying machine. + +To be able to navigate a machine at ten, or fifteen +miles an hour, would scarcely be interesting +enough to merit a paragraph; but such an accomplishment +would be of far more value than all of +Pequod's feats, and be more far-reaching in its +effects than a flight of two hundred miles per hour. + + + +CHAPTER VIII + +KITES AND GLIDERS + + +KITES are of very ancient origin, and in China, +Japan, and the Malayan Peninsula, they have been +used for many years as toys, and for the purposes +of exhibiting forms of men, animals, and particularly +dragons, in their periodical displays. + +THE DRAGON KITE.--The most noted of all are +the dragon kites, many of them over a hundred +feet in length, are adapted to sail along majestically, +their sinuous or snake-like motions lending +an idea of reality to their gorgeously-colored appearance +in flight. + +ITS CONSTRUCTION.--It is very curiously +wrought, and as it must be extremely light, bamboo +and rattan are almost wholly used, together +with rice paper, in its construction. + +Fig. 33 shows one form of the arrangement, in +which the bamboo rib, A, in which only two sections +are shown, as B, B, form the backbone, and +these sections are secured together with pivot +pins C. Each section has attached thereto a +hoop, or circularly-formed rib, D, the rib passing +through the section B, and these ribs are +connected together loosely by cords E, which run +from one to the other, as shown. + +These circular ribs, D, are designed to carry a +plurality of light paper disks, F, which are attached +at intervals, and they are placed at such +angles that they serve as small wing surfaces or +aeroplanes to hold the structure in flight. + +_Fig. 33. Ribs of Dragon Kite_ + +THE MALAY KITE.--The Malay kite, of which +Fig. 34 shows the structure, is merely made up of +two cross sticks, A, B, the vertical strip, A, being +bent and rigid, whereas the cross stick, B, is light +and yielding, so that when in flight it will bend, +as shown, and as a result it has wonderful stability +due to the dihedral angles of the two surfaces. This kite +requires no tail to give it stability. + +_Fig. 34. The Malay Kite._ + +DIHEDRAL ANGLES.--This is a term to designate +a form of disposing of the wings which has been +found of great service in the single plane machines. +A plane which is disposed at a rising +angle, as A, A, Fig. 35, above the horizontal line, +is called dihedral, or diedral. + +_Fig. 35. Dihedral Angle._ + +This arrangement in monoplanes does away +with the necessity of warping the planes, or +changing them while in flight. If, however, the angle +is too great, the wind from either quarter is liable +to raise the side that is exposed. + +THE COMMON KITE.--While the Malay kite has +only two points of cord attachment, both along +the vertical rib, the common kite, as shown in +Fig. 36, has a four-point connection, to which the +flying cord is attached. Since this form has no +dihedral angle, it is necessary to supply a tail, +which thus serves to keep it in equilibrium, while +in flight. + +_Fig. 36. Common Kite._ + +Various modifications have grown out of the +Malay kite. One of these forms, designed by +Eddy, is exactly like the Malay structure, but instead +of having a light flexible cross piece, it is +bent to resemble a bow, so that it is rigidly held +in a bent position, instead of permitting the wind +to give it the dihedral angle. + +THE BOW KITE.--Among the different types are +the bow kite, Fig. 37, and the sexagonal structure, +Fig. 38, the latter form affording an especially +large surface. + +_Fig. 37. Bow Kite.- + +_Fig. 38. Hexagonal Kite._ + +THE BOX KITE.--The most marked improvement +in the form of kites was made by Hargreaves, +in 1885, and called the box kite. It has wonderful +stability, and its use, with certain modifications, +in Weather Bureau experiments, have proven its +value. + +It is made in the form of two boxes, A, B, open +at the ends, which are secured together by means +of longitudinal bars, C, that extends from one to +the other, so that they are held apart a distance, +approximately, equal to the length of one of the +boxes. + +_Fig. 39. Hargreave Kite._ + +Their fore and aft stability is so perfect that +the flying cord D is attached at one point only, +and the sides of the boxes provide lateral stability +to a marked degree. + +THE VOISON BIPLANE.--This kind of kite furnished +the suggestion for the Voison biplane, +which was one of the earlier productions in flying +machines. + +Fig. 40 shows a perspective of the Voison plane, +which has vertical planes A, A, at the ends, and +also intermediate curtains B, B. This was found +to be remarkably stable, but during its turning +movements, or in high winds, was not satisfactory, +and for that reason was finally abandoned. + +LATERAL STABILITY IN KITES NOT CONCLUSIVE AS +TO PLANES.--This is instanced to show that while +such a form is admirably adapted for kite purposes, +where vertical curtains are always in line +with the wind movement, and the structure is held +taut by a cord, the lateral effect, when used on a +machine which does not at all times move in line +with the moving air current. A condition is thus +set up which destroys the usefulness of the box +kite formation. + +_Fig. 40. Voison Biplane._ + +THE SPEAR KITE.--This is a novel kite, with +remarkable steadiness and is usually made with +the wings on the rear end larger than those on +the forward end (Fig. 41), as thereby the cord +A can be attached to the spear midway between +the two sets of wings. + +_Fig. 41. Spear Kite._ + +THE CELLULAR KITE.--Following out the suggestion +of the Hargreaves kite, numerous forms +embodying the principle of the box structure were +made and put on the market before the aeroplane +became a reality. + +_Fig. 42. Cellular Kite._ + +A structure of this form is illustrated in Fig. +42. Each box, as A, B, has therein a plurality of +vertical and horizontal partitions, so that a number +of cells are provided, the two cell-like boxes +being held apart by a bar C, axially arranged. + +This type is remarkably stable, due to the small +cells, and kites of this kind are largely used for +making scientific experiments. + +THE TETRAHEDRAL KITE.--Prof. Bell, inventor +of the telephone, gave a great deal of study to +kites, which resulted in the tetrahedral formation, +as shown in Fig. 43. + +_Fig. 43. Tetrahedral Kite._ + +The structure, apparently, is somewhat complicated, +but an examination of a single pair of +blades, as shown at A, shows that it is built up of +triangularly-formed pieces, and that the openings +between the pieces are equal to the latter, thereby +providing a form of kite which possesses equilibrium +to a great degree. + +It has never been tried with power, and it is +doubtful whether it would be successful as a sustaining +surface for flying machines, for the same +reasons that caused failure with the box-like formation +of the Voison Machine. + +THE DELTOID.--The deltoid is the simplest, and +the most easily constructed of all the kites. It is +usually made from stiff cardboard, A-shaped in +outline, as shown in Figs. 44 and 45, and bent along +a central line, as at A, forming two wings, each +of which is a right-angled triangle. + +_Fig. 44. and 45. Deltoid Formation._ + +The peculiarity of this formation is, that it has +remarkable stability when used as a kite, with +either end foremost. If a small weight is placed +at the pointed end, and it is projected through the +air, it will fly straight, and is but little affected +by cross currents. + +THE DUNNE FLYING MACHINE.--A top view of +this biplane is shown in Fig. 46. The A-shaped +disposition of the planes, gives it good lateral +stability, but it has the disadvantage under which +all aeroplanes labor, that the entire body of the +machine must move on a fore and aft vertical +plan in order to ascend or descend. + +_Fig. 46. The Dunne Bi-plane._ + +This is a true deltoid formation, as the angle of +incidence of the planes is so disposed that when +the planes are horizontal from end to end, the inclination +is such as to make it similar to the deltoid +kite referred to. + +ROTATING KITE.--A type of kite unlike the +others illustrated is a rotating structure, which +gives great stability, due to the gyroscopic action +on the supporting surfaces. + +Fig. 47 shows a side view with the top in section. +The supporting surface is umbrella-shaped. +In fact, the ordinary umbrella will answer if not +dished too much. An angularly-bent piece of wire +A, provided with loops B, B, at the ends, serve as +bearings for the handle of the umbrella. + +At the bend of the wire loop C, the cord D is +attached. The lower side of the umbrella top has +cup-shaped pockets E, near the margin, so arranged +that their open ends project in the same +direction, and the wind catching them rotates the +circular plane. + +_Fig. 47. Rotable Umbrella Kite._ + +KITE PRINCIPLES.--A careful study of the examples +here given, will impress the novice with +one important fact, which, in its effect has a more +important bearing on successful flight, than all +the bird study and speculations concerning its +mysteries. + +This fact, in essence, is, that the angle of the +kite is the great factor in flight next to the power +necessary to hold it. Aside from this, the +comparison between kites and aeroplanes is of no +practical value. + +Disregarding the element of momentum, the +drift of a machine against a wind, is the same, +dynamically, as a plane at rest with the wind +moving past it. But there is this pronounced +difference: The cord which supports the kite +holds it so that the power is in one direction only. + +When a side gust of wind strikes the kite it +is moved laterally, in sympathy with the kite, +hence the problem of lateral displacement is not +the same as with the aeroplane. + +LATERAL STABILITY IN KITES.--In the latter the +power is definitely fixed with relation to the machine +itself, and if we should assume that a plane +with a power on it sufficient to maintain a flight +of 40 miles an hour, should meet a wind moving +at the same speed, the machine would be stationary +in space. + +Such a condition would be the same, so far as +the angles of the planes are concerned, with a +kite held by a string, but there all similarity in +action ends. + +The stabilizing quality of the kite may be perfect, +as the wind varies from side to side, but the +aeroplane, being free, moves to the right or to +the left, and does not adjust itself by means of a +fixed point, but by a movable one. + +SIMILARITY OF FORE AND AFT CONTROL.--Fore +and aft, however, the kite and aeroplane act the +same. Fig. 48 shows a diagram which illustrates +the forces which act on the kite, and by means +of which it adjusts its angle automatically. + +Let us assume that the kite A is flown from +a cord B, so that its angle is 22 1/2 degrees, the +wind being 15 miles per hour to maintain the +cord B at that angle. When the wind increases +to 20 miles an hour there is a correspondingly +greater lift against the kite. + +_Fig. 48. Action of Wind forces on Kite._ + +As its angle is fixed by means of the loop C, +it cannot change its angle with reference to the +cord, or independently of it, and its only course +is to move up higher and assume the position +shown by the figure at D, and the angle of incidence +of the kite is therefore changed to 15 degrees, +or even to 10 degrees. + +In the case of the aeroplane the effect is similar +from the standpoint of power and disposition +of the planes. If it has sufficient power, and the +angle of the planes is not changed, it will ascend; +if the planes are changed to 15 degrees to correspond +with the kite angle it will remain stationary. + +GLIDING FLIGHT.--The earliest attempt to fly +by gliding is attributed to Oliver, a Monk of +Malmesbury who, in 1065 prepared artificial +wings, and with them jumped from a tower, being +injured in the experiment. + +Nearly 700 years later, in 1801, Resnier, a +Frenchman, conducted experiments with varying +results, followed by Berblinger, in 1842, and +LeBris, a French sailor, in 1856. + +In 1884, J. J. Montgomery, of California, designed +a successful glider, and in 1889 Otto and +Gustav Lilienthal made the most extended tests, +in Germany, and became experts in handling +gliders. + +Pilcher, in England, was the next to take up the +subject, and in 1893 made many successful glides, +all of the foregoing machines being single plane +surfaces, similar to the monoplane. + +Long prior to 1896 Octave Chanute, an +engineer, gave the subject much study, and in that +year made many remarkable flights, developing +the double plane, now known as the biplane. + +He was an ardent believer in the ability of man +to fly by soaring means, and without using power +for the purpose. + +It is doubtful whether gliders contributed much +to the art in the direction of laterally stabilizing +aeroplanes. They taught useful lessons with respect +to area and fore and aft control. + +The kite gave the first impulse to seek out a +means for giving equilibrium to planes, and +Montgomery made a kite with warping wings as +early as 1884. + +Penaud, a Frenchman, in 1872, made a model +aeroplane which had the stabilizing means in the +tail. All these grew out of kite experiments; and +all gliders followed the kite construction, or the +principles involved in them, so that, really, there +is but one intervening step between the kite and +the flying machine, as we know it, the latter being +merely kites with power attached, as substitutes +for the cords. + +ONE OF THE USES OF GLIDER EXPERIMENTS.-- +There is one direction in which gliders are valuable +to the boy and to the novice who are interested +in aviation. He may spend a lifetime in +gliding and not advance in the art. It is +questionable whether in a scientific way it will be of +any service to him; but experiments of this character +give confidence, the ability to quickly grasp +a situation, and it will thus teach self reliance in +emergencies. + +When in a glider quick thinking is necessary. +The ability to shift from one position to another; +to apply the weight where required instantaneously; +to be able during the brief exciting moment +of flight to know just what to do, requires alertness. + +Some are so wedded to the earth that slight +elevation disturbs them. The sensation in a +glider while in flight is unlike any other experience. +It is like riding a lot of tense springs, and the +exhilaration in gliding down the side of a hill, +with the feet free and body suspended, is quite +different from riding in an aeroplane with power +attached. + +HINTS IN GLIDING.--It seems to be a difficult +matter to give any advice in the art of gliding. It +is a feat which seems to necessitate experiment +from first to last. During the hundreds of tests +personally made, and after witnessing thousands +of attempts, there seems to be only a few suggestions +or possible directions in which caution might +be offered. + +First, in respect to the position of the body at +the moment of launching. The glider is usually +so made that in carrying it, preparatory to making +the run and the leap required to glide, it is held +so that it balances in the hands. + +Now the center of air pressure in gliding may +not be at the same point as its sustaining weight +when held by the hand, and furthermore, as the +arm-pits, by which the body of the experimenter +are held while gliding, are not at the same point, +but to the rear of the hands, the moment the glider +is launched too great a weight is brought to the +rear margin of the planes, hence its forward end +lifts up. + +This condition will soon manifest itself, and be +corrected by the experimenter; but there is another +difficulty which is not so easy to discover +and so quick to remedy, and that is the swing of +the legs the moment the operator leaves the +ground. + +The experimenter learns, after many attempts, +that gliding is a matter of a few feet only, and he +anticipates landing too soon, and the moment he +leaps from the ground the legs are swung forwardly +ready to alight. + +This is done unconsciously, just as a jumper +swings his legs forwardly in the act of alighting. +Such a motion naturally disturbs the fore and aft +stability of the gliding machine, by tilting up the +forward margin, and it banks against the air, +instead of gliding. + +The constant fear of all gliders is, that the +machine will point downwardly, and his motion, +as well as the position of the body, tend to shoot +it upwardly, instead. + + + +CHAPTER IX + +AEROPLANE CONSTRUCTION + + +As may be inferred from the foregoing statements, +there are no definite rules for the construction +of either type of flying machine, as the +flying models vary to such an extent that it is +difficult to take either of them as a model to represent +the preferred type of construction. + +LATERAL, AND FORE AND AFT.--The term lateral +should be understood, as applied to aeroplanes. +It is always used to designate the direction at +right angles to the movement of the machine. +Fore and aft is a marine term meaning lengthwise, +or from front to rear, hence is always at right +angles to the lateral direction. + +The term transverse is equivalent to lateral, +in flying machine parlance, but there is this +distinction: Transverse has reference to a machine +or object which, like the main planes of an aeroplane, +are broader, (that is,--from end to end) +than their length, (from front to rear). + +On the other hand, lateral has reference to side +branches, as, for instance, the monoplane wings, +which branch out from the sides of the fore and +aft body. + +STABILITY AND STABILIZATION.--These terms constantly +appear in describing machines and their +operations. If the flying structure, whatever it +may be, has means whereby it is kept from rocking +from side to side, it has stability, which is usually +designated as lateral stability. The mechanism +for doing this is called a stabilizer. + +THE WRIGHT SYSTEM.--The Wright machine has +reference solely to the matter of laterally controlling +the flying structure, and does not pertain +to the form or shape of the planes. + +In Fig. 49 A designates the upper and lower +planes of a Wright machine, with the peculiar +rounded ends. The ends of the planes are so +arranged that the rear margins may be raised or +lowered, independently of the other portions of +the planes, which are rigid. This movement is +indicated in sketch 1, where the movable part B +is, as we might say, hinged along the line C. + +The dotted line D on the right hand end, shows +how the section is depressed, while the dotted +lines E at the left hand end shows the section +raised. It is obvious that the downturned ends, +as at D, will give a positive angle at one end of the +planes, and the upturned wings E at the other end +will give a negative angle, and thus cause the right +hand end to raise, and the other end to move +downwardly, as the machine moves forwardly +through the air. + +CONTROLLING THE WARPING ENDS.--Originally +the Wrights controlled these warping sections by +means of a cradle occupied by the aviator, so that +the cradle would move or rock, dependent on the +tilt of the machine. This was what was termed +automatic control. This was found to be unsatisfactory, +and the control has now been placed so +that it connects with a lever and is operated by +the aviator, and is called Manually-operated control. + +In all forms of control the wings on one side are +depressed on one side and correspondingly elevated +on the other. + +THE CURTIS WINGS.--Curtis has small wings, +or ailerons, intermediate the supporting surfaces, +and at their extremities, as shown in sketch 2. +These are controlled by a shoulder rack or swinging +frame operated by the driver, so that the body +in swinging laterally will change the two wings +at the same time, but with angles in different +directions. + +THE FARMAN AILERONS.