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If you are not located in the United States, you'll have -to check the laws of the country where you are located before using this ebook. - -Title: Flying Machines Today - -Author: William Duane Ennis - -Release Date: March 17, 2016 [EBook #51481] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK FLYING MACHINES TODAY *** - - - - -Produced by Chris Curnow, Ralph Carmichael and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - - - - - - -FLYING MACHINES TODAY - - - - -"Hitherto aviation has been almost monopolized by that much-overpraised -and much-overtrusted person, 'the practical man.' It is much in need -of the services of the theorist--the engineer with his mathematical -calculations of how a flying machine ought to be built and of how the -material used in its construction should be distributed to give the -greatest possible amount of strength and efficiency." - - --From the _New York Times_, January 16, 1911. - - - [Illustration: THE FALL OF ICARUS] - - - - -FLYING MACHINES TODAY - - BY - WILLIAM DUANE ENNIS - - _Professor of Mechanical Engineering in the Polytechnic - Institute of Brooklyn_ - -_123 ILLUSTRATIONS_ - - [Illustration: VAN NOSTRAND LOGO] - - NEW YORK - D. VAN NOSTRAND COMPANY - 23 MURRAY AND 1911 27 WARREN STS. - - - - - _Copyright, 1911, by_ - D. VAN NOSTRAND COMPANY - - -THE · PLIMPTON · PRESS · NORWOOD · MASS · U · S · A - - - - - To - MY MOTHER - - - - -PREFACE - - -Speaking with some experience, the writer has found that instruction -in the principles underlying the science and sport of aviation must be -vitalized by some contemporaneous study of what is being accomplished -in the air. No one of the revolutionizing inventions of man has -progressed as rapidly as aerial navigation. The "truths" of today are -the absurdities of tomorrow. - -The suggestion that some grasp of the principles and a very fair -knowledge of the current practices in aeronautics may be had without -special technical knowledge came almost automatically. If this book -is comprehensible to the lay reader, and if it conveys to him even a -small proportion of the writer's conviction that flying machines are to -profoundly influence our living in the next generation, it will have -accomplished its author's purpose. - - POLYTECHNIC INSTITUTE OF BROOKLYN, - NEW YORK, April, 1911. - - - - -CONTENTS - - - PAGE - THE DELIGHTS AND DANGERS OF FLYING.--Dangers of - Aviation.--What it is Like to Fly 1 - - SOARING FLIGHT BY MAN.--What Holds it Up?--Lifting - Power.--Why so Many Sails?--Steering 17 - - TURNING CORNERS.--What Happens when Making a Turn.-- - Lateral Stability.--Wing Warping.--Automatic Control.-- - The Gyroscope.--Wind Gusts 33 - - AIR AND THE WIND.--Sailing Balloons.--Field and Speed 43 - - GAS AND BALLAST.--Buoyancy in Air.--Ascending and - Descending.--The Ballonet.--The Equilibrator 57 - - DIRIGIBLE BALLOONS AND OTHER KINDS.--Shapes.-- - Dimensions.--Fabrics.--Framing.--Keeping the Keel - Horizontal.--Stability.--Rudders and Planes.--Arrangement - and Accessories.--Amateur Dirigibles.--The Fort - Omaha Plant.--Balloon Progress 71 - - THE QUESTION OF POWER.--Resistance of Aeroplanes.-- - Resistance of Dirigibles.--Independent Speed and - Time-Table.--The Cost of Speed.--The Propeller 101 - - GETTING UP AND DOWN; MODELS AND GLIDERS; - AEROPLANE DETAILS.--Launching.--Descending.-- - Gliders.--Models.--Balancing.--Weights.-- - Miscellaneous.--Things to Look After 121 - - SOME AEROPLANES.--SOME ACCOMPLISHMENTS 143 - - THE POSSIBILITIES IN AVIATION.--The Case of the - Dirigible.--The Orthopter.--The Helicopter.--Composite - Types.--What is Promised 170 - - AERIAL WARFARE 189 - - - - - LIST OF ILLUSTRATIONS - - - PAGE - - The Fall of Icarus _Frontispiece_ - The Aviator 3 - The Santos-Dumont "_Demoiselle_" 4 - View from a Balloon 9 - Anatomy of a Bird's Wing 10 - Flight of a Bird 11 - In a Meteoric Shower 13 - How a Boat Tacks 15 - Octave Chanute 18 - Pressure of the Wind 19 - Forces Acting on a Kite 20 - Sustaining Force in the Aeroplane 23 - Direct Lifting and Resisting Forces 24 - Shapes of Planes 26 - Balancing Sail 28 - Roe's Triplane at Wembley 30 - Action of the Steering Rudder 31 - Recent Type of Wright Biplane 31 - Circular Flight 33 - The Aileron 35 - Wing Tipping 36 - Wing Warping 37 - The Gyroscope 39 - Diurnal Temperatures at Different Heights 45 - Seasonal Variation in Wind Velocities 47 - The Wind Rose for Mt. Weather, Va. 49 - Diagram of Parts of a Drifting Balloon 51 - Glidden and Stevens Getting Away in the "_Boston_" 52 - Relative and Absolute Balloon Velocities 53 - Field and Speed 53 - Influence of Wind on Possible Course 54 - Count Zeppelin 55 - Buoyant Power of Wood 57 - One Cubic Foot of Wood Loaded in Water 58 - Buoyant Power of Hydrogen 59 - Lebaudy's "_Jaune_" 60 - Air Balloon 62 - Screw Propeller for Altitude Control 66 - Balloon with Ballonets 67 - Construction of the Zeppelin Balloon 68 - The Equilibrator 69 - Henry Giffard's Dirigible 71 - Dirigible of Dupuy de Lome 72 - Tissandier Brothers' Dirigible Balloon 73 - The "_Baldwin_" 74 - The "_Zeppelin_" on Lake Constance 75 - The "_Patrie_" 77 - Manufacturing the Envelope of a Balloon 79 - Andrée's Balloon, "_L'Oernen_" 80 - Wreck of the "_Zeppelin_" 82 - Car of the "_Zeppelin_" 84 - Stern View of the "_Zeppelin_" 86 - The "_Clément-Bayard_" 87 - The "_Ville de Paris_" 88 - Car of the "_Liberté_" 89 - The "_Zodiac No. 2_" 92 - United States Signal Corps Balloon Plant at Fort Omaha 93 - The "_Caroline_" 94 - The Ascent at Versailles, 1783 95 - Proposed Dirigible 96 - The "_République_" 97 - The First Flight for the Gordon-Bennett Cup 99 - The Gnome Motor 102 - Screw Propeller 103 - One of the Motors of the "_Zeppelin_" 104 - The Four-Cycle Engine 105 - Action of Two-Cycle Engine 106 - Motor and Propeller 108 - Two-Cylinder Opposed Engine 110 - Four-Cylinder Vertical Engine 110 - Head End Shapes 113 - The Santos-Dumont Dirigible No. 2 115 - In the Bay of Monaco: Santos-Dumont 117 - Wright Biplane on Starting Rail 121 - Launching System for Wright Aeroplane 122 - The Nieuport Monoplane 124 - A Biplane 125 - Ely at Los Angeles 126 - Trajectory During Descent 127 - Descending 128 - The Witteman Glider 130 - French Monoplane 132 - A Problem in Steering 133 - Lejeune Biplane 134 - Tellier Monoplane 135 - A Monoplane 137 - Cars and Framework 139 - Some Details 139 - Recent French Machines 141 - Orville Wright at Fort Myer 143 - The First Flight Across the Channel 144 - Wright Motor 145 - Voisin-Farman Biplane 147 - The Champagne Grand Prize Flight 148 - Farman's First Biplane 149 - The "_June Bug_" 150 - Curtiss Biplane 151 - Curtiss' Hydro-Aeroplane at San Diego Bay 152 - Flying Over the Water 153 - Blériot-Voisin Cellular Biplane with Pontoons 154 - Latham's "_Antoinette_" 155 - James J. Ward at Lewiston Fair 156 - Marcel Penot in the "_Mohawk_" 157 - Santos-Dumont's "_Demoiselle_" 159 - Blériot Monoplane 160 - Latham's Fall into the Channel 161 - De Lesseps Crossing the Channel 163 - The Maxim Aeroplane 164 - Langley's Aeroplane 165 - Robart Monoplane 166 - Vina Monoplane 167 - Blanc Monoplane 170 - Melvin Vaniman Triplane 171 - Jean de Crawhez Triplane 171 - A Triplane 172 - Giraudon's Wheel Aeroplane 175 - Bréguet Gyroplane (Helicopter) 177 - Wellman's "_America_" 181 - The German Emperor Watching the Progress of Aviation 189 - Automatic Gun for Attacking Airships 193 - Gun for Shooting at Aeroplanes 197 - Santos-Dumont Circling the Eiffel Tower 199 - Latham, Farman and Paulhan 202 - - - - -FLYING MACHINES TODAY - - - - -THE DELIGHTS AND DANGERS OF FLYING - - -Few things have more charm for man than flight. The soaring of a bird -is beautiful and the gliding of a yacht before the wind has something -of the same beauty. The child's swing; the exercise of skating on -good ice; a sixty-mile-an-hour spurt on a smooth road in a motor car; -even the slightly passé bicycle: these things have all in their time -appealed to us because they produce the illusion of flight--of progress -through the intangible air with all but separation from the prosaic -earth. - -But these sensations have been only illusions. To actually leave the -earth and wander at will in aerial space--this has been, scarcely a -hope, perhaps rarely even a distinct dream. From the days of Dædalus -and Icarus, of Oriental flying horses and magic carpets, down to -"Darius Green and his flying machine," free flight and frenzy were -not far apart. We were learnedly told, only a few years since, that -sustention by heavier-than-air machines was impossible without the -discovery, first, of some new matter or some new force. It is now -(1911) only eight years since Wilbur Wright at Kitty Hawk, with the -aid of the new (?) matter--aluminum--and the "new" force--the gasoline -engine--in three successive flights proved that a man could travel -through the air and safely descend, in a machine weighing many times -as much as the air it displaced. It is only five years since two -designers--Surcouf and Lebaudy--built dirigible balloons approximating -present forms, the _Ville de Paris_ and _La Patrie_. It is only now -that we average people may confidently contemplate the prospect of an -aerial voyage for ourselves before we die. A contemplation not without -its shudder, perhaps; but yet not altogether more daring than that of -our grandsires who first rode on steel rails behind a steam locomotive. - - -The Dangers of Aviation - -We are very sure to be informed of the fact when an aviator is -killed. Comparatively little stir is made nowadays over an automobile -fatality, and the ordinary railroad accident receives bare mention. For -instruction and warning, accidents to air craft cannot be given too -much publicity; but if we wish any accurate conception of the danger we -must pay regard to factors of proportion. There are perhaps a thousand -aeroplanes and about sixty dirigible balloons in the world. About 500 -men--amateurs and professionals--are continuously engaged in aviation. -The Aero Club of France has issued in that country nearly 300 licenses. -In the United States, licenses are held by about thirty individuals. -We can form no intelligent estimate as to the number of unlicensed -amateurs of all ages who are constantly experimenting with gliders at -more or less peril to life and limb. - -A French authority has ascertained the death rate among air-men to -have been--to date--about 6%. This is equivalent to about one life for -4000 miles of flight: but we must remember that accidents will vary -rather with the number of ascents and descents than with the mileage. -Four thousand miles in 100 flights would be much less perilous, under -present conditions, than 4000 miles in 1000 flights. - - [Illustration: THE AVIATOR] - -There were 26 fatal aeroplane accidents between September 17, 1908, -and December 3, 1910. Yet in that period there were many thousands of -ascents: 1300 were made in one week at the Rheims tournament alone. -Of the 26 accidents, 1 was due to a wind squall, 3 to collision, -6 (apparently) to confusion of the aviator, and 12 to mechanical -breakage. An analysis of 40 British accidents shows 13 to have been -due to engine failures, 10 to alighting on bad ground, 6 to wind -gusts, 5 to breakage of the propeller, and 6 to fire and miscellaneous -causes. These casualties were not all fatal, although the percentage of -fatalities in aeronautic accidents is high. The most serious results -were those due to alighting on bad ground; long grass and standing -grain being very likely to trip the machine and throw the occupant. -French aviators are now strapping themselves to their seats in order to -avoid this last danger. - - [Illustration: THE SANTOS-DUMONT "DEMOISELLE" - (From _The Aeroplane_, by Hubbard, Ledeboer and Turner)] - -Practically all of the accidents occur to those who are flying; but -spectators may endanger themselves. During one of the flights of -Mauvais at Madrid, in March of the present year, the bystanders rushed -through the barriers and out on the field before the machine had well -started. A woman was decapitated by the propeller, and four other -persons were seriously injured. - -Nearly all accidents result from one of three causes: bad design, -inferior mechanical construction, and the taking of unnecessary risks -by the operator. Scientific design at the present writing is perhaps -impossible. Our knowledge of the laws of air resistance and sustention -is neither accurate nor complete. Much additional study and experiment -must be carried on; and some better method of experimenting must be -devised than that which sends a man up in the air and waits to see what -happens. A thorough scientific analysis will not only make aviation -safer, it will aid toward making it commercially important. Further -data on propeller proportions and efficiencies, and on strains in the -material of screws under aerial conditions, will do much to standardize -power plant equipment. The excessive number of engine breakdowns -is obviously related to the extremely light weight of the engines -employed: better design may actually increase these weights over those -customary at present. Great weight reduction is no longer regarded -as essential at present speeds in aerial navigation: we have perhaps -already gone too far in this respect. - -Bad workmanship has been more or less unavoidable, since no one has -yet had ten years' experience in building aeroplanes. The men who have -developed the art have usually been sportsmen rather than mechanics, -and only time is necessary to show the impropriety of using "safety -pins" and bent wire nails for connections. - -The taking of risks has been an essential feature. When one man earns -$100,000 in a year by dare-devil flights, when the public flocks in -hordes--and pays good prices--to see a man risk his neck, he will -usually aim to satisfy it. This is not developing aerial navigation: -this is circus riding--looping-the-loop performances which appeal to -some savage instinct in us but lead us nowhere. Men have climbed two -miles into the clouds, for no good purpose whatever. All that we need -to know of high altitude conditions is already known or may be learned -by ascents in anchored balloons. Records up to heights of sixteen miles -have been obtained by sounding balloons. - -If these high altitudes may under certain conditions be desirable for -particular types of balloon, they are essentially undesirable for the -aeroplane. The supporting power of a heavier-than-air machine decreases -in precisely inverse ratio with the altitude. To fly high will then -involve either more supporting surface and therefore a structurally -weaker machine, or greater speed and consequently a larger motor. It -is true that the resistance to propulsion decreases at high altitudes, -just as the supporting power decreases: and on this account, given only -a sufficient margin of supporting power, we might expect a standard -machine to work about as well at a two-mile elevation as at a height of -200 feet; but rarefaction of the air at the higher altitudes decreases -the weight of carbureted mixture drawn into the motor, and consequently -its output. Any air-man who attempts to reach great heights in a -machine not built for such purpose is courting disaster. - -Flights over cities, spectacular as they are, and popular as they are -likely to remain, are doubly dangerous on account of the irregular air -currents and absence of safe landing places. They have at last been -officially discountenanced as not likely to advance the sport. - -All flights are exhibition flights. The day of a quiet, -mind-your-own-business type of aerial journey has not yet arrived. -Exhibition performances of any sort are generally hazardous. There -were nine men killed in one recent automobile meet. If the automobile -were used exclusively for races and contests, the percentage of -fatalities might easily exceed that in aviation. It is claimed that no -inexperienced aviator has ever been killed. This may not be true, but -there is no doubt that the larger number of accidents has occurred to -the better-known men from whom the public expects something daring. - -Probably the best summing up of the danger of aviation may be obtained -from the insurance companies. The courts have decided that an -individual does not forfeit his life insurance by making an occasional -balloon trip. Regular classified rates for aeroplane and balloon -operators are in force in France and Germany. It is reported that Mr. -Grahame-White carries a life insurance policy at 35% premium--about -the same rate as that paid by a "crowned head." Another aviator of a -less professional type has been refused insurance even at 40% premium. -Policies of insurance may be obtained covering damage to machines by -fire or during transportation and by collisions with other machines; -and covering liability for injuries to persons other than the aviator. - -On the whole, flying is an ultra-hazardous _occupation_; but an -_occasional_ flight by a competent person or by a passenger with a -careful pilot is simply a thrilling experience, practically no more -dangerous than many things we do without hesitation. Nearly all -accidents have been due to preventable causes; and it is simply a -matter of science, skill, perseverance, and determination to make an -aerial excursion under proper conditions as safe as a journey in a -motor car. Men who for valuable prizes undertake spectacular feats will -be killed as frequently in aviation as in bicycle or even in automobile -racing; but probably not very much more frequently, after design and -workmanship in flying machines shall have been perfected. The total -number of deaths in aviation up to February 9, 1911, is stated to have -been forty-two. - - -What It Is Like to Fly - -We are fond of comparing flying machines with birds, with fish, -and with ships: and there are useful analogies with all three. A -drifting balloon is like a becalmed ship or a dead fish. It moves at -the speed of the aerial fluid about it and the occupants perceive no -movement whatever. The earth's surface below appears to move in the -opposite direction to that in which the wind carries the balloon. With -a dirigible balloon or flying machine, the sensation is that of being -exposed to a violent wind, against which (by observation of landmarks) -we find that we progress. It is the same experience as that obtained -when standing in an exposed position on a steamship, and we wonder if a -bird or a fish gradually gets so accustomed to the opposing current as -to be unconscious of it. But in spite of jar of motors and machinery, -there is a freedom of movement, a detachment from earth-associations, -in air flight, that distinguishes it absolutely from the churning of a -powerful vessel through the waves. - - [Illustration: VIEW FROM A BALLOON] - - [Illustration: ANATOMY OF A BIRD'S WING - (From Walker's _Aerial Navigation_)] - - [Illustration: FLIGHT OF A BIRD] - -Birds fly in one of three ways. The most familiar bird flight is -by a rapid wing movement which has been called oar-like, but which -is precisely equivalent to the usual movement of the arms of a man -in swimming. The edge of the wing moves forward, cutting the air; on -the return stroke the leading edge is depressed so as to present a -nearly flat surface to the air and thus propel the bird forward. A -slight downward direction of this stroke serves to impel the flight -sufficiently upward to offset the effect of gravity. Any man can learn -to swim, but no man can fly, because neither in his muscular frame nor -by any device which he can attach thereto can he exert a sufficient -pressure to overcome his own weight against as imponderable a fluid -as air. If air were as heavy as water, instead of 700 times lighter, -it would be as easy to fly as to swim. The bird can fly because of -the great surface, powerful construction, and rapid movement of its -wings, in proportion to the weight of its body. But compared with -the rest of the animal kingdom, flying birds are all of small size. -Helmholz considered that the vulture represented the heaviest body that -could possibly be raised and kept aloft by the exercise of muscular -power, and it is understood that vultures have considerable difficulty -in ascending; so much so that unless in a position to take a short -preliminary run they are easily captured. - -Every one has noticed a second type of bird flight--soaring. It is this -flight which is exactly imitated in a glider. An aeroplane differs -from a soaring bird only in that it carries with it a producer of -forward impetus--the propeller--so that the soaring flight may last -indefinitely: whereas a soaring bird gradually loses speed and descends. - - [Illustration: IN A METEORIC SHOWER] - -A third and rare type of bird flight has been called _sailing_. The -bird faces the wind, and with wings outspread and their forward edge -elevated rises while being forced backward under the action of the -breeze. As soon as the wind somewhat subsides, the bird turns and -_soars_ in the desired direction. Flight is thus accomplished without -muscular effort other than that necessary to properly incline the -wings and to make the turns. It is practicable only in squally winds, -and the birds which practice "sailing"--the albatross and frigate -bird--are those which live in the lower and more disturbed regions of -the atmosphere. This form of flight has been approximately imitated in -the man[oe]uvering of aeroplanes. - -Comparison of flying machines and ships suggests many points of -difference. Water is a fluid of great density, with a definite upper -surface, on which marine structures naturally rest. A vessel in the air -may be at any elevation in the surrounding rarefied fluid, and great -attention is necessary to keep it at the elevation desired. The air has -no surface. The air ship is like a submarine--the dirigible balloon -of the sea--and perhaps rather more safe. An ordinary ship is only -partially immersed; the resistance of the fluid medium is exerted over -a portion only of its head end: but the submarine or the flying machine -is wholly exposed to this resistance. The submarine is subjected to -ocean currents of a very few miles per hour, at most; the currents to -which the flying machine may be exposed exceed a mile a minute. Put a -submarine in the Whirlpool Rapids at Niagara and you will have possible -air ship conditions. - -A marine vessel may _tack_, _i.e._, may sail partially against the -wind that propels it, by skillful utilization of the resistance to -sidewise movement of the ship through the water: but the flying machine -is wholly immersed in a single fluid, and a head wind is nothing else -than a head wind, producing an absolute subtraction from the proper -speed of the vessel. - - [Illustration: HOW A BOAT TACKS - The wind always exerts a pressure, perpendicular to the sail, - which tends to drift the boat sidewise (R) and also to propel - it forward (L). Sidewise movement is resisted by the hull. - An air ship cannot tack because there is no such resistance - to drift.] - -Aerial navigation is thus a new art, particularly when heavier-than-air -machines are used. We have no heavier-than-water _ships_. The flying -machine must work out its own salvation. - - - - -SOARING FLIGHT BY MAN - - -Flying machines have been classified as follows:-- - - Lighter than Air - Fixed balloon, - Drifting balloon, - Sailing balloon, - Dirigible balloon - rigid (Zeppelin), - ballonetted. - - Heavier than Air - Orthopter, - Helicopter, - Aeroplane - monoplane, - multiplane. - -We will fall in with the present current of popular interest and -consider the aeroplane--that mechanical grasshopper--first. - - -What Holds It Up? - - [Illustration: OCTAVE CHANUTE (DIED 1910)] - -To the researches of Chanute and Langley must be ascribed much of -American progress in aviation. - -When a flat surface like the side of a house is exposed to the breeze, -the velocity of the wind exerts a force or pressure directly against -the surface. This principle is taken into account in the design of -buildings, bridges, and other structures. The pressure exerted per -square foot of surface is equal (approximately) to the square of the -wind velocity in miles per hour, divided by 300. Thus, if the wind -velocity is thirty miles, the pressure against a house wall on which it -acts directly is 30 × 30 ÷ 300 = 3 pounds per square foot: if the wind -velocity is sixty miles, the pressure is 60 × 60 ÷ 300 = 12 pounds: -if the velocity is ninety miles, the pressure is 90 × 90 ÷ 300 = 27 -pounds, and so on. - - [Illustration: PRESSURE OF THE WIND] - -If the wind blows obliquely toward the surface, instead of directly, -the pressure at any given velocity is reduced, but may still be -considerable. Thus, in the sketch, let _ab_ represent a wall, toward -which we are looking downward, and let the arrow _V_ represent the -direction of the wind. The air particles will follow some such paths -as those indicated, being deflected so as to finally escape around -the ends of the wall. The result is that a pressure is produced which -may be considered to act along the dotted line _P_, perpendicular to -the wall. This is the invariable law: that no matter how oblique the -surface may be, with reference to the direction of the wind, there is -always a pressure produced against the surface by the wind, and this -pressure always acts _in a direction perpendicular to the surface_. The -amount of pressure will depend upon the wind velocity and the obliquity -or inclination of the surface (_ab_) with the wind (_V_). - -Now let us consider a kite--the "immediate ancestor" of the aeroplane. -The surface _ab_ is that of the kite itself, held by its string _cd_. -We are standing