The Project Gutenberg eBook, The Aeroplane, by Claude Grahame-White and Harry Harper

“ROMANCE OF REALITY” SERIES
Edited by Ellison Hawks

THE AEROPLANE

VOLUMES ALREADY ISSUED
1. THE AEROPLANE. By Grahame White and Harry Harper.
2. THE MAN-OF-WAR. By Commander E. H. Currey, R.N.
3. MODERN INVENTIONS. By V. E. Johnson, M.A.
4. ELECTRICITY. By W. H. McCormick.
5. ENGINEERING. By Gordon D. Knox.

THE AIR LINER OF THE FUTURE.

By the use of such a machine as this, twenty years hence, we shall be able to spend a week-end in New York, as we do now in Paris or Scotland. Flying at immense heights, and at speeds of 200 miles an hour, these huge aircraft—carrying hundreds of passengers in vibrationless luxury—will pass from London to New York in less than twenty hours.

“ROMANCE OF REALITY” SERIES

THE AEROPLANE

BY

CLAUDE GRAHAME-WHITE

AND

HARRY HARPER

JOINT AUTHORS OF
“THE AEROPLANE; PAST, PRESENT, AND FUTURE”
“THE AEROPLANE IN WAR” “HEROES OF THE AIR”
“WITH THE AIRMEN” “THE AIR KING’S TREASURE”
ETC. ETC.

LONDON: T. C. & E. C. JACK

67 LONG ACRE, W.C., & EDINBURGH

Printed in Great Britain

PREFACE

Our aim in these pages is to tell a complete story of the aerial conquest, beginning from crude experiments, made hundreds of years ago; passing thence to the first serious experimenters, with their difficulties and triumphs; and so carrying on the tale to present-day achievements and the latest-type machines.

There is one aspect of this history which has an especial fascination; and it is the personality of the men who—braving ridicule and scorn and surmounting obstacles without number—laid the foundation-stones of flight. Instead of being a compilation of dates, with certain explanatory matter added, our book endeavours to make these men live: to show what induced them to embark upon their seemingly hopeless quest; to tell of their dreams and longings, and how they built their first frail craft; to trace them to their boyhood and their play with kites; to reveal them, in a word, as living beings, and not merely as names.

With this strongly human note, emphasizing the romance of the tale, there goes also a series of explanations—made clearer by drawings and diagrams—and tending always to show how, link by link and step by step, data and experience were secured; how each pioneer, however humble, played his individual and useful part; and how in the end, by sifting all such knowledge and carrying experiment to its final stage, the Wrights achieved the apparent miracle, and flew safely and successfully in a power-driven machine.

The book divides itself naturally into sections. First there is the story of the very early and haphazard tests, and of the notes and speculations of scientists; then of the advent of the practical, patient experimenter—the man who, taking a hint from the birds, realized that ere he could hope to fly he must learn first to balance himself when in the air. This stage, of course, introduces Otto Lilienthal—the German engineer who, by his gliding flights from hilltops with outstretched, bird-like wings, has won the honour of being styled “the father of the aeroplane.”

From a narration of his work, so vital a link in the chain of progress, the story passes to those two men—unflurried, reserved, and infinitely painstaking—who at last evolved order out of chaos: Wilbur and Orville Wright. Their diligent study is described; their perfected glider; the building of their own motor; and, finally, that great day of triumph which came in 1903—just eleven years ago.

The world being given thus an aeroplane which would fly, the steps which followed were mainly those of perfection and improvement. One by one the limitations were removed. At first men dared only to fly above a smooth-surfaced aerodrome, in case their motors should stop and send them gliding back to earth; but soon, gaining confidence in themselves and in their engines, they were passing high across country. So, also, in regard to their enemy the wind. Dreading even a gentle gust at first, for fear it might overturn them, they have gained so rapidly in skill that, thanks to their experience and the stability of their machines, the airmen of to-day will do battle with a gale. In this section of our book is a description of the greatest feats, both of early days and of modern times—such as speed flying, altitude records, and the touring of continents by air.

Thus logically may the tale be told: with digressions of course to cover the risks of aviation, and to explain how they are being overcome; to deal with aerial warfare and its many problems; to describe the advent of the sea-plane; and to discuss the day when—a perfected passenger craft being available—men will journey by air as they do now by land or sea.

CLAUDE GRAHAME-WHITE.

HARRY HARPER.

London, 1914.

Note.— The authors thank most cordially the proprietors of The Daily Mirror for permission to reproduce certain photographs, of an historical interest, which depict incidents from the cross-Channel flying both of Latham and Bleriot; also F. N. Birkett, Esq., the Topical Postcard Company, and The Central News for permission to use photographs illustrative of modern aviation.

CONTENTS

LIST OF PLATES

THE AEROPLANE

CHAPTER I
WHAT EARLY HISTORY TELLS

Simon the magician—A monk who sprang from a tower—The Saracen who “rose like a bird.”