--Farman's disposition +is somewhat different, as shown in sketch 3. The +wings are hinged to the upper planes at their rear +edges, and near the extremities of the planes. +Operating wires lead to a lever within reach of the +aviator, and, by this means, the wings are held at +any desired angle, or changed at will. + +The difficulty of using any particular model, is +true, also, of the arrangement of the fore and aft +control, as well as the means for laterally stabilizing +it. In view of this we shall submit a general +form, which may be departed from at will. + +FEATURES WELL DEVELOPED.--Certain features +are fairly well developed, however. One is the +angle of the supporting plane, with reference to +the frame itself; and the other is the height at +which the tail and rudder should be placed above +the surface of the ground when the machine is at +rest. + +DEPRESSING THE REAR END.--This latter is a +matter which must be taken into consideration, +because in initiating flight the rear end of the +frame is depressed in order to give a sufficient +angle to the supporting planes so as to be able to +inaugurate flight. + +In order to commence building we should have +some definite idea with respect to the power, as +this will, in a measure, determine the area of the +supporting surfaces, as a whole, and from this +the sizes of the different planes may be determined. + +DETERMINING THE SIZE.--Suppose we decide on +300 square feet of sustaining surface. This may +require a 30, a 40 or a 50 horse power motor, +dependent on the speed required, and much higher +power has been used on that area. + +However, let us assume that a forty horse power +motor is available, our 300 square feet of surface +may be put into two planes, each having 150 square +feet of surface, which would make each 5' by 30' +in size; or, it may be decided to make the planes +narrower, and proportionally longer. This is immaterial. +The shorter the planes transversely, +the greater will be the stability, and the wider the +planes the less will be the lift, comparatively. + +RULE FOR PLACING THE PLANES.--The rule for +placing the planes is to place them apart a distance +equal to the width of the planes themselves, +so that if we decide on making them five feet wide, +they should be placed at least five feet apart. +This rule, while it is an admirable one for slow +movements or when starting flight, is not of any +advantage while in rapid flight. + +If the machine is made with front and rear +horizontally-disposed rudders, or elevators, they +also serve as sustaining surfaces, which, for the +present will be disregarded. + +Lay off a square A, Fig. 49a, in which the vertical +lines B, B, and the horizontal lines C, C, are +5' long, and draw a cross D within this, the lines +running diagonally from the corners. + +Now step off from the center cross line D, three +spaces, each five feet long, to a point E, and join +this point by means of upper and lower bars F, +G, with the upper and lower planes, so as to form +the tail frame. + +_Fig. 49a. Rule for spacing Planes._ + +As shown in Fig. 50, the planes should now be +indicated, and placed at an angle of about 8 degrees +angle, which are illustrated, H being the +upper and I the lower plane. Midway between the +forward edges of the two planes, is a horizontal +line J, extending forwardly, and by stepping off +the width of two planes, a point K is made, which +forms the apex of a frame L, the rear ends of the +bars being attached to the respective planes H, I, +at their forward edges. + +_Fig. 50. Frame of Control Planes._ + +_Fig. 51. and Fig. 52._ + +ELEVATING PLANES.--We must now have the general +side elevation of the frame, the planes, their +angles, the tail and the rudder support, and the +frame for the forward elevator. + +To this may be added the forward elevating +plane L, the rear elevator, or tail M, and the vertical +steering rudder N. + +The frame which supports the structure thus +described, may be made in a variety of ways, the +object being to provide a resilient connection for +the rear wheel O. + +Fig. 52 shows a frame which is simple in construction +and easily attached. The lower fore +and aft side bars P have the single front wheel +axle at the forward end, and the aft double wheels +at the rear end, a flexible bar Q, running from the +rear wheel axle to the forward end of the lower +plane. + +A compression spring R is also mounted between +the bar and rear end of the lower plane to +take the shock of landing. The forward end of +the bar P has a brace S extending up to the front +edge of the lower plane, and another brace T connects +the bars P, S, with the end of the forwardly- +projecting frame. + +_Fig. 53. Plan view._ + +The full page view, Fig. 53, represents a plan +view, with one of the wings cut away, showing the +general arrangement of the frame, and the three +wheels required for support, together with the +brace bars referred to. + +The necessity of the rear end elevation will +now be referred to. The tail need not, necessarily, +be located at a point on a horizontal line +between the planes. It may be higher, or lower +than the planes, but it should not be in a position +to touch the ground when the machine is about +to ascend. + +_Fig. 54. Alighting._ + +The angle of ascension in the planes need not +exceed 25 degrees so the frame does not require +an angle of more than 17 degrees. This is shown +in Fig. 54, where the machine is in a position +ready to take the air at that angle, leaving ample +room for the steering rudder. + +ACTION IN ALIGHTING.--Also, in alighting, the +machine is banked, practically in the same +position thus shown, so that it alights on the rear +wheels O. + +The motor U is usually mounted so its shaft is +midway between the planes, the propeller V being +connected directly with the shaft, and being behind +the planes, is on a medial line with the +machine. + +The control planes L, M, N, are all connected up +by means of flexible wires with the aviator at the +set W, the attachments being of such a character +that their arrangement will readily suggest themselves +to the novice. + +THE MONOPLANE.--From a spectacular standpoint +a monoplane is the ideal flying machine. It +is graceful in outline, and from the fact that it +closely approaches the form of the natural flyer, +seems to be best adapted as a type, compared with +the biplane. + +THE COMMON FLY.--So many birds have been +cited in support of the various flying theories that +the house fly, as an example has been disregarded. +We are prone to overlook the small insect, but it +is, nevertheless, a sample which is just as potent +to show the efficiency of wing surface as the condor +or the vulture. + +The fly has greater mobility than any other flying +creature. By the combined action of its legs +and wings it can spring eighteen inches in the +tenth of a second; and when in flight can change +its course instantaneously. + +If a sparrow had the same dexterity, proportionally, +it could make a flight of 800 feet in the +same time. The posterior legs of the fly are the +same length as its body, which enable it to spring +from its perch with amazing facility. + +_Fig. 55. Common Fly. Outstretched Wings._ + +The wing surface, proportioned to its body and +weight, is no less a matter for wonder and consideration. + +In Fig. 55 is shown the outlines of the fly with +outstretched wings. Fig. 56 represents it with +the wing folded, and Fig. 57 is a view of a wing +with the relative size of the top of the body shown +in dotted lines. + +_Fig. 56. Common Fly. Folded Wings._ + +The first thing that must attract attention, after +a careful study is the relative size of the body +and wing surface. Each wing is slightly smaller +than the upper surface of the body, and the thickness +of the body is equal to each wing spread. + +_Fig. 57. Relative size of wing and body._ + +The weight, compared with sustaining surface, +if expressed in understandable terms, would be +equal to sixty pounds for every square foot of surface. + +STREAM LINES.--The next observation is, that +what are called stream lines do not exist in the fly. +Its head is as large in cross section as its body, +with the slightest suggestion only, of a pointed +end. Its wings are perfectly flat, forming a true +plane, not dished, or provided with a cambre, even, +that upward curve, or bulge on the top of the aeroplane +surface, which seems to possess such a fascination +for many bird flight advocates. + +It will also be observed that the wing connection +with the body is forward of the line A, which +represents the point at which the body will balance +itself, and this line passes through the wings +so that there is an equal amount of supporting +surface fore and aft of the line. + +Again, the wing attachment is at the upper side +of the body, and the vertical dimension of the +body, or its thickness, is equal to four-fifths of the +length of he wing. + +The wing socket permits a motion similar to a +universal joint, Fig. 55 showing how the inner +end of the wing has a downward bend where it +joins the back, as at B. + +THE MONOPLANE FORM.--For the purpose of +making comparisons the illustrations of the monoplane +show a machine of 300 square feet of surface, +which necessitates a wing spread of forty +feet from tip to tip, so that the general dimensions +of each should be 18 1/2 feet by 8 1/2 feet at its +widest point. + +First draw a square forty feet each way, as in +Fig. 58, and through this make a horizontal line +1, and four intermediate vertical lines are then +drawn, as 2, 3, 4, 5, thus providing five divisions, +each eight feet wide. In the first division the +planes A, B, are placed, and the tail, or elevator +C, is one-half the width of the last division. + +_Fig. 58. Plan of Monoplane._ + +The frame is 3 1/2 feet wide at its forward end, +and tapers down to a point at its rear end, where +the vertical control plane D is hinged, and the +cross struts E, E, are placed at the division lines +3, 4, 5. + +The angles of the planes, with relation to the +frame, are usually greater than in the biplane, +for the reason that the long tail plane requires +a greater angle to be given to the planes when +arising; or, instead of this, the planes A, B, are +mounted high enough to permit of sufficient angle +for initiating flight without injuring the tail D. + +Some monoplanes are built so they have a support +on wheels placed fore and aft. In others +the tail is supported by curved skids, as shown +at A, Fig. 59, in which case the forward +supporting wheels are located directly beneath the planes. +As the planes are at about eighteen degrees +angle, relative to the frame, and the tail plane +B is at a slight negative angle of incidence, as +shown at the time when the engine is started, the +air rushing back from the propeller, elevates the +tail, and as the machine moves forwardly over +the ground, the tail raises still higher, so as to +give a less angle of incidence to the planes while +skimming along the surface of the ground. + +_Fig. 59. Side Elevation, Monoplane._ + +In order to mount, the tail is suddenly turned +to assume a sharp negative angle, thus swinging +the tail downwardly, and this increases the angle +of planes to such an extent that the machine leaves +the ground, after which the tail is brought to the +proper angle to assure horizontal flight. + +The drawing shows a skid at the forward end, +attached to the frame which carries the wheels. +The wheels are mounted beneath springs so that +when the machine alights the springs yield sufficiently +to permit the skids to strike the ground, +and they, therefore, act as brakes, to prevent the +machine from traveling too far. + + + +CHAPTER X + +POWER AND ITS APPLICATION + + +THIS is a phase of the flying machine which has +the greatest interest to the boy. He instinctively +sees the direction in which the machine has its +life,--its moving principle. Planes have their +fascination, and propellers their mysterious elements, +but power is the great and absorbing question +with him. + +We shall try to make its application plain in +the following pages. We have nothing to do here +with the construction and operation of the motor +itself, as, to do that justice, would require pages. + +FEATURES IN POWER APPLICATION.--It will be +more directly to the point to consider the following +features of the power and its application: + +1. The amount of power necessary. + +2. How to calculate the power applied. + +3. Its mounting. + + +WHAT AMOUNT OF POWER IS NECESSARY.--In the +consideration of any power plant certain calculations +must be made to determine what is required. +A horse power means the lifting of a certain +weight, a definite distance, within a specified +time. + +If the weight of the vehicle, with its load, are +known, and its resistance, or the character of the +roadway is understood, it is a comparatively easy +matter to calculate just how much power must be +exerted to overcome that resistance, and move the +vehicle a certain speed. + +In a flying machine the same thing is true, but +while these problems may be known in a general +way, the aviator has several unknown elements +ever present, which make estimates difficult to +solve. + +THE PULL OF THE PROPELLER.--Two such factors +are ever present. The first is the propeller +pull. The energy of a motor, when put into a +propeller, gives a pull of less than eight pounds +for every horse power exerted. + +FOOT POUNDS.--The work produced by a motor +is calculated in Foot Pounds. If 550 pounds +should be lifted, or pulled, one foot in one second +of time, it would be equal to one horse power. + +But here we have a case where one horse power +pulls only eight pounds, a distance of one foot +within one second of time, and we have utilized +less than one sixty-fifth of the actual energy produced. + +SMALL AMOUNT OF POWER AVAILABLE.--This is +due to two things: First, the exceeding lightness +of the air, and its great elasticity; and, second, +the difficulty of making a surface which, when it +strikes the air, will get a sufficient grip to effect +a proper pull. + +Now it must be obvious, that where only such +a small amount of energy can be made available, +in a medium as elusive as air, the least change, or +form, of the propeller, must have an important +bearing in the general results. + +HIGH PROPELLER SPEED IMPORTANT.--Furthermore, +all things considered, high speed is important +in the rotation of the propeller, up to a certain +point, beyond which the pull decreases in +proportion to the speed. High speed makes a +vacuum behind the blade and thus decreases the +effective pull of the succeeding blade. + +WIDTH AND PITCH OF BLADES.--If the blade is +too wide the speed of the engine is cut down to a +point where it cannot exert the proper energy; if +the pitch is very small then it must turn further to +get the same thrust, so that the relation of diameter, +pitch and speed, are three problems far from +being solved. + +It may be a question whether the propeller form, +as we now know it, is anything like the true or +ultimate shape, which will some day be discovered. + +EFFECT OF INCREASING PROPELLER PULL.--If the +present pull could be doubled what a wonderful +revolution would take place in aerial navigation, +and if it were possible to get only a quarter of +the effective pull of an engine, the results would +be so stupendous that the present method of flying +would seem like child's play in comparison. + +It is in this very matter,--the application of +the power, that the bird, and other flying creatures +so far excel what man has done. Calculations +made with birds as samples, show that many +of them are able to fly with such a small amount +of power that, if the same energy should be applied +to a flying machine, it would scarcely drive +it along the ground. + +DISPOSITION OF THE PLANES.--The second factor +is the disposition or arrangement of the planes +with relation to the weight. Let us illustrate this +with a concrete example: + +We have an aeroplane with a sustaining surface +of 300 square feet which weighs 900 pounds, +or 30 pounds per square foot of surface. + +DIFFERENT SPEEDS WITH SAME POWER.--Now, we +may be able to do two things with an airship under +those conditions. It may be propelled through +the air thirty miles an hour, or sixty miles, with +the expenditure of the same power. + +An automobile, if propelled at sixty, instead of +thirty miles an hour, would require an additional +power in doing so, but an airship acts differently, +within certain limitations. + +When it is first set in motion its effective pull +may not be equal to four pounds for each horse +power, due to the slow speed of the propeller, and +also owing to the great angle of incidence which +resists the forward movement of the ship. + +INCREASE OF SPEED ADDS TO RESISTANCE.--Finally, +as speed increases, the angle of the planes +decrease, resistance is less, and up to a certain +point the pull of the propeller increases; but beyond +that the vacuum behind the blades becomes +so great as to bring down the pull, and there is +thus a balance,--a sort of mutual governing motion +which, together, determine the ultimate speed +of the aeroplane. + +HOW POWER DECREASES WITH SPEED.--If now, +with the same propeller, the speed should be +doubled, the ship would go no faster, because the +bite of the propeller on the air would be ineffective, +hence it will be seen that it is not the amount +of power in itself, that determines the speed, but +the shape of the propeller, which must be so made +that it will be most effective at the speed required +for the ship. + +While that is true when speed is the matter of +greatest importance, it is not the case where it is +desired to effect a launching. In that case the +propeller must be made so that its greatest pull +will be at a slow speed. This means a wider +blade, and a greater pitch, and a comparatively +greater pull at a slow speed. + +No such consideration need be given to an automobile. +The constant accretion of power adds +to its speed. In flying machines the aviator must +always consider some companion factor which +must be consulted. + +HOW TO CALCULATE THE POWER APPLIED.--In a +previous chapter reference was made to a plane +at an angle of forty-five degrees, to which two +scales were attached, one to get its horizontal pull, +or drift, and the other its vertical pull, or lift. + +PULLING AGAINST AN ANGLE.--Let us take the +same example in our aeroplane. Assuming that +it weighs 900 pounds, and that the angle of the +planes is forty-five degrees. If we suppose that +the air beneath the plane is a solid, and frictionless, +and a pair of scales should draw it up the incline, +the pull in doing so would be one-half of its +weight, or 450 pounds. + +It must be obvious, therefore, that its force, in +moving downwardly, along the surface A, Fig. 60, +would be 450 pounds. + +The incline thus shown has thereon a weight B, +mounted on wheels a, and the forwardly-projecting +cord represents the power, or propeller pull, +which must, therefore, exert a force of 450 pounds +to keep it in a stationary position against the surface +A. + +In such a case the thrust along the diagonal +line E would be 900 pounds, being the composition +of the two forces pulling along the lines D, F. + +THE HORIZONTAL AND VERTICAL PULL.--Now it +must be obvious, that if the incline takes half of +the weight while it is being drawn forwardly, in +the line of D, if we had a propeller drawing along +that line, which has a pull of 450 pounds, it would +maintain the plane in flight, or, at any rate hold +it in space, assuming that the air should be moving +past the plane. + +_Fig. 60. Horizontal and Vertical pull._ + +The table of lift and drift gives a fairly accurate +method of determining this factor, and we refer to +the chapter on that subject which will show the +manner of making the calculations. + +THE POWER MOUNTING.--More time and labor +has been wasted, in airship experiments, in poor +motor mounting, than in any other direction. +This is especially true where two propellers are +used, or where the construction is such that the +propeller is mounted some distance from the motor. + +SECURING THE PROPELLER TO THE SHAFT.--But +even where the propeller is mounted on the engine +shaft, too little care is exercised to fix it securely. +The vibratory character of the mounting +makes this a matter of first importance. If there +is a solid base a poorly fixed propeller will hold +much longer, but it is the extreme vibration that +causes the propeller fastening to give way. + +VIBRATIONS.