at one side and looking at the _edge_ of the kite. The -wind is moving horizontally against the face of the kite, and produces -a pressure _P_ directly against the latter. The pressure tends both to -move it toward the left and to lift it. If the tendency to move toward -the left be overcome by the string, then the tendency toward lifting -may be offset--and in practice _is_ offset--by the weight of the kite -and tail. - - [Illustration: FORCES ACTING ON A KITE] - -We may represent the two tendencies to movement produced by the force -_P_, by drawing additional dotted lines, one horizontally to the left -(_R_) and the other vertically (_L_); and it is known that if we let -the length of the line _P_ represent to some convenient scale the -amount of direct pressure, then the lengths of _R_ and _L_ will also -represent to the same scale the amounts of horizontal and vertical -force due to the pressure. If the weight of kite and tail exceeds the -vertical force _L_, the kite will descend: if these weights are less -than that force, the kite will ascend. If they are precisely equal to -it, the kite will neither ascend nor descend. The ratio of _L_ to _R_ -is determined by the slope of _P_; and this is fixed by the slope of -_ab_; so that we have the most important conclusion: _not only does -the amount of direct pressure (P) depend upon the obliquity of the -surface with the breeze (as has already been shown), but the relation -of vertical force (which sustains the kite) to horizontal force also -depends on the same obliquity_. For example, if the kite were flying -almost directly above the boy who held the string, so that _ab_ became -almost horizontal, _P_ would be nearly vertical and _L_ would be much -greater than _R_. On the other hand, if _ab_ were nearly vertical, the -kite flying at low elevation, the string and the direct pressure would -be nearly horizontal and _L_ would be much less than _R_. The force _L_ -which lifts the kite seems to increase while _R_ decreases, as the kite -ascends: but _L_ may not actually increase, because it depends upon the -amount of direct pressure, _P_, as well as upon the direction of this -pressure; and the amount of direct pressure steadily decreases during -ascent, on account of the increasing obliquity of _ab_ with _V_. All of -this is of course dependent on the assumption that the kite always has -the same inclination to the string, and the described resolution of the -forces, although answering for illustrative purposes, is technically -incorrect. - -It seems to be the wind velocity, then, which holds up the kite: but -in reality the string is just as necessary as the wind. If there is -no string, and the wind blows the kite with it, the kite comes down, -because the pressure is wholly due to a relative velocity as between -kite and wind. The wind exerts a pressure against the rear of a railway -train, if it happens to be blowing in that direction, and if we -stood on the rear platform of a stationary train we should feel that -pressure: but if the train is started up and caused to move at the same -speed as the wind there would be no pressure whatever. - -One of the very first heavier-than-air flights ever recorded is said -to have been made by a Japanese who dropped bombs from an immense -man-carrying kite during the Satsuma rebellion of 1869. The kite as -a flying machine has, however, two drawbacks: it needs the wind--it -cannot fly in a calm--and it stands still. One early effort to improve -on this situation was made in 1856, when a man was towed in a sort of -kite which was hauled by a vehicle moving on the ground. In February -of the present year, Lieut. John Rodgers, U.S.N., was lifted 400 feet -from the deck of the cruiser _Pennsylvania_ by a train of eleven large -kites, the vessel steaming at twelve knots against an eight-knot -breeze. The aviator made observations and took photographs for about -fifteen minutes, while suspended from a tail cable about 100 feet -astern. In the absence of a sufficient natural breeze, an artificial -wind was thus produced by the motion imparted to the kite; and the -device permitted of reaching some destination. The next step was -obviously to get rid of the tractive vehicle and tow rope by carrying -propelling machinery on the kite. This had been accomplished by Langley -in 1896, who flew a thirty-pound model nearly a mile, using a steam -engine for power. The gasoline engine, first employed by Santos-Dumont -(in a dirigible balloon) in 1901, has made possible the present day -_aeroplane_. - - [Illustration: SUSTAINING FORCE IN THE AEROPLANE] - -What "keeps it up", in the case of this device, is likewise its -velocity. Looking from the side, _ab_ is the sail of the aeroplane, -which is moving toward the right at such speed as to produce the -equivalent of an air velocity _V_ to the left. This velocity causes the -direct pressure _P_, equivalent to a lifting force _L_ and a retarding -force _R_. The latter is the force which must be overcome by the motor: -the former must suffice to overcome the whole weight of the apparatus. -Travel in an aeroplane is like skating rapidly over very thin ice: the -air literally "doesn't have time to get away from underneath." - - [Illustration: DIRECT, LIFTING, AND RESISTING FORCES - If the pressure is 10 lbs. when the wind blows directly toward the - surface (at an angle of 90 degrees), then the forces for other angles - of direction are as shown on the diagram. The _amounts_ of all forces - depend upon the wind velocity: that assumed in drawing the diagram - was about 55 miles per hour. But the _relations_ of the forces are - the same for the various angles, no matter what the velocity.] - -If we designate the angle made by the wings (_ab_) with the horizontal -(_V_) as _B_, then _P_ increases as _B_ increases, while (as has been -stated) the ratio of _L_ to _R_ decreases. When the angle _B_ is a -right angle, the wings being in the position _a´b´_, _P_ has its -maximum value for direct wind--1/300 of the square of the velocity, -in pounds per square foot; but _L_ is zero and _R_ is equal to _P_. -The plane would have no lifting power. When the angle _B_ becomes -zero, position _a´´b´´_, wings being horizontal, _P_ becomes zero -and (so far as we can now judge) the plane has neither lifting power -nor retarding force. At some intermediate position, like _ab_, there -will be appreciable lifting and retarding forces. The chart shows the -approximate lifting force, in pounds per square foot, for various -angles. This force becomes a maximum at an angle of 45° (half a -right angle). We are not yet prepared to consider why in all actual -aeroplanes the angle of inclination is much less than this. The reason -will be shown presently. At this stage of the discussion we may note -that the lifting power per square foot of sail area varies with - - the square of the velocity, _and_ - the angle of inclination. - -The total lifting power of the whole plane will also vary with its -area. As we do not wish this whole lifting power to be consumed in -overcoming the dead weight of the machine itself, we must keep the -parts light, and in particular must use for the wings a fabric of light -weight per unit of surface. These fabrics are frequently the same as -those used for the envelopes of balloons. - -Since the total supporting power varies both with the sail area and -with the velocity, we may attain a given capacity either by employing -large sails or by using high speed. The size of sails for a given -machine varies inversely as the square of the speed. The original -Wright machine had 500 square feet of wings and a speed of forty -miles per hour. At eighty miles per hour the necessary sail area for -this machine would be only 125 square feet; and at 160 miles per hour -it would be only 31-1/4 square feet: while if we attempted to run the -machine at ten miles per hour we should need a sail area of 8000 square -feet. This explains why the aeroplane cannot go slowly. - -It would seem as if when two or more superposed sails were used, as in -biplanes, the full effect of the air would not be realized, one sail -becalming the other. Experiments have shown this to be the case; but -there is no great reduction in lifting power unless the distance apart -is considerably less than the width of the planes. - -In all present aeroplanes the sails are concaved on the under side. -This serves to keep the air from escaping from underneath as rapidly -as it otherwise would, and increases the lifting power from one-fourth -to one-half over that given by our 1/300 rule: the divisor becoming -roughly about 230 instead of 300. - - [Illustration: SHAPES OF PLANES] - -Why are the wings placed crosswise of the machine, when the other -arrangement--the greatest dimension in the line of flight--would seem -to be stronger? This is also done in order to "keep the air from -escaping from underneath." The sketch shows how much less easily the -air will get away from below a wing of the bird-like spread-out form -than from one relatively long and narrow but of the same area. - -A sustaining force of two pounds per square foot of area has been -common in ordinary aeroplanes and is perhaps comparable with the -results of bird studies: but this figure is steadily increasing as -velocities increase. - - -Why so Many Sails? - -Thus far a single wing or pair of wings would seem to fully answer -for practicable flight: yet every actual aeroplane has several small -wings at various points. The necessity for one of these had already -been discovered in the kite, which is built with a balancing tail. In -the sketch on page 18 it appears that the particles of air which are -near the upper edge of the surface are more obstructed in their effort -to get around and past than those near the lower edge. They have to -turn almost completely about, while the others are merely deflected. -This means that on the whole the upper air particles will exert more -pressure than the lower particles and that the "center of pressure" -(the point where the entire force of the wind may be assumed to act) -will be, not at the center of the surface, but at a point some distance -_above_ this center. This action is described as the "displacement of -the center of pressure." It is known that the displacement is greatest -for least inclinations of surface (as might be surmised from the -sketch already referred to), and that it is always proportional to the -dimension of the surface in the direction of movement; _i.e._, to the -length of the line _ab_. - - [Illustration: BALANCING SAIL] - -If the weight _W_ of the aeroplane acts downward at the center of the -wing (at _o_ in the accompanying sketch), while the direct pressure -_P_ acts at some point _c_ farther along toward the upper edge of -the wing, the two forces _W_ and _P_ tend to revolve the whole wing -in the direction indicated by the curved arrow. This rotation, in an -aeroplane, is resisted by the use of a tail plane or planes, such as -_mn_. The velocity produces a direct pressure _P´_ on the tail plane, -which opposes, like a lever, any rotation due to the action of _P_. -It may be considered a matter of rather nice calculation to get the -area and location of the tail plane just right: but we must remember -that the amount of pressure _P´_ can be greatly varied by changing -the inclination of the surface _mn_. This change of inclination is -effected by the operator, who has access to wires which are attached to -the pivoted tail plane. It is of course permissible to place the tail -plane _in front_ of the main planes--as in the original Wright machine -illustrated: but in this case, with the relative positions of _W_ and -_P_ already shown, the forward edge of the tail plane would have to be -depressed instead of elevated. The illustration shows the tail built as -a biplane, just as are the principal wings (page 141). - -Suppose the machine to be started with the tail plane in a horizontal -position. As its speed increases, it rises and at the same time (if -the weight is suspended from the center of the main planes) tilts -backward. The tilting can be stopped by swinging the tail plane on its -pivot so as to oppose the rotative tendency. If this control is not -carried too far, the main planes will be allowed to maintain some of -their excessive inclination and ascent will continue. When the desired -altitude has been attained, the inclination of the main planes will, by -further swinging of the tail plane, be reduced to the normal amount, -at which the supporting power is precisely equal to the load; and the -machine will be in vertical equilibrium: an equilibrium which demands -at every moment, however, the attention of the operator. - -In many machines, ascent and tilting are separately controlled by using -two sets of transverse planes, one set placed forward, and the other -set aft, of the main planes. In any case, quick ascent can be produced -only by an increase in the lifting force _L_ (see sketch, page 24) of -the main planes: and this force is increased by enlarging the angle of -inclination of the main planes, that is, by a controlled and partial -tilting. The forward transverse wing which produces this tilting is -therefore called the _elevating rudder_ or elevating plane. The rear -transverse plane which checks the tilting and steadies the machine is -often described as the _stabilizing plane_. _Descent_ is of course -produced by _decreasing_ the angle of inclination of the main planes. - - [Illustration: ROE'S TRIPLANE AT WEMBLEY - (From Brewer's _Art of Aviation_)] - - -Steering - -If we need extra sails for stability and ascent or descent, we need -them also for changes of horizontal direction. Let _ab_ be the top view -of the main plane of a machine, following the course _xy_. At _rs_ -is a vertical plane called the _steering rudder_. This is pivoted, -and controlled by the operator by means of the wires _t_, _u_. Let -the rudder be suddenly shifted to the position _r´s´_. It will then -be subjected to a pressure _P´_ which will swing the whole machine -into the new position shown by the dotted lines, its course becoming -_x´y´_. The steering rudder may of course be double, forming a vertical -biplane, as in the Wright machine shown below. - - [Illustration: ACTION OF THE STEERING RUDDER] - -Successful steering necessitates lateral resistance to drift, _i.e._, -a fulcrum. This is provided, to some extent, by the stays and frame of -the machine; and in a much more ample way by the vertical planes of the -original Voisin cellular biplane. A recent Wright machine had vertical -planes forward probably intended for this purpose. - - [Illustration: RECENT TYPE OF WRIGHT BIPLANE] - -It now begins to appear that the aviator has a great many things to -look after. There are many more things requiring his attention than -have yet been suggested. No one has any business to attempt flying -unless he is superlatively cool-headed and has the happy faculty of -instinctively doing the right thing in an emergency. Give a chauffeur -a high power automobile running at maximum speed on a rough and -unfamiliar road, and you have some conception of the position of the -operator of an aeroplane. It is perhaps not too much to say that to -make the two positions fairly comparable we should _blindfold_ the -chauffeur. - -Broadly speaking, designers may be classed in one of two groups--those -who, like the Wrights, believe in training the aviator so as to -qualify him to properly handle his complicated machine; and those -who aim to simplify the whole question of control so that to acquire -the necessary ability will not be impossible for the average man. If -aviation is to become a popular sport, the latter ideal must prevail. -The machines must be more automatic and the aviator must have time -to enjoy the scenery. In France, where amateur aviation is of some -importance, progress has already been made in this direction. The -universal steering head, for example, which not only revolves like that -of an automobile, but is hinged to permit of additional movements, -provides for simultaneous control of the steering rudder and the main -plane warping, while scarcely demanding the conscious thought of the -operator. - - - - -TURNING CORNERS - - -A year elapsed after the first successful flight at Kitty Hawk before -the aviator became able to describe a circle in the air. A later date, -1907, is recorded for the first European half-circular flight: and the -first complete circuit, on the other side of the water, was made a year -after that; by both biplane and monoplane. It was in the same year that -Louis Blériot made the pioneer cross-country trip of twenty-one miles, -stopping at will _en route_ and returning to his starting point. - - -What Happens When Making a Turn - - [Illustration: CIRCULAR FLIGHT] - -We are looking downward on an aeroplane _ab_ which has been moving -along the straight path _cd_. At _d_ it begins to describe the circle -_de_, the radius of which is _od_, around the center _o_. The outer -portion of the plane, at the edge _b_, must then move faster than the -inner edge _a_. We have seen that the direct air pressure on the plane -is proportional to the square of the velocity. The direct pressure -_P_ (see sketch on page 22) will then be greater at the outer than at -the inner limb; the lifting force _L_ will also be greater and the -outer limb will tend to rise, so that the plane (viewed from the rear) -will take the inclined position shown in the lower view: and this -inclination will increase as long as the outer limb travels faster than -the inner limb; that is, as long as the orbit continues to be curved. -Very soon, then, the plane will be completely tipped over. - -Necessarily, the two velocities have the ratio _om_:_om´_; the -respective lifting forces must then be proportional to the squares of -these distances. The difference of lifting forces, and the tendency to -overturn, will be more important as the distances most greatly differ: -which is the case when the distance _om_ is small as compared with -_mm´_. The shorter the radius of curvature, the more dangerous, for a -given machine, is a circling flight: and in rounding a curve of given -radius the most danger is attached to the machine of greatest spread of -wing. - - -Lateral Stability - -This particular difficulty has considerably delayed the development -of the aeroplane. It may, however, be overcome by very simple -methods--simple, at least as far as their mechanical features are -concerned. If the outer limb of the plane is tilted upward, it is -because the wind pressure is greater there. The wind pressure is -greater because the velocity is greater. We have only to increase the -wind pressure at the inner limb, in order to restore equilibrium. This -cannot be done by adjusting the velocity, because the velocity is fixed -by the curvature of path required: but the total wind pressure depends -upon the _sail area_ as well as the velocity; so that by increasing the -surface at the inner limb we may equalize the value of _L_, the lifting -force, at the two ends of the plane. This increase of surface must be -a temporary affair, to be discontinued when moving along a straight -course. - - [Illustration: THE AILERON] - -Let us stand in the rear of an aeroplane, the main wing of which is -represented by _ab_. Let the small fan-shaped wings _c_ and _d_ be -attached near the ends, and let the control wires, _e_, _f_, passing -to the operator at _g_, be employed to close and unclasp the fans. If -these fans are given a forward inclination at the top, as indicated in -the end view, they will when spread out exert an extra lifting force. -A fan will be placed at each end. They will be ordinarily folded up: -but when rounding a curve the aviator will open the fan on the inner or -more slowly moving limb of the main plane. This represents one of the -first forms of the _aileron_ or wing-tip for lateral control. - -The more common present form of aileron is that shown in the lower -sketch, at _s_ and _t_. The method of control is the same. - - [Illustration: WING TIPPING] - -The cellular Voisin biplanes illustrate an attempt at self-sufficing -control, without the interposition of the aviator. Between the upper -and lower sails of the machine there were fore and aft vertical -partitions. The idea was that when the machine started to revolve, the -velocity of rotation would produce a pressure against these partitions -which would obstruct the tipping. But rotation may take place slowly, -so as to produce an insufficient pressure for control, and yet be amply -sufficient to wreck the apparatus. The use of extra vertical rudder -planes, hinged on a horizontal longitudinal axis, is open to the same -objection. - - -Wing Warping - -In some monoplanes with the inverted _V_ wing arrangement, a dipping -of one wing answers, so to speak, to increase its concavity and thus -to augment the lifting force on that side. The sketch shows the normal -and distorted arrangement of wings: the inner limb being the one bent -down in rounding a curve. An equivalent plan was to change the angle -of inclination of one-half the sail by swinging it about a horizontal -pivot at the center or at the rear edge: some machines have been built -with sails divided in the center. The obvious objection to both of -these plans is that too much mechanism is necessary in order to distort -what amounts to nearly half the whole machine. They remind one of -Charles Lamb's story of the discovery of roast pig. - - [Illustration: WING WARPING] - -The distinctive feature of the Wright machines lies in the warping -or distorting of the _ends only_ of the main planes. This is made -possible, not by hinging the wings in halves, but by the flexibility -of the framework, which is sufficiently pliable to permit of a -considerable bending without danger. The operator, by pulling on a -stout wire linkage, may tip up (or down) the corners _cc´_ of the sails -at one limb, thus decreasing or increasing the effective surface acted -on by the wind, as the case may require. The only objection is that -the scheme provides one more thing for the aviator to think about and -manipulate. - - -Automatic Control - -Let us consider again the condition of things when rounding a curve, -as in the sketch on page 32. As long as the machine is moving forward -in a straight line, the operator sits upright. When it begins to tip, -he will unconsciously tip himself the other way, as represented by -the line _xy_ in the rear view. Any bicyclist will recognize this as -plausible. Why not take advantage of this involuntary movement to -provide a stabilizing force? If operating wires are attached to the -aviator's belt and from thence connected with ailerons or wing-warping -devices, then by a proper proportioning of levers and surfaces to the -probable swaying of the man, the control may become automatic. The idea -is not new; it has even been made the subject of a patent. - - -The Gyroscope - - [Illustration: THE GYROSCOPE] - -This device for automatic control is being steadily developed and may -ultimately supersede all others. It uses the inertia of a fast-moving -fly wheel for control, in a manner not unlike that contemplated in -proposed methods of automatic balancing by the action of a suspended -pendulum. Every one has seen the toy gyroscope and perhaps has wondered -at its mysterious ways. The mathematical analysis of its action fills -volumes: but some idea of what it does, and why, may perhaps be -gathered at the expense of a very small amount of careful attention. -The wheel _acbd_, a thin disc, is spinning rapidly about the axle _o_. -In the side view, _ab_ shows the edge of the wheel, and _oo´_ the -axle. This axle is not fixed, but may be conceived as held in some -one's fingers. Now suppose the right-hand end of the axle (_o´_) to -be suddenly moved toward us (away from the paper) and the left-hand -(_o_) to be moved away. The wheel will now appear in both views as an -ellipse, and it has been so represented, as _afbe_. Now, any particle, -like _x_, on the rim of the wheel, will have been regularly moving -in the circular orbit _cb_. The tendency of any body in motion is to -move indefinitely in a straight line. The cohesion of the metal of -the disc prevents the particle _x_ from flying off at a straight line -tangent, _xy_, and it is constrained, therefore, to move in a circular -orbit. Unless some additional constraint is imposed, it will at least -remain in this orbit and will try to remain in its plane of rotation. -When the disc is tipped, the plane of rotation is changed, and the -particle is required, instead of (so to speak) remaining in the plane -of the paper--in the side view--to approach and pass through that plane -at _b_ and afterward to continue receding from us. Under ordinary -circumstances, this is just what it would do: but if, as in the -gyroscope, the axle _oo´_ is perfectly free to move in any direction, -the particle _x_ will refuse to change its direction of rotation. -Its position has been shifted: it no longer lies in the plane of the -paper: but it will at least persist in rotating in a parallel plane: -and this persistence forces the revolving disc to swing into the new -position indicated by the curve _hg_, the axis being tipped into the -position _pq_. The whole effect of all particles like _x_ in the entire -wheel will be found to produce precisely this condition of things: if -we undertake to change the plane of rotation by shifting the axle in -a horizontal plane, the device itself will (if not prevented) make -a further change in the plane of rotation by shifting the axle in a -vertical plane. - -A revolving disc mounted on the gyroscopic framework therefore resists -influences tending