--If experimenters realized that an +insecure, shaking, or weaving bed would cause a +loss of from ten to fifteen per cent. in the pull of +the propeller, more care and attention would be +given to this part of the structure. + +WEAKNESSES IN MOUNTING.--The general weaknesses +to which attention should be directed are, +first, the insecure attachment of the propeller to +the shaft; second, the liability of the base to +weave; or permit of a torsional movement; third, +improper bracing of the base to the main body of +the aeroplane. + +If the power is transferred from the cylinder +to the engine shaft where it could deliver its output +without the use of a propeller, it would not +be so important to consider the matter of vibration; +but the propeller, if permitted to vibrate, +or dance about, absorbs a vast amount of energy, +while at the same time cutting down its effective +pull. + +Aside from this it is dangerous to permit the +slightest displacement while the engine is running. +Any looseness is sure to grow worse, instead +of better, and many accidents have been +registered by bolts which have come loose from +excessive vibration. It is well, therefore, to have +each individual nut secured, or properly locked, +which is a matter easily done, and when so secured +there is but little trouble in going over the machine +to notice just how much more the nut must +be taken up to again make it secure. + +THE GASOLINE TANK.--What horrid details have +been told of the pilots who have been burned to +death with the escaping gasoline after an accident, +before help arrived. There is no excuse for +such dangers. Most of such accidents were due +to the old practice of making the tanks of exceedingly +light or thin material, so that the least +undue jar would tear a hole at the fastening +points, and thus permit the gasoline to escape. + +A thick copper tank is by far the safest, as this +metal will not readily rupture by the wrench which +is likely in landing. + +WHERE TO LOCATE THE TANK.--There has been +considerable discussion as to the proper place to +locate the tank. Those who advocate its placement +overhead argue that in case of an accident +the aeroplane is likely to overturn, and the tank +will, therefore, be below the pilot. Those who +believe it should be placed below, claim that in +case of overturning it is safer to have the tank +afire above than below. + +DANGER TO THE PILOT.--The great danger to the +pilot, in all cases of accidents, lies in the +overturning of the machine. Many have had accidents +where the machine landed right side up, even +where the fall was from a great height, and the +only damage to the aviator was bruises. Few, if +any, pilots have escaped where the machine has +overturned. + +It is far better, in case the tank is light, to have +it detached from its position, when the ship strikes +the earth, because in doing so, it will not be so +likely to burn the imprisoned aviator. + +In all cases the tank should be kept as far away +from the engine as possible. There is no reason +why it cannot be placed toward the tail end of +the machine, a place of safety for two reasons: +First, it is out of the reach of any possible +danger from fire; and, second, the accidents in the +past show that the tail frame is the least likely to +be injured. + +In looking over the illustrations taken from the +accidents, notice how few of the tails are even +disarranged, and in many of them, while the entire +fore body and planes were crushed to atoms, +the tail still remained as a relic, to show its +comparative freedom from the accident. + +In all monoplanes the tail really forms part of +the supporting surface of the machine, and the +adding of the weight of the gasoline would be +placing but little additional duty on the tail, and +it could be readily provided for by a larger tail +surface, if required. + +THE CLOSED-IN BODY.--The closed-in body is a +vast improvement, which has had the effect of +giving greater security to the pilot, but even this +is useless in case of overturning. + +STARTING THE MACHINE.--The direction in which +improvements have been slow is in the starting +of the machine. The power is usually so mounted +that the pilot has no control over the starting, +as he is not in a position to crank it. + +The propeller being mounted directly on the +shaft, without the intervention of a clutch, makes +it necessary, while on the ground, for the propeller +to be started by some one outside, while +others hold the machine until it attains the proper +speed. + +This could be readily remedied by using a +clutch, but in the past this has been regarded as +one of the weight luxuries that all have been trying +to avoid. Self starters are readily provided, +and this with the provision that the propeller can +be thrown in or out at will, would be a vast improvement +in all machines. + +PROPELLERS WITH VARYING PITCH.--It is growing +more apparent each day, that a new type of +propeller must be devised which will enable the +pilot to change the pitch, as the speed increases, +and to give a greater pitch, when alighting, so +as to make the power output conform to the conditions. + +Such propellers, while they may be dangerous, +and much heavier than the rigid type, will, no +doubt, appear in time, and the real improvement +would be in the direction of having the blades +capable of automatic adjustment, dependent on +the wind pressure, or the turning speed, and thus +not impose this additional duty on the pilot. + + + +CHAPTER XI + +FLYING MACHINE ACCESSORIES + + +THE ANEMOMETER.--It requires an expert to +judge the force or the speed of a wind, and even +they will go astray in their calculations. It is +an easy matter to make a little apparatus which +will accurately indicate the speed. A device of +this kind is called an Anemometer. + +Two other instruments have grown out of this, +one to indicate the pressure, and the other the +direction of the moving air current. + +THE ANEMOGRAPH.--While these instruments indicate, +they are also made so they will record the +speed, the pressure and the direction, and the device +for recording the speed and pressure is called +a Anemograph. + +All these instruments may be attached to the +same case, and thus make a handy little device, +which will give all the information at a glance. + +THE ANEMOMETROGRAPH.--This device for recording, +as well as indicating the speed, pressure +and direction, is called an Anemometrograph, +The two important parts of the combined +apparatus, for the speed and pressure, are illustrated, +to show the principle involved. While the speed +will give the pressure, it is necessary to make a +calculation to get the result while the machine does +this for you. + +_Fig. 61. Speed Indicator._ + +THE SPEED INDICATOR.--Four hemispherical +cups A are mounted on four radiating arms B, +which are secured to a vertical stem C, and +adapted to rotate in suitable bearings in a +case, which, for convenience in explaining, is not +shown. + +On the lower end of the stem C, is a small bevel +pinion, which meshes with a smaller bevel pinion +within the base. This latter is on a shaft which +carries a small gear on its other end, to mesh +with a larger gear on a shaft which carries a +pointer D that thus turns at a greatly reduced +speed, so that it can be easily timed. + +_Fig. 62. Air Pressure Indicator._ + +AIR PRESSURE INDICATOR.--This little apparatus +is readily made of a base A which is provided +with two uprights B, C, through the upper ends of +which are holes to receive a horizontally-disposed +bar D. One end of the bar is a flat plane +surface E, which is disposed at right angles to the +bar, and firmly fixed thereto. + +The other end of the bar has a lateral pin to +serve as a pivot for the end of a link F, its other +end being hinged to the upper end of a lever G, +which is pivoted to the post C, a short distance +below the hinged attachment of the link F, so +that the long end of the pointer which is constituted +by the lever G is below its pivot, and has, +therefore, a long range of movement. + +A spring I between the upper end of the pointer +G and the other post B, serves to hold the pointer +at a zero position. A graduated scale plate J, +within range of the pointer will show at a glance +the pressure in pounds of the moving wind, and +for this purpose it would be convenient to make +the plane E exactly one foot square. + +DETERMINING THE PRESSURE FROM THE SPEED.-- +These two instruments can be made to check each +other and thus pretty accurately enable you to +determine the proper places to mark the pressure +indicator, as well as to make the wheels in the +anemometer the proper size to turn the pointer +in seconds when the wind is blowing at a certain +speed, say ten miles per hour. + +Suppose the air pressure indicator has the scale +divided into quarter pound marks. This will +make it accurate enough for all purposes. + +CALCULATING PRESSURES FROM SPEED.--The following +table will give the pressures from 5 to 100 +miles per hour: + +Velocity of wind in Pressure Velocity of wind in Pressure +miles per hour per sq. ft. miles per hour per sq ft + 5 .112 55 15.125 + 10 .500 60 18.000 + 15 1.125 65 21.125 + 20 2.000 70 22.500 + 25 3.125 75 28.125 + 30 4.600 80 32.000 + 35 6.126 86 36.126 + 40 8.000 90 40.500 + 45 10.125 95 45.125 + 50 12.5 100 50.000 + + +HOW THE FIGURES ARE DETERMINED.--The foregoing +figures are determined in the following manner: +As an example let us assume that the velocity +of the wind is forty-five miles per hour. If +this is squared, or 45 multiplied by 45, the product +is 2025. In many calculations the mathematician +employs what is called a constant, a figure that +never varies, and which is used to multiply or +divide certain factors. + +In this case the constant is 5/1000, or, as usually +written, .005. This is the same as one two hundredths +of the squared figure. That would make +the problem as follows: + + 45 X 45 = 2025 / 200 = 10.125; or, + 45 X 45 - 2025 X .005 = 10.125. + + +Again, twenty-five miles per hour would be +25 X 25 = 625; and this multiplied by .005 equals +2 pounds pressure. + +CONVERTING HOURS INTO MINUTES.--It is sometimes +confusing to think of miles per hour, when +you wish to express it in minutes or seconds. A +simple rule, which is not absolutely accurate, but +is correct within a few feet, in order to express +the speed in feet per minute, is to multiply the +figure indicating the miles per hour, by 8 3/4. + +To illustrate: If the wind is moving at the +rate of twenty miles an hour, it will travel in that +time 105,600 feet (5280 X 20). As there are sixty +minutes in an hour, 105,600 divided by 60, equals +1760 feet per minute. Instead of going through +all this process of calculating the speed per minute, +remember to multiply the speed in miles per +hour by 90, which will give 1800 feet. + +This is a little more then two per cent. above +the correct figure. Again; 40 X 90 equals 3600. +As the correct figure is 3520, a little mental calculation +will enable you to correct the figures so +as to get it within a few feet. + +CHANGING SPEED HOURS TO SECONDS.--As one- +sixtieth of the speed per minute will represent the +rate of movement per second, it is a comparatively +easy matter to convert the time from speed in +miles per hour to fraction of a mile traveled in +a second, by merely taking one-half of the speed +in miles, and adding it, which will very nearly express +the true number of feet. + +As examples, take the following: If the wind +is traveling 20 miles an hour, it is easy to take +one-half of 20, which is 10, and add it to 20, making +30, as the number of feet per second. If the +wind travels 50 miles per hour, add 25, making +75, as the speed per second. + +The correct speed per second of a wind traveling +20 miles an hour is a little over 29 feet. At +50 miles per hour, the correct figure is 73 1/3 feet, +which show that the figures under this rule are +within about one per cent. of being correct. + +With the table before you it will be an easy +matter, by observing the air pressure indicator, +to determine the proper speed for the anemometer. +Suppose it shows a pressure of two pounds, +which will indicate a speed of twenty miles an +hour. You have thus a fixed point to start from. + +PRESSURE AS THE SQUARE OF THE SPEED.--Now +it must not be assumed that if the pressure at +twenty miles an hour is two pounds, that forty +miles an hour it is four pounds. The pressure +is as the square of the speed. This may be explained +as follows: As the speed of the wind +increases, it has a more effective push against an +object than its rate of speed indicates, and this +is most simply expressed by saying that each time +the speed is doubled the pressure is four times +greater. + +As an example of this, let us take a speed of ten +miles an hour, which means a pressure of one- +half pound. Double this speed, and we have 20 +miles. Multiplying one-half pound by 4, the result +is 2 pounds. Again, double 20, which means +40 miles, and multiplying 2 by 4, the result is 8. +Doubling forty is eighty miles an hour, and again +multiplying 8 by 4, we have 32 as the pounds pressure +at a speed of 80 miles an hour. + +The anemometer, however, is constant in its +speed. If the pointer should turn once a second +at 10 miles an hour, it would turn twice at 20 miles +an hour, and four times a second at 40 miles an +hour. + +GYROSCOPIC BALANCE.--Some advance has been +made in the use of the gyroscope for the purpose +of giving lateral stability to an aeroplane. While +the best of such devices is at best a makeshift, +it is well to understand the principle on which they +operate, and to get an understanding how they are +applied. + +THE PRINCIPLE INVOLVED.--The only thing +known about the gyroscope is, that it objects to +changing the plane of its rotation. This statement +must be taken with some allowance, however, +as, when left free to move, it will change in +one direction. + +To explain this without being too technical, examine +Fig. 63, which shows a gyroscopic top, one +end of the rim A, which supports the rotating +wheel B, having a projecting finger C, that is +mounted on a pin-point on the upper end of the +pedestal D. + +_Fig. 63. The Gyroscope._ + +When the wheel B is set in rotation it will maintain +itself so that its axis E is horizontal, or at +any other angle that the top is placed in when the +wheel is spun. If it is set so the axis is horizontal +the wheel B will rotate on a vertical plane, +and it forcibly objects to any attempt to make it +turn except in the direction indicated by the +curved arrows F. + +The wheel B will cause the axis E to swing +around on a horizontal plane, and this turning +movement is always in a certain direction in relation +to the turn of the wheel B, and it is obvious, +therefore, that to make a gyroscope that +will not move, or swing around an axis, the placing +of two such wheels side by side, and rotated +in opposite directions, will maintain them in a +fixed position; this can also be accomplished by +so mounting the two that one rotates on a plane +at right angles to the other. + +_Fig. 64. Application of the Gyroscope._ + +THE APPLICATION OF THE GYROSCOPE.--Without +in any manner showing the structural details of +the device, in its application to a flying machine, +except in so far as it may be necessary to explain +its operation, we refer to Fig. 64, which +assumes that A represents the frame of the aeroplane, +and B a frame for holding the gyroscopic +wheel C, the latter being mounted so it rotates on +a horizontal plane, and the frame B being hinged +fore and aft, so that it is free to swing to the right +or to the left. + +For convenience in explaining the action, the +planes E are placed at right angles to their regular +positions, F being the forward margin of the +plane, and G the rear edge. Wires H connect +the ends of the frame B with the respective +planes, or ailerons, E, and another wire I joins +the downwardly-projecting arms of the two +ailerons, so that motion is transmitted to both at +the same time, and by a positive motion in either +direction. + +_Fig. 65. Action of the Gyroscope._ + +In the second figure, 65, the frame of the aeroplane +is shown tilted at an angle, so that its right +side is elevated. As the gyroscopic wheel remains +level it causes the aileron on the right side to +change to a negative angle, while at the same +time giving a positive angle to the aileron on the +left side, which would, as a result, depress the +right side, and bring the frame of the machine +back to a horizontal position. + +FORE AND AFT GYROSCOPIC CONTROL.--It is +obvious that the same application of this force may +be applied to control the ship fore and aft, although +it is doubtful whether such a plan would +have any advantages, since this should be wholly +within the control of the pilot. + +Laterally the ship should not be out of balance; +fore and aft this is a necessity, and as the great +trouble with all aeroplanes is to control them +laterally, it may well be doubted whether it would +add anything of value to the machine by having +an automatic fore and aft control, which might, +in emergencies, counteract the personal control of +the operator. + +ANGLE INDICATOR.--In flight it is an exceedingly +difficult matter for the pilot to give an accurate +idea of the angle of the planes. If the air is +calm and he is moving over a certain course, and +knows, from experience, what his speed is, he may +be able to judge of this factor, but he cannot tell +what changes take place under certain conditions +during the flight. + +For this purpose a simple little indicator may +be provided, shown in Fig. 66, which is merely a +vertical board A, with a pendulum B, swinging +fore and aft from a pin a which projects out +from the board a short distance above its center. + +The upper end of the pendulum has a heart- +shaped wire structure D, that carries a sliding +weight E. Normally, when the aeroplane is on +an even keel, or is even at an angle, the weight +E rests within the bottom of the loop D, but +should there be a sudden downward lurch or a +quick upward inclination, which would cause the +pendulum below to rapidly swing in either +direction, the sliding weight E would at once move +forward in the same direction that the pendulum +had moved, and thus counteract, for the instant +only, the swing, when it would again drop back +into its central position. + +_Fig. 66. Angle Indicator._ + +With such an arrangement, the pendulum would +hang vertically at all times, and the pointer below, +being in range of a circle with degrees +indicated thereon, and the base attached to the +frame of the machine, can always be observed, +and the conditions noted at the time the changes +take place. + +PENDULUM STABILIZER.--In many respects the +use of a pendulum has advantages over the gyroscope. +The latter requires power to keep it in +motion. The pendulum is always in condition +for service. While it may be more difficult to +adjust the pendulum, so that it does not affect +the planes by too rapid a swing, or an oscillation +which is beyond the true angle desired, still, these +are matters which, in time, will make the pendulum +a strong factor in lateral stability. + +_Fig. 67. Simple Pendulum Stabilizer._ + +It is an exceedingly simple matter to attach the +lead wires from an aileron to the pendulum. In +Fig. 67 one plan is illustrated. The pendulum +A swings from the frame B of the machine, the +ailerons a being in this case also shown at right +angles to their true positions. + +The other, Fig. 68, assumes that the machine is +exactly horizontal, and as the pendulum is in a +vertical position, the forward edges of both ailerons +are elevated, but when the pendulum swings +both ailerons will be swung with their forward +margins up or down in unison, and thus the proper +angles are made to right the machine. + +STEERING AND CONTROLLING WHEEL.--For the +purpose of concentrating the control in a single +wheel, which has not alone a turning motion, but +is also mounted in such a manner that it will oscillate +to and fro, is very desirable, and is adapted +for any kind of machine. + +_Fig. 68. Pendulum Stabilizers._ + +Fig. 69 shows such a structure, in which A +represents the frame of the machine, and B a +segment for the stem of the wheel, the segment +being made of two parts, so as to form a guideway +for the stem a to travel between, and the segment +is placed so that the stem will travel in a +fore and aft direction. + +The lower end of the stem is mounted in a +socket, at D, so that while it may be turned, it +will also permit this oscillating motion. Near its +lower end is a cross bar E from which the wires +run to the vertical control plane, and also to the +ailerons, if the machine is equipped with them, or +to the warping ends of the planes. + +_Fig. 69. Steering and Control Wheel._ + +Above the cross arms is a loose collar F to +which the fore and aft cords are attached that go +to the elevators, or horizontal planes. The upper +end of the stem has a wheel G, which may also be +equipped with the throttle and spark levers. + +AUTOMATIC STABILIZING WINGS.--Unquestionably, +the best stabilizer is one which will act on +its own initiative. The difficulty with automatic +devices is, that they act too late, as a general +thing, to be effective. The device represented in +Fig. 70 is very simple, and in practice is found to +be most efficient. + +In this Fig. 70 A and B represent the upper +and the lower planes, respectively. Near the end +vertical standards a, D, are narrow wings E E, +F F, hinged on a fore and aft line close below +each of the planes, the wings being at such distances +from the standards C D that when they +swing outwardly they will touch the standards, +and when in that position will be at an angle of +about 35 degrees from the planes A B. + +_Fig. 70. Automatic Stabilizing Wings._ + +_Fig. 71. Action of Stabilizing Wings._ + +Inwardly they are permitted to swing up and +lie parallel with the planes, as shown in Fig. 71 +where the planes are at an angle. In turning, all +machines skid,--that is they travel obliquely +across the field, and this is also true when the +ship is sailing at right angles to the course of the +wind. + +This will be made clear by reference to Fig. +72, in which the dart A represents the direction +of the movement of the aeroplane, and B the +direction of the wind, the vertical rudder a being +almost at right angles to the course of the wind. + +_Fig. 72. Into the Wind at an Angle._ + +In turning a circle the same thing takes place +as shown in Fig. 73, with the tail at a different +angle, so as to give a turning movement to the +plane. It will be seen that in the circling movement +the tendency of the aeroplane is to fly out +at a tangent, shown by the line D, so that the +planes of the machine are not radially-disposed +with reference to the center of the circle, the line +E showing the true radial line. + +Referring now to Fig. 71, it will be seen that +this skidding motion of the machine swings the +wings E F inwardly, so that they offer no resistance +to the oblique movement, but the wings E +E, at the other end of the planes are swung outwardly, +to provide an angle, which tends to raise +up the inner end of the planes, and thereby seek +to keep the planes horizontal. + +_Fig. 73. Turning a Circle._ + +BAROMETERS.--These instruments are used for +registering heights. A barometer is a device for +measuring the weight or pressure of the air. +The air is supposed to extend to a height of 40 +miles from the surface of the sea. A column of +air one inch square, and forty miles high, weighs +the same as a column of mercury one inch square +and 30 inches high. + +Such a column of air, or of mercury, weighs +14 3/4 pounds. If the air column should be +weighed at the top of the mountain, that part +above would weigh less than if measured at the +sea level, hence, as we ascend or descend the pressure +becomes less or more, dependent on the altitude. + +Mercury is also used to indicate temperature, +but this is brought about by the expansive quality +of the mercury, and not by its weight. + +_Fig. 74. Aneroid Barometer._ + +ANEROID BAROMETER.--The term Aneroid barometer +is frequently used in connection with air- +ship experiments. The word aneroid means not +wet, or not a fluid, like mercury, so that, while +aneroid barometers are being made which do use +mercury, they are generally made without. + +One such form is illustrated in Fig. 74, which +represents a cylindrical shell A, which has at each +end a head of concentrically formed corrugations. +These heads are securely fixed to the ends of the +shell A. Within, one of the disk heads has a +short stem C, which is attached to the short end +of a lever D, this lever being pivoted at E. The +outer end of this lever is hinged to the short end +of another lever F, and so by compounding the +levers, it will be seen that a very slight movement +of the head B will cause a considerable movement +in the long end of the lever F. + +This end of the lever F connects with one limb +of a bell-crank lever G, and its other limb has a +toothed rack connection with a gear H, which +turns the shaft to which the pointer I is attached. + +Air is withdrawn from the interior of the shell, +so that any change in the pressure, or weight of +the atmosphere, is at once felt by the disk heads, +and the finger turns to indicate the amount of +pressure. + +HYDROPLANES.--Hydro means water, hence the +term hydroplane has been given to machines +which have suitable pontoons or boats, so they +may alight or initiate flight from water. + +There is no particular form which has been +adopted to attach to aeroplanes, the object generally +being to so make them that they will sustain +the greatest amount of weight with the least +submergence, and also offer the least resistance +while the motor is drawing the machine along the +surface of the water, preparatory to launching it. + +SUSTAINING WEIGHT OF PONTOONS.--A pontoon +having within nothing but air, is merely a measuring +device which determines the difference between +the weight of water and the amount placed +on the pontoon. Water weighs 62 1/2 pounds per +cubic foot. Ordinary wood, an average of 32 +pounds, and steel 500 pounds. + +It is, therefore, an easy matter to determine +how much of solid matter will be sustained by a +pontoon of a given size, or what the dimensions +of a pontoon should be to hold up an aeroplane +which weighs, with the pilot, say, 1100 pounds. + +As we must calculate for a sufficient excess to +prevent the pontoons from being too much immersed, +and also allow a sufficient difference in +weight so that they will keep on the surface when +the aeroplane strikes the surface in alighting, we +will take the figure of 1500 pounds to make the +calculations from. + +If this figure is divided by 62 1/2 we shall find +the cubical contents of the pontoons, not considering, +of course, the weight of the material of which +they are composed. This calculation shows that +we must have 24 cubic feet in the pontoons. + +As there should be two main pontoons, and a +smaller one for the rear, each of the main ones +might have ten cubic feet, and the smaller one +four cubic feet. + +SHAPES OF THE PONTOONS.--We are now ready +to design the shapes. Fig. 75 shows three general +types, A being made rectangular in form, +with a tapering forward end, so constructed as to +ride up on the water. + +The type B has a rounded under body, the forward +end being also skiff-shaped to decrease as +much as possible the resistance of the water impact. + +_Fig. 75. Hydroplane Floats._ + +The third type C is made in the form of a +closed boat, with both ends pointed, and the bottom +rounded, or provided with a keel. Or, as in +some cases the body may be made triangular in +cross section so that as it is submerged its sustaining +weight will increase at a greater degree +as it is pressed down than its vertical measurement +indicates. + +All this, however, is a matter left to the judgment +of the designer, and is, in a great degree, +dependent on the character of the craft to which +it is to be applied. + + + + +CHAPTER XII + +EXPERIMENTAL WORK IN FLYING + + +THE novice about to take his first trial trip in +an automobile will soon learn that the great task +in his mind is to properly start the machine. He +is conscious of one thing, that it will be an easy +matter to stop it by cutting off the fuel supply +and applying the brakes. + +CERTAIN CONDITIONS IN FLYING.--In an aeroplane +conditions are reversed. Shutting off the +fuel supply and applying the brakes only bring +on the main difficulty. He must learn to stop the +machine after all this is done, and this is the +great test of flying. It is not the launching,-- +the ability to get into the air, but the landing, that +gives the pupil his first shock. + +Man is so accustomed to the little swirls of air +all about him, that he does not appreciate what +they mean to a machine which is once free to +glide along in the little currents which are so unnoticeable +to him as a pedestrian. + +The contour of the earth, the fences, trees, little +elevations and other natural surroundings, all +have their effect on a slight moving air current, +and these inequalities affect the air and disturb +it to a still greater extent as the wind increases. +Even in a still air, with the sun shining, there are +air eddies, caused by the uneven heating of the +air in space. + +HEAT IN AIR.--Heat is transmitted through the +air by what is called convection, that is, the particles +of the air transmit it from one point to the +next. If a room is closed up tight, and a little +aperture provided so as to let in a streak of sunlight, +it will give some idea of the unrest of the +atmosphere. This may be exhibited by smoke +along the line of the sun's rays, which indicates +that the particles of air are constantly in motion, +although there may be absolutely nothing in the +room to disturb it. + +MOTION WHEN IN FLIGHT.--If you can imagine +a small airship floating in that space, you can +readily conceive that it will be hurled hither and +thither by the motion which is thus apparent to +the eye. + +This motion is greatly accentuated by the surface +of the earth, independently of its uneven contour. +If a ball is thrown through the air, its +dynamic force is measured by its impact. So +with light, and heat. In the space between the +planets it is very cold. The sunlight, or the rays +from the sun are there, just the same as on the +earth. + +Unless the rays come into contact with something, +they produce no effect. When the beams +from the sun come into contact with the atmosphere +a dynamic force is exerted, just the same +as when the ball struck an object. When the rays +reach the earth, reflection takes place, and these +reflected beams act on the air under different conditions. + +CHANGING ATMOSPHERE.--If the air is full of +moisture, as it may be at some places, while +comparatively dry at other points, the reflection +throughout the moist area is much greater than in +the dry places, hence evaporation will take place +and whenever a liquid vaporizes it means heat. + +On the other hand, when the vapor is turning +to a liquid, condensation takes place, and that +means cooling. If the air should be of the same +degree of saturation throughout,--that is, have +the same amount of moisture everywhere, there +would be few winds. These remarks apply to +conditions which exist over low altitudes all over +the earth. + +But at high altitudes the conditions are entirely +different. As we ascend the air becomes rarer. +It has less moisture, because a wet atmosphere, +being heavier, lies nearer the surface of the earth. +Being rarer the action of sunlight on the particles +is less intense. Reflection and refraction of the +rays acting on the light atmosphere do not produce +such a powerful effect as on the air near the +ground. + +All these conditions--the contour of the earth; +the uneven character of the moisture in the air; +the inequalities of the convection currents; and +the unstable, tenuous, elastic nature of the atmosphere, +make the trials of the aviator a hazardous +one, and it has brought out numerous theories +connected with bird flight. One of these assumes +that the bird, by means of its finely organized +sense, is able to detect rising air currents, and it +selects them in its flight, and by that means is enabled +to continue in flight indefinitely, by soaring, +or by flapping its wings. + +ASCENDING CURRENTS.--It has not been explained +how it happens that these particular "ascending +currents" always appear directly in the line of +the bird flight; or why it is that when, for instance, +a flock of wild geese which always fly through +space in an A-shaped formation, are able to get +ascending air currents over the wide scope of space +they cover. + +ASPIRATE CURRENTS.--Some years ago, in making +experiments with the outstretched wings of +one of the large soaring birds, a French sailor +was surprised to experience a peculiar pulling motion, +when the bird's wings were held at a certain +angle, so that the air actually seemed to draw it +into the teeth of the current. + +It is known that if a ball is suspended by a +string, and a jet of air is directed against it, in +a particular way, the ball will move toward the +jet, instead of being driven away from it. A well +known spraying device, called the "ball nozzle," +is simply a ball on the end of a nozzle, and the +stream of water issuing is not effectual to drive +the ball away. + +From the bird incident alluded to, a new theory +was propounded, namely, that birds flew because +of the aspirated action of the air, and the wings +and body were so made as to cause the moving air +current to act on it, and draw it forwardly. + +OUTSTRETCHED WINGS.--This only added to the +"bird wing" theory a new argument that all flying +things must have outstretched wings, in order +to fly, forgetting that the ball, which has no +outstretched wings, has also the same "aspirate" +movement attributed to the wings of the bird. + +The foregoing remarks are made in order to impress +on the novice that theories do not make +flying machines, and that speculations, or analogies +of what we see all about us, will not make an +aviator. A flying machine is a question of +dynamics, just as surely as the action of the sun on +the air, and the movements of the currents, and +the knowledge of applying those forces in the flying +machine makes the aviator. + +THE STARTING POINT.--Before the uninitiated +should attempt to even mount a machine he should +know what it is composed of, and how it is made. +His investigation should take in every part of the +mechanism; he should understand about the plane +surface, what the stresses are upon its surface, +what is the duty of each strut, or brace or wire +and be able to make the proper repairs. + +THE VITAL PART OF THE MACHINE.--The motor, +the life of the machine itself, should be like a +book to him. It is not required that he should +know all the theories which is necessary in the +building, as to the many features which go to +make up a scientifically-designed motor; but he +must know how and why it works. He should understand +the cam action, whereby the valves are +lifted at the proper time; what the effect of the +spark advance means; the throttling of the engine; +air admission and supply; the regulation +of the carbureter; its mechanism and construction; +the propeller should be studied, and its action +at various speeds. + +STUDYING THE ACTION OF THE MACHINE.--Then +comes the study on the seat of the machine itself. +It will be a novel sensation. Before him is the +steering wheel, if it should be so equipped. Turning +it to the right, swings the vertical tail plane +so the machine will turn to the right. Certainly, +he knows that; but how far must he turn the +wheel to give it a certain angle. + +It is not enough to know that a lever or a wheel +when moved a certain way will move a plane a +definite direction. He should learn to know +instinctively, how FAR a movement to make to get +a certain result in the plane itself, and under running +conditions, as well. + +Suppose we have an automobile, running at the +rate of ten miles an hour, and the chauffeur turns +the steering wheel ten degrees. He can do so with +perfect safety; but let the machine be going forty +miles an hour, and turn the wheel ten degrees, +and it may mean an accident. In one case the +machine is moving 14 1/2 feet a second, and in the +other instance 58 feet. + +If the airship has a lever for controlling the +angle of flight, he must study its arrangement, +and note how far it must be moved to assume +the proper elevating angle. Then come the means +for controlling the lateral stability of the machine. +All these features should be considered and studied +over and over, until you have made them your +friends. + +While thus engaged, you are perfectly sure that +you can remember and act on a set of complicated +movements. You imagine that you are skimming +over the ground, and your sense tells you that you +have sufficient speed to effect a launching. In +your mind the critical time has come. + +ELEVATING THE MACHINE.--Simply give the elevator +lever the proper angle, sharp and quick and +up you go. As the machine responds, and you can +feel the cushioning motion, which follows, as it begins +to ride the air, you are aware of a sensation +as though the machine were about to turn over +to one side; you think of the lateral control at +once, but in doing so forget that the elevator must +be changed, or you will go too high. + +You forget about the earth; you are too busy +thinking about several things which seem to need +your attention. Yes, there are a variety of matters +which will crowd upon you, each of which require +two things; the first being to get the proper +lever, and the second, to move it just so far. + +In the early days of aeroplaning, when accidents +came thick and fast, the most usual explanation +which came from the pilot, when he recovered, +was: "I pushed the lever too far." + +Hundreds of trial machines were built, when +man learned that he could fly, and in every instance, +it is safe to say, the experimenter made the +most strenuous exertion to get up in the air the +first time the machine was put on the trial ground. + +It is a wonder that accidents were not recorded +by the hundreds, instead of by the comparatively +few that were heard from. It was very discouraging, +no doubt, that the machines would not fly, +but that all of them, if they had sufficient power, +would fly, there can be no doubt. + +HOW TO PRACTICE.--Absolute familiarity with +every part of the machine and conditions is the +first thing. The machine is brought out, and the +engine tested, the machine being held in leash +while this is done. It is then throttled down so +that the power of the engine will be less than is +necessary to raise the machine from the ground. + +THE FIRST STAGE.--Usually it will require over +25 miles an hour to raise the machine. The engine +is set in motion, and now, for the first time a new +sensation takes possession of you, for the reason +that you are cut off from communication with +those around you as absolutely as though they +were a hundred miles away. + +This new dependence on yourself is, in itself, +one of the best teachers you could have, because +it begins to instill confidence and control. As the +machine darts forward, going ten or fifteen miles +an hour, with the din of the engine behind you, +and feeling the rumbling motion of the wheels +over the uneven surface of the earth, you have the +sensation of going forty miles an hour. + +The newness of the first sensation, which is +always under those conditions very much augmented +in the mind, wears away as the machine +goes back and forth. There is only one control +that requires your care, namely, to keep it on a +straight course. This is easy work, but you are +learning to make your control a reflex action,--to +do it without exercising a distinct will power. + +PATIENCE THE MOST DIFFICULT THING.