to change its plane of rotation. If the device -is placed on a steamship, so that when the vessel rolls a change of -rotative plane is produced, the action of the gyroscope will resist -the rolling tendency of the vessel. All that is necessary is to have -the wheel revolving in a fore and aft plane on the center line of the -vessel, the axle being transverse and firmly attached to the vessel -itself. A small amount of power (consumed in revolving the wheel) gives -a marked steadying effect. The same location and arrangement on an -aeroplane will suffice to overcome tendencies to transverse rotation -when rounding curves. The device itself is automatic, and requires no -attention, but it does unfortunately require power to drive it and it -adds some weight. - -The gyroscope is being tested at the present time on some of the -aeroplanes at the temporary army camps near San Antonio, Texas. - - -Wind Gusts - -This feature of aeronautics is particularly important, because any -device which will give automatic stability when turning corners will go -far toward making aviation a safe amusement. Inequalities of velocity -exist not only on curves, but also when the wind is blowing at anything -but uniform velocity across the whole front of the machine. The -slightest "flaw" in the wind means an at least temporary variation in -lifting force of the two arms. Here is a pregnant source of danger, and -one which cannot be left for the aviator to meet by conscious thought -and action. It is this, then, that blindfolds him: he cannot see the -wind conditions in advance. The conditions are upon him, and may have -done their destructive work, before he can prepare to control them. We -must now study what these conditions are and what their influence may -be on various forms of aerial navigation: after which, a return to our -present subject will be possible. - - - - -AIR AND THE WIND - -The air that surrounds us weighs about one-thirteenth of a pound per -cubic foot and exerts a pressure, at sea level, of nearly fifteen -pounds per square inch. Its temperature varies from 30° below to 100° -above the Fahrenheit zero. The pressure of the air decreases about -one-half pound for each thousand feet of altitude; at the top of Mt. -Blanc it would be, therefore, only about six pounds per square inch. -The temperature also decreases with the altitude. The weight of a cubic -foot, or _density_, which, as has been stated, is one-thirteenth of a -pound ordinarily, varies with the pressure and with the temperature. -The variation with pressure may be described by saying that the -_quotient_ of the pressure by the density is constant: one varies in -the same ratio as the other. Thus, at the top of Mt. Blanc (if the -temperature were the same as at sea level), the density of air would be -about 6/15 × 1/13 = 2/65: less than half what it is at sea level. As to -temperature, if we call our Fahrenheit zero 460°, and correspondingly -describe other temperatures--for instance, say that water boils at -672°--then (pressure being unchanged) the _product_ of the density -and the temperature is constant. If the density at sea level and zero -temperature is one-thirteenth pound, then that at sea level and 460° -Fahrenheit would be - - (0 + 460)/(460 + 460) × 1/13 = 1/26. - -These relations are particularly important in the design of all -balloons, and in computations relating to aeroplane flight at -high altitudes. We shall be prepared to appreciate some of their -applications presently. - -Generally speaking, the atmosphere is always in motion, and moving air -is called wind. Our meteorologists first studied winds near the surface -of the ground: it is only of late years that high altitude measurements -have been considered practically desirable. Now, records are obtained -by the aid of kites up to a height of nearly four miles: estimates of -cloud movements have given data on wind velocities at heights above six -miles: and much greater heights have been obtained by free balloons -equipped with instruments for recording temperatures, pressures, -altitude, time, and other data. - -When the Eiffel Tower was completed, it was found that the average wind -velocity at its summit was about four times that at the base. Since -that time, much attention has been given to the contrasting conditions -of surface and upper breezes as to direction and velocity. - -Air is easily impeded in its movement, and the well-known uncertainties -of the weather are closely related to local variations in atmospheric -pressure and temperature. When near the surface of the ground, -impingement against irregularities therein--hills, cliffs, and -buildings--makes the atmospheric currents turbulent and irregular. -Where there are no surface irregularities, as on a smooth plain or -over water, the friction of the air particles passing over the surface -still results in a stratification of velocities. Even on a mountain -top, the direction and speed of the wind are less steady than in the -open where measured by a captive balloon. The stronger the wind, -the greater, relatively, is the irregularity produced by surface -conditions. Further, the earth's surface and its features form a vast -sponge for sun heat, which they transfer in turn to the air in an -irregular way, producing those convectional currents peculiar to low -altitudes, the upper limit of which is marked by the elevation of the -cumulus clouds. Near the surface, therefore, wind velocities are lowest -in the early morning, rising to a maximum in the afternoon. - - [Illustration: DIURNAL TEMPERATURES AT DIFFERENT HEIGHTS - (From Rotch's _The Conquest of the Air_)] - -Every locality has its so-called "prevailing winds." Considering the -compass as having eight points, one of those points may describe -as many as 40% of all the winds at a given place. The direction of -prevalence varies with the season. The range of wind velocities is -also a matter of local peculiarity. In Paris, the wind speed exceeds -thirty-four miles per hour on only sixty-eight days in the average -year, and exceeds fifty-four miles on only fifteen days. Observations -at Boston show that the velocity of the wind exceeds twenty miles per -hour on half the days in winter and on only one-sixth the days in -summer. Our largest present dirigible balloons have independent speeds -of about thirty-four miles per hour and are therefore available (at -some degree of effectiveness) for nearly ten months of the year, in the -vicinity of Paris. In a region of low wind velocities--like western -Washington, in this country--they would be available a much greater -proportion of the time. To make the dirigible able to at least move -nearly every day in the average year--in Paris--it must be given a -speed of about fifty-five miles per hour. - -Figures as to wind velocity mean little to one unaccustomed to using -them. A five-mile breeze is just "pleasant." Twelve miles means a brisk -gale. Thirty miles is a high wind: fifty miles a serious storm (these -are the winds the aviator constantly meets): one hundred miles is -perhaps about the maximum hurricane velocity. - -As we ascend from the surface of the earth, the wind velocity steadily -increases; and the excess velocity of winter winds over summer winds -is as steadily augmented. Thus, Professor Rotch found the following -variations: - - Altitude in Feet Annual Average - Wind Velocity, Feet per Second - 656 23.15 - 1,800 32.10 - 3,280 35. - 8,190 41. - 11,440 50.8 - 17,680 81.7 - 20,970 89. - 31,100 117.5 - - Average Wind Velocities, - Altitude in Feet Feet per Second - Summer Winter - 656 to 3,280 24.55 28.80 - 3,280 to 9,810 26.85 48.17 - 9,810 to 16,400 34.65 71.00 - 16,400 to 22,950 62.60 161.5 - 22,950 to 29,500 77.00 177.0 - - [Illustration: DIURNAL TEMPERATURES AT DIFFERENT HEIGHTS] - -These results are shown in a more striking way by the chart. At a five -or six mile height, double-barreled hurricanes at speeds exceeding 200 -miles per hour are not merely possible; they are part of the regular -order of things, during the winter months. - -The winds of the upper air, though vastly more powerful, are far less -irregular than those near the surface: and the directions of prevailing -winds are changed. If 50% of the winds, at a given location on the -surface, are from the southwest, then at as moderate an elevation -as even 1000 feet, the prevailing direction will cease to be from -southwest; it may become from west-southwest; and the proportion of -total winds coming from this direction will not be 50%. These factors -are represented in meteorological papers by what is known as the _wind -rose_. From the samples shown, we may note that 40% of the surface -winds at Mount Weather are from the northwest; while at some elevation -not stated the most prevalent of the winds (22% of the total) are -westerly. The direction of prevalence has changed through one-eighth -of the possible circle, and in a _counter-clockwise_ direction. This -is contrary to the usual variation described by the so-called Broun's -Law, which asserts that as we ascend the direction of prevalence -rotates around the circle like the hands of a watch; being, say, from -northwest at the surface, from north at some elevation, from northeast -at a still higher elevation, and so on. At a great height, the change -in direction may become total: that is, the high altitude winds blow -in the exactly opposite direction to that of the surface winds. In -the temperate regions, most of the high altitude winds are from the -west: in the tropics, the surface winds blow _toward_ the west and -toward the equator; being northeasterly in the northern hemisphere -and southeasterly in the southern: and there are undoubtedly equally -prevalent high-altitude counter-trades. - - [Illustration: THE WIND ROSE FOR MOUNT WEATHER, VA. - (From the _Bulletin_ of the Mount Weather Observatory, II, 6)] - -The best flying height for an aeroplane over a flat field out in the -country is perhaps quite low--200 or 300 feet: but for cross-country -trips, where hills, rivers, and buildings disturb the air currents, a -much higher elevation is necessary; perhaps 2000 or 3000 feet, but in -no case more than a mile. The same altitude is suitable for dirigible -balloons. At these elevations we have the conditions of reasonable -warmth, dryness, and moderate wind velocities. - - -Sailing Balloons - -In classifying air craft, the sailing balloon was mentioned as a type -intermediate between the drifting balloon and the dirigible. No such -type has before been recognized: but it may prove to have its field, -just as the sailing vessel on the sea has bridged the gap between the -raft and the steamship. It is true that tacking is impossible, so that -our sailing balloons must always run before the wind: but they possess -this great advantage over marine sailing craft, that by varying their -altitude they may always be able to find a favorable wind. This implies -adequate altitude control, which is one of the problems not yet solved -for lighter-than-air flying machines: but when it has been solved we -shall go far toward attaining a dirigible balloon without motor or -propeller; a true sailing craft. - - [Illustration: DIAGRAM OF PARTS OF A DRIFTING BALLOON] - -This means more study and careful utilization of stratified atmospheric -currents. Professor Rotch suggests the utilization of the upper -westerly wind drift across the American continent and the Atlantic -Ocean, which would carry a balloon from San Francisco to southern -Europe at a speed of about fifty feet per second--thirty-four miles -per hour. Then by transporting the balloon to northern Africa, the -northeast surface trade wind would drive it back to the West Indies at -twenty-five miles per hour. This without any motive power: and since -present day dirigibles are all short of motive power for complete -dirigibility, we must either make them much more powerful or else adopt -the sailing principle, which will permit of actually decreasing present -sizes of motors, or even possibly of omitting them altogether. Our next -study is, then, logically, one of altitude control in balloons. - - [Illustration: GLIDDEN AND STEVENS GETTING AWAY IN THE "BOSTON" - (Leo Stevens, N.Y.)] - - -Field and Speed - - [Illustration: RELATIVE AND ABSOLUTE BALLOON VELOCITIES] - - [Illustration: FIELD AND SPEED] - -An _aerostat_ (non-dirigible balloon), unless anchored, drifts at the -speed of the wind. To the occupants, it seems to stand still, while -the surface of the earth below appears to move in a direction opposite -to that of the wind. In the sketch, if the independent velocity of a -_dirigible_ balloon be _PB_, the wind velocity _PV_, then the actual -course pursued is _PR_, although the balloon always points in the -direction _PB_, as shown at 1 and 2. If the speed of the wind exceed -that of the balloon, there will be some directions in which the latter -cannot progress. Thus, let _PV_ be the wind velocity and _TV_ the -independent speed of the balloon. The tangents _PX_, _PX´_, include the -whole "field of action" possible. The wind direction may change during -flight, so that the initial objective point may become unattainable, -or an initially unattainable point may be brought within the field. The -present need is to increase independent speeds from thirty or forty -to fifty or sixty miles per hour, so that the balloon will be truly -dirigible (even if at low effectiveness) during practically the whole -year. - - [Illustration: INFLUENCE OF WIND ON POSSIBLE COURSE] - -Suppose a dirigible to start on a trip from New York to Albany, -150 miles away. Let the wind be a twenty-five mile breeze from the -southwest. The wind alone tends to carry the balloon from New York to -the point _d_ in four hours. If the balloon meanwhile be headed due -west, it would need an independent velocity of its own having the same -ratio to that of the wind as that of _de_ to _fd_, or about seventeen -and one-half miles per hour. Suppose its independent speed to be only -twelve and one-half miles; then after four hours it will be at the -position _b_, assuming it to have been continually headed due west, as -indicated at _a_. It will have traveled northward the distance _fe_, -apparently about sixty-nine miles. - - [Illustration: COUNT ZEPPELIN] - -After this four hours of flight, the wind suddenly changes to -south-southwest. It now tends to carry the balloon to _g_ in the next -four hours. Meanwhile the balloon, heading west, overcomes the easterly -drift, and the balloon actually lands at _c_. Unless there is some -further favorable shift of the wind it cannot reach Albany. If, during -the second four hours, its independent speed could have been increased -to about fifteen and a half miles it would have just made it. The -actual course has been _fbc_: a drifting balloon would have followed -the course _fdh_, _dh_ being a course parallel to _bg_. - - - - -GAS AND BALLAST - - -A cubical block of wood measuring twelve inches on a side floats on -water because it is lighter than water; it weighs, if yellow pine, -thirty-eight pounds, whereas the same volume of water weighs about -sixty-two pounds. Any substance weighing more than sixty-two pounds to -the cubic foot would sink in water. - - [Illustration: BUOYANT POWER OF WOOD] - -If our block of wood be drilled, and _lead_ poured in the hole, the -total size of wood-and-lead block being kept constantly at one cubic -foot, the block will sink as soon as its whole weight exceeds sixty-two -pounds. Ignoring the wood removed by boring (as, compared with the lead -which replaces it, an insignificant amount), the weight of lead plugged -in may reach twenty-four pounds before the block will sink. - -This figure, twenty-four pounds, the difference between sixty-two and -thirty-eight pounds, then represents the maximum buoyant power of a -cubic foot of wood in water. It is the difference between the weight of -the wood block and the weight of the water it displaces. If any weight -less than this is added to that of the wood, the block will float, -projecting above the water's surface more or less, according to the -amount of weight buoyed up. It will not rise entirely from the water, -because to do this it would need to be lighter, not only than water, -but than air. - - [Illustration: ONE CUBIC FOOT OF WOOD LOADED IN WATER] - - -Buoyancy in Air - -There are _gases_, if not woods, lighter than air: among them, coal gas -and hydrogen. A "bubble" of any of these gases, if isolated from the -surrounding atmosphere, cannot sink but must rise. At the same pressure -and temperature, hydrogen weighs about one-fifteenth as much as air; -coal gas, about one-third as much. If a bubble of either of these gases -be isolated in the atmosphere, it must continually rise, just as wood -immersed in water will rise when liberated. But the wood will stop -when it reaches the surface of the water, while there is no reason -to suppose that the hydrogen or coal gas bubbles will ever stop. The -hydrogen bubble can be made to remain stationary if it is weighted down -with something of about fourteen times its own weight (thirteen and -one-half times, accurately). Perhaps it would be better to say that it -would still continue to rise slowly because that additional something -would itself displace some additional air; but if the added weight is a -solid body, its own buoyancy in air is negligible. - - [Illustration: BUOYANT POWER OF HYDROGEN] - -Our first principle is, then, that at the same pressure and -temperature, any gas lighter than air, if properly confined, will exert -a net lifting power of (_n_-1) times its own weight, where _n_ is the -ratio of weights of air and gas per cubic foot. - - [Illustration: LEBAUDY'S "JAUNE"] - -If the pressures and temperatures are different, this principle is -modified. In a balloon, the gas is under a pressure slightly in -excess of that of the external atmosphere: this decreases its lifting -power, because the weight of a given volume of gas is greater as the -pressure to which it is subjected is increased. The weight of a given -volume we have called the _density_: and, as has been stated, if the -temperature be unchanged, the density varies directly as the pressure. - -The pressure in a balloon is only about 1% greater than that of -the atmosphere at sea level, so that this factor has only a slight -influence on the lifting power. That it leads to certain difficulties -in economy of gas will, however, soon be seen. - -The temperature of the gas in a balloon, one might think, would -naturally be the same as that of the air outside: but the surface -of the balloon envelope has an absorbing capacity for heat, and on -a bright sunny day the gas may be considerably warmed thereby. This -action increases the lifting power, since increase of temperature (the -pressure remaining fixed) decreases the density of a gas. To avoid -this possibly objectionable increase in lifting power, balloons are -sometimes painted with a non-absorbent color. One of the first Lebaudy -balloons received a popular nickname in Paris on account of the yellow -hue of its envelope. - -Suppose we wish a balloon to carry a total weight, including that of -the envelope itself, of a ton. If of hydrogen, it will have to contain -one fifteenth of this weight or about 133 pounds of that gas, occupying -a space of about 23,000 cubic feet. If coal gas is used, the size -of the balloon would have to be much greater. If hot air is used--as -has sometimes been the case--let us assume the temperature of the air -inside the envelope such that the density is just half that of the -outside air. This would require a temperature probably about 500°. -The air needed would be just a ton, and the balloon would be of about -52,000 cubic feet. It would soon lose its lifting power as the air -cooled; and such a balloon would be useful only for short flights. - - [Illustration: AIR BALLOON - (Photo by Paul Thompson, N.Y.) - Built by some Germans in the backwoods of South Africa] - -The 23,000 cubic foot hydrogen balloon, designed to carry a ton, would -just answer to sustain the weight. If anchored at sea level, it would -neither fall to the ground nor tug upward on its holding-down ropes. -In order to ascend, something more is necessary. This "something more" -might be some addition to the size and to the amount of hydrogen. Let -us assume that we, instead, drop one hundred pounds of our load. Thus -relieved of so much ballast, the balloon starts upward, under the net -lifting force of one hundred pounds. It is easy to calculate how far -it will go. It will not ascend indefinitely, because, as the altitude -increases, the pressure (and consequently the density) of the external -atmosphere decreases. At about a 2000-foot elevation, this decrease -in density will have been sufficient to decrease the buoyant power of -the hydrogen to about 1900 pounds, and the balloon will cease to rise, -remaining at this level while it moves before the wind. - -There are several factors to complicate any calculations. Any -expansion of the gas bag--stretching due to an increase in internal -pressure--would be one; but the envelope fabrics do not stretch much; -there is indeed a very good reason why they must not be allowed to -stretch. The pressure in the gas bag is a factor. If there is no -stretching of the bag, this pressure will vary directly with the -temperature of the gas, and might easily become excessive when the sun -shines on the envelope. - -A more serious matter is the increased difference between the internal -pressure of the gas and the external pressure of the atmosphere at high -altitudes. Atmospheric pressure decreases as we ascend. The difference -between gas pressure and air pressure thus increases, and it is this -difference of pressure which tends to burst the envelope. Suppose the -difference of pressure at sea level to have been two-tenths of a pound. -For a balloon of twenty feet diameter, this would give a stress on -the fabric, per lineal inch, of twenty-four pounds. At an altitude of -2000 feet, the atmospheric pressure would decrease by one pound, the -difference of pressures would become one and two-tenths pounds, and the -stress on the fabric would be 144 pounds per lineal inch--an absolutely -unpermissible strain. There is only one remedy: to allow some of the -gas to escape through the safety valve; and this will decrease our -altitude. - - -Ascending and Descending - -To ascend, then, we must discard ballast: and we cannot ascend beyond -a certain limit on account of the limit of allowable pressure on the -envelope fabric. To again descend, we must discharge some of the gas -which gives us lifting power. Every change of altitude thus involves -a loss either of gas or of ballast. Our vertical field of control -may then be represented by a series of oscillations of gradually -decreasing magnitude until finally all power to ascend is gone. And -even this situation, serious as it is, is made worse by the gradual but -steady leakage of gas through the envelope fabric. Here, in a word, -is the whole problem of altitude regulation. Air has no surface of -equilibrium like water. Some device supplementary to ballast and the -safety valve is absolutely necessary for practicable flight in any -balloon not staked to the ground. - -A writer of romance has equipped his aeronautic heroes with a complete -gas-generating plant so that all losses might be made up; and in -addition, heating arrangements were provided so that when the gas -supply had been partially expended its lifting power could be augmented -by warming it so as to decrease its density below even the normal. -There might be something to say in favor of this latter device, if used -in connection with a collapsible gas envelope. - -Methods of mechanically varying the size of the balloon, so as by -compressing the gas to cause descent and by giving it more room to -increase its lifting power and produce ascent, have been at least -suggested. The idea of a vacuum balloon, in which a rigid hollow shell -would be exhausted of its contents by a continually working pump, may -appear commendable. Such a balloon would have maximum lifting power for -its size; but the weight of any rigid shell would be considerable, and -the pressure tending to rupture it would be about 100 times that in -ordinary gas balloons. - -It has been proposed to carry stored gas at high pressure (perhaps -in the liquefied condition) as a supplementary method of prolonging -the voyage while facilitating vertical movements: but hydrogen gas -at a pressure of a ton to the square inch in steel cylinders would -give an ultimate lifting power of only about one-tenth the weight of -the cylinders which contain it. These cylinders might be regarded as -somewhat better than ordinary ballast: but to throw them away, with -their gas charge, as ballast, would seem too tragic. Liquefied gas -might possibly appear rather more desirable, but would be altogether -too expensive. - - [Illustration: SCREW PROPELLER FOR ALTITUDE CONTROL] - -If a screw propeller can be used on a steamship, a dirigible balloon, -or an aeroplane to produce forward motion, there is no reason why it -could not also be used to produce upward motion in any balloon; and the -propeller with its operating machinery would be a substitute for twice -its equivalent in ballast, since it could produce motion either upward -or downward. Weight for weight, however, the propeller and engine give -only (in one computed case) about half the lifting power of hydrogen. -If we are to use the screw for ascent, we might well use a helicopter, -heavier than air, rather than a balloon. - - -The Ballonet - -The present standard method of improving altitude regulation involves -the use of the ballonet, or compartment air