--If you +have the patience, as you should, to continue this +running practice, until you absolutely eliminate +the right and left control, as a matter of thought, +occasionally, if the air is still turning the machine, +and eventually, bringing it back, by turning +it completely around, while skimming the ground, +you will be ready for the second stage in the +trials. + +THE SECOND STAGE.--The engine is now arranged +so that it will barely lift, when running +at its best. After the engine is at full speed, and +you are sure the machine is going fast enough, +the elevator control is turned to point the machine +in the air. It is a tense moment. You are on the +alert. + +The elevator is turned, and the forward end +changes its relation with the ground before you. +There was a slight lift, but your caution induces +you to return the planes to their normal running +angle. You try it again. You are now certain +that the machine made a leap and left the ground. +This is the exhilarating moment. + +With a calm air the machine is turned while +running, by means of the vertical rudders. This +is an easy matter, because while going at twenty +miles an hour, the weight of the machine on the +surface of the ground is less than one-tenth of its +weight when at rest. + +Thus the trial spins, half the time in the air, +in little glides of fifty to a hundred feet, increasing +in length, give practice, practice, PRACTICE, +each turn of the field making the sport less exciting +and fixing the controls more perfectly in the +mind. + +THE THIRD STAGE.--Thus far you have been +turning on the ground. You want to turn in the +air. Only the tail control was required while on +the ground. Now two things are required after +you leave the ground in trying to make a turn: +namely, putting the tail at the proper angle, and +taking charge of the stabilizers, because in making +the turn in the air, the first thing which will +arrest the attention will be the tendency of the +machine to turn over in the direction that you are +turning. + +After going back and forth in straight-away +glides, until you have perfect confidence and full +control, comes the period when the turns should +be practiced on. These should be long, and tried +only on that portion of the field where you have +plenty of room. + +OBSERVATIONS WHILE IN FLIGHT.--If there are +any bad spots, or trees, or dangerous places, they +should be spotted out, and mentally noted before +attempting to make any flight. When in the air +during these trials you will have enough to occupy +your mind without looking out for the hazardous +regions at the same time. + +Make the first turns in a still air. If you should +attempt to make the first attempts with a wind +blowing you will find a compound motion that will +very likely give you a surprise. In making the +first turn you will get the sensation of trying to +fly against a wind. Assuming that you are turning +to the left, it will have the sensation of a wind +coming to you from the right. + +FLYING IN A WIND.--Suppose you are flying directly +in the face of a wind, the moment you begin +to turn the action, or bite of the wind, will cause +the ends of the planes to the right to be unduly +elevated, much more so than if the air should be +calm. This raising action will be liable to startle +you, because up to this time you have been accustomed +to flying along in a straight line. + +While flying around at the part of the circle +where the wind strikes you directly on the right +side the machine has a tendency to climb, and you +try to depress the forward end, but as soon as you +reach that part of the circle where the winds begin +to strike on your back, an entirely new thing +occurs. + +As the machine is now traveling with the wind, +its grip on the air is less, and since the planes were +set to lower the machine, at the first part of the +turn, the descent will be pretty rapid unless the +angle is corrected. + +FIRST TRIALS IN QUIET ATMOSPHERE.--All this +would be avoided if the first trials were made in +a quiet atmosphere. Furthermore, you will be +told that in making a turn the machine should be +pointed downwardly, as though about to make a +glide. This can be done with safety, in a still +air, although you may be flying low, but it would +be exceedingly dangerous with a wind blowing. + +MAKING TURNS.--When making a turn, under no +circumstances try to make a landing. This +should never be done except when flying straight, +and then safety demands that the landing should +be made against the wind and not with it. There +are two reasons for this: First, when flying with +the wind the speed must be greater than when flying +against it. + +By greater speed is meant relative to the earth. +If the machine has a speed of thirty miles an hour, +in still air, the speed would be forty miles an hour +going with the wind, but only twenty miles against +the wind. Second, the banking of the planes +against the air is more effective when going into +the wind than when traveling with it, and, therefore, +the speed at which you contact with the earth +is lessened to such an extent that a comparatively +easy landing is effected. + +THE FOURTH STAGE.--After sufficient time has +been devoted to the long turns shorter turns may +be made, and these also require the same care, +and will give an opportunity to use the lateral +controls to a greater extent. Begin the turns, not +by an abrupt throw of the turning rudder, but +bring it around gently, correcting the turning +movement to a straight course, if you find the +machine inclined to tilt too much, until you get used +to the sensation of keeling over. Constant practice +at this will soon give confidence, and assure +you that you have full control of the machine. + +THE FIGURE 8.--You are now to increase the +height of flying, and this involves also the ability +to turn in the opposite direction, so that you may +be able to experience the sensation of using the +stabilizers in the opposite direction. You will +find in this practice that the senses must take in +the course of the wind from two quarters now, as +you attempt to describe the figure 8. + +This is a test which is required in order to obtain +a pilot's license. It means that you shall +be able to show the ability to turn in either direction +with equal facility. To keep an even flying +altitude while describing this figure in a wind, is +the severest test that can be exacted. + +THE VOLPLANE.--This is the technical term for +a glide. Many accidents have been recorded owing +to the stopping of the motor, which in the +past might have been avoided if the character of +the glide had been understood. The only thing +that now troubles the pilot when the engine "goes +dead," is to select a landing place. + +The proper course in such a case is to urge +the machine to descend as rapidly as possible, in +order to get a headway, for the time being. As +there is now no propelling force the glide is depended +upon to act as a substitute. The experienced +pilot will not make a straight-away glide, +but like the vulture, or the condor, and birds of +that class, soar in a circle, and thus, by passing +over and over the same surfaces of the earth, enable +him to select a proper landing place. + +THE LANDING.--The pilot who can make a good +landing is generally a good flyer. It requires +nicety of judgment to come down properly. One +thing which will appear novel after the first altitude +flights are attempted is the peculiar sensation +of the apparently increased speed as the earth +comes close up to the machine. + +At a height of one hundred feet, flying thirty +miles an hour, does not seem fast, because the surface +of the earth is such a distance away that particular +objects remain in view for some moments; +but when within ten feet of the surface the same +object is in the eye for an instant only. + +This lends a sort of terror to the novice. He +imagines a great many things, but forgets some +things which are very important to do at this +time. One is, that the front of the machine must +be thrown up so as to bank the planes against the +wind. The next is to shut off the power, which +is to be done the moment the wheels strike the +ground, or a little before. + +Upon his judgment of the time of first touching +the earth depends the success of safely alighting. +He may bank too high, and come down on the tail +with disastrous results. If there is plenty of field +room it is better to come down at a less angle, or +even keep the machine at an even keel, and the +elevator can then depress the tail while running +over the ground, and thus bring the machine to +rest. + +Frequently, when about to land the machine +will rock from side to side. In such a case it is +far safer to go up into the air than to make the +land, because, unless the utmost care is exercised, +one of the wing tips will strike the earth and +wreck the machine. + +Another danger point is losing headway, as the +earth is neared, due to flying at too flat an angle, +or against a wind that happens to be blowing particularly +hard at the landing place. If the motor +is still going this does not make so much difference, +but in a volplane it means that the descent +must be so steep, at the last moment of flight, that +the chassis is liable to be crushed by the impact. + +FLYING ALTITUDE.--It is doubtful whether the +disturbed condition of the atmosphere, due to +the contour of the earth's surface, reaches higher +than 500 feet. Over a level area it is certain that +it is much less, but in some sections of the country, +where the hill ranges extend for many miles, +at altitudes of three and four hundred feet, the +upper atmosphere may be affected for a thousand +feet above. + +Prof. Lowe, in making a flight with a balloon, +from Cincinnati to North Carolina, which lasted +a day and all of one night, found that during the +early morning the balloon, for some reason, began +to ascend, and climbed nearly five thousand +feet in a few hours, and as unaccountably +began to descend several hours before he landed. + +Before it began to ascend, he was on the western +side of the great mountain range which extends +south from Pennsylvania and terminates in +Georgia. He was actually climbing the mountain +in a drift of air which was moving eastwardly, +and at no time was he within four thousand feet +of the earth during that period, which shows that +air movements are of such a character as to exert +their influence vertically to great heights. + +For cross country flying the safest altitude is +1000 feet, a distance which gives ample opportunity +to volplane, if necessary, and it is a height +which enables the pilot to make observations of the +surface so as to be able to judge of its character. + +But explanations and statements, and the experiences +of pilots might be detailed in pages, and +still it would be ineffectual to teach the art of flying. +The only sure course is to do the work on +an actual machine. + +Many of the experiences are valuable to the +learner, some are merely in the nature of cautions, +and it is advisable for the beginner to learn what +the experiences of others have been, although they +may never be called upon to duplicate them. + +All agree that at great elevations the flying +conditions are entirely different from those met +with near the surface of the ground, and the history +of accidents show that in every case where +a mishap was had at high altitude it came about +through defect in the machine, and not from gusts +or bad air condition. + +On the other hand, the uptilting of machines, +the accidents due to the so-called "Holes in the +air," which have dotted the historic pages with +accidents, were brought about at low altitudes. + +At from two to five thousand feet the air may be +moving at speeds of from twenty to forty miles +an hour,--great masses of winds, like the trade +stream, which are uniform over vast areas. To +the aviator flying in such a field, with the earth +hidden from him, there would be no wind to indicate +that he was moving in any particular direction. + +He would fly in that medium, in any direction, +without the slightest sense that he was in a gale. +It would not affect the control of the machine, +because the air, though moving as a mass, would +be the same as flying in still air. It is only when +he sees fixed objects that he is conscious of the +movement of the wind. + + + +CHAPTER XIII + +THE PROPELLER + + +BY far the most difficult problem connected +with aviation is the propeller. It is the one great +vital element in the science and art pertaining to +this subject which has not advanced in the slightest +degree since the first machine was launched. + +The engine has come in for a far greater share +of expert experimental work, and has advanced +most rapidly during the past ten years. But, +strange to say, the propeller is, essentially, the +same with the exception of a few small changes. + +PROPELLER CHANGES.--The changes which have +been made pertaining to the form of structure, +principally, and in the use of new materials. The +kind of wood most suitable has been discovered, +but the lines are the same, and nothing has been +done to fill the requirement which grows out of +the difference in speed when a machine is in the +act of launching and when it is in full flight. + +PROPELLER SHAPE.--It cannot be possible that +the present shape of the propeller will be its ultimate +form. It is inconceivable that the propeller +is so inefficient that only one sixty-fifth of the +power of the engine is available. The improvement +in propeller efficiency is a direction which +calls for experimental work on the part of inventors +everywhere. + +The making of a propeller, although it appears +a difficult task, is not as complicated as would appear, +and with the object in view of making the +subject readily understood, an explanation will be +given of the terms "Diameter," and "Pitch," as +used in the art. + +The Diameter has reference to the length of +the propeller, from end to end. In calculating +propeller pull, the diameter is that which indicates +the speed of travel, and for this reason is +a necessary element. + +Thus, for instance, a propeller three feet in +diameter, rotating 500 times a minute, has a tip +speed of 1500 feet, whereas a six foot propeller, +rotating at the same speed, moves 3000 feet at the +tips. + +PITCH.--This is the term which is most confusing, +and is that which causes the most frequent +trouble in the mind of the novice. The term will +be made clear by carefully examining the accompanying +illustration and the following description: + +In Fig. 76 is shown a side view of a propeller +A, mounted on a shaft B, which is free to move +longitudinally. Suppose we turn the shaft so the +tip will move along on the line indicated by the +arrow C. + +Now the pitch of the blade at D is such that it +will be exactly in line with the spirally-formed +course E, for one complete turn. As the propeller +shaft has now advanced, along the line E, and +stopped after one turn, at F, the measure between +the points F and G represents the pitch of the propeller. +Another way to express it would be to +call the angle of the blade a five, or six, or a seven +foot pitch, as the pitches are measured in feet. + +_Fig. 76. Describing the Pitch Line._ + +In the illustration thus given the propeller shaft, +having advanced six feet, we have what is called +a six foot pitch. + +Now, to lay out such a pitch is an easy matter. +Assume, as in Fig. 77, that A represents the end +of the blank from which the propeller is to be cut, +and that the diameter of this blank, or its length +from end to end is seven feet. The problem now +is to cut the blades at such an angle that we shall +have a six foot pitch. + +_Fig. 77. Laying out the Pitch._ + +LAYING OUT THE PITCH.--First, we must get the +circumference of the propeller, that is, the distance +the tip of the propeller will travel in making +one complete turn. This is done by multiplying +7 by 3.1416. This equals 21.99, or, practically, 22 +feet. + +A line B is drawn, extending out horizontally +along one side of the blank A, this line being made +on a scale, to represent 22 feet. Secondly, at the +end of this line drawn a perpendicular line C, 6 +feet long. A perpendicular line is always one +which is at right angles to a base line. In this +case B is the base line. + +Line C is made 6 feet long, because we are trying +to find the angle of a 6 foot pitch. If, now, a +line D is drawn from the ends of the two lines B, +C, it will represent the pitch which, marked across +the end of the blank A, will indicate the line to cut +the blade. + +PITCH RULE.--The rule may, therefore, be +stated as follows: Multiply the diameter (in +feet) of the propeller by 3.1416, and draw a line +the length indicated by the product. At one end +of this line draw a perpendicular line the length +of the pitch requirement (in feet), and join the +ends of the two lines by a diagonal line, and this +line will represent the pitch angle. + +Propellers may be made of wood or metal, the +former being preferred for the reason that this +material makes a lighter article, and is stronger, +in some respects, than any metal yet suggested. + +LAMINATED CONSTRUCTION.--All propellers +should be laminated,--that is, built up of layers +of wood, glued together and thoroughly dried, +from which the propeller is cut. + +A product thus made is much more serviceable +than if made of one piece, even though the laminated +parts are of the same wood, because the +different strips used will have their fibers overlapping +each other, and thus greatly augment the +strength of the whole. + +Generally the alternate strips are of different +materials, black walnut, mahogany, birch, spruce, +and maple being the most largely used, but mahogany +and birch seem to be mostly favored. + +LAYING UP A PROPELLER FORM.--The first step +necessary is to prepare thin strips, each, say, +seven feet long, and five inches wide, and three- +eighths of an inch thick. If seven such pieces are +put together, as in Fig. 78, it will make an assemblage +of two and five-eighth inches high. + +_Fig. 78. A Laminated Blank._ + +Bore a hole centrally through the assemblage, +and place therein a pin B. The contact faces of +these strips should be previously well painted +over with hot glue liberally applied. When they +are then placed in position and the pin is in place, +the ends of the separate pieces are offset, one beyond +the other, a half inch, as shown, for instance, +in Fig. 79. + +This will provide ends which are eight and a +half inches broad, and thus furnish sufficient +material for the blades. The mass is then subjected +to heavy pressure, and allowed to dry before the +blades are pared down. + +_Fig. 79. Arranging the Strips._ + +MAKING WIDE BLADES.--If a wider blade is desired, +a greater number of steps may be made by +adding the requisite number of strips; or, the +strips may be made thicker. In many propellers, +not to exceed four different strips are thus glued +together. The number is optional with the +maker. + +An end view of such an assemblage of strips +is illustrated in Fig. 80. The next step is to lay +off the pitch, the method of obtaining which has +been explained. + +_Fig. 80. End view of Blank._ + +Before starting work the sides, as well as the +ends, should be marked, and care observed to +place a distinctive mark on the front side of the +propeller. + +Around the pin B, Fig. 81, make S-shaped +marks C, to indicate where the cuts on the faces +of the blades are to begin. Then on the ends of +the block; scribe the pitch angle, which is indicated +by the diagonal line D, Fig. 80. + +_Fig. 81. Marking the Side._ + +This line is on the rear side of the propeller, +and is perfectly straight. Along the front of this +line is a bowline E, which indicates the front surface +of the propeller blade. + +PROPELLER OUTLINE.--While the marks thus +given show the angles, and are designed to indicate +the two faces of the blades, there is still another +important element to be considered, and +that is the final outline of the blades. + +_Fig. 82. Outlining._ + +It is obvious that the outline may be varied +so that the entire width at 1, Fig. 82, may be used, +or it may have an outline, as represented by the +line 2, in this figure, so that the widest part will +be at or near the dotted line 3, say two-thirds of +the distance from the center of the blade. + +This is the practice with most of the manufacturers +at the present time, and some of them +claim that this form produces the best results. + +FOR HIGHER SPEEDS.