bag, inside the main -envelope. For stability and effective propulsion, it is important that -the balloon preserve its shape, no matter how much gas be allowed to -escape. Dirigible balloons are divided into two types, according to -the method employed for maintaining the shape. In the Zeppelin type, a -rigid internal metal framework supports the gas envelope. This forms -a series of seventeen compartments, each isolated from the others. No -matter what the pressure of gas, the shape of the balloon is unchanged. - -In the more common form of balloon, the internal air ballonet is empty, -or nearly so, when the main envelope is full. As gas is vented from the -latter, air is pumped into the former. This compresses the remaining -gas and thus preserves the normal form of the balloon outline. - - [Illustration: BALLOON WITH BALLONETS] - -But the air ballonet does more than this. It provides an opportunity -for keeping the balloon on a level keel, for by using a number of -compartments the air can be circulated from one to another as the case -may require, thus altering the distribution of weights. Besides this, -if the pressure in the air ballonet be initially somewhat greater -than that of the external atmosphere, a considerable ascent may be -produced by merely venting this air ballonet. This involves no loss of -gas; and when it is again desired to descend, air may be pumped into -the ballonet. If any considerable amount of gas should be vented, to -produce quick and rapid descent, the pumping of air into the ballonet -maintains the shape of the balloon and also facilitates the descent. - - [Illustration: CONSTRUCTION OF THE ZEPPELIN BALLOON] - - -The Equilibrator - - [Illustration: THE EQUILIBRATOR IN NEUTRAL POSITION] - -Suppose a timber block of one square foot area, ten feet long, weighing -380 pounds, to be suspended from the balloon in the ocean, and let -mechanism be provided by which this block may be raised or lowered -at pleasure. When completely immersed in water it exerts an upward -pressure (lifting force) of 240 pounds, which may be used to supplement -the lifting power of the balloon. If wholly withdrawn from the water, -it pulls down the balloon with its weight of 380 pounds. It seems to be -equivalent, therefore, to about 620 pounds of ballast. When immersed a -little over six feet--the upper four feet being out of the water--it -exerts neither lifting nor depressing effect. The amount of either -may be perfectly adjusted between the limits stated by varying the -immersion. - -In the Wellman-Vaniman equilibrator attached to the balloon _America_, -which last year carried six men (and a cat) a thousand miles in three -days over the Atlantic Ocean, a string of tanks partly filled with fuel -was used in place of the timber block. As the tanks were emptied, the -degree of control was increased; and this should apparently have given -ideal results, equilibration being augmented as the gas supply was lost -by leakage: but the unsailorlike disregard of conditions resulting from -the strains transferred from a choppy sea to the delicate gas bag led -to disaster, and it is doubtful whether this method of control can ever -be made practicable. The _America's_ trip was largely one of a drifting -rather than of a dirigible balloon. The equilibrator could be used only -in flights over water in any case: and if we are to look to water for -our buoyancy, why not look wholly to water and build a ship instead of -a balloon? - - - - -DIRIGIBLE BALLOONS AND OTHER KINDS - - -Shapes - - [Illustration: HENRY GIFFARD'S DIRIGIBLE - (The first with steam power)] - -The cylindrical Zeppelin balloon with approximately conical ends -has already been shown (page 68). Those balloons in which the shape -is maintained by internal pressure of air are usually _pisciform_, -that is, fish-shaped. Studies have actually been made of the contour -lines of various fishes and equivalent symmetrical forms derived, -the outline of the balloon being formed by a pair of approximately -parabolic curves. - - [Illustration: DIRIGIBLE OF DUPUY DE LOME - (Man Power)] - -The first flight in a power driven balloon was made by Giffard in 1852. -This balloon had an independent speed of about ten feet per second, but -was without appliances for steering. A ballonetted balloon of 120,000 -cubic feet capacity was directed by man power in 1872: eight men turned -a screw thirty feet in diameter which gave a speed of about seven miles -per hour. Electric motors and storage batteries were used for dirigible -balloons in 1883-'84: in the latter year, Renard and Krebs built the -first fish-shaped balloon. The first dirigible driven by an internal -combustion motor was used by Santos-Dumont in 1901. - - [Illustration: TISSANDIER BROTHERS' DIRIGIBLE BALLOON - (Electric Motor)] - - -Dimensions - -The displacements of present dirigibles vary from 20,000 cubic feet (in -the United States Signal Corps airship) up to 460,000 cubic feet (in -the Zeppelin). The former balloon has a carrying capacity only about -equivalent to that of a Wright biplane. While anchored or drifting -balloons are usually spherical, all dirigibles are elongated, with -a length of from four to eleven diameters. The Zeppelin represents -an extreme elongation, the length being 450 feet and the diameter -forty-two feet. At the other extreme, some of the English military -dirigibles are thirty-one feet in diameter and only 112 feet long. -Ballonet capacities may run up to one-fifth the gas volume. All present -dirigibles have gasoline engines driving propellers from eight to -twenty feet in diameter. The larger propellers are connected with -the motors by gearing, and make from 250 to 700 turns per minute. -The smaller propellers are direct connected and make about 1200 -revolutions. Speeds are usually from fifteen to thirty miles per hour. - - [Illustration: THE BALDWIN - Dirigible of the United States Signal Corps] - -The present-day elongated shape is the result of the effort to -decrease the proportion of propulsion resistance due to the pressure -of the air against the head of the balloon. This has led also to the -pointed ends now universal; and to avoid eddy resistance about the -rear it is just as important to point the stern as the bow. As far as -head end resistance alone is concerned, the longer the balloon the -better: but the friction of the air along the side of the envelope -also produces resistance, so that the balloon must not be too much -elongated. Excessive elongation also produces structural weakness. From -the standpoint of stress on the fabric of the envelope, the greatest -strain is that which tends to break the material along a longitudinal -line, and this is true no matter what the length, as long as the seams -are equally strong in both directions and the load is so suspended as -not to produce excessive bending strain on the whole balloon. In the -_Patrie_ (page 77), some distortion due to loading is apparent. The -stress per lineal inch of fabric is obtained by multiplying the net -pressure by half the diameter of the envelope (in inches). - - [Illustration: THE ZEPPELIN ENTERING ITS HANGAR ON LAKE CONSTANCE] - -Ample steering power (provided by vertical planes, as in -heavier-than-air machines) is absolutely necessary in dirigibles: else -the head could not be held up to the wind and the propelling machinery -would become ineffective. - - -Fabrics - -The material for the envelope and ballonets should be light, strong, -unaffected by moisture or the atmosphere, non-cracking, non-stretching, -and not acted upon by variations in temperature. The same -specifications apply to the material for the wings of an aeroplane. In -addition, for use in dirigible balloons, fabrics must be impermeable, -resistent to chemical action of the gas, and not subject to spontaneous -combustion. The materials used are vulcanized silk, gold beater's -skin, Japanese silk and rubber, and cotton and rubber compositions. -In many French balloons, a middle layer of rubber has layers of -cotton on each side, the whole thickness being the two hundred and -fiftieth part of an inch. In the _Patrie_, this was supplemented by -an outside non-heat-absorbent layer of lead chromate and an inside -coating of rubber, all rubber being vulcanized. The inner rubber layer -was intended to protect the fabric against the destructive action of -impurities in the gas. - - [Illustration: THE "PATRIE." DESTROYED BY A STORM] - -Fabrics are obtainable in various colors, painted, varnished, or wholly -uncoated. The rubber and cotton mixtures are regularly woven in France -and Germany for aeroplanes and balloons. The cars and machinery are -frequently shielded by a fabricated wall. Weights of envelope materials -range from one twenty-third to one-fourteenth pound per square foot, -and breaking stresses from twenty-eight to one hundred and thirty -pounds. Pressures (net) in the main envelope are from three-fifths to -one and a quarter _ounces_ per square inch, those in the ballonets -being somewhat less. The _Patrie_ of 1907 had an envelope guaranteed -not to allow the leakage of more than half a cubic inch of hydrogen per -square foot of surface per twenty-four hours. - - [Illustration: MANUFACTURING THE ENVELOPE OF A BALLOON] - - [Illustration: INSPECTING THE ENVELOPE OF ANDRÉE'S BALLOON "L'OERNEN"] - -The best method of cutting the fabric is to arrange for building up the -envelope by a series of strips about the circumference, the seams being -at the bottom. The two warps of the cloth should cross at an angle so -as to localize a rip or tear. Bands of cloth are usually pasted over -the seams, inside and out, with a rubber solution; this is to prevent -leakage at the stitches. - - -Framing - -In the _Zeppelin_, the rigid aluminum frame is braced every forty-five -feet by transverse diametral rods which make the cross-sections -resemble a bicycle wheel (page 68). This cross-section is not circular, -but sixteen-sided. The pressure is resisted by the framework itself, -the envelope being required to be impervious only. The seventeen -compartments are separated by partitions of sheet aluminum. There is a -system of complete longitudinal bracing between these partitions. Under -the main framework, the cars and machinery are carried by a truss about -six feet deep which runs the entire length. The cars are boat-shaped, -twenty feet long and six feet wide, three and one-half feet high, -enclosed in aluminum sheathing. These cars, placed about one hundred -feet from the ends, are for the operating force and machinery. The -third car, carrying passengers, is built into the keel. - - [Illustration: WRECK OF THE "ZEPPELIN"] - -In non-rigid balloons like the _Patrie_, the connecting frame must be -carefully attached to the envelope. In this particular machine, cloth -flaps were sewed to the bag, and nickel steel tubes then laced in -the flaps. With these tubes as a base, a light framework of tubes -and wires, covered with a laced-on waterproof cloth, was built up -for supporting the load. Braces ran between the various stabilizing -and controlling surfaces and the gas bag; these were for the most -part very fine wire cables. The weight of the car was concentrated -on about seventy feet of the total length of 200 feet. This accounts -for the deformation of the envelope shown in the illustration (page -77). The frame and car of this balloon were readily dismantled for -transportation. - -In some of the English dirigibles the cars were suspended by network -passing over the top of the balloon. - - -Keeping the Keel Horizontal - -In the _Zeppelin_, a sliding weight could be moved along the keel so as -to cause the center of gravity to coincide with the center of upward -pressure in spite of variations in weight and position of gas, fuel, -and ballast. In the German balloon _Parseval_, the car itself was -movable on a longitudinal suspending cable which carried supporting -sheaves. This balloon has figured in recent press notices. It was -somewhat damaged by a collision with its shed in March: the sixteen -passengers escaped unharmed. A few days later, emergency deflation by -the rip-strip was made necessary during a severe storm. In the ordinary -non-rigid balloon, the pumping of air between the ballonets aids in -controlling longitudinal equilibrium. The pump may be arranged for -either hand or motor operation: that in the _Clément-Bayard_ had a -capacity of 1800 liters per minute against the pressure of a little -over three-fifths of an ounce. The _Parseval_ has two ballonets. Into -the rear of these air is pumped at starting. This raises the bow and -facilitates ascent on the principle of the inclined surface of an -aeroplane. After some elevation is attained, the forward ballonet is -also filled. - - [Illustration: CAR OF THE ZEPPELIN - (From the _Transactions_ of the American Society of - Mechanical Engineers)] - - -Stability - -Besides proper distribution of the loads, correct vertical location of -the propeller is important if the balloon is to travel on a level keel. -In some early balloons, two envelopes side by side had the propeller -at the height of the axes of the gas bags and midway between them. The -modern forms carry the car, motor, and propeller below the balloon -proper. The air resistance is mostly that of the bow of the envelope: -but there is some resistance due to the car, and the propeller shaft -should properly be at the equivalent center of all resistance, which -will be between car and axis of gas bag and nearer the latter than -the former. With a single envelope and propeller, this arrangement -is impracticable. By using four (or even two) propellers, as in the -_Zeppelin_ machine (page 68), it can be accomplished. If only one -propeller is employed, horizontal rudder planes must be disposed at -such angles and in such positions as to compensate for the improper -position of the tractive force. Even on the _Zeppelin_, such planes -were employed with advantage (pages 66 and 73). - -Perfect stability also involves freedom from rolling. This is usually -inherent in a balloon, because the center of mass is well below the -center of buoyancy: but in machines of the non-rigid type the absence -of a ballonet might lead to both rolling and pitching when the gas was -partially exhausted. - - [Illustration: STERN VIEW OF THE ZEPPELIN] - -What is called "route stability" describes the condition of straight -flight. The balloon must point directly in its (independent) course. -This involves the use of a steering rudder, and, in addition, of fixed -vertical planes, which, on the principle of the vertical partitions -of Voisin, probably give some automatic steadiness to the course. To -avoid the difficulty or impossibility of holding the head up to the -wind at high speeds, an _empennage_ or feathering tail is a feature of -all present balloons. The empennage of the _Patrie_ (page 77) consisted -of pairs of vertical and horizontal planes at the extreme stern. In -the _France_, thirty-two feet in maximum diameter and nearly 200 feet -long, empennage planes aggregating about 400 square feet were placed -somewhat forward of the stern. In the _Clément-Bayard_, the empennage -consisted of cylindro-conical ballonets projecting aft from the stern. -A rather peculiar grouping of such ballonets was used about the -prolonged stern of the _Ville de Paris_. - - [Illustration: THE "CLÉMENT-BAYARD"] - - [Illustration: THE "VILLE DE PARIS"] - - -Rudders and Planes - -The dirigible has thus several air-resisting or gliding surfaces. -The approximately "horizontal" (actually somewhat inclined) planes -permit of considerable ascent and descent by the expenditure of power -rather than gas, and thus somewhat influence the problem of altitude -control. Each of the four sets of horizontal rudder planes on the -_Zeppelin_, for example, has, at thirty-five miles per hour, with an -inclination equal to one-sixth a right angle, a lifting power of nearly -a ton; about equal to that of all of the gas in one of the sixteen -compartments. - - [Illustration: CAR OF THE "LIBERTÉ"] - -Movable rudders may be either hand or motor-operated. The double -vertical steering rudder of the _Ville de Paris_ had an area of 150 -square feet. The horizontally pivoted rudders for vertical direction -had an area of 130 square feet. - - -Arrangement and Accessories - -The motor in the _Ville de Paris_ was at the front of the car, the -operator behind it. This car had the excessive weight of nearly 700 -pounds. The _Patrie_ employed a non-combustible shield over the motor, -for the protection of the envelope: its steering wheel was in front and -the motor about in the middle of the car. The gasoline tank was under -the car, compressed air being used to force the fuel up to the motor, -which discharged its exhaust downward at the rear through a spark -arrester. Motors have battery and magneto ignition and decompression -cocks, and are often carried on a spring-supported chassis. The -interesting _Parseval_ propeller has four cloth blades which hang limp -when not revolving. When the motor is running, these blades, which are -weighted with lead at the proper points, assume the desired form. - -Balloons usually carry guide ropes at head and stern, the aggregate -weight of which may easily exceed a hundred pounds. In descending, the -bow rope is first made fast, and the airship then stands with its head -to the wind, to be hauled in by the stern rope. For the large French -military balloons, this requires a force of about thirty men. The -_Zeppelin_ descends in water, being lowered until the cars float, when -it is docked like a ship (see page 84). Landing skids are sometimes -used, as with aeroplanes. - -The balloon must have escape valves in the main envelope and ballonets. -In addition it has a "rip-strip" at the bottom by which a large cut -can be made and the gas quickly vented for the purpose of an emergency -descent. Common equipment includes a siren, megaphone, anchor pins, -fire extinguisher, acetylene search light, telephotographic apparatus, -registering and indicating gages and other instruments, anemometer, -possibly carrier pigeons; besides fuel, oil and water for the motor, -and the necessary supplies for the crew. The glycerine floated compass -of Moisant must now also be included if we are to contemplate genuine -navigation without constant recourse to landmarks. - - -Amateur Dirigibles - -The French Zodiac types of "aerial runabout" displace 700 cubic -meters, carrying one passenger with coal gas or two passengers with a -mixture of coal gas and hydrogen. The motor is four-cylinder, sixteen -horse-power, water-cooled. The stern screw, of seven feet diameter, -makes 600 turns per minute, giving an independent speed of nineteen -miles per hour. The machine can remain aloft three hours with 165 -pounds of supplies. It costs $5000. Hydrogen costs not far from a cent -per cubic foot (twenty cents per cubic meter) so that the question -of gas leakage may be at least as important as the tire question with -automobiles. - - [Illustration: THE ZODIAC NO. 2 - May be deflated and easily transported] - - -The Fort Omaha Plant - -The Signal Corps post at Fort Omaha has a plant comprising a steel -balloon house of size sufficient to house one of the largest dirigibles -built, an electrolytic plant for generating hydrogen gas, having a -capacity of 3000 cubic feet per hour, a 50,000 cubic foot gas storage -tank, and the compressing and carrying equipment involved in preparing -gas for shipment at high pressure in steel cylinders. - - [Illustration: UNITED STATES SIGNAL CORPS BALLOON PLANT AT - FORT OMAHA, NEB. - (From the _Transactions_ of the American Society of - Mechanical Engineers)] - - -Balloon Progress - - [Illustration: THE "CAROLINE" OF ROBERT BROTHERS, 1784 - The ascent terminated tragically] - -The first aerial buoy of Montgolfier brothers, in 1783, led to the -suggestion of Meussier that two envelopes be used; the inner of an -impervious material to prevent gas leakage, and the outer for strength. -There was perhaps a foreshadowing of the Zeppelin idea. Captive and -drifting balloons were used during the wars of the French Revolution: -they became a part of standard equipment in our own War of Secession -and in the Franco-Prussian conflict. The years 1906 to 1908 recorded -rapid progress in the development of the dirigible: the record-breaking -_Zeppelin_ trip was in 1909 and Wellman's _America_ exploit in -October, 1910. Unfortunately, dirigibles have had a bad record for -stanchness: the _Patrie_, _République_, _Zeppelin_ (_I_ and _II_), -_Deutschland_, _Clément-Bayard_--all have gone to that bourne whence no -balloon returns. - - [Illustration: THE ASCENT AT VERSAILLES, 1783 - The first balloon carrying living beings in the air] - - [Illustration: PROPOSED DIRIGIBLE - Investors were lacking to bring about the realization of this project] - -It is gratifying to record that Count Zeppelin's latest machine, the -_Deutschland II_, is now in operation. During the present month (April, -1911), flights have been made covering 90 miles and upward at speeds -exceeding 20 miles per hour with the wind unfavorable. This balloon -is intended for use as a passenger excursion vehicle during the coming -summer, under contract with the municipality of Düsseldorf. - - [Illustration: THE "RÉPUBLIQUE"] - -At the present moment, Neale, in England, is reported to be -building a dirigible for a speed of a hundred miles per hour. The -Siemens-Schuckart non-rigid machine, nearly 400 feet long and of 500 -horse-power, is being tried out at Berlin: it is said to carry fifty -passengers.[A] Fabrice, of Munich, is experimenting with the _Inchard_, -with a view to crossing the Atlantic at an early date. Mr. Vaniman, -partner of Wellman on the _America_ expedition, is planning a new -dirigible which it is proposed to fly across the ocean before July 4. -The engine, according to press reports, will develop 200 horse-power, -and the envelope will be more elongated than that of the _America_. -And meanwhile a Chicago despatch describes a projected fifty-passenger -machine, to have a gross lifting power of twenty-five tons! - - [Illustration: THE FIRST FLIGHT FOR THE GORDON-BENNET CUP. - Won by Lieut. Frank P. Lahm, U.S.A., 1906. Figures on the map denote - distances in kilometers. The cup has been offered annually by Mr. - James Gordon-Bennet for international competition under such - conditions as may be prescribed by the International Aeronautic - Federation.] - -Germany has a slight lead in number of dirigible balloons--sixteen -in commission and ten building. France follows closely with fourteen -active and eleven authorized. This accounts for two-thirds of all the -dirigible balloons in the world. Great Britain, Italy, and Russia -rank in the order named. The United States has one balloon of the -smallest size. Spain has, or had, one dirigible. As to aeroplanes, -however, the United States and England rank equally, having each about -one-fourth as many machines as France (which seems, therefore, to -maintain a "four-power standard"). Germany, Russia, and Italy follow, -in order, the United States. These figures include all machines, -whether privately or nationally owned. Until lately, our own government -operated but one aeroplane. A recent appropriation by Congress of -$125,000 has led to arrangements for the purchase of a few additional -biplanes of the Wright and Curtiss types; and a training school for -army officers has been regularly conducted at San Diego, Cal., during -the past winter. The Curtiss machine to be purchased is said to carry -700 pounds of dead weight with a sail area of 500 square feet. It is -completely demountable and equipped with pontoons. - - - - -THE QUESTION OF POWER - - -In the year 1810, a steam engine weighed something over a ton to -the horse-power. This was reduced to about 200 pounds in 1880. The -steam-driven dirigible balloon of Giffard, in 1852, carried a complete -power plant weighing a little over 100 pounds per horse-power; about -the weight of a modern locomotive. The unsuccessful Maxim flying -machine of 1894 brought this weight down to less than 20 pounds. The -gasoline engine on the original Wright machines weighed about 5 pounds -to the horse-power; those on some recent French machines not far from 2 -pounds. - -Pig iron is worth perhaps a cent a pound. An ordinary steam or gas -engine may cost eight cents a pound; a steam turbine, perhaps forty -cents. A high grade automobile or a piano may sell for a dollar a -pound; the Gnome aeroplane motor is priced at about twenty dollars a -pound. This is considerably more than the price of silver. The motor -and accessories account for from two-thirds to nine-tenths of the total -cost of an aeroplane. - -A man weighing 150 pounds can develop at the outside about one-eighth -of a horse-power. It would require 1200 pounds of man to exert one -horse-power. Considered as an engine, then, a man is (weight for -weight) only one six-hundredth as effective as a Gnome motor. In the -original Wright aeroplane, a weight of half a ton was sustained at the -expenditure of about twenty-five horse-power. The motor weight was -about one-eighth of the total weight. If traction had been produced by -man-power, 30,000 pounds of man would have been necessary: thirty times -the whole weight supported. - - [Illustration: THE GNOME MOTOR - (Aeromotion Company of America)] - -Under the most favorable conditions, to support his own weight of -150 pounds (at very high gliding velocity and a slight angle of -inclination, disregarding the weight of sails necessary), a man would -need to have the strength of about fifteen men. No such thing as an -aerial bicycle, therefore, appears possible. The man can not emulate -the bird. - - [Illustration: SCREW