--Fig. 83 shows a propeller +cut from a blank, 4" x 6" in cross section, not +laminated. + +_Fig. 83. Cut from a 4" x 6" Single Blank._ + +It should be borne in mind that for high speeds +the blades must be narrow. A propeller seven +feet in diameter with a six foot pitch, turning +950 revolutions per minute, will produce a pull of +350 pounds, if properly made. + +Such a propeller can be readily handled by a +forty horse power motor, such as are specially +constructed for flying machine purposes. + +INCREASING PROPELLER EFFICIENCY.--Some experiments +have been made lately, which, it is +claimed, largely increase the efficiency of propellers. +The improvement is directed to the outline +shape of the blade. + +The typical propeller, such as we have illustrated, +is one with the wide part of the blade at +the extremity. The new type, as suggested, reverses +this, and makes the wide part of the blade +near the hub, so that it gradually tapers down to +a narrow tip. + +Such a form of construction is shown in Fig. +84. This outline has some advantages from one +standpoint, namely, that it utilizes that part of +the blade near the hub, to produce a pull, and +does not relegate all the duty to the extreme ends +or tips. + +_Fig. 84. A Suggested Form._ + +To understand this more fully, let us take a +propeller six feet in diameter, and measure the +pull or thrust at the tips, and also at a point half +way between the tip and the hub. + +In such a propeller, if the blade is the same +width and pitch at the two points named, the pull +at the tips will be four times greater than at the +intermediate point. + + + +CHAPTER XIV + +EXPERIMENTAL GLIDERS AND MODEL AEROPLANES + + +AN amusing and very instructive pastime is +afforded by constructing and flying gliding machines, +and operating model aeroplanes, the latter +being equipped with their own power. + +Abroad this work has been very successful as +a means of interesting boys, and, indeed, men +who have taken up the science of aviation are +giving this sport serious thought and study. + +When a machine of small dimensions is made +the boy wonders why a large machine does not +bear the same relation in weight as a small machine. +This is one of the first lessons to learn. + +THE RELATION OF MODELS TO FLYING MACHINES. +--A model aeroplane, say two feet in length, which +has, we will assume, 50 square inches of supporting +surface, seems to be a very rigid structure, +in proportion to its weight. It may be dropped +from a considerable height without injuring it, +since the weight is only between two and three +ounces. + +An aeroplane twenty times the length of this +model, however strongly it may be made, if +dropped the same distance, would be crushed, and +probably broken into fragments. + +If the large machine is twenty times the dimensions +of the small one, it would be forty feet in +length, and, proportionally, would have only +seven square feet of sustaining surface. But an +operative machine of that size, to be at all rigid, +would require more than twenty times the material +in weight to be equal in strength. + +It would weigh about 800 pounds, that is, 4800 +times the weight of the model, and instead of +having twenty times the plane surface would require +one thousand times the spread. + +It is this peculiarity between models and the +actual flyers that for years made the question of +flying a problem which, on the basis of pure calculation +alone, seemed to offer a negative; and +many scientific men declared that practical flying +was an impossibility. + +LESSONS FROM MODELS.--Men, and boys, too, +can learn a useful lesson from the model aeroplanes +in other directions, however, and the principal +thing is the one of stability. + +When everything is considered the form or +shape of a flying model will serve to make a large +flyer. The manner of balancing one will be a +good criterion for the other in practice, and +experimenting with these small devices is, therefore, +most instructive. + +The difference between gliders and model aeroplanes +is, that gliders must be made much lighter +because they are designed to be projected through +the air by a kick of some kind. + +FLYING MODEL AEROPLANES.--Model aeroplanes +contain their own power and propellers which, +while they may run for a few seconds only, serve +the purpose of indicating how the propeller will +act, and in what respect the sustaining surfaces +are efficient and properly arranged. + +It is not our purpose to give a treatise on this +subject but to confine this chapter to an exposition +of a few of the gliders and model forms which +are found to be most efficient for experimental +work. + +AN EFFICIENT GLIDER.--Probably the simplest +and most efficient glider, and one which can be +made in a few moments, is to make a copy of the +deltoid kite, previously referred to. + +This is merely a triangularly-shaped piece of +paper, or stiff cardboard A, Fig. 84, creased in +the middle, along the dotted line B, the side wings +C, C, being bent up so as to form, what are called +diedral angles. This may be shot through the +air by a flick of the finger, with the pointed end +foremost, when used as a glider. + +_Fig. 85. Deltoid Glider._ + +THE DELTOID FORMATION.--This same form may +be advantageously used as a model aeroplane, but +in that case the broad end should be foremost. + +_Fig. 86. The Deltoid Racer._ + +Fig. 86 shows the deltoid glider, or aeroplane, +with three cross braces, A, B, C, in the two forward +braces of which are journaled the propeller +shaft D, so that the propeller E is at the broad +end of the glider. + +A short stem F through the rear brace C, provided +with a crank, has its inner end connected +with the rear end of the shaft D by a rubber band +G, by which the propeller is driven. + +A tail may be attached to the rear end, or at +the apex of the planes, so it can be set for the +purpose of directing the angle of flight, but it will +be found that this form has remarkable stability +in flight, and will move forwardly in a straight +line, always making a graceful downward movement +when the power is exhausted. + +It seems to be a form which has equal stabilizing +powers whether at slow or at high speeds, +thus differing essentially from many forms which +require a certain speed in order to get the best +results. + +RACING MODELS.--Here and in England many +racing models have been made, generally of the +A-shaped type, which will be explained hereinafter. +Such models are also strong, and able to +withstand the torsional strain required by the +rubber which is used for exerting the power. + +It is unfortunate that there is not some type of +cheap motor which is light, and adapted to run +for several minutes, which would be of great value +in work of this kind, but in the absence of such +mechanism rubber bands are found to be most +serviceable, giving better results than springs or +bows, since the latter are both too heavy to be +available, in proportion to the amount of power +developed. + +Unlike the large aeroplanes, the supporting +surfaces, in the models, are at the rear end of +the frames, the pointed ends being in front. + +_Fig. 87. A-Shaped Racing Glider._ + +Fig. 87 shows the general design of the A- +shaped gliding plane or aeroplane. This is composed +of main frame pieces A, A, running fore +and aft, joined at their rear ends by a cross bar +B, the ends of which project out slightly beyond +their juncture with the side bars A, A. These +projecting ends have holes drilled therein to receive +the shafts a, a, of the propeller D, D. + +A main plane E is mounted transversely across +this frame at its rear end, while at its forward +end is a small plane, called the elevator. The +pointed end of the frame has on each side a turnbuckle +G, for the purpose of winding up the shaft, +and thus twisting the propeller, although this is +usually dispensed with, and the propeller itself +is turned to give sufficient twist to the rubber for +this purpose. + +THE POWER FOR MODEL AEROPLANES.--One end +of the rubber is attached to the hook of the shaft +C, and the other end to the hook or to the turnbuckle +G, if it should be so equipped. + +The rubbers are twisted in opposite directions, +to correspond with the twist of the propeller +blades, and when the propellers are permitted to +turn, their grip on the air will cause the model to +shoot forwardly, until the rubbers are untwisted, +when the machine will gradually glide to the +ground. + +MAKING THE PROPELLER.--These should have +the pitch uniform on both ends, and a simple +little device can be made to hold the twisted blade +after it has been steamed and bent. Birch and +holly are good woods for the blades. The strips +should be made thin and then boiled, or, what is +better still, should be placed in a deep pan, and +held on a grid above the water, so they will be +thoroughly steamed. + +They are then taken out and bent by hand, or +secured between a form specially prepared for +the purpose. The device shown in Fig. 88 shows +a base board which has in the center a pair of +parallel pins A, A, slightly separated from each +other. + +_Fig. 88. Making the Propeller._ + +At each end of the base board is a pair of holes +C, D, drilled in at an angle, the angles being the +pitch desired for the ends of the propeller. In +one of these holes a pin E is placed, so the pins +at the opposite ends project in different directions, +and the tips of the propeller are held +against the ends of these pins, while the middle +of the propeller is held between the parallel pins +A, A. + +The two holes, at the two angles at the ends of +the board, are for the purpose of making right +and left hand propellers, as it is desirable to use +two propellers with the A-shaped model. Two +propellers with the deltoid model are not so necessary. + +After the twist is made and the blade properly +secured in position it should be allowed to thoroughly +dry, and afterwards, if it is coated with +shellac, will not untwist, as it is the changing +character of the atmosphere which usually causes +the twisted strips to change their positions. +Shellac prevents the moist atmosphere from affecting +them. + +MATERIAL FOR PROPELLERS.--Very light propellers +can also be made of thin, annealed aluminum +sheets, and the pins in that case will serve as +guides to enable you to get the desired pitch. +Fiber board may also be used, but this is more +difficult to handle. + +Another good material is celluloid sheets, +which, when cut into proper strips, is dipped in +hot water, for bending purposes, and it readily +retains its shape when cooled. + +RUBBER--Suitable rubber for the strips are +readily obtainable in the market. Experiment +will soon show what size and lengths are best +adapted for the particular type of propellers +which you succeed in making. + +PROPELLER SHAPE AND SIZE.--A good proportion +of propeller is shown in Fig. 89. This also +shows the form and manner of connecting the +shaft. The latter A has a hook B on one end to +which the rubber may be attached, and its other +end is flattened, as at C, and secured to the blade +by two-pointed brads D, clinched on the other +side. + +_Fig. 89. Shape and Size._ + +The collar E is soldered on the shaft, and in +practice the shaft is placed through the bearing +hole at the end of the frame before the hook is +bent. + +SUPPORTING SURFACES.--The supporting surfaces +may be made perfectly flat, although in this +particular it would be well to observe the rules +with respect to the camber of large machines. + + + +CHAPTER XV + +THE AEROPLANE IN THE GREAT WAR + + +DURING the civil war the Federal forces used +captive balloons for the purpose of discovering +the positions of the enemy. They were of great +service at that time, although they were stationed +far within the lines to prevent hostile guns from +reaching them. + +BALLOON OBSERVATIONS.--Necessarily, observations +from balloons were and are imperfect. It +was found to be very unsatisfactory during the +Russian-Japanese war, because the angle of vision +is very low, and, furthermore, at such distances the +movements, or even the location of troops is not +observable, except under the most favorable conditions. + +Balloon observation during the progress of a +battle is absolutely useless, because the smoke +from the firing line is, necessarily, between the +balloon and the enemy, so that the aerial scout +has no opportunity to make any observations, even +in detached portions of the fighting zone, which +are of any value to the commanders. + +CHANGED CONDITIONS OF WARFARE.--Since our +great war, conditions pertaining to guns have been +revolutionized. Now the ranges are so great that +captive balloons would have to be located far in +the rear, and at such a great distance from the +firing line that even the best field glasses would +be useless. + +The science of war has also evolved another +condition. Soldiers are no longer exposed during +artillery attacks. Uniforms are made to imitate +natural objects. The khaki suits were designed +to imitate the yellow veldts of South Africa; +the gray-green garments of the German +forces are designed to simulate the green fields +of the north. + +THE EFFORT TO CONCEAL COMBATANTS.--The +French have discarded the historic red trousers, +and the elimination of lace, white gloves, and +other telltale insignias of the officers, have been +dispensed with by special orders. + +In the great European war armies have burrowed +in the earth along battle lines hundreds of +miles in length; made covered trenches; prepared +artificial groves to conceal batteries, and in many +ingenious ways endeavored to make the battlefield +an imitation field of nature. + +SMOKELESS POWDER.--While smokeless powder +has been utilized to still further hide a fighting +force, it has, in a measure, uncovered itself, as +the battlefield is not now, as in olden times, overspread +with masses of rolling smoke. + +Nevertheless, over every battlefield there is a +haze which can be penetrated only from above, +hence the possibilities of utilizing the aeroplane +in war became the most important study with all +nations, as soon as flying became an accomplished +fact. + +INVENTIONS TO ATTACK AERIAL CRAFT.--Before +any nation had the opportunity to make an actual +test on the battlefield, inventors were at work to +devise a means whereby an aerial foe could be +met. In a measure the aerial gun has been successful, +but months of war has shown that the +aeroplane is one of the strongest arms of the +service in actual warfare. + +It was assumed prior to the European war that +the chief function of the aeroplane would be the +dropping of bombs,--that is for service in attacking +a foe. Actual practice has not justified +this theory. In some places the appearance of +the aeroplane has caused terror, but it has been +found the great value is its scouting advantages. + +FUNCTION OF THE AEROPLANE IN WAR.--While +bomb throwing may in the future be perfected, +it is not at all an easy problem for an aviator to +do work which is commensurate with the risk +involved. The range is generally too great; the +necessity of swift movement in the machine too +speedy to assure accuracy, and to attack a foe at +haphazard points can never be effectual. Even +the slowly-moving gas fields, like the Zeppelin, +cannot deliver bombs with any degree of precision +or accuracy. + +BOMB-THROWING TESTS.--It is interesting, however, +to understand how an aviator knows where +or when to drop the bomb from a swiftly-moving +machine. Several things must be taken into consideration, +such as the height of the machine from +the earth; its speed, and the parabolic curve that +the bomb will take on its flight to the earth. + +When an object is released from a moving machine +it will follow the machine from which it is +dropped, gradually receding from it, as it descends, +so that the machine is actually beyond +the place where the bomb strikes the earth, due +to the retarding motion of the atmosphere against +the missile. + +The diagram Fig. 90 will aid the boy in grasping +the situation. A is the airship; B the path +of its flight; a the course of the bomb after it +leaves the airship; and D the earth. The question +is how to determine the proper movement +when to release the bomb. + +METHOD FOR DETERMINING MOVEMENT OF A +BOMB.--Lieut. Scott, U. S. A., of the Coast Survey +Artillery, suggested a method for determining +these questions. It was necessary to ascertain, +first, the altitude and speed. While the barometer +is used to determine altitudes, it is +obvious that speed is a matter much more difficult +to ascertain, owing to the wind movements, +which in all cases make it difficult for a flier to +determine, even with instruments which have +been devised for the purpose. + +_Fig. 90. Course of a Bomb._ + +Instead, therefore, of relying on the barometer, +the ship is equipped with a telescope which may +be instantly set at an angle of 45 degrees, or vertically. + +Thus, Fig 91 shows a ship A, on which is +mounted a telescope B, at an angle of 45 degrees. +The observer first notes the object along the line +of 45 degrees, and starts the time of this observation +by a stop watch. + +The telescope is then turned so it is vertical, +as at C, and the observer watches through the +telescope until the machine passes directly over +the object, when the watch is stopped, to indicate +the time between the two observations. + +_Fig. 91. Determining Altitude and Speed._ + +The height of the machine along the line D is +thus equal to the line E from B to C, and the time +of the flight from B to a being thus known, as +well as the height of the machine, the observer +consults specially-prepared tables which show +just what kind of a curve the bomb will make at +that height and speed. + +All that is necessary now is to set the sighter +of the telescope at the angle given in the tables, +and when the object to be hit appears at the sight, +the bomb is dropped. + +THE GREAT EXTENT OF MODERN BATTLE LINES.-- +The great war brought into the field such stupendous +masses of men that the battle lines have +extended over an unbroken front of over 200 +miles. + +In the battle of Waterloo, about 140,000 men +were engaged on both sides, and the battle front +was less than six miles. There were, thus massed, +along the front, over 20,000 men every mile of +the way, or 10,000 on each side. + +In the conflict between the Allies and the Germans +it is estimated that there were less than +7500 along each mile. It was predicted in the +earlier stages of the war that it would be an easy +matter for either side to suddenly mass such an +overwhelming force at one point as to enable the +attacking party to go through the opposing force +like a wedge. + +Such tactics were often employed by Napoleon +and other great masters of war; but in every effort +where it has been attempted in the present +conflict, it was foiled. + +The opposing force was ready to meet the attack +with equal or superior numbers. The eye +of the army, the aeroplane, detected the movements +in every instance. + +THE AEROPLANE DETECTING THE MOVEMENTS OF +ARMIES.--In the early stages of the war, when +the Germans drove the left of the French army +towards Paris, the world expected an investment +of that city. Suddenly, and for no apparent +reason, the German right was forced back and +commenced to retreat. + +It was not known until weeks afterwards that +the French had assembled a large army to the +west and northwest of Paris, ready to take the +Germans in flank the moment an attempt should +be made to encircle the Paris forts. + +The German aviators, flying over Paris, discovered +the hidden army, and it is well they did +so, for it is certain if they had surrounded the +outlying forts, it would have been an easy matter +for the concealed forces to destroy their communications, +and probably have forced the surrender +of a large part of the besiegers. + +The aeroplane in warfare, therefore, has constantly +noted every disposition of troops, located +the positions and judged the destination of convoys; +the battery emplacements; and the direction +in which large forces have been moved from +one part of the line to the other, thus keeping the +commanders so well informed that few surprises +were possible. + +THE EFFECTIVE HEIGHT FOR SCOUTING.--It has +been shown that aeroplane scouting is not effective +at high altitudes. It is not difficult for aviators +to reach and maintain altitudes of five thousand +feet and over, but at that elevation it is impossible +to distinguish anything but the movement +of large forces. + +SIZES OF OBJECTS AT GREAT DISTANCES.--At a +distance of one mile an automobile, twenty feet +in length, is about as large as a piece of pencil +one inch long, viewed at a distance of thirty-five +feet. A company of one hundred men, which in +marching order, say four abreast, occupies a space +of eight by one hundred feet, looks to the aviator +about as large as an object one inch in length, four +and a half feet from the eye. + +The march of such a body of men, viewed at +that distance, is so small as almost to be imperceptible +to the eye of an observer at rest. How +much more difficult it is to distinguish a movement +if the observer is in a rapidly-moving machine. + +For these reasons observations must be made +at altitudes of less than a mile, and the hazard +of these enterprises is, therefore, very great, +since the successful scout must bring himself +within range of specially designed guns, which +are effective at a range of 3000 yards or more, +knowing that his only hope of safety lies in the +chance that the rapidly-moving machine will avoid +the rain of bullets that try to seek him out. + +SOME DARING FEATS IN WAR.--It would be impossible +to recount the many remarkable aerial +fights which have taken place in the great war. +Some of them seem to be unreal, so startling are +the tales that have been told. We may well imagine +the bravery that will nerve men to fight +thousands of feet above the earth. + +One of the most thrilling combats took place +between a Russian aeroplane and a Zeppelin, over +Russian Poland, at the time of the first German +invasion. The Zeppelin was soaring over the +Russian position, at an altitude of about a mile. +A Russian aviator ascended and after circling +about, so as to gain a position higher than the +airship, darted down, and crashed into the great +gas field. + +The aviator knew that it meant death to him, +but his devotion led him to make the sacrifice. +The Zeppelin, broken in two, and robbed of its +gas, slowly moved toward the earth, then gradually +increased the speed of its descent, as the +aeroplane clung to its shattered hulk, and by the +time it neared the earth its velocity was great +enough to assure the destruction of all on board, +while the ship itself was crushed to atoms. + +One of the most spectacular fights of the war +occurred outside Paris, when one of the German +Taubes attempted to make its periodical tour +of observation. One of the French aeroplanes, +which had the advantage of greater speed, +mounted to a greater altitude, and circled about +the Taube. + +The latter with its machine gun made a furious +attack, during these maneuvers, but the French +ship did not reply until it was at such an elevation +that it could deliver the attack from above. +Then its machine gun was brought into play. As +was afterwards discovered, the wings and body +of the Taube were completely riddled, and it was +a marvel how it was possible for the German aviator +to remain afloat as long as he did. + +Soon the Taube was noticed to lurch from side +to side, and then dart downwardly. The monoplane, +in the pursuit, gradually descended, but it +was not able to follow the destroyed Taube to the +earth, as the latter finally turned over, and went +swirling to destruction. + +The observer, as well as the aviator, had both +been killed by the fire from the monoplane. + +In the trenches on the Marne, to the northeast +of Paris, where the most stubborn conflict raged +for over a week, the air was never clear of aeroplanes. +They could be seen in all directions, and +almost all types of machines were represented. +The principal ones, however, were monoplanes. + +THE GERMAN TAUBE.--The German Taube is a +monoplane, its main supporting surfaces, as well +as the tail planes, are so constructed that they +represent a bird. Taube means dove. It would +have been more appropriate to call it a hawk. + +On the other hand, the French monoplane, of +which the Bleriot is the best known example, has +wings with well rounded extremities, and flaring +tail, so that the two can be readily distinguished. + +On one occasion, during the lull in the battle, +two of the Taubes approached the area above the +French lines, and after ascending to a great +height, began the volplane toward their own lines. +Such a maneuver was found to be the most advantageous, +as it gave the scouting aeroplane the +advantage of being able to discover the positions +and movements with greater ease, and at the same +time, in case of accident to the machine, the impetus +of the flight would be to their own lines. + +Three of the French aeroplanes at once began +their circling flight, mounting higher and higher, +but without attempting to go near the Taubes. +When the French ships had gained the proper +altitude, they closed in toward the German ships, +before the latter could reach their own lines in +their volplaning act. + +This meant that they must retreat or fight, and +the crack of the guns showed that it meant a +struggle. The monoplanes circled about with +incredible skill, pouring forth shot after shot. +Soon one of the Taubes was seen to flutter. +This was the signal for a more concentrated attack +on her. + +The army in the trenches, and on the fields below, +witnessed the novel combat. The flying +ships were now approaching the earth, but the +gunners below dared not use their guns, because +in the maneuvers they would be as likely to strike +friend as foe. + +The wounded Taube was now shooting to the +earth, and the two monoplanes began to give their +attention to the other ship, which was attempting +to escape to the north. The flash of the guns of +all the fliers could be plainly seen, but the sounds +were drowned by the roar of the great conflict all +about them. + +The Taube could not escape the net around her. +She, too, was doomed. A shot seemed to strike +the gasoline tank, and the framework was soon +enveloped in flames. Then she turned sidewise, +as the material on one side burned away, and +skidding to the left she darted to the earth, +a shapeless mass. + +It was found that the aviator was not hurt by +the shot, but was, undoubtedly, killed by the impact +with the earth. The observer was riddled +with bullets, and was likely dead before the ship +reached the earth. + +In the western confines of Belgium, near Ypres, +the British employed numerous aircraft, many of +them biplanes, and at all times they were in the +air, reporting observations. Many of the flying +fights have been recorded, and the reports when +published will be most thrilling reading. + +HOW AEROPLANES REPORT OBSERVATIONS.--It +may be of some interest to know how aeroplanes +are able to report observations to the commanders +in the field, from the airship itself. Many +ingenious devices have been devised for this purpose. + +SIGNAL FLAGS.--The best known and most universally +used method is by the use of signaling +flags. Suppose the commander of a force is desirous +of getting the range of a hidden battery, +or a massed force in his front. The observer in +the aeroplane will sail over the area at an understood +altitude, say one mile in height. + +The officer in charge of the battery, knowing +the height of the airship, is able, by means of +the angle thus given him, to get the distance between +his battery and the concealed point beneath +the airship. The observer in the airship, of +course, signals the engineer officer, the exact point +or time when the airship is directly above, and +this gives him the correct angle. + +The guns of the battery are then directed and +fired so as to reach the concealed point. It is +now important to be able to send intelligible signals +to the officer in charge of the battery. If the +shot goes beyond the mark, the observer in the +airship raises the flag above his head, which indicates +that it was too high. + +HOW USED.--If the shot fell short he would +lower the flag. If the shot landed too far to the +right, this would be indicated by the flag, and if +too far to the left, the signal would, in like manner, +be sufficient to enable the gunners to correct +the guns. + +When the exact range is obtained the observer +in the ship waves the flag about his head, in +token of approval. All this work of noting the +effect of the shots must be taken while the airship +is under fire, and while circling about within +visual range of the concealed object below. + +The officer in charge of the battery, as well as +the observer on the flying craft, must be equipped +with powerful glasses, so the effect of the shots +may be noted on the one hand, and the signals +properly read by the officer on the other hand. + +It may be said, however, that air battles have +not been frequent and that they have been merely +incidents of the conditions under which they were +operated. The mission of the aeroplane is now +conceded to be purely one of observation, such as +we have described. + +Both French and German reports are full of +incidents showing the value of observations, and +also concerning the effects of bombs. Extracts +from the diaries of prisoners gave many interesting +features of the results of aeroplane work. + +CASUALTIES DUE TO AEROPLANES.--In the diary +of one was found the remark: "I was lucky to +escape the bomb thrown by a French aviator at +Conrobet, which killed eight of my companions." + +Another says: "The Seventh Company of the +Third Regiment of the Guard had eight killed and +twenty-two wounded by bomb from a French aeroplane." + +Another: "An officer showed us a torn coat +taken from one of sixty soldiers wounded by a +bomb from an aeroplane." + +A prisoner says: "Near Neuville an aeroplane +bomb dropped on a supply train, killed four men, +wounded six, and killed a considerable number of +horses." + +The Belgians, after their defeat and the capture +of Antwerp, were forced to the west along +the coast. In some way they learned that the +Kaiser was about to occupy a chateau near Dixmunde. +Several aviators flew above the position +and dropped a number of bombs on the building, +completely wrecking it, and it was fortunate that +the Emperor left the building only twenty minutes +before, as several of his aides and soldiers +on duty were killed. + +On numerous occasions the headquarters of the +different commanders have been discovered and +had to be moved to safer places. + +During all these wonderful exploits which will +live in history because men had the opportunity +during the war to use them for the first time in +actual conflict, the official reports have not +mentioned the aviators by name. The deaths of the +brave men have brought forth the acknowledgments +of their services. During the first three +months of the war it is estimated that over sixty +aviators and aides had lost their lives in the conflict +on the two great battle lines. This does not +take into account those who met death on the +Zeppelins, of which five had been destroyed during +that time. + +THE END + + +GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME + +Where a word has various meanings, that definition is given +which will express the terms used by the author in explaining +the mechanism or subject to which it refers. + +Aviation. The art of flying. + +Altitude. Height; a vertical distance above any point. + +Attraction. The art or process of drawing towards. + +Allusion. Referring to a certain thing. + +Assume. Taking it for granted. + +Accentuated. To lay great stress upon a thing. + +Angle of Movement. Any direction which is upwardly or downwardly, +as distinguished from the direction of movement which is either +to the right or to the left. + +Acquire. To obtain; to recover; to procure. + +Analogous. Corresponding to or resembling some other thing or +object. + +Air Hole. A term used to express a condition in flying where the +machine while in horizontal flight takes a sudden drop, due to +counter currents. + +Ailerons. Literally, small planes. Used to designate the small +planes which are designed to stabilize a machine. + +Angle. A figure, or two straight lines which start at the same +point. The sides of these lines are termed the angle. + +Analysis. To separate; to take apart and examine the various +parts or elements of a thing. + +Aeroplane. Any form of machine which has planes, and is heavier +than air. Usually a flying structure which is propelled by some +motive power. + +Accumulation. Adding to; bringing together the same or unlike +articles. + +Ascribable. A reference to some antecedent source. + +Aeronautics. The science of flying. + +Anterior. Meaning the front or forward margin or portion of a +body. + +Artifices. Any artificial product, or workmanship. + +Axially. Through the central portion. Thus, the shaft which goes +through a cylinder is axially arranged. + +Automatic. A thing which operates by its own mechanism; a +contrivance which is made in such a manner that it will run +without manual operation or care. + +Alertness. Quick; being active. + +Apex. The point at which two lines meet; also the extreme pointed +end of a conical figure. + +Ascension. Moving upwardly. + +Accessories. The parts of a machine, or artielee which may ha +used in connection therewith. + +Anemometer. An instrument for measuring the force or the velocity +of wind. + +Anemograph. An instrument that usually traces a curved line OH +paper to make a record of the force or direction, or velocity of +the wind. + +Anemometrograph. A device which determines the force, velocity +and direction of the wind. + +Accretion. Adding to little by little. + +Accelerated. Quiekening; hurrying the process. + +Abridged. Partly taken away from; shortened. + +Abrogate. To dispense with; to set aside. + +Abnormal Not in the usual manner; not in a regular way. + +Alternate. First one and then another; going from one side to the +other. + +Ancient Lights. An old English law which prevents a neighbor from +shutting off sunlight. + +Angularly. A line which runs out from another so that the two are +not parallel. + +Aneroid. Not wet. Applied to the type of barometer where the +medium for determ,ining the pressure is not made of mercury. + +Aspirate. A term given by the French to that peculiar action of +wing, or other body, which, when placed in certain positions, +relative to a current of air, will cause it to be drawn into the +current. + +Assemblage. The bringing together of the parts or elements of a +machine. + +Augment. To aid; to add to or increase. + +Banked. The term used in aviation which indicates that the +machine is turned up so that its supporting surfaces +rest against the air, as in alighting. + +Barometer. An instrument for determining the air pressure, and +thereby indicating altitudes. + +Bevel Pinion. A toothed wheel driven by a larger wheel. + +Bi-Plane. Two planes. In aviation that type which has two planes, +similar in size, usually, and generally placed one above the +other so they are separated the same distance from each other, as +the width of each of the planes. + +Bulge. A hump; an enlargement beyond the normal at any point. + +Camber, also Cambre. The upward curve in a plane. + +Catapult. A piece of mechanism for projecting or throwing a +missile. + +Carbureter. The device which breaks up the fuel oil, and mixes +the proper quantity of air with it before it is drawn into the +engine. + +Catastrophe. A calamity; a sad ending; loss of life or of +property. + +Cellular. Made up of small hollows, or compartments; filled with +holes. + +Celestial. Pertaining to the heavens. + +Centrifugal. That force which throws outwardly from a rotating +body. + +Centripetal. That force, like the attraction of gravity, which +draws a body to the center. + +Characteristic. Striking; that which is peculiar to some thing or +object. + +Commensurate. Sufficient; in proper proportion; sufficient for +the occasion. + +Commercially. Pertaining to the nature of trade; the making of +money. + +Complicated. Not easily explainable; not easy to separate. + +Comparatively. Judged by something else; taken with reference to +another object or thing. + +Compression. The drawing together; forcing into a smaller +compass, or space. + +Composition. Made up of different elements, or things. + +Conceivable. Made up from the imagination. + +Concaved. Hollowed: In aviation it has reference to the underside +of the plane, which is usually provided, structurally, with a +hollow or trough formation. + +Conforming. To make alike in form; to bring into harmony. + +Conjunction. In eonneetion with; joining together. + +Convex. A rounded surface; a bulging out. + +Conclusion. The end; a finding in law; a reasoning from a certain +condition. + +Conductivity. The property of materials whereby they will +transmit heat along from one part to another, also electricity. + +Concentrated. Brought together; assembled in a smaller space. + +Conclusive. A positive ending; decisive of the matter at issue. + +Concentrically. A line which is at all points at the same +distance from one point. + +Condensation. The act or process of making denser, or being +brought together. + +Contemplate. To consider; to judge. + +Convoys. A protecting force which aeeompanies the transfer of +property. + +Convection. The diffusion of heat through a liquid or gas. + +Consistent. A state of harmony; the same at &11 times. + +Constant. In mathematics, a figure which never changes; or a +figure used as a fixed valuation in a problem. + +Controllable. Held within bounds; that which can be within the +power to accomplish. + +Correctional. The means whereby a fault may be made right. + +Consequence. The result; that which flows from a preceding +action. + +Counterforce. An action contrary or opposite to the main force. + +Counter-balance. Any power equally opposing another. + +Counteract. A force acting in opposition to another. + +Countercurrent. An air current which sets up in an opposite +direction in the path of a moving aeroplane. + +Cushioned. An action which takes place against a moving +aeroplane, by a sudden gust of air or countercurrent. + +Dedicated. To set apart for some special purpose. + +Degree. An interval; a grade; a stage; a certain proportion. + +Deltoid. Shaped like the Greek letter delta. + +Density. Closeness of parts. + +Demonstration. Making clear; showing up; an exhibition or +expression. + +Deceptive. The power or tendency to give a false impression. + +Deterrent. To hold back; to prevent action. + +Detracting. The tendency to take away; to belittle. + +Depressed. To move downwardly. + +Destination. The place set for the end of the journey. + +Despoiling. To take away from; robbing or taking from another + by force or by stealth. + +Dependant. Hanging below; projecting from the lower side. + +Dexterity. Agility; smartness in action. + +Deranged. Put out of order; wrongly arranged. + +Develop. Brought out; to put into a correct shape or form. + +Deferred. Put over to another time. + +Designedly. With a direct purpose. + +Diagonal. Across an object at an angle to one or more aides. + +Diametrically. Across an object through or near the center +thereof. + +Diagram. A mechanical plan or outline of an object. + +Dimension. The distance across an object. The measurement, for +instance, of a propeller from tip to tip. + +Dynamically. Pertaining to motion as a result of force. + +Dispossessed. A term used to indicate the act which removes a +person from the possession of property. + +Diameter. The measurement across an object. + +Divest. Taken away from; removed out of. + +Disregard. Deliberate