PROPELLER (American Propeller Company)] - -The power plant of an air craft includes motor, water and water tank, -radiator and piping, shaft and bearings, propeller, controlling wheels -and levers, carbureter, fuel, lubricating oil and tanks therefor. Some -of the weight may eventually be eliminated by employing a two-cycle -motor (which gives more power for its size) or by using rotary -air-cooled cylinders. Propellers are made light by employing wood or -skeleton construction. One eight-foot screw of white oak and spruce, -weighing from twelve to sixteen pounds, is claimed to give over 400 -pounds of propelling force at a thousand turns per minute. - - [Illustration: ONE OF THE MOTORS OF THE ZEPPELIN] - -The cut shows the action of the so-called "four-cycle" motor. Four -strokes are required to produce an impulse on the piston and return -the parts to their original positions. On the first, or suction -stroke, the combustible mixture is drawn into the cylinder, the inlet -valve being open and the outlet valve closed. On the second stroke, -both valves are closed and the mixture is highly compressed. At about -the end of this stroke, a spark ignites the charge, a still greater -pressure is produced in consequence, and the energy of the gas now -forces the piston outward on its third or "working" stroke, the valves -remaining closed. Finally, the outlet valve is opened and a fourth -stroke sweeps the burnt gas out of the cylinder. - - [Illustration: ACTION OF THE FOUR-CYCLE ENGINE] - -In the "two-cycle" engine, the piston first moves to the left, -compressing a charge already present in the cylinder at _F_, and -meanwhile drawing a fresh supply through the valve _A_ and passages -_C_ to the space _D_. On the return stroke, the exploded gas in _F_ -expands, doing its work, while that in _D_ is slightly compressed, the -valve _A_ being now closed. When the piston, moving toward the right, -opens the passage _E_, the burnt gas rushes out. A little later, when -the passage _I_ is exposed, the fresh compressed gas in _D_ rushes -through _C_, _B_, and _I_ to _F_. The operation may now be repeated. -Only two strokes have been necessary. The cylinder develops power twice -as rapidly as before: but at the cost of some waste of gas, since the -inlet (_I_) and outlet (_E_) passages are for a brief interval _both -open at once_: a condition not altogether remedied by the use of a -deflector at _G_. A two-cycle cylinder should give nearly twice the -power of a four-cycle cylinder of the same size, and the two-cycle -engine should weigh less, per horse-power; but it requires from 10 to -30% more fuel, and fuel also counts in the total weight. - - [Illustration: ACTION OF TWO-CYCLE ENGINE] - -The high temperatures in the cylinder would soon make the cast-iron -walls red-hot, unless the latter where artificially cooled. The -usual method of cooling is to make the walls hollow and circulate -water through them. This involves a pump, a quantity of water, and a -"radiator" (cooling machine) so that the water can be used over and -over again. To cool by air blowing over the surface of the cylinder is -relatively ineffective: but has been made possible in automobiles by -building fins on the cylinders so as to increase the amount of cooling -surface. When the motors are worked at high capacity, or when two-cycle -motors are used, the heat is generated so rapidly that this method of -cooling is regarded as inapplicable. By rapidly rotating the cylinders -themselves through the air, as in motors like the Gnome, air cooling is -made sufficiently adequate, but the expenditure of power in producing -this rotation has perhaps not been sufficiently regarded. - - [Illustration: MOTOR AND PROPELLER - (Detroit Aeronautic Construction Co.)] - -Possible progress in weight economy is destined to be limited by the -necessity for reserve motor equipment. - -The engine used is usually the four-cycle, single-acting, four-cylinder -gasoline motor of the automobile, designed for great lightness. The -power from each cylinder of such a motor is approximately that obtained -by dividing the square of the diameter in inches by the figure 2-1/2. -Thus a five-inch cylinder should give ten horse-power--at normal piston -speed. On account of friction losses and the wastefulness of a screw -propeller, not more than half this power is actually available for -propulsion. - -The whole power plant of the _Clément-Bayard_ weighed about eleven -pounds to the horse-power. This balloon was 184 feet long and 35 -feet in maximum diameter, displacing about 100,000 cubic feet. It -carried six passengers, about seventy gallons of fuel, four gallons of -lubricating oil, fifteen gallons of water, 600 pounds of ballast, and -130 pounds of ropes. The motor developed 100 horse-power at a thousand -revolutions per minute. About eight gallons of fuel and one gallon of -oil were consumed per hour when running at the full independent speed -of thirty-seven miles per hour. - -The Wellman balloon _America_ is said to have consumed half a ton of -gasoline per twenty-four hours: an eight days' supply was carried. The -gas leakage in this balloon was estimated to have been equivalent to a -loss of 500 pounds of lifting power per day. - -The largest of dirigibles, the _Zeppelin_, had two motors of 170 -horse-power each. It made, in 1909, a trip of over 800 miles in -thirty-eight hours. - -The engine of the original Voisin cellular biplanes was an -eight-cylinder Antoinette of fifty horse-power, set near the rear -edge of the lower of the main planes. The Wright motors are placed near -the front edge. A twenty-five horse-power motor at 1400 revolutions -propelled the Fort Myer machine, which was built to carry two -passengers, with fuel for a 125 mile flight: the total weight of the -whole flying apparatus being about half a ton. - - [Illustration: TWO-CYLINDER OPPOSED ENGINE. - (From _Aircraft_)] - - [Illustration: FOUR-CYLINDER VERTICAL ENGINE - (The Dean Manufacturing Co.)] - -The eight-cylinder Antoinette motor on a Farman biplane, weighing 175 -pounds, developed thirty-eight horse-power at 1050 revolutions. The -total weight of the machine was nearly 1200 pounds, and its speed -twenty-eight miles per hour. - -The eight-cylinder Curtiss motor on the _June Bug_ was air cooled. This -aeroplane weighed 650 pounds and made thirty-nine miles per hour, the -engine developing twenty-five horse-power at 1200 turns. - - -Resistance of Aeroplanes - -The chart on page 24 (see also the diagram of page 23) shows that the -lifting power of an aeroplane increases as the angle of inclination -increases, up to a certain limit. The resistance to propulsion also -increases, however: and the ratio of lifting power to resistance is -greatest at a very small angle--about five or six degrees. Since the -motor power and weight are ruling factors in design, it is important to -fly at about this angle. The supporting force is then about two pounds, -and the resistance about three-tenths of a pound, per square foot of -sail area, if the velocity is that assumed in plotting the chart: -namely, about fifty-five miles per hour. - -But the resistance _R_ indicated on pages 23 and 24 is not the -only resistance to propulsion. In addition, we have the frictional -resistance of the air sliding along the sail surface. The amount of -this resistance is independent of the angle of inclination: it depends -directly upon the area of the planes, and in an indirect way on their -dimensions in the direction of movement. It also varies nearly with -the square of the velocity. At any velocity, then, the addition of -this frictional resistance, which does not depend on the angle of -inclination, modifies our views as to the desirable angle: and the -total resistance reaches a minimum (in proportion to the weight -supported) when the angle is about three degrees and the velocity about -fifty miles per hour. - -This is not quite the best condition, however. The skin friction does -not vary exactly with the square of the velocity: and when the true law -of variation is taken into account, it is found that the _horse-power_ -is a minimum at an angle of about five degrees and a speed of about -forty miles per hour. The weight supported per horse-power may then be -theoretically nearly a hundred pounds: and the frictional resistance is -about one-third the direct pressure resistance. This must be regarded -as the approximate condition of best effectiveness: not the exact -condition, because in arriving at this result we have regarded the -sails as square flat planes whereas in reality they are arched and of -rectangular form. - -At the most effective condition, the resistance to propulsion is only -about one-tenth the weight supported. Evidently the air is helping the -motor. - - -Resistance of Dirigibles - -If the bow of a balloon were cut off square, its head end resistance -would be that given by the rule already cited (page 19): one -three-hundredth pound per square foot, multiplied by the square of -the velocity. But by pointing the bow an enormous reduction of this -pressure is possible. If the head end is a hemisphere (as in the -English military dirigible), the reduction is about one-third. If it -is a sharp cone, the reduction may be as much as four-fifths. Unless -the stern is also tapered, however, there will be a considerable eddy -resistance at that point. - - [Illustration: HEAD END SHAPES] - -If head end resistance were the only consideration, then for a balloon -of given diameter and end shape it would be independent of the length -and capacity. The longer the balloon, the better. Again, since the -volume of any solid body increases more rapidly than its surface (as -the linear dimensions are increased), large balloons would have a -distinct advantage over small ones. The smallest dirigible ever built -was that of Santos-Dumont, of about 5000 cubic feet. - -Large balloons, however, are structurally weak: and more is lost by -the extra bracing necessary than is gained by reduction of head end -resistance. It is probable that the Zeppelin represents the limit of -progress in this direction; and even in that balloon, if it had not -been that the adoption of a rigid type necessitated great structural -strength, it is doubtful if as great a length would have been fixed -upon, in proportion to the diameter. - -The frictional resistance of the air gliding along the surface of the -envelope, moreover, invalidates any too arbitrary conclusions. This, -as in the aeroplane, varies nearly as the square of the velocity, and -is usually considerably greater than the direct head end resistance. -Should the steering gear break, however, and the wind strike the _side_ -of the balloon, the pressure of the wind against this greatly increased -area would absolutely deprive it of dirigibility. - -A stationary, drifting, or "sailing" balloon may as well have the -spherical as well as any other shape: it makes the wind a friend -instead of a foe and requires nothing in the way of control other than -regulation of altitude. - - -Independent Speed and Time Table - -The air pressure, direct and frictional resistances, and power depend -upon the _relative_ velocity of flying machine and air. It is this -relative velocity, not the velocity of the balloon as compared with a -point on the earth's surface, that marks the limit of progression. -Hence the speed of the wind is an overwhelming factor to be reckoned -with in developing an aerial time table. If we wish to travel east at -an effective speed of thirty miles per hour, while the wind is blowing -due west at a speed of ten miles, our machine must have an independent -speed of forty miles. On the other hand, if we wish to travel west, an -independent speed of twenty miles per hour will answer. - - [Illustration: THE SANTOS-DUMONT DIRIGIBLE NO. 2 (1909)] - -Again, if the wind is blowing north at thirty miles per hour, and the -minimum (relative) velocity at which an aeroplane will sustain its load -is forty miles per hour, we cannot progress northward any more slowly -than at seventy miles' speed. And we have this peculiar condition of -things: suppose the wind to be blowing north at fifty miles per hour. -The aeroplane designed for a forty mile speed may then face this wind -and sustain itself while actually moving backward at an absolute speed -(as seen from the earth) of ten miles per hour. - -We are at the mercy of the wind, and wind velocities may reach a -hundred miles an hour. The inherent disadvantage of aerial flight is -in what engineers call its "low load factor." That is, the ratio of -normal performance required to possible abnormal performance necessary -under adverse conditions is extremely low. To make a balloon truly -dirigible throughout the year involves, at Paris, for example, as -we have seen, a speed exceeding fifty-four miles per hour: and even -then, during one-tenth the year, the _effective_ speed would not -exceed twenty miles per hour. A time table which required a schedule -speed reduction of 60% on one day out of ten would be obviously -unsatisfactory. - - [Illustration: IN THE BAY OF MONACO SANTOS-DUMONT'S NO. 6 - The flights terminated with a fall into the sea, - happily without injury to the operator] - -Further, if we aim at excessively high independent speeds for our -dirigible balloons, in order to become independent of wind conditions, -we soon reach velocities at which the gas bag is unnecessary: that -is, a simple wing surface would at those speeds give ample support. -The increased difficulty of maintaining rigidity of the envelope, and -of steering, at the great pressures which would accompany these high -velocities would also operate against the dirigible type. - -With the aeroplane, higher speed means less sail area for a given -weight and a stronger machine. Much higher speeds are probable. We have -already a safe margin as to weight per horse-power of motor, and many -aeroplane motors are for stanchness purposely made heavier than they -absolutely need to be. - - -The Cost of Speed - -Since the whole resistance, in either type of flying machine, is -approximately proportional to the square of the velocity; and since -horse-power (work) is the product of resistance and velocity, the -horse-power of an air craft of any sort varies about as the cube of the -speed. To increase present speeds of dirigible balloons from thirty to -sixty miles per hour would then mean eight times as much horse-power, -eight times as much motor weight, eight times as rapid a rate of fuel -consumption, and (since the speed has been doubled) four times as rapid -a consumption of fuel in proportion to the distance traveled. Either -the radius of action must be decreased, or the weight of fuel carried -must be greatly increased, if higher velocities are to be attained. -Present (independent) aeroplane speeds are usually about fifty miles -per hour, and there is not the necessity for a great increase which -exists with the lighter-than-air machines. We have already succeeded in -carrying and propelling fifty pounds of total load or fifteen pounds -of passenger load per horse-power of motor, with aeroplanes; the ratio -of net load to horse-power in the dirigible is considerably lower; but -the question of weight in relation to power is of relatively smaller -importance in the latter machine, where support is afforded by the gas -and not by the engine. - - -The Propeller - -Very little effort has been made to utilize paddle wheels for aerial -propulsion; the screw is almost universally employed. Every one knows -that when a bolt turns in a stationary nut, it moves forward a distance -equal to the _pitch_ (lengthwise distance between two adjacent threads) -at every revolution. A screw propeller is a bolt partly cut away for -lightness, and the "nut" in which it works is water or air. It does -not move forward quite as much as its pitch, at each revolution, -because any fluid is more or less slippery as compared with a nut of -solid metal. The difference between the pitch and the actual forward -movement of the vessel at each revolution is called the "slip," or -"slip ratio." It is never less than ten or twelve per cent in marine -work, and with aerial screws is much greater. Within certain limits, -the less the slip, the greater the efficiency of the propeller. Small -screws have relatively greater slips and less efficiency, but are -lighter. The maximum efficiency of a screw propeller in water is under -80%. According to Langley's experiments, the usual efficiency in air -is only about 50%. This means that only half the power of the motor -will be actually available for producing forward movement--a conclusion -already foreshadowed. - -In common practice, the pitch of aerial screws is not far from equal -to the diameter. The rate of forward movement, if there were no slip, -would be proportional to the pitch and the number of revolutions per -minute. If the latter be increased, the former may be decreased. -Screws direct-connected to the motors and running at high speeds will -therefore be of smaller pitch and diameter than those run at reduced -speed by gearing, as in the machine illustrated on page 134. The number -of blades is usually two, although this gives less perfect balance than -would a larger number. The propeller is in many monoplanes placed in -_front_: this interferes, unfortunately, with the air currents against -the supporting surfaces. - -There is always some loss of power in the bearings and -power-transmitting devices between the motor and propeller. This may -decrease the power usefully exerted even to _less_ than half that -developed by the motor. - - - - -GETTING UP AND DOWN: MODELS AND GLIDERS: AEROPLANE DETAILS - - -Launching - -The Wright machines (at least in their original form) have usually -been started by the impetus of a falling weight, which propels them -along skids until the velocity suffices to produce ascent. The -preferred designs among French machines have contemplated self-starting -equipment. This involves mounting the machine on pneumatic-tired -bicycle wheels so that it can run along the ground. If a fairly long -stretch of good, wide, straight road is available, it is usually -possible to ascend. The effect of altitude and atmospheric density on -sustaining power is forcibly illustrated by the fact that at Salt Lake -City one of the aviators was unable to rise from the ground. - - [Illustration: WRIGHT BIPLANE ON STARTING RAIL, SHOWING PYLON AND - WEIGHT] - -To accelerate a machine from rest to a given velocity in a given time -or distance involves the use of propulsive force additional to that -necessary to maintain the velocity attained. Apparently, therefore, any -self-starting machine must have not only the extra weight of framework -and wheels but also extra motor power. - - [Illustration: LAUNCHING SYSTEM FOR WRIGHT AEROPLANE - (From Brewer's _Art of Aviation_)] - -Upon closer examination of the matter, we may find a particularly -fortunate condition of things in the aeroplane. Both sustaining power -and resistance vary with the inclination of the planes, as indicated -by the chart on page 24. It is entirely possible to start with no such -inclination, so that the direct wind resistance is eliminated. The -motor must then overcome only air friction, in addition to providing -an accelerating force. The machine runs along the ground, its velocity -rapidly increasing. As soon as the necessary speed (or one somewhat -greater) is attained, the planes are tilted and the aeroplane rises -from the ground. - - [Illustration: THE NIEUPORT MONOPLANE - Self-Starting with an 18 hp. motor (From _The Air Scout_)] - -The velocity necessary to just sustain the load at a given angle of -inclination is called the _critical_ or _soaring_ velocity. For a given -machine, there is an angle of inclination (about half a right angle) -at which the minimum speed is necessary. This speed is called the -"least soaring velocity." If the velocity is now increased, the angle -of inclination may be reduced and the planes will soar through the -air almost edgewise, apparently with diminished resistance and power -consumption. This decrease in power as the speed increases is called -_Langley's Paradox_, from its discoverer, who, however, pointed out -that the rule does not hold in practice when frictional resistances -are included. We cannot expect to actually save power by moving more -rapidly than at present; but we should have to provide much more power -if we tried to move much more slowly. - - [Illustration: A BIPLANE - (From _Aircraft_)] - - [Illustration: ELY AT LOS ANGELES - (Photo by American Press Association)] - -Economical and practicable starting of an aeroplane thus requires a -free launching space, along which the machine may accelerate with -nearly flat planes: a downward slope would be an aid. When the planes -are tilted for ascent, after attaining full speed, quick control is -necessary to avoid the possibility of a back-somersault. A fairly -wide launching platform of 200 feet length would ordinarily suffice. -The flight made by Ely in January of this year, from San Francisco -to the deck of the cruiser _Pennsylvania_ and back, demonstrated the -possibility of starting from a limited area. The wooden platform built -over the after deck of the warship was 130 feet long, and sloped. On -the return trip, the aeroplane ran down this slope, dropped somewhat, -and then ascended successfully. - -If the effort is made to ascend at low velocities, then the motor -power must be sufficient to propel the machine at an extreme angle of -inclination--perhaps the third of a right angle, approximating to the -angle of least velocity for a given load. According to Chatley, this -method of starting by Farman at Issy-les-Moulineaux involved the use of -a motor of fifty horse-power: while Roe's machine at Brooklands rose, -it is said, with only a six horse-power motor. - - -Descending - - [Illustration: TRAJECTORY DURING DESCENT] - -What happens when the motor stops? The velocity of the machine -gradually decreases: the resistance to forward movement stops its -forward movement and the excess of weight over upward pressure due to -velocity causes it to descend. It behaves like a projectile, but the -details of behavior are seriously complicated by the variation in head -resistance and sustaining force due to changes in the angle of the -planes. The "angle of inclination" is now not the angle made by the -planes with the horizontal, but the angle which they make with the path -of flight. Theory indicates that this should be about two-thirds the -angle which the path itself makes with the horizontal: that is, the -planes themselves are inclined downward toward the front. The forces -which determine the descent are fixed by the velocity and the angle -between the planes and the path of flight. Manipulation of the rudders -and main planes or even the motor may be practised to ensure lancing -to best advantage; but in spite of these (or perhaps on account of -these) scarcely any part of aviation offers more dangers, demands more -genius on the part of the operator, and has been less satisfactorily -analyzed than the question of "getting down." It is easy to stay up -and not very hard to "get up," weather conditions being favorable; but -it is an "all-sufficient job" to _come down_. Under the new rules of -the International Aeronautic Federation, a test flight for a pilot's -license must terminate with a descent (motor stopped) in which the -aviator is to land within fifty yards of the observers and come to -a full stop inside of fifty yards therefrom. The elevation at the -beginning of descent must be at least 150 feet. - - [Illustration: DESCENDING] - - -Gliders - -If the motor and its appurtenances, and some of the purely auxiliary -planes, be omitted, we have a _glider_. The glider is not a toy; some -of the most important problems of balancing may perhaps be some day -solved by its aid. Any boy may build one and fly therewith, although -a large kite promises greater interest. The cost is trifling, if the -framework is of bamboo and the surfaces are cotton. Areas of glider -surfaces frequently exceed 100 square feet. This amount of surface -is about right for a person of moderate weight if the machine itself -does not weigh over fifty pounds. By running down a slope, sufficient -velocity may be attained to cause ascent; or in a favorable wind (up -the slope) a considerable backward flight may be experienced. Excessive -heights have led to fatal accidents in gliding experiments. - - [Illustration: THE WITTEMAN GLIDER] - - -Models - -The building of flying models has become of commercial importance. -It is not difficult to attain a high ratio of surface to weight, -but it is almost impossible to get motor power in the small units -necessary without exceeding the permissible limit of motor weight. No -gasoline engine or electric motor can be made sufficiently light for -a toy model. Clockwork springs, if especially designed, may give the -necessary power for short flights, but no better form of power is known -just now than the twisted rubber band. For the small boy, a biplane -with sails about eighteen inches by four feet, eighteen inches apart, -anchored under his shoulders by six-foot cords while he rides his -bicycle, will give no small amount of experience in balancing and will -support enough of a load to make the experiment interesting. - - -Some Details: Balancing - - [Illustration: FRENCH MONOPLANE - (From _Aircraft_)] - -It is easily possible to compute the areas, angles, and positions -of auxiliary planes to give desired controlling or stabilizing -effects; but the computation involves the use of accurate data as to -positions of the various weights, and on the whole it is simpler to -correct preliminary calculations by actually supporting the machine -at suitable points and observing its balance. Stability is especially -uncertain at very small angles of inclination, and such angles are -to be avoided whether in ordinary operation or in descent. The -necessity for rotating main planes in order to produce ascent is -disadvantageous on this ground; but the proposed use of sliding or -jockey weights for supplementary balancing appears to be open to -objections no less serious. Steering may be perceptibly assisted, in -as delicately a balanced device as the aeroplane, by the inclination -of the body of the operator, just as in a bicycle. The direction of -the wind in relation to the required course may seriously influence -the steering power. Suppose the course to be northeast, the wind east, -the independent speed of the machine and that of the wind being the -same. The car will head due north. By bringing the rudder in position -(_a_), the course may be changed to north, or nearly so, the wind -exerting a powerful pressure on the rudder; but if a more easterly or -east-northeast course be desired, and the rudder be thrown into the -usual position therefor (_b_), it will exert no influence whatever, -because it is moving before the wind and precisely at the speed of the -wind. - - [Illustration: A PROBLEM IN STEERING] - -It might be thought that, following analogies of marine engineering, -the center of gravity of an aeroplane should be kept low. The effect -of any unbalanced pressure or force against the widely extended sails -of the machine is to rotate the whole apparatus about its center of -gravity. The further the force from the center of gravity, the -more powerful is the force in producing rotation. The defect in most -aeroplanes (especially biplanes) is that the center of gravity is _too_ -low. If it could be made to coincide with the center of disturbing -pressure, there would be no unbalancing effect from the latter. It is -claimed that the steadiest machines are those having a high center of -gravity; and the claim, from these considerations, appears reasonable. - - [Illustration: LEJEUNE BIPLANE (385 LBS., 10-12 HP.)] - - -Weights - -It has been found not difficult to keep down the weight of framework -and supporting surfaces to about a pound per square foot. The most -common ratio of surface to total weight is about one to two: so that -the machinery and operator will require one square foot of surface -for each pound of their weight. On this basis, the smallest possible -man-carrying aeroplane would have a surface scarcely below 250 square -feet. Most biplanes have twice this surface: a thousand square feet -seems to be the limit without structural weakness. Some recent French -machines, designed for high speeds, show a greatly increased ratio -of weight to surface. The _Hanriot_, a monoplane with wings upwardly -inclined toward the outer edge, carries over 800 pounds on less than -300 square feet. The Farman monoplane of only 180 square feet sustains -over 600 pounds. The same aviator's racing biplane is stated to support -nearly 900 pounds on less than 400 square feet. - - [Illustration: THE TELLIER TWO-SEAT SIX-CYLINDER MONOPLANE AT - THE PARIS SHOW - One of this type has been sold to the Russian Government - (From _Aircraft_)] - -Motor weights can be brought down to about two pounds per horse-power, -but such extreme lightness is not always needed and may lead to -unreliability of operation. The effect of an accumulation of ice, -sleet, snow, rain, or dew might be serious in connection with flights -in high altitudes or during bad weather. After one of his last year's -flights at Étampes Mr. Farman is said to have descended with an extra -load of nearly 200 pounds on this account. With ample motor power, -great flexibility in weight sustention is made possible by varying the -inclination of the planes. In January of this year, Sommer at Douzy -carried six passengers in a large biplane on a cross-country flight: -and within the week afterward a monoplane operated by Le Martin flew -for five minutes with the aeronaut and seven passengers, at Pau. The -total weight lifted was about half a ton, and some of the passengers -must have been rather light. The two-passenger Fort Myer biplane of -the Wright brothers is understood to have carried about this total -weight. These records have, however, been surpassed since they were -noted. Bréguet, at Douai, in a deeply-arched biplane of new design, -carried eleven passengers, the total load being 2602 pounds, and that -of aeronaut and passengers alone 1390 pounds. The flight was a short -one, at low altitude; but the same aviator last year made a long flight -with five passengers, and carried a load of 1262 pounds at 62 miles per -hour. And as if in reply to this feat, Sommer carried a live load of -1436 pounds (13 passengers) for nearly a mile, a day or two later, at -Mouzon. One feels less certain than formerly, now, in the snap judgment -that the heavier-than-air machine will never develop the capacity for -heavy loads. - - [Illustration: A MONOPLANE - (From _Aircraft_)] - - -Miscellaneous - -French aviators are fond of employing a carefully designed car for the -operator and control mechanism. The Wright designs practically ignore -the car: the aviator sits on the forward edge of the lower plane with -his legs hanging over. - -It has been found that auxiliary planes must not be too close to the -main wings: a gap of a distance about 50% greater than the width of -the widest adjacent plane must be maintained if interference with the -supporting air currents is to be avoided. Main planes are now always -arched; auxiliary planes, not as universally. The concave under surface -of supporting wings has its analogy in the wing of the bird and had -long years since been applied in the parachute. - - [Illustration: CARS AND FRAMEWORK] - -The car (if used) and all parts of the framework should be of "wind -splitter" construction, if useless resistance is to be avoided. The -ribs and braces of the frame are of course stronger, weight for weight, -in this shape, since a narrow deep beam is always relatively stronger -than one of square or round section. Excessive frictional resistance is -to be avoided by using a smoothly finished fabric for the wings, and -the method of attaching this fabric to the frame should be one that -keeps it as flat as possible at all joints. - - [Illustration: SOME DETAILS] - -The sketches give the novel details of some machines recently exhibited -at the Grand Central Palace in New York. The stabilizing planes were -invariably found in the rear, in all machines exhibited. - - -The Things to Look After - -The operator of an aeroplane has to do the work of at least two men. No -vessel in water would be allowed to attain such speeds as are common -with air craft, unless provided with both pilot and engineer. The -aviator is his own pilot and his own engineer. He must both manage his -propelling machinery and steer. Separate control for vertical rudders, -elevating rudders and ailerons, for starting the engine; the adjustment -of the carbureter, the spark, and the throttle to get the best results -from the motor; attention to lubrication and constant watchfulness of -the water-circulating system: these are a few of the things for him to -consider; to say nothing of the laying of his course and the necessary -anticipation of wind and altitude conditions. - -These things demand great resourcefulness, but--for their best -control--involve also no small amount of scientific knowledge. For -example, certain adjustments at the motor may considerably increase its -power, a possibly necessary increase under critical conditions: but if -such adjustments also decrease the motor efficiency there must be a -nice analysis of the two effects so that extra power may not be gained -at too great a cost in radius of action. - - [Illustration: SOME RECENT FRENCH MACHINES (From _Aircraft_)] - -The whole matter of flight involves both sportsman's and engineers -problems. Wind gusts produce the same effects as "turning corners"; -or worse--rapidly changing the whole balance of the machines and -requiring immediate action at two or three points of control. Both -ascent and descent are influenced by complicated laws and are scarcely -rendered safe--under present conditions--by the most ample experience. -A lateral air current bewilders the steering and also demands special -promptness and skill. To avoid disturbing surface winds, even over open -country, a minimum flying height of 300 feet is considered necessary. -This height, furthermore, gives more choice in the matter of landing -ground than a lower elevation. - -When complete and automatic balance shall have been attained--as it -must be attained--we may expect to see small amateur aeroplanes flying -along country roads at low elevations--perhaps with a guiding wheel -actually in contact with the ground. They will cost far less than even -a small automobile, and the expense for upkeep will be infinitely less. -The grasshopper will have become a water-spider. - - - - -SOME AEROPLANES--SOME ACCOMPLISHMENTS - - - [Illustration: ORVILLE WRIGHT AT FORT MYER, VA., 1908] - - [Illustration: THE FIRST BALLOON FLIGHT ACROSS THE BRITISH CHANNEL - More than a century before Blériot's feat, Blanchard crossed from - Dover to Calais] - -The Wright biplane has already been shown (see pages 31, 37, 121, 122). -It was distinguished by the absence of a wheel frame or car and by the -wing-warping method of stabilizing. Later Wright machines have the -spring frame and wheels for self-starting. The best known aeroplane of -this design was built to meet specifications of the United States -Signal Corps issued in 1907. It was tried out during 1908 at Fort -Myer, Va., while one of the Wright brothers was breaking all records -in Europe: making over a hundred flights in all, first carrying a -passenger and attaining the then highest altitude (360 feet) and -greatest distance of flight (seventy-seven miles). - - [Illustration: WRIGHT MOTOR. DIMENSIONS IN MILLIMETERS - (From Petit's _How to Build an Aeroplane_)] - -The ownership of the Wrights in the wing-warping method of control is -still the subject of litigation. The French infringers, it is stated, -concede priority of application to the Wright firm, but maintain that -such publicity was given the device that it was in general use before -it was patented. - -The Fort Myer machine had sails of forty feet spread, six and one-half -feet deep, with front elevating planes three by sixteen feet. It made -about forty miles per hour with two passengers. The apparatus was -specified to carry a passenger weight of 350 pounds, with fuel for a -125-mile flight. The main planes were six feet apart. The steering -rudder (double) was of planes one foot deep and nearly six feet high. -The four-cylinder-four-cycle, water-cooled motor developed twenty-five -horse-power at 1400 revolutions. The two propellers, eight and one-half -feet in diameter, made 400 revolutions. - -The flight by Mr. Wilbur Wright from the Statue of Liberty to the tomb -of General Grant, in New York, 1909, and the exploits of his brother -in the same year, when a new altitude record of 1600 feet was made -and H.R.H. the Crown Prince of Germany was taken up as a passenger, -are only specimens of the later work done by these pioneers in aerial -navigation. - -Like the Wrights, the Voisin firm from the beginning adhered firmly to -the biplane type of machine. The sketch gives dimensions of one of the -early cellular forms built for H. Farman (see illustration, page 147). -The metal screw makes about a thousand revolutions. The wings are of -india rubber sheeting on an ash frame, the whole frame and car body -being of wood, the latter covered with canvas and thirty inches wide by -ten feet long. The engine weighed 175 pounds. The whole weight of this -machine was nearly 1200 pounds; that built later for Delagrange was -brought under a thousand pounds. The ratio of weight to main surface in -the Farman aeroplane was about 2-3/4 to 1. - -A modified cellular biplane also built for Farman had a main wing area -of 560 square feet, the planes being seventy-nine inches wide and only -fifty-nine inches apart. The tail was an open box, seventy-nine inches -wide and of about ten feet spread. The cellular partitions in this tail -were pivoted along the vertical front edges so as to serve as steering -rudders. The elevating rudder was in front. The total weight was about -the same as that of the first machine and the usual speed twenty-eight -miles per hour. - - [Illustration: VOISIN-FARMAN BIPLANE] - -Henry Farman has been flying publicly since 1907. He made the first -circular flight of one kilometer, and attained a speed of about a mile -a minute, in the year following. In 1909 he accomplished a trip of -nearly 150 miles, remaining four hours in the air. Farman was probably -the first man to ascend with two passengers. - - [Illustration: THE CHAMPAGNE GRAND PRIZE WON BY HENRY FARMAN - 80 Kilometers in 3 hours] - - [Illustration: FARMAN'S FIRST BIPLANE AT ISSY-LES-MOULINEAUX - Returning to the Hangar After a Flight] - -The _June Bug_, one of the first Curtiss machines, is shown below. This -was one of the lightest of biplanes, having a wing spread of forty-two -feet and an area of 370 square feet. The wings were transversely -arched, being furthest apart at the center: an arrangement which has -not been continued. It had a box tail, with a steering rudder of about -six square feet area, _above_ the tail. The horizontal rudder, in -front, had a surface of twenty square feet. Four triangular ailerons -were used for stability. The machine had a landing frame and wheels, -made about forty miles per hour, and weighed, in operation, 650 pounds. - - [Illustration: THE "JUNE BUG"] - -Mr. Curtiss first attained prominence in aviation circles by winning -the _Scientific American_ cup by his flight at the speed of fifty-seven -miles per hour, in 1908. In the following year he exhibited intricate -curved flights at Mineola, and circled Governor's Island in New York -harbor. In 1910 he made his famous flight from Albany to New York, -stopping _en route_, as prearranged. At Atlantic City he flew fifty -miles over salt water. A flight of seventy miles over Lake Erie was -accomplished in September of the same year, the return trip being -made the following day. On January 26, 1911, Curtiss repeatedly -ascended and descended, with the aid of hydroplanes, in San Diego bay, -California: perhaps one of the most important of recent achievements. -It is understood that Mr. Curtiss is now attempting to duplicate some -of these performances under the high-altitude conditions of Great -Salt Lake. According to press reports, he has been invited to give a -similar demonstration before the German naval authorities at Kiel. - - [Illustration: CURTIS BIPLANE - (Photo by Levick, N.Y.)] - - [Illustration: CURTISS' HYDRO-AEROPLANE AT SAN DIEGO GETTING UNDER WAY - (From the _Columbian Magazine_)] - -The _aeroscaphe_ of Ravard was a machine designed to move either on -water or in air. It was an aeroplane with pontoons or floaters. The -supporting surface aggregated 400 square feet, and the gross weight -was about 1100 pounds. A fifty horse-power Gnome seven-cylinder motor -at 1200 revolutions drove two propellers of eight and ten and one-half -feet diameter respectively: the propellers being mounted one behind -the other on the same shaft. - - [Illustration: FLYING OVER THE WATER AT FIFTY MILES PER HOUR - Curtiss at San Diego Bay - (From the _Columbian Magazine_)] - -Ely's great shore-to-warship flight was made without the aid of the -pontoons which he carried. Ropes were stretched across the landing -platform, running over sheaves and made fast to heavy sand bags. As a -further precaution, a canvas barrier was stretched across the forward -end of the platform. The descent brought the machine to the platform at -a distance of forty feet from the upper end: grappling hooks hanging -from the framework of the aeroplane then caught the weighted ropes, and -the speed was checked (within about sixty feet) so gradually that "not -a wire or bolt of the biplane was injured." - - [Illustration: BLÉRIOT-VOISIN CELLULAR BIPLANE WITH PONTOONS - Hauled by a Motor Boat] - - [Illustration: LATHAM'S "ANTOINETTE"] - - [Illustration: JAMES J. WARD AT LEWISTON FAIR, IDAHO - (Photo copyright 1910 by Burns) - Flying Machine Mfg. Co. Biplane (30 hp. Motor)] - - [Illustration: MARCEL PENOT IN THE MOHAWK BIPLANE, - Mineola to Hicksville, L. I. - 26 miles cross-country in 30 minutes (50 hp. Harriman Engine)] - -Recent combinations of aeroplane and automobile, and aeroplane with -motor boat, have been exhibited. One of the latter devices is like any -monoplane, except that the lower part is a water-tight aluminum boat -body carrying three passengers. It is expected to start of itself from -the water and to fly at a low height like a flying fish at a speed of -about seventy-five miles per hour. Should anything go wrong, it is -capable of floating on the water. - -In the San Diego Curtiss flights, the machine skimmed along the surface -of the bay, then rose to a height of a hundred feet, moved about two -miles through the air in a circular course, and finally alighted -close to its starting-point in the water. Turns were made in water as -well as in air, a speed of forty miles per hour being attained while -"skimming." The "hydroplanes" used are rigid flat surfaces which -utilize the pressure of the water for sustention, just as the main -wings utilize air pressure. On account of the great density of water, -no great amount of surface is required: but it must be so distributed -as to balance the machine. The use of pontoons makes it possible to -rest upon the water and to start from rest. A trip like Ely's could -be made without a landing platform, with this type of machine; the -aeroplane could either remain alongside the war vessel or be hoisted -aboard until ready to venture away again. - -There are various other biplanes attracting public attention in this -country. In France the tendency is all toward the monoplane form, and -many of the "records" have, during the past couple of years, passed -from the former to the latter type of machine. The monoplane is simpler -and usually cheaper. The biplane may be designed for greater economy -in weight and power. Farman has lately experimented with the monoplane -type of machine: the large number of French designs in this class -discourages any attempt at complete description. - - [Illustration: SANTOS-DUMONT'S "DEMOISELLE"] - -The smallest of aeroplanes is the Santos-Dumont _Demoiselle_. The -original machine is said to have supported 260 pounds on 100 square -feet of area, making a speed of sixty miles per hour. Its proprietor -was the first aviator in Europe of the heavier-than-air class. After -having done pioneer work with dirigible balloons, he won the Deutsch -prize for a hundred meter aeroplane flight (the first outside of the -United States) in 1906; the speed being twenty-three miles per hour. -His first flight, of 400 feet, in a monoplane was made in 1907. - - [Illustration: BLÉRIOT MONOPLANE] - -The master of the monoplane has been Louis Blériot. Starting in -1907 with short flights in a Langley type of machine, he made his -celebrated cross-country run, and the first circling flights ever -achieved in a monoplane, the following year. On July 25, 1909, he -crossed the British Channel, thirty-two miles, in thirty-seven minutes. - - [Illustration: LATHAM'S FALL INTO THE CHANNEL] - -The Channel crossing has become a favorite feat. Mr. Latham, only two -days after Blériot, all but completed it in his Antoinette monoplane. -De Lesseps, in a Blériot machine, was more fortunate. Sopwith, last -year, won the de Forest prize of $20,000 by a flight of 174 miles -from England into Belgium. The ill-fated Rolls made the round trip -between England and France. Grace, contesting for the same prize, -reached Belgium, was driven back to Calais, started on the return -voyage, and vanished--all save some few doubtful relics lately found. -Moisant reached London from Paris--the first trip on record between -these cities without change of conveyance: and one which has just been -duplicated by Pierre Prier, who, on April 12, made the London to Paris -journey, 290 miles, in 236 minutes, without a stop. This does not, -however, make the record for a continuous flight: which was attained by -Tabuteau, who at Buc, on Dec. 30, 1910, flew around the aerodrome for -465 minutes at the speed of 48-1/2 miles per hour. - -Other famous crossings include those of the Irish Sea, 52 miles, by -Loraine; Long Island Sound, 25 miles, by Harmon; and Lake Geneva, 40 -miles, by Defaux. - -It was just about a century ago that Cayley first described a soaring -machine, heavier than air, of a form remarkably similar to that of the -modern aeroplane. Aside from Henson's unsuccessful attempt to build -such a machine, in 1842, and Wenham's first gliding experiments with a -triplane in 1857, soaring flight made no real progress until Langley's -experiments. That investigator, with Maxim and others, ascertained -those laws of aerial sustention the application of which led to success -in 1903. - - [Illustration: DE LESSEPS IN A BLÉRIOT CROSSING THE CHANNEL - (Photo by Levick, N.Y.)] - -The eight years since have held the crowded hours of aviation. Before -this book is printed, it may be rendered obsolete by new developments. -The exploits of Paulhan, of R. E. Peltèrie since 1907, Bell's work with -his tetrahedral kites--all have been either stimulating or directly -fruitful. Delagrange began to break speed records in 1908. A year -later he attained a speed of fifty miles. The first woman to enjoy an -aeroplane voyage was Mme. Delagrange, in Turin, in 1908. - - [Illustration: THE MAXIM AEROPLANE] - - [Illustration: LANGLEY'S AEROPLANE (1896) - Steam driven] - -The first flight in England by an English-built machine was made in -January, 1909. That year, Count de Lambert flew over Paris, and in -1910 Grahame-White circled his machine over the city of Boston. The -year 1910 surpassed all its predecessors in increasing the range and -control of aeroplanes; over 1500 ascents were made by Wright machines -alone; but 1911 promises to show even greater results. Three men made -cross-country flights from Belmont Park to the Statue of Liberty and -back, in New York;[B] at least five men attained altitudes exceeding -9,000 feet. Hamilton made the run from New York to Philadelphia and -return, in June. The unfortunate Chavez all but abolished the fames of -Hannibal and Napoleon by crossing the icy barrier of the Alps, from -Switzerland to Italy--in forty minutes! - - [Illustration: ROBART MONOPLANE.] - -Tabuteau, almost on New Year's eve, broke all distance records by a -flight of 363 miles in less than eight hours; while Barrier at Memphis -probably reached a speed of eighty-eight miles per hour (timing -unofficial). With the new year came reports of inconceivable speeds by -a machine skidding along the ice of Lake Erie; the successful receipt -by Willard and McCurdy of wireless messages from the earth to their -aeroplanes; and the proposal by the United States Signal Corps for the -use of flying machines for carrying Alaskan mails. - - [Illustration: VINA MONOPLANE.] - -McCurdy all but succeeded in his attempt to fly from Key West to -Havana, surpassing previous records by remaining aloft above salt water -while traveling eighty miles. Lieutenant Bague, in March, started from -Antibes, near Nice, for Corsica. After a 124-mile flight, breaking all -records for sea journeys by air, he reached the islet of Gorgona, near -Leghorn, Italy, landing on bad ground and badly damaging his machine. -The time of flight was 5-1/2 hours. Bellinger completed the 500-mile -"accommodation train" flight from Vincennes to Pau; Vedrine, on April -12, by making the same journey in 415 minutes of actual flying time, -won the Béarn prize of $4000; Say attained a speed of 74 miles per hour -in circular flights at Issy-les-Moulineaux. Aeroplane flights have been -made in Japan, India, Peru, and China. - -One of the most spectacular of recent achievements is that of Renaux, -competing for the Michelin Grand Prize. A purse of $20,000 was offered -in 1909 by M. Michelin, the French tire manufacturer, for the first -successful flight from Paris to Clermont-Ferrand--260 miles--in less -than six hours. The prize was to stand for ten years. It was prescribed -that the aviator must, at the end of the journey, circle the tower of -the Cathedral and alight on the summit of the Puy de Dome--elevation -4500 feet--on a landing place measuring only 40 by 100 yards, -surrounded by broken and rugged ground and usually obscured by fog. - -The flight was attempted last year by Weymann, who fell short of the -goal by only a few miles. Leon Morane met with a serious accident, -a little later, while attempting the trip with his brother as a -passenger. Renaux completed the journey with ease in his Farman -biplane, carrying a passenger, his time being 308 minutes. - -This Michelin Grand Prize is not to be confused with the Michelin -Trophy of $4000 offered yearly for the longest flight in a closed -circuit. - -Speeds have increased 50% during the past year; even with passengers, -machines have moved more than a mile a minute: average motor capacities -have been doubled or tripled. The French men and machines hold the -records for speed, duration, distance, and (perhaps) altitude. The -highest altitude claimed is probably that attained by Garros at Mexico -City, early this year--12,052 feet above sea level. The world's speed -record for a two-man flight appears