lack of attention. + +Diversity. The state wherein one is unlike another; +dissimilarity. + +Drift. The term used to indicate the horizontal motion, or the +pull of an aeroplane. + +Dragon. A fabulous monster, usually in the form of a serpent. + +Duplicate. Two; made in exact imitation of an original. + +Easement. A legal phrase to designate that right which man +possesses, irrespective of any law, to gain access to his +property. + +Effrontery. Boldness with insolence; rashness without propriety. + +Effective. To be efficient. + +Element. One part of a whole. + +Elasticity. Material which will go back to its original form +after being distorted, is said to be elastic. + +Eliminate. To take away from; to remove a part, or the whole. + +Elliptical. Oblong with rounded ends. + +Elusive. Capable of escaping from; hard to hold. + +Elevator. The horizontal planes in front or rear, or in both +front and rear of the supporting surfaces of an aeroplane. + +Emergency. A sudden occurrence calling for immediate action. + +Emplacement. A spot designed to hold heavy field pieces in +intrenchments. + +Enactment. The formulation of a law; the doing of a special +thing. + +Enunciated. Announced; setting forth of an act or a condition. + +Energy. That quality by reason of which anything tends to move or +act. + +Equidistant. Two points or objects at equal distance from a +common point. + +Equilibrinm. A balance produced by the action of two or more +forces. + +Equalizing, One made equal to the other; one side the same as the +other. + +Equipped. Armed; provided with the proper material, or in the +same condition. + +Essential. The important part or element. + +Essence The real charaeter or element of the thing itself. + +External. The outermost portion. + +Evolution. A gradual change or building up; from a lower to a +higher order. + +Evolved. Brought out from a crude condition to a better form. + +Expression. The art of explaining or setting forth. + +Expansion. Growing larger; to occupy a greater space. + +Exerted. To work to the utmost; to put forth in action. + +Exhilaratiorn. A lively, pleasing or happy sensation. + +Exploited. To fully examine and consider, as well as carry out. + +Extremity. The end; as far as ean be considered. + +Facility. Ease of management; to do things without difficulty. + +Factor. One of the elements in a problem, or in mechanical +action. + +Fascination, Attraetiveness that is pleasing. + +Flexure. The capacity to bend and yield, and return to its +original position. + +Flexible, That which will yield; springy. + +Fore and Aft. Lengthwise, as from stem to stern of a ship. + +Formation. The shape or arrangement of an article or thing. + +Formulated. Put into some eonerete form, or so arranged that it +may be understood. + +Frictionless. Being without a grinding or retarding aotion. + +Fulcrumed. A resting place for a lever. + +Function. The duty or sphere of action in a person, or object. + +Glider. An aeroplane, without power, adapted to be operated +by an aviator. + +Governing. An element which is designed to control a machine in a +regular manner. + +Graduated. A marked portion, which is regularly laid off to +indicate measurements or quantities. + +Gravity. The attraction of mass for mass. The tendency of bodies +to move toward the earth. + +Gravitatior The force with which all bodies attract each other. + +Gyratory. Having a circular and wheeling as well as a rotary +motion. + +Gyroscope. A wheel, designed to illustrate the laws of motion, +which freely revolves in gimbals within a ring, and when set into +motion, objects to change its plane of rotation. + +Hemispherical. The half of a sphere. The half of an apple would +be hemispherical. + +Hazardous. That which is doubtful; accompanied by danger. + +Helicopter. A type of flying machine which has a large propeller, +or more than one, revolubly fixed on vertical shafts, by means of +which the machine is launched and projected through the air. + +Horizontal. Level, like water. + +Hydroplane. A term used to designate an aeroplane which is +provided with pontoons, whereby it may alight on the water, and +be launched from the surface. The term hydroaeroplane is most +generally used to indicate this type of machine. + +Impact. The striking against; the striking force of one body +against another. + +Immersed. Placed under water below the surface. + +Impinge. To strike against; usually applied where air strikes +a plane or a surface at an angle. + +Imitation. Similarity; the same in appearance. + +Incompatible. Without harmony; incapable of existing together. + +Incurved. Applied to a surface formation where there is a +depression, or hollow. + +Inequalities. Not smooth, or regular; uneven. + +Infinitely, Boundless; in great number, or quality; without +measure. + +Initial. The first; that which is at the beginning. + +Indestructibility. Not capable of being injured or destroyed. + +Influenced. Swayed; to be induced to change. + +Inherent. That which is in or belongs to itself. + +Initiating. To teach; to instill; to give an insight. + +Indicator. A term applied to mechanism which shows the results of +certain operations and enables the user to read the measure, +quantity, or quality shown. + +Inconceivable. Not capable of understanding; that which cannot be +understood by the human mind. + +Institute. To start; to bring into operation. + +Insignias. Things which are significant of any particular calling +or profession. + +Instinct. That quality in man or animals which prompts the doing +of things independently of any direct knowledge or understanding. + +Intermediate. Between; that which may be within or inside the +scope of the mind, or of certain areas. + +Intervening. The time between; also applied to the action of a +person who may take part in an affair between two or more +persons. + +Interval. A time between. + +Investigator. One who undertakes to find out certain things. + +Incidence. In physics this is a term to indicate the line which +falls upon or strikes another at an angle. + +Inverted. Upside down. + +Invest. To give to another thing something that it lacked before. + +Kinetic. Consisting in or depending upon motion. + +Laminated. Made up of a plurality of parts. When wooden strips, +of different or of the same kinds are glued and then laid +together and put under heavy pressure +until thoroughly dried, the mass makes a far more rigid structure +than if cut out of a single piece. + +Launchiug. The term applied to the raising, or starting of a +boat, or of a flying object. + +Lateral. In mining this is a term to indicate the drifts or +tunnels which branch out from the main tunnel. Generally it has +reference to a transverse position or direction,--that is, at +right angles to a fore and aft direction. + +Lift. The vertical motion, or direction in an airship; thus the +lift may be the load, or the term used to designate +what the ship is capable of raising up. + +Ligament. The exceedingly strong tendons or muscles of birds and +animals, usually of firm, compact tissues. + +Limitations. Within certain bounds; in a prescribed scope. + +Longitudinally. Usually that direction across the longest part. + +Majestically. Grand; exalted dignity; the quality which inspires +reverence or fear. + +Manipulate. To handle; to conduct so that it will result in a +certain way. + +Maneuver. A methodical movement or change in troops. + +Manually. To perform by hand. + +Manifestations. The act of making plain to the eye or to the +understanding. + +Manually-operated. With the hands; a term applied to such +machines as have the control planes operated by hand. + +Maintained. Kept up; to provide for; to sustain. + +Material. The substance, or the matter from which an article is +made; also the important thing, or element. + +Mass. In physics it is that which in an article is always the +same. It differs from weight in the particular that the mass of +an article is the same, however far it may be from the center of +the earth, whereas weight changes, and becomes less and less as +it recedes from the center of the earth. + +Margin. The edge; the principal differecee between this word and +edge, is, that margin has reference also to a border, or narrow +strip along the edge, as, for instance, the blank spaces at the +edges of a printed page. + +Medievral. Belonging to the Middle Ages. + +Mercury. A silver-white liquid metal, usually called quicksilver, +and rather heavy. It dissolves most metals, and this process is +called amalgamation. + +Militate. In determining a question, to have weight, or to +influence a decision. + +Mobility. Being freely movable; capable of quick change. + +Modifieation. A change; making a difference. + +Monitor. Advising or reproving. Advising or approving by way of +caution. + +Monstrosities. Anything which is huge, or distorted, or wrong in +structure. + +Monorail. A railway with a single track, designed to be used by a +bicycle form of carriage, with two wheels, fore and aft of each +other, and depending for its stability upon gyroscopes, mounted +on the carriage. + +Momentum. That which makes a moving body difficult to stop. It is +the weight of a moving body, multiplied by its speed. + +Monoplane. The literal meaning is one plane. As monoplane +machines are all provided with a fore and aft body, and each has +a wing or plane projecting out from each side of this body, it is +obvious that it has two planes instead of one. The term, however, +has reference to the fact that it has only one supporting surface +on the same plane. Biplanes have two supporting surfaces, one +above the other. + +Multiplicity. Frequently confounded with plurality. The latter +means more than one, whereas multiplicity has reference to a +great number, or to a great variety. + +Muscular. Being strong; well developed. + +Negative. The opposite of positive; not decisive. + +Neutralize. From the word neuter, which means neither, hence the +term may be defined as one which is not a part of either, or does +not take up with either side. + +Normal Pressure. Normal means the natural or usual, and when +applied to air it would have reference to the condition of the +atmosphere at that particular place. If the pressure could change +from its usual condition, it would be an abnormal pressure. + +Notoriously. Generally known, but not favorably so; the subject +of general remark; or unfavorably known. + +Obscurity. Not well known; in the background; without clear +vision; hidden from view. + +Obliquely. That which differs from a right angle; neither + obtuse nor acute; deviating from a line by any angle except a +right angle. + +Obvious. That which is readily observed and understood. + +Orthopter. That type of flying machine which depends on flapping +wings to hold it in space, and to transport it, in imitation of +the motion of the wings of birds in flying. + +Oscillate. Moving to and fro; the piston of a steam engine has an +oscillating motion. + +Outline. Describing a marginal line on a drawing; setting forth +the principal features of an argument, or the details of a story, +or the like. + +Overlapping. One placed over the other. + +Parabolic. A form of curve somewhat similar to an ellipse. + +Pedestal. A standard or support; an upright to hold machinery. + +Pertinent. Appropriate; pertaining to the subject. + +Pectoral. The bone which forms the main rib or support at the +forward edge of a bird's wing. + +Persistent. Keeping at it; determination to proceed. + +Perpendicular. At right angles to a surface. This term is +sometimes wrongly applied in referring to an object, particularly +to an object which is vertical, meaning up and down. The blade of +a square is perpendieular to the handle at all times, but the +blade is vertical only when it points to the center of the earth. + +Pernicious. Bad; not having good features or possessing wrong +attributes. + +Pendulum. A bar or body suspended at a point and adapted to swing +to and fro. + +Perpetual. For all time; unending or unlimited time. + +Phenomena. Some peculiar happening, or event, or object. + +Pitch. In aviation this applies to the angle at which the blades +of a propeller are cut. If a propeller is turned, and it moves +forwardly in the exact path made by the angle, for one complete +turn, the distance traveled by the propeller axially indicates +the pitch in feet. + +Placement. When an object is located at any particular point, so +that it is operative the location is called the placement. + +Plane. A flat surface for supporting a flying machine in the air. +Plane of movement pertains to the imaginary surface described by +a moving body. A bicycle wheel, for instance, when moving +forwardly in a straight line, has a plane of movement which is +vertical; but when the machine turns in a circle the upper end of +the wheel is turned inwardly, and the plane of rhovement is at an +angle. + +Pliant. Easily yielding; capable of being bent; liable to be +put out of shape. + +Plurality. See multiplicity. More than one. + +Poise. Held in suspension; disposed in a particular way. + +Pontoon. Applied to a series of boats ranged side by side to +support a walk laid thereon. In aviation it has reference to a +float for supporting an aeroplane. + +Ponderous. Large; heavy; difficult to handle. + +Posterior. The rear end; the opposite of anterior. + +Principles. The very nature or essence of a thing; the source or +cause from which a thing springs. + +Proportion. The relation that exists between different parts or +things. + +Propounded. Questioned; stated; to state formally for +consideration + +Proprietary. A right; the ownership of certain property. + +Primitive. The beginning or early times; long ago. + +Prelude. A statement or action which precedes the main feature +to be presented. + +Proximity. Close to; near at hand. + +Prototype. That which is used as the sample from, which something +is made or judged. + +Propeller. The piece of meebanism, with screw shaped blade, +designed to be rapidly rotated in order to drive a vessel +forwardly. It is claimed by some that the word Impeller would be +the more proper term. + +Primarily. At the first; the commencement. + +Precedes. Goes ahead; forward of all. + +Propulsive. The force which gives motion to an object. + +Projected. Thrown forward; caused to fly through the air. + +Radially. Out from the center; projecting like the spokes of a +wheel. + +Ratio. The relation of degree, number, amount; one with another. + +Reaction. A counterforce; acting against. + +Recognize. To know; seeing, hearing, or feeling, and having +knowledge therefrom. + +Reflection. Considering; judging one thing by the examination of +another. A beam of light, or an object, leaving a surface. + +Refraction. That peculiarity in a beam of light, which, in +passing through water at an angle, bends out of its course and +again assumes a direct line after passing through. + +Reflex. Turned back on itself, or in the direction from which it +came. + +Requisite. Enough; suffieient for all purposes. + +Relegate. To put back or away. + +Rectangular. Having one or more right angles. + +Reservations. Land which is held by the Government for various +purposes. + +Resistance. That which holds back; preventing movement. + +Retarding. Preventing a free movement. + +Revoluble. The turning or swinging motion of a body like the +earth in its movement around the sun. See Rotative. To cause to +move as in an orbit or circle. + +Resilient. Springy; having the quality of elasticity. + +Reversed. Changed about; turned front side to the rear. + +Rotative. That which turns, like a shaft. The movement of the +earth on its axis is rotative. + +Saturation. Putting one substance into another until it will hold +no more. For instance, adding salt to water until the water +cannot take up any more. + +Security. Safety, assuredness that there will be no danger. + +Segment. A part eut off from a circle. Distinguished from a +sector, which might be likened to the form of one of the sections +of an orange. + +Sexagonal. Six-sided. + +Sine of the Angle. The line dropped from the highest point of an + angle to the line which runs out horizontally. + +Sinuous. Wavelike; moving up and down like the waves of the +ocean. + +Simulates. To pattern or copy after; the making of the like. + +Skipper. A thin flat stone. + +Spirally-formed. Made like an auger; twisted. + +Stability. In airships that quality which holds the ship on an +even and unswerving course, and prevents plunging and side +motions. + +Structural. Belonging to the features of eonstruetion. + +Strata. Two or more layers; one over or below the other. + +Stream line. In expressing the action of moving air, or an +aeroplane transported through air, every part is acted upon by +the air. Stream lines are imaginary lines which act upon the +planes at all points, and all in the same direction, or angle. + +Stupendous. Great; important; above the ordinary. + +Substitute. One taken for another; replacing one thing by +something else. + +Supporting. Giving aid; helping another. + +Synchronous. Acting at the same time, and to the same extent. +Thus if two wheels, separated from each other at great distances, +are so arranged that they turn at exactly the same speed, they +are said to turn synchronously. + +Tactics. The art of handling troops in the presence of an enemy. +It differs from strategy in the particular that the latter word +is used to explain the movements or arrangement of forces before +they arrive at the battle line. + +Tandem. One before the other; one after the other. + +Tangent. A line drawn from a circle at an angle, instead of +radially. + +Technically. Pertaining to some particular trade, science or art. + +Tenuous. Thin, slender, willowy, slight. + +Tetrahedral. This has reference to a form which is made up of a +multiplicity of triangularly shaped thin blades, so as to form +numerous cells, and thus make a large number of supporting +surfaces. Used as a kite. + +Theories. Views based upon certain consideration. + +Theoretical. Where opinions are founded on certain information, +and expressed, not from the standpoint of actual knowledge, but +upon conclusions derived from such examinations. + +Torsion. A twist; a circular motion around a body. + +Transmitted. Sent out; conveyed from one point to another. + +Transformed. Changed; entirely made over from one thing to +another. + +Transverse. When a body is shorter from front to rear than from +side to side its longest dimension is transversely. +Distinguish from lateral, which has reference only to the +distance at right angles from the main body. + +Translation. The transportation of a body through the air. + +Trajectory. The path made by a body projected through the air. + +Triangular. A form or body having three sides and three angles. + +Typical. In the form of; a likeness to. + +Ultimate. The end; the finality; the last that can be said. + +Uninitiated. Not having full knowledge; withont information. + +Unique. Peculiar; something that on account of its peculiar +construction or arrangements stands out beyond the others. + +Universal. Everywhere; all over the world. + +Undulate. To move up and down; a wave-like motion. + +Utility. Of use; to take advantageous use of. + +Unstable. Not having anything permanent; in a ship in flight one +that will not ride on an even keel, and is liable to pitch about. + +Vacuum. Where air is partly taken away, or rendered rarer. + +Valved. A surface which has a multiplicity of openings with +valves therein, or, through which air can move in one direction. + +Vaunted. To boast concerning; to give a high opinion. + +Velocity. Speed; the rate at which an object can move from place +to place. + +Vertical. A line running directly to the center of the earth; a +line at right angles to the surface of water. + +Vibratory. Moving from side to side; a regular motion. + +Volplane. The glide of a machine without the use of power. + +Warping. The twist given to certain portions of planes, so as to +cause the air to aet against the warped portions. + +Weight. The measure of the force which gravity exerts on all +objects. + + + + + +End of The Project Gutenberg Etext of Aeroplanes, by J. S. 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