to be that of Foulois and Parmalee, -made at Laredo, Texas, March 3, 1911: 106 miles, cross-country, in 127 -minutes. Three-fourths of all flights made up to this time have been -made in France--a fair proportion, however, in American machines. - - -NOTE - -The rapidity with which history is made in aeronautics is forcibly -suggested by the revision of text made necessary by recent news. -The new _Deutschland_ has met the fate of its predecessors; the -Paris-Rome-Turin flight is at this moment under way; and Lieutenant -Bayne, attempting once more his France-to-Corsica flight, has--for the -time being at least--disappeared. - - - - -THE POSSIBILITIES IN AVIATION - - -Men now fly and will probably keep on flying; but aviation is still -too hazardous to become the popular sport of the average man. The -overwhelmingly important problem with the aeroplane is that of -stability. These machines must have a better lateral balance when -turning corners or when subjected to wind gusts: and the balance must -be automatically, not manually, produced. - - [Illustration: BLANC MONOPLANE] - -Other necessary improvements are of minor urgency and in some cases -will be easy to accomplish. Better mechanical construction, especially -in the details of attachments, needs only persistence and common sense. -Structural strength will be increased; the wide spread of wing presents -difficulties here, which may be solved either by increasing the number -of superimposed surfaces, as in triplanes, or in some other manner. -Greater carrying capacity--two men instead of one--may be insisted -upon: and this leads to the difficult question of motor weights. -The revolving air-cooled motor may offer further possibilities: the -two-cycle idea will help if a short radius of action is permissible: -but a weight of less than two pounds to the horse-power seems -to imply, almost essentially, a lack of ruggedness and surety of -operation. A promising field for investigation is in the direction of -increasing propeller efficiencies. If such an increase can be effected, -the whole of the power difficulty will be greatly simplified. - - [Illustration: MELVIN VANIMAN TRIPLANE] - - [Illustration: JEAN DE CRAWHEZ TRIPLANE] - - [Illustration: A TRIPLANE] - -This same motor question controls the proposal for increased speed. -The use of a reserve motor would again increase weights; though not -necessarily in proportion to the aggregate engine capacity. Perhaps -something may be accomplished with a gasoline turbine, when one -is developed. In any case, no sudden increase in speeds seems to -be probable; any further lightening of motors must be undertaken -with deliberation and science. If much higher maximum speeds are -attained, there will be an opportunity to vary the speed to suit the -requirements. Then clutches, gears, brakes, and speed-changing devices -of various sorts will become necessary, and the problem of weights of -journal bearings--already no small matter--will be made still more -serious. And with variable speed must probably come variable sail -area--in preference to tilting--so that the fabric must be reefed on -its frame. Certainly two men, it would seem, will be needed! - -Better methods for starting are required. The hydroplane idea promises -much in this respect. With a better understanding and control of the -conditions associated with successful and safe descent--perhaps with -improved appliances therefor--the problem of ascent will also be partly -solved. If such result can be achieved, these measures of control must -be made automatic. - -The building of complete aeroplanes to standard designs would be -extremely profitable at present prices, which range from $2500 to -$5000. Perhaps the most profitable part would be in the building of the -motor. The framing and fabric of an ordinary monoplane could easily -be constructed at a cost below $300. The propeller may cost $50 more. -The expense for wires, ropes, etc., is trifling; and unless special -scientific instruments and accessories are required, all of the rest -of the value lies in the motor and its accessories. Within reasonable -limits, present costs of motors vary about with the horse-power. The -amateur designer must therefore be careful to keep down weight and -power unless he proposes to spend money quite freely. - - -The Case of the Dirigible - -Not very much is being heard of performances of dirigible balloons just -at present. They have shown themselves to be lacking in stanchness -and effectiveness under reasonable variations of weather. We must -have fabrics that are stronger for their weight and more impervious. -Envelopes must be so built structurally as to resist deformation at -high speeds, without having any greatly increased weight. A cheap way -of preparing pure hydrogen gas is to be desired. - -Most important of all, the balloon must have a higher speed, to make it -truly dirigible. This, with sufficient steering power, will protect it -against the destructive accidents that have terminated so many balloon -careers. Here again arises the whole question of power in relation -to motor weight, though not as formidably as is the case with the -aeroplane. The required higher speeds are possible now, at the cost -merely of careful structural design, reduced radius of action, and -reduced passenger carrying capacity. - -Better altitude control will be attained with better fabrics and -the use of plane fin surfaces at high speeds. The employment of a -vertically-acting propeller as a somewhat wasteful but perhaps finally -necessary measure of safety may also be regarded as probable. - - [Illustration: GIRAUDON'S WHEEL AEROPLANE] - - -The Orthopter - -The _aviplane_, _ornithoptère_ or _orthopter_ is a flying machine with -bird-like flapping wings, which has received occasional attention -from time to time, as the result of a too blind adherence to Nature's -analogies. Every mechanical principle is in favor of the screw as -compared with any reciprocating method of propulsion. There have been -few actual examples of this type: a model was exhibited at the Grand -Central Palace in New York in January of this year. - -The mechanism of an orthopter would be relatively complex, and the -flapping wings would have to "feather" on their return stroke. The -flapping speed would have to be very high or the surface area very -great. This last requirement would lead to structural difficulties. -Propulsion would not be uniform, unless additional complications were -introduced. The machine would be the most difficult of any type to -balance. The motion of a bird's wing is extremely complicated in its -details--one that it would be as difficult to imitate in a mechanical -device as it would be for us to obtain the structural strength of an -eagle's wing in fabric and metal, with anything like the same extent of -surface and limit of weight. According to Pettigrew, the efficiency of -bird and insect flight depends largely upon the elasticity of the wing. -Chatley gives the ratio of area to weight as varying from fifty (gnat) -to one-half (Australian crane) square feet per pound. The usual ratio -in aeroplanes is from one-third to one-half. - -About the only advantages perceptible with the orthopter type of -machine would be, first, the ability "to start from rest without -a preliminary surface glide"; and second, more independence of -irregularity in air currents, since the propulsive force is exerted -over a greater extent than is that of a screw propeller. - - -The Helicopter - -The _gyroplane_ or _helicopter_ was the type of flying machine -regarded by Lord Kelvin as alone likely to survive. It lifts itself -by screw propellers acting vertically. This form was suggested in -1852. When only a single screw was used, the whole machine rotated -about its vertical axis. It was attempted to offset this by the use -of vertical fin-planes: but these led to instability in the presence -of irregular air currents. One early form had two oppositely-pitched -screws driven by a complete steam engine and boiler plant. One of the -Cornu helicopters had adjustable inclined planes under the two large -vertically propelling screws. The air which slipped past the screws -imposed a pressure on the inclined planes which was utilized to produce -horizontal movement in any desired direction--if the wind was not too -adverse. A gasoline engine was carried in a sort of well between the -screws. - - [Illustration: BRÉGUET GYROPLANE DURING CONSTRUCTION - (Helicopter type)] - -The helicopter may be regarded as the limiting type of aeroplane, the -sail area being reduced nearly to zero; the wings becoming mere fins, -the smaller the better. It therefore requires maximum motor power and -is particularly dependent upon the development of an excessively light -motor. It is launched and descends under perfect control, without -regard to horizontal velocity. It has very little exposed surface and -is therefore both easy to steer and independent of wind conditions. By -properly arranging the screws it can be amply balanced: but it must -have a particularly stout and strong frame. - -The development of this machine hinges largely on the propeller. It is -not only necessary to develop _power_ (which means force multiplied by -velocity) but actual propulsive vertical _force_: and this must exceed -or at least equal the whole weight of the machine. From ten to forty -pounds of lifting force per horse-power have been actually attained: -and with motors weighing less than five pounds there is evidently some -margin. The propellers are of special design, usually with very large -blades. Four are commonly used: one, so to speak, at each "corner" of -the machine. The helicopter is absolutely dependent upon its motors. -It cannot descend safely if the power fails. If it is to do anything -but ascend and descend it must have additional propulsive machinery for -producing horizontal movement. - - -Composite Types - -The aeroplane is thus particularly weak as to stability, launching, -and descending: but it is economical in power because it uses the -air to hold itself up. The dirigible balloon is lacking in power and -speed, but can ascend and descend safely, even if only by wasteful -methods; and it can carry heavy weights, which are impossible with the -structurally fragile aeroplane. The helicopter is wasteful in power, -but is stable and sure in ascending and descending, providing only that -the motor power does not fail. - -Why, then, not combine the types? An aeroplane-dirigible would -be open to only one objection: on the ground of stability. The -dirigible-helicopter would have as its only disadvantage a certain -wastefulness of power, while the aeroplane-helicopter would seem to -have no drawback whatever. - -All three combinations have been, or are being, tried. An Italian -engineer officer has designed a balloon-aeroplane. The balloon is -greatly flattened, or lens-shaped, and floats on its side, presenting -its edge to the horizon--if inclination be disregarded. With some -inclination, the machine acts like an aeroplane and is partially -self-sustaining at any reasonable velocity. - -The use of a vertically-acting screw on a dirigible combines the -features of that type and the helicopter. This arrangement has also -been the subject of design (as in Captain Miller's flexible balloon) -if not of construction. The combination of helicopter and aeroplane -seems especially promising: the vertical propellers being employed for -starting and descending, as an emergency safety feature and perhaps for -aid in stabilizing. The fact that composite types of flying machine -have been suggested is perhaps, however, an indication that the -ultimate type has not yet been established. - - -What is Promised - -The flying machine will probably become the vehicle of the explorer. -If Stanley had been able to use a small high-powered dirigible in -the search for Livingstone, the journey would have been one of hours -as compared with months, the food and general comfort of the party -would have been equal in quality to those attainable at home, and the -expense in money and in human life would have been relatively trifling. - - [Illustration: WELLMAN'S AMERICA - (From Wellman's _Aerial Age_)] - -Most readers will remember the fate of Andrée, and the projected polar -expeditions of Wellman in 1907 and 1909. Misfortune accompanied both -attempts; but one has only to read Peary's story of the dogged tramp -over the Greenland ice blink to realize that danger and misfortune -in no less degree have accompanied other plans of Arctic pioneering. -With proper design and the right men, it does not seem unreasonable to -expect that a hundred flying machines may soar above Earth's invisible -axial points during the next dozen years.[C] - -The report of Count Zeppelin's Spitzbergen expedition of last year -has just been made public. This was undertaken to ascertain the -adaptability of flying machines for Arctic navigation. Besides speed -and radius of action, the conclusive factors include that of freedom -from such breakdowns as cannot be made good on the road. - -For exploration in other regions, the balloon or the aeroplane is -sure to be employed. Rapidity of progress without fatigue or danger -will replace the floundering through swamps, shivering with ague, and -bickering with hostile natives now associated with tropical and other -expeditions. The stereoscopic camera with its scientific adjuncts will -permit of almost automatic map-making, more comprehensive and accurate -than any now attempted in other than the most settled sections. It -is not too much to expect that arrangements will be perfected for -conducting complete topographical surveys without more than occasional -descents. If extremely high altitudes must be attained--over a -mile--the machines will be of special design; but as far as can now be -anticipated, there will be no insurmountable difficulties. The virgin -peaks of Ruwenzori and the Himalayas may become easily accessible--even -to women and children if they desire it. We may obtain direct evidence -as to the contested ascent of Mt. McKinley. A report has been current -that a Blériot monoplane has been purchased for use in the inspection -of construction work for an oil pipe line across the Persian desert; -the aeroplane being regarded as "more expeditious and effectual" than -an automobile. - -The flying machine is the only land vehicle which requires no -"permanent way." Trains must have rails, bicycles and automobiles -must have good roads. Even the pedestrian gets along better on a -path. The ships of the air and the sea demand no improvement of the -fluids in which they float. To carry mails, parcels, persons, and even -light freight--these applications, if made commercially practicable -tomorrow,[D] would surprise no one; their possibility has already -been amply demonstrated. With the dirigible as the transatlantic -liner and the aeroplane as the naphtha launch of the air, the whole -range of applications is commanded. Hangars and landing stages--the -latter perhaps on the roofs of buildings, revolutionizing our domestic -architecture--may spring up as rapidly as garages have done. And the -aeroplane is potentially (with the exception of the motorcycle) the -cheapest of self-propelled vehicles. - -Governments have already considered the possibilities of aerial -smuggling. Perhaps our custom-house officers will soon have to watch a -fence instead of a line: to barricade in two dimensions instead of one. -They will need to be provided with United States Revenue aeroplanes. -But how are aerial frontiers to be marked? And does a nation own the -air above it, or is this, like the high seas, "by natural right, common -to all"? Can a flying-machine blockade-runner above the three-mile -height claim extraterritoriality? - -The flying machine is no longer the delusion of the "crank," because -it has developed a great industry. A now antiquated statement put -the capitalization of aeroplane manufactories in France at a million -dollars, and the development expenditure to date at six millions. -There are dozens of builders, in New York City alone, of monoplanes, -biplanes, gliders, and models. A permanent exhibition of air craft is -just being inaugurated. We have now even an aeronautic "trust," since -the million-dollar capitalization of the Maxim, Blériot, Grahame-White -firm. - -According to the New York _Sun_, over $500,000 has been subscribed for -aviation prizes in 1911. The most valuable prizes are for new records -in cross-country flights. The Paris _Journal_ has offered $70,000 for -the best speed in a circling race from Paris to Berlin, Brussels, -London, and back to Paris--1500 miles. Supplementary prizes from other -sources have increased the total stake in this race to $100,000. A -purse of $50,000 is offered by the London _Daily Mail_ for the "Circuit -of Britain" race, from London up the east coast to Edinburgh, across -to Glasgow, and home by way of the west coast, Exeter, and the Isle of -Wight; a thousand miles, to be completed in two weeks, beginning July -22, with descents only at predetermined points. This contest will be -open (at an entrance fee of $500) to any licensee of the International -Federation. A German circuit, from Berlin to Bremen, Magdeburg, -Düsseldorf, Aix-la-Chapelle, Dresden, and back to the starting point, -is proposed by the _Zeitung am Mittag_ of Berlin, a prize of $25,000 -having been offered. In this country, a comparatively small prize -has been established for a run from San Francisco to New York, _via_ -Chicago. Besides a meet at Bridgeport, May 18-20, together with those -to be held by several of the colleges and the ones at Bennings and -Chicago, there will be, it is still hoped, a national tournament at -Belmont Park at the end of the same month. Here probably a dozen -aviators will contest in qualification for the international meet in -England, to which three American representatives should be sent as -competitors for the championship trophy now held by Mr. Grahame-White. -It is anticipated that the chances in the international races favor -the French aviators, some of whom--in particular, Leblanc--have been -making sensational records at Pau. Flights between aviation fields in -different cities are the leading feature in the American program for -the year. A trip is proposed from Washington to Belmont Park, _via_ -Atlantic City, the New Jersey coast, and lower New York bay. The -distance is 250 miles and the time will probably be less than that of -the best passenger trains between Washington and New York. If held, -this race will probably take place late in May. It is wisely concluded -that the advancement of aviation depends upon cross-country runs under -good control and at reasonable speeds and heights rather than upon -exhibition flights in enclosures. It is to be hoped that commercial -interests will not be sufficiently powerful to hinder this development. - -We shall of course have the usual international championship balloon -race, preceded by elimination contests. From present indications Omaha -is likely to be chosen as the point of departure. - -The need for scientific study of aerial problems is recognized. The -sum of $350,000 has been offered the University of Paris to found an -aeronautic institute. In Germany, the university at Göttingen has for -years maintained an aerodynamic laboratory. Lord Rayleigh, in England, -is at the head of a committee of ten eminent scientists and engineers -which has, under the authority of Parliament, prepared a program of -necessary theoretical and experimental investigations in aerostatics -and aerodynamics. Our American colleges have organized student aviation -societies and in some of them systematic instruction is given in the -principles underlying the art. A permanent aeronautic laboratory, to be -located at Washington, D.C., is being promoted. - -Aviation as a sport is under the control of the International -Aeronautic Federation, having its headquarters at Paris. Bodies -like the Royal Aero Club of England and the Aero Club of America -are subsidiaries to the Federation. In addition, we have in this -country other clubs, like the Aeronautic Society, the United States -Aeronautical Reserve, etc. The National Council of the Aero Clubs of -America is a sort of supreme court for all of these, having control of -meets and contests; but it has no affiliation with the International -body, which is represented here by the Aero Club of America. The -Canadian Auto and Aero Club supervises aviation in the Dominion. - -Aviation has developed new legal problems: problems of liability for -accidents to others; the matter of supervision of airship operators. -Bills to license and regulate air craft have been introduced in at -least two state legislatures. - -Schools for instruction in flying as an art or sport are being -promoted. It is understood that the Wright firm is prepared to organize -classes of about a dozen men, supplying an aeroplane for their -instruction. Each man pays a small fee, which is remitted should he -afterward purchase a machine. Mr. Grahame-White, at Pau, in the south -of France, conducts a school of aviation, and the arrangements are now -being duplicated in England. Instruction is given on Blériot monoplanes -and Farman biplanes, at a cost of a hundred guineas for either. The -pupil is coached until he can make a three-mile flight; meanwhile, he -is held partially responsible for damage and is required to take out a -"third-party" insurance policy. - -There is no lack of aeronautic literature. Major Squier's paper in the -_Transactions_ of the American Society of Mechanical Engineers, 1908, -gave an eighteen-page list of books and magazine articles of fair -completeness up to its date; Professor Chatley's book, _Aeroplanes_, -1911, discusses some recent publications; the Brooklyn Public Library -in New York issued in 1910 (misdated 1909) a manual of fourteen pages -critically referring to the then available literature, and itself -containing a list of some dozen bibliographies. - - -Aerial Warfare - - [Illustration: THE GERMAN EMPEROR WATCHING THE PROGRESS OF AVIATION] - -The use of air craft as military auxiliaries is not new. As early -as 1812 the Russians, before retreating from Moscow, attempted to -drop bombs from balloons: an attempt carried to success by Austrian -engineers in 1849. Both contestants in our own War of Secession -employed captive and drifting balloons. President Lincoln organized a -regular aeronautic auxiliary staff in which one Lowe held the official -rank of chief aeronaut. This same gentleman (who had accomplished a -reconnaissance of 350 miles in eight hours in a 25,000 cubic foot -drifting balloon) was subjected to adverse criticism on account of a -weakness for making ascents while wearing the formal "Prince Albert" -coat and silk hat! A portable gas-generating plant was employed by -the Union army. We are told that General Stoneman, in 1862, directed -artillery fire from a balloon, which was repeatedly fired at by the -enemy, but not once hit. The Confederates were less amply equipped. -Their balloon was a patchwork of silk skirts contributed (one doubts -not, with patriotic alacrity) by the daughters of the Confederacy. - -It is not forgotten that communication between besieged Paris and the -external world was kept up for some months during 1870-71 by balloons -exclusively. Mail was carried on a truly commercial scale: pet animals -and--the anticlimax is unintended--164 persons, including M. Gambetta, -escaped in some sixty-five flights. Balloons were frequently employed -in the Franco-Prussian contest; and they were seldom put _hors de -combat_ by the enemy. - -During our war with Spain, aerial craft were employed in at least -one instance, namely, at San Juan, Porto Rico, for reconnoitering -entrenchments. Frequent ascents were made from Ladysmith, during the -Boer war. The balloons were often fired at, but never badly damaged. -Cronje's army was on one occasion located by the aid of a British -scout-balloon. Artillery fire was frequently directed from aerial -observations. Both sides employed balloons in the epic conflict between -Russia and Japan. - -A declaration introduced at the second international peace conference -at the Hague proposed to prohibit, for a limited period, the discharge -of projectiles or explosives from flying machines of any sort. The -United States was the only first-class power which endorsed the -declaration. It does not appear likely, therefore, that international -law will discountenance the employment of aerial craft in international -disputes. The building of airships goes on with increasing eagerness. -Last year the Italian chamber appropriated $5,000,000 for the -construction and maintenance of flying machines. - -A press report dated February 4 stated that a German aeronaut had -been spending some weeks at Panama, studying the air currents of the -Canal Zone. No flying machine may in Germany approach more closely -than within six miles of a fort, unless specially licensed. At the -Krupp works in Essen there are being tested two new guns for shooting -at aeroplanes and dirigibles. One is mounted on an armored motor -truck. The other is a swivel-mounted gun on a flat-topped four-wheeled -carriage. - -The United States battleship _Connecticut_ cost $9,000,000. It -displaces 18,000 tons, uses 17,000 horse-power and 1000 men, and makes -twenty miles an hour. An aeroplane of unusual size with nearly three -times this speed, employing from one to three men with an engine of 100 -horse-power, would weigh one ton and might cost $5000. A Dreadnought -costs $16,000,000, complete, and may last--it is difficult to say, but -few claim more than ten years. It depreciates, perhaps, at the rate -of $2,000,000 a year. Aeroplanes built to standard designs in large -quantities would cost certainly not over $1000 each. The ratio of cost -is 16,000 to 1. Would the largest Dreadnought, exposed unaided to the -attack of 16,000 flying machines, be in an entirely enviable situation? - -An aeroplane is a fragile and costly thing to hazard at one blow: but -not more fragile or costly than a Whitehead torpedo. The aeroplane -soldier takes tremendous risks; but perhaps not greater risks than -those taken by the crew of a submarine. There is never any lack of -daring men when daring is the thing needed. - -All experience goes to show that an object in the air is hard to -hit. The flying machine is safer from attack where it works than it -is on the ground. The aim necessary to impart a crippling blow to an -aeroplane must be one of unprecedented accuracy. The dirigible balloon -gives a larger mark, but could not be immediately crippled by almost -any projectile. It could take a good pounding and still get away. -Interesting speculations might be made as to the outcome of an aerial -battle between the two types of craft. The aeroplane might have a -sharp cutting beak with which to ram its more cumbersome adversary, -but this would involve some risk to its own stability: and the balloon -could easily escape by a quick ascent. It has been suggested that each -dirigible would need an aeroplane escort force for its defense against -ramming. Any collision between two opposing heavier-than-air machines -could not, it would seem, be other than disastrous: but perhaps -the dirigible could rescue the wrecks. Possibly gas-inflated life -buoys might be attached to the individual combatants. In the French -man[oe]uvers, a small aeroplane circled the dirigible with ease, flying -not only around it, but in vertical circles over and under it. - - [Illustration: 7.5 CENTIMETER GERMAN AUTOMATIC GUN FOR ATTACKING - AIRSHIPS - (From Brewer's _Art of Aviation_)] - -The French war office has exploited both types of machine. In -Germany, the dirigible has until recently received nearly all the -attention of strategists: but the results of a recent aerial war -game have apparently suggested a change in policy, and the Germans -are now, without neglecting the balloon, actively developing its -heavier-than-air competitor. England seems to be muddled as to its -aerial policy, while the United States has been waiting and for the -most part doing nothing. Now, however, the mobilizations in Texas have -been associated with a considerable amount of aeroplane enthusiasm. -A half-dozen machines, it is expected, will soon be housed in the -aerodrome at San Antonio. Experiments are anticipated in the carrying -of light ammunition and emergency supplies, and one of the promised -man[oe]uvers is to be the locating of concealed bodies of troops by air -scouts. Thirty army officers are to be detailed for aeroplane service -this year; five training schools are to be established. - -If flying machines are relatively unsusceptible to attack, there is -also some question as to their effectiveness _in_ attack. Rifles have -been discharged from moving balloons with some degree of accuracy in -aim; but long-range marksmanship with any but hand weapons involves the -mastery of several difficult factors additional to those present in -gunnery at sea. The recoil of guns might endanger stability; and it is -difficult to estimate the possible effects of a powerful concussion, -with its resulting surges of air, in the immediate vicinity of a -delicately balanced aerial vessel. - -But aside from purely combative functions, air craft may be -superlatively useful as messengers. To send despatches rapidly and -without interference, or to carry a general 100 miles in as many -minutes--these accomplishments would render impossible the romance -of a "Sheridan's Ride," but might have a romance of their own. With -the new sense added to human equipment by wireless communication, -the results of observations may be signaled to friends over miles of -distance without intervening permanent connections of however fragile a -nature. - -Flying machines would seem to be the safest of scouts. They could pass -over the enemy's country with as little direct danger--perhaps as -unobserved--as a spy in disguise; yet their occupants would scarcely -be subjected to the penalty accompanying discovery of a spy. They -could easily study the movements of an opposing armed force: a study -now frequently associated with great loss of life and hampering of -effective handling of troops. They could watch for hostile fleets with -relatively high effectiveness (under usual conditions), commanding -distant approaches to a long coast line at slight cost. From their -elevated position, they could most readily detect hostile submarines -threatening their own naval fleet. Maximum effective reconnaissance in -minimum time would be their chief characteristic: in fact, the high -speeds might actually constitute an objection, if they interfered with -thorough observation. But if air craft had been available at Santiago -in 1898, Lieutenant Blue's expedition would have been unnecessary, and -there would have been for no moment any doubt that Admiral Cervera's -fleet was actually bottled up behind the Morro. No besieged fortress -need any longer be deprived of communication with--or even some -medical or other supplies from--its friends. Suppose that Napoleon had -been provided with a flying machine at Elba--or even at St. Helena! - -The applications to rapid surveying of unknown ground that have been -suggested as possible in civil life would be equally possible in time -of war. Even if the scene of conflict were in an unmapped portion of -the enemy's territory, the map could be quickly made, the location of -temporary defenses and entrenchments ascertained, and the advantage -of superior knowledge of the ground completely overcome prior to an -engagement. The searchlight and the compass for true navigation on long -flights over unknown country would be the indispensable aids in such -applications. - -During the current mobilization of the United States Army at Texas, a -dispatch was carried 21 miles on a map-and-compass flight, the round -trip occupying less than two hours and being made without incident. The -machine flew at a height of 1500 feet and was sighted several miles off. - -A dirigible balloon, it has been suggested, is comparatively safe while -moving in the air, but is subjected to severe strains when anchored to -the ground, if exposed. It must have either safe harbors of refuge or -actual shelter buildings--dry docks, so to speak. In an enemy's country -a ravine or even a deep railway cut might answer in an emergency, but -the greatest reliance would have to be placed on quick return trips -from a suitable base. The balloon would be, perhaps, a more effective -weapon in defense than in attack. Major Squier regards a flying height -of one mile as giving reasonable security against hostile projectiles -in the daytime. A lower elevation would be sufficient at night. Given a -suitable telephotographic apparatus, all necessary observations could -easily be made from this altitude. Even in the enemy's territory, -descent to the earth might be possible at night under reasonably -favorable conditions. Two sizes of balloon would seem to be indicated: -the scouting work described would be done by a small machine having the -greatest possible radius of action. Frontiers would be no barrier to -it. Sent from England in the night it could hover over a Kiel canal or -an island of Heligoland at sunrise, there to observe in most leisurely -fashion an enemy's mobilizations. - - [Illustration: GERMAN GUN FOR SHOOTING AT AEROPLANES - (From Brewer's _Art of Aviation_)] - -At the London meeting of the Institute of Naval Architects, in April, -1911, the opinion was expressed that the only effective way of meeting -attack from a flying machine at sea would be by a counter-attack from -the same type of craft. The ship designers concluded that the aeroplane -would no more limit the sizes of battleships than the torpedo has -limited them. - -For the more serious work of fighting, larger balloons would be needed, -with net carrying capacities perhaps upward from one ton. Such a -machine could launch explosives and combustibles against the enemy's -forts, dry docks, arsenals, magazines, and battleships. It could easily -and completely destroy his railroads and bridges; perhaps even his -capital itself, including the buildings housing his chief executive -and war office staff. Nothing--it would seem--could effectually combat -it save air craft of its own kind. The battles of the future may be -battles of the air. - -There are of course difficulties in the way of dropping missiles -of any great size from flying machines. Curtiss and others have -shown that accuracy of aim is possible. Eight-pound shrapnel shells -have been dropped from an aeroplane with measurably good effect, -without upsetting the vessel; but at best the sudden liberation of -a considerable weight will introduce stabilizing and controlling -difficulties. The passengers who made junketing trips about Paris on -the _Clément-Bayard_ complained that they were not allowed to throw -even a chicken-bone overboard! But it does not seem too much to expect -that these purely mechanical difficulties will be overcome by purely -mechanical remedies. An automatic venting of a gas ballonet of just -sufficient size to compensate for the weight of the dropped shell would -answer in a balloon: a similar automatic change in propeller speed and -angle of planes would suffice with the aeroplane. There is no doubt -but that air craft may be made efficient agents of destruction on a -colossal scale. - - [Illustration: SANTOS-DUMONT CIRCLING THE EIFFEL TOWER - (From Walker's _Aerial Navigation_)] - -A Swedish engineer officer has invented an aerial torpedo, -automatically propelled and balanced like an ordinary submarine -torpedo. It is stated to have an effective radius of three miles while -carrying two and one-half pounds of explosive at the speed of a bullet. -One can see no reason why such torpedoes of the largest size are not -entirely practicable: though much lower speeds than that stated should -be sufficient. - -According to press reports, the Krupps have developed a non-recoiling -torpedo, having a range exceeding 5000 yards. The percussion device is -locked at the start, to prevent premature explosion: unlocking occurs -only after a certain velocity has been attained. - -Major Squier apparently contends that the prohibition of offensive -aerial operations is unfair, unless with it there goes the reciprocal -provision that a war balloon shall not be fired at from below. Again, -there seems to be no good reason why aerial mines dropped from above -should be forbidden, while submarine mines--the most dangerous naval -weapons--are allowed. Modern strategy aims to capture rather than to -destroy: the man[oe]uvering of the enemy into untenable situations by -the rapid mobilization of troops being the end of present-day highly -organized staffs. Whether the dirigible (certainly not the aeroplane) -will ever become an effective vehicle for transport of large bodies of -troops cannot yet be foreseen. - -Differences in national temper and tradition, and the conflict of -commercial enterprise, perhaps the very recentness of the growth of a -spirit of national unity on the one hand, are rapidly bringing the two -foremost powers of Europe into keen competition: a competition which -is resulting in a bloodless revolution in England, necessitated by the -financial requirements of its naval program. Germany, by its strategic -geographical position, its dominating military organization, and the -enforced frugality, resourcefulness, and efficiency of its people, -possesses what must be regarded as the most invincible army in the -world. Its avowed purpose is an equally invincible navy. Whether the -Gibraltar-Power can keep its ascendancy may well be doubted. The one -doubtful--and at the same time perhaps hopeful--factor lies in the -possibilities of aerial navigation. - - [Illustration: LATHAM, FARMAN, AND PAULHAN] - -If one battleship, in terms of dollars, represents 16,000 airships, -and if one or a dozen of the latter can destroy the former--a feat -not perhaps beyond the bounds of possibility--if the fortress that -represents the skill and labor of generations may be razed by twoscore -men operating from aloft, then the nations may beat their spears into -pruning-hooks and their swords into plowshares: then the battle ceases -to hinge on the power of the purse. Let war be made so costly that -nations can no more afford it than sane men can wrestle on the brink -of a precipice. Let armed international strife be viewed as it really -is--senseless as the now dying duello. Let the navy that represents -the wealth, the best engineering, the highest courage and skill, of -our age, be powerless at the attack of a swarm of trifling gnats like -Gulliver bound by Lilliputians--what happens then? It is a _reductio ad -absurdum_. Destructive war becomes so superlatively destructive as to -destroy itself. - -There is only one other way. Let the two rival Powers on whom the peace -of the world depends settle their difficulties--surely the earth must -be big enough for both!--and then as one would gently but firmly take -away from a small boy his too destructive toy rifle, spike the guns -and scuttle the ships, their own and all the rest, leaving to some -unambitious and neutral power the prosaic task of policing the world. -Here is a work for red blood and national self-consciousness. If war -were ever needed for man's best development, other things will answer -now. The torn bodies and desolated homes of millions of men have paid -the price demanded. No imaged hell can surpass the unnamed horrors that -our fathers braved. - -"Enforced disarmament!" Why not? Force (and public opinion) have -abolished private duels. Why not national duels as well? Civilization's -control of savagery always begins with compulsion. For a generation, -no first-class power has had home experience in a serious armed -conflict. We should not willingly contemplate such experience now. We -have too much to do in the world to fight. - - * * * * * - -The writer has felt some hesitancy in letting these words stand as -the conclusion of a book on flying machines: but as with the old -Roman who terminated every oration with a defiance of Carthage, the -conviction prevails that no other question of the day is of comparable -importance; and on a matter of overwhelming consequence like this -no word can ever be out of place. The five chief powers spent for -war purposes (officially, as Professor Johnson puts it, for the -"preservation of peace") about $1,000,000,000 in the year 1908. In -the worst period of the Napoleonic operations the French military and -naval budget was less than $100,000,000 annually. Great Britain, on -the present peace footing, is spending for armament more rapidly than -from 1793 to 1815. The gigantic "War of the Spanish Succession" (which -changed the map of Europe) cost England less than a present year's -military expenditure. Since the types for these pages have been set, -the promise of international peace has been distinctly strengthened. -President Taft has suggested that as, first, questions of individual -privilege, and, finally, even those of individual honor, have been -by common consent submitted to adjudication, so also may those -so-called "issues involving national honor" be disposed of without -dishonor by international arbitration. Sir Edward Grey, who does not -hesitate to say that increase of armaments may end in the destruction -of civilization unless stopped by revolt of the masses against the -increasing burdens of taxation, has electrified Europe by his reception -of the Taft pronouncement. England and the United States rule one-third -the inhabitants of the earth. It is true that a defensive alliance -might be more advantageous to the former and disagreeably entangling to -the latter; but a binding treaty of arbitration between these powers -would nevertheless be a worthy climax to our present era. And if it -led to alliance against a third nation which had refused to arbitrate -(led--as Sir Edward Grey suggests--by the logic of events and not by -subterranean device) would not such be the fitting and conclusive -outcome? - -The Taft-Grey program--one would wish to call it that--has had all -reputable endorsement; in England, no factional opposition may be -expected. Our own jingoes are strangely silent. Mr. Dillon's fear that -compulsory disarmament would militate against the weaker nations is -offset by the hearty adherence of Denmark. A resolution in favor of the -establishment of an international police force has passed the House of -Commons by a heavy majority. It looks now as if we might hope before -long to re-date our centuries. We have had Olympiads and Years of Rome, -B.C. and A.D. Perhaps next the dream of thoughtful men may find its -realization in the new (and, we may hope, English) prefix, Y.P.--Year -of Peace. - - - - -FOOTNOTES - -[A] According to press reports, temporary water ballast will -be taken on during the daytime, to offset the ascensional effect of the -hot sun on the envelope. - -[B] The contestants for the Ryan prize of $10,000 were -Moisant, Count de Lesseps, and Grahame-White. Owing to bad weather, -there was no general participation in the preliminary qualifying -events, and some question exists as to whether such qualification was -not tacitly waived; particularly in view of the fact that the prize was -awarded to the technically unqualified competitor, Mr. Moisant, who -made the fastest time. This award was challenged by Mr. Grahame-White, -and upon review by the International Aeronautic Federation the prize -was given to de Lesseps, the slowest of the contestants, Grahame-White -being disqualified for having fouled a pylon at the start. This -gentleman has again appealed the case, and a final decision cannot be -expected before the meeting of the Federation in October, 1911. - -[C] The high wind velocities of the southern circumpolar -regions may be an insurmountable obstacle in the Antarctic. Yet Mawson -expects to take with him a 2-passenger monoplane having a 180-mile -radius of action on the expedition proposed for this year. - -[D] It seems that tomorrow has come; for an aeroplane is being -regularly used (according to a reported interview with Dr. Alexander -Graham Bell) for carrying mails in India. - - - - -Books on Aeronautics - - - =FLYING MACHINES TO-DAY.= By WILLIAM D. ENNIS, M. E., Professor of - Mechanical Engineering, Polytechnic Institute, Brooklyn. 12mo., - cloth, 218 pp., 123 illustrations =$1.50 net= - =CONTENTS=: THE DELIGHTS AND DANGERS OF FLYING--Dangers of - Aviation--What it is Like to Fly. SOARING FLIGHT BY MAN--What Holds - it Up. Lifting Power. Why so Many Sails. Steering. TURNING - CORNERS--What Happens When Making a Turn. Lateral Stability. Wing - Warping. Automatic Control. The Gyroscope. Wind Gusts. AIR AND THE - WIND--Sailing Balloons. Field and Speed. GAS AND BALLAST--Buoyancy in - Air. Ascending and Descending. The Ballonet. The Equilibrator. - DIRIGIBLE BALLOONS AND OTHER KINDS--Shapes. Dimensions. Fabrics. - Framing. Keeping the Keel Horizontal. Stability. Rudders and Planes. - Arrangement and Accessories. Amateur Dirigibles. Fort Omaha Plant. - Balloon Progress. QUESTION OF POWER--Resistance of Aeroplanes. - Resistance of Dirigibles. Independent Speed and Timetable. Cost of - Speed. Propeller. GETTING UP AND DOWN; MODELS AND GLIDERS; AEROPLANE - DETAILS--Launching. Descending. Gliders. Models. Balancing. Weights. - Miscellaneous. Things to Look After. SOME AEROPLANES--SOME - ACCOMPLISHMENTS. THE POSSIBILITIES IN AVIATION--Case of the - Dirigible. The Orthopter. The Helicopter. Composite Types. What is - Promised. AERIAL WARFARE. - - =AERIAL FLIGHT. Vol. 1. Aerodynamics.= By F. W. LANCHESTER. 8vo., - cloth, 438 pp., 162 illustrations =$6.00 net= - =CONTENTS=: Fluid Resistance and Its Associated Phenomena. Viscosity - and Skin Friction. The Hydrodynamics of Analytical Theory. Wing - Form and Motion in the Periphery. The Aeroplane. The Normal Plane. - The Inclined Aeroplane. The Economics of Flight. The Aerofoil. On - Propulsion, the Screw Propeller, and the Power Expended in Flight. - Experimental Aerodynamics. Glossary. Appendices. - =Vol. II. Aerodonetics.= By F. W. LANCHESTER. 8vo., cloth, 433 pp., - 208 illustrations =$6.00 net= - =CONTENTS=: Free Flight. General Principles and Phenomena. The Phugoid - Theory--The Equations of the Flight Path. The Phugoid 1852-1872. - Dirigible Balloons from 1883-1897; 1898-1906. Flying Machine - Theory--The Flight Path Plotted. Elementary Deductions from the - Phugoid Theory. Stability of the Flight Path as Affected by Resistance - and Moment of Inertia. Experimental Evidence and Verification of the - Phugoid Theory. Lateral and Directional Stability. Review of Chapters - I to VII and General Conclusions. Soaring. Experimental. Aerodonetics. - - =AERIAL NAVIGATION. A practical handbook on the construction of - dirigible balloons, aerostats, aeroplanes and aeromotors=, by - FREDERICK WALKER. 12mo., cloth, 151 pp., 100 illustrations - =$3.00 net.= - =CONTENTS=: Laws of Flight. Aerostatics. Aerostats. Aerodynamics. - Screw Propulsion. Paddles and Aeroplanes. Motive Power. Structure of - Airships and Materials. Airships. Appendix. - - =AEROPLANE PATENTS.= By ROBERT M. NEILSON. 8vo., cloth, 101 pp., 77 - illustrations =$2.00 net= - =CONTENTS=: Advice to Inventors. Review of British Patents. British - Patents and Applications for Patents from 1860 to 1910, arranged in - Order of Application. British Patentees, arranged alphabetically. - United States Patents from 1896 to 1909, arranged in order of issue. - United States Patentees, arranged alphabetically. - - =THE PRINCIPLES OF AEROPLANE CONSTRUCTION.= By RANKIN KENNEDY, C. E. - 8vo., cloth, 145 pp., 51 diagrams =$1.50 net= - =CONTENTS=: Elementary Mechanics and Physics. Principles of Inclined - Planes. Air and Its Properties. Principles of the Aeroplane. The - Curves of the Aeroplane. Centers of Gravity: Balancing; Steering. The - Propeller. The Hélicoptère. The Wing Propeller. The Engine. The Future - of the Aeroplane. - - =HOW TO DESIGN AN AEROPLANE.= By HERBERT CHATLEY. 16mo., boards, 109 - pp., illustrated (Van Nostrand's Science Series) =50 cents= - =CONTENTS=: The Aeroplane. Air Pressure. Weight. Propellers and - Motors. Balancing. Construction. Difficulties. Future Developments. - Cost. Other Flying-Machines (Gyroplane and Orinthoptere). - - =HOW TO BUILD AN AEROPLANE.= By ROBERT PETIT. Translated from the - French by T. O'B. Hubbard and J. H. Ledeboer. 8vo., cloth, 131 pp., 93 - illustrations =$1.50 net= - =CONTENTS=: General Principles of Aeroplane Design. Theory and - Calculation. Resistance, Lift, Power, Calculations for the Design of - an Aeroplane, Application of Power, Design of Propeller, Arrangements - of Surfaces, Stability, Center of Gravity, etc. Materials. - Construction of Propellers. Arrangements for Starting and Landing. - Controls. Placing Motor. The Planes. Curvatures. Motors. - - =AIRSHIPS, PAST AND PRESENT. Together with chapters on the use of - balloons in connection with meteorology, photography, and the carrier - pigeon.= By A. HILDEBRANDT, Captain and Instructor in the Prussian - Balloon Corps. Translated by W. H. Story. 8vo., cloth, 361 pp., 222 - illustrations =$3.50 net= - =CONTENTS=: Early History of the Art. Invention of the Air Balloon. - Montgolfieres, Charlieres, and Rozieres. Theory of the Balloon. - Development of the Dirigible Balloon. History of the Dirigible - Balloon, 1852-1872. Dirigible Balloons from 1883-1897; 1898-1906. - Flying Machines. Kites. Parachutes. Development of Military - Ballooning. Ballooning in Franco-Prussian War. Modern Organization - of Military Ballooning in France, Germany, England and Russia. - Military Ballooning in Other Countries. Balloon Construction and the - Preparation of the Gas. Instruments. Ballooning as a Sport. Scientific - Ballooning. Balloon Photography. Photographic Outfit for Balloon Work. - Interpretation of Photographs. Hectography by Means of Kites and - Rockets. Carrier Pigeons for Balloons. Balloon Law. - - [Illustration: VAN NOSTRAND LOGO] - - -D. VAN NOSTRAND CO., Publishers - -23 MURRAY and 27 WARREN STREETS, NEW YORK - - - - -Transcriber's Note: Italics are delimited by underscores; bold by equal -signs. Four occurrences of the oe-ligature in the word man[oe]uver -are left as [oe]. The four footnotes have been moved to the end of the -book. A few words were judged to be printer errors and were changed. -These include two occurrences of horse-power in the unhyphenated form, -the spelling of Tabuteau as Tabuteaw on p. 162, and the spelling of -hélicoptère as helicoptéré on p.208. On a few of the -figure captions, missing accents were added to some French names. - - - - - - - -End of Project Gutenberg's Flying Machines Today, by William Duane Ennis - -*** END OF THIS PROJECT GUTENBERG EBOOK FLYING MACHINES TODAY *** - -***** This file should be named 51481-8.txt or 51481-8.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/1/4/8/51481/ - -Produced by Chris Curnow, Ralph Carmichael and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive) - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law means that no one owns a United States copyright in these works, -so the Foundation (and you!) can copy and distribute it in the United -States without permission and without paying copyright -royalties. 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