In learning to fly, men have passed through five definite and clearly-marked stages which have extended over centuries, and cost many lives. These five stages may be summarized thus:

1. Haphazard and foolhardy tests—ending generally in death.

2. A period of scientific research, in which the flight of birds was studied and experiments made with lifting planes of various shapes.

3. A phase during which engineers built large, power-driven machines, but had not the skill to control them when in flight.

4. A stage in which, making a simple apparatus of wings, men glided from hilltops, and learned to balance themselves while in the air.

5. The stage in which, perfecting the gliding machines they had learned to control, men fitted petrol motors to them, and achieved at last a power-driven flight.

In dim, remote ages, watching winged creatures as they skimmed above the earth, men longed passionately to fly; instead of scaling hills or creeping through woods, they desired to pass high above them; to spurn the obstructions of creatures earth-bound, and fly over mountains and seas. This longing to fly, even at the risk of life itself, was expressed beautifully by Otto Lilienthal, the greatest of the pioneers. He wrote:

“With each advent of spring, when the air is alive with innumerable happy creatures; when the storks, on their arrival at their old northern resorts, fold up the imposing flying apparatus which carries them thousands of miles, lay back their heads and announce their arrival by joyfully rattling their beaks; when the swallows have made their entry and hurry through our streets and pass our windows in sailing flight; when the lark appears as a dot in the ether and manifests its joy of existence by its song; then a certain desire takes possession of man. He longs to soar upward and to glide free as a bird over smiling fields, leafy woods, and mirror-like lakes, and so enjoy the fairy landscape as only a bird can do.”

But man’s first attempts to fly were ill-judged and foolish. He failed to understand the problems involved; he forgot that, even were he able to build a machine which would navigate the air, he must learn to control this craft; must learn to steer and balance it, and make it ride the gusts. One might, for example, take a bicycle and say to a man: “Here is a machine that can be propelled along the road; mount it and ride away.” But if the man had not learned to handle a bicycle, and balance himself on one, he would swerve for a few yards and then fall. So with the man who, without forethought or study, sought to navigate the air.

Probing the recesses of history we find that, even as far back as the reign of the Emperor Nero, there was one Simon the magician who—if legend can be credited—sought “to rise towards Heaven.” Simon, it would seem, actually lifted himself into the air by the use of some apparatus; but what this device was legend does not state. The spectators seem to have been horrified, and Simon’s ascent into the air was attributed to “the assistance of Beelzebub.” His triumph was short-lived, for, as the legend goes on to record, he fell to the earth and was killed. And this fate befell many who, in those very early days, made flimsy wings and threw themselves from towers or the tops of hills. Simon, it is thought, may have had some method in his apparent madness. He may, for instance, have made a lifting plane and discovered that, if he placed himself in a rising current of air, the effect would be to raise him from the ground; and this suggestion has a greater probability when we remember that in warm, southern lands there are often strong up-currents of air upon which birds will soar, with wings motionless. But what machine Simon used, and how he made his flight—if he did—are questions that remain unanswered.

Fig. 1.

Looking back into history, one fact is striking; and this is the part that monks played in studying flight. They had leisure to think, and time in which to make tests; and in many a monastery, hundreds of years ago, quaint theories were propounded and queer craft planned. In the eleventh century, at Malmesbury in England, there was a Benedictine monk named Elmerus, or Oliver, more ambitious than many of his brethren. He built himself a machine with wings; then, in order to put it to the test, he ascended a tall tower, faced the wind, and sprang into the air. That he had studied weighting and balance to some purpose was evident, for he glided a short distance without accident; then, struck perhaps by a sudden gust, lost equilibrium and came crashing to the ground. He was not killed, as were many less rash than he; but broke his legs, and nothing more is read of him as an experimenter. Of the doings of another of these brave but reckless men—a Saracen who tried to fly in the twelfth century—there is fuller information. He provided himself with wings which he stiffened with wooden rods, and held out upon either side of his body. Wearing these, he mounted to the top of a tower in Constantinople ([Fig. 1]) and stood waiting for a favourable gust of wind. When this came and caught his wings, he “rose into the air like a bird.” And then, of course, seeing that he had no idea of balancing himself when actually aloft, he fell pell-mell and “broke his bones.” People who had gathered to watch, seeing this inglorious ending to the flight, burst into laughter: ridicule rather than praise, indeed, was the fate of the pioneers, even to the days when the first real flights were made.

In the fifteenth century, working upon more sensible lines of thought, Leonardo da Vinci—an Italian genius who was painter, inventor, sculptor, writer, and musician —devised several machines by which men might navigate the air. Success did not come to him, as he had no motive power with which he could equip a craft; but how keen a watcher he was of the birds is shown by a passage from one of his manuscripts:

“The kite and other birds, which beat their wings little, go seeking the course of the wind, and when the wind prevails on high then will they be seen at a great height, and if it prevails low they will hold themselves low. When the wind does not prevail at all, then the kite beats its wings several times in its flight in such a way that it raises itself high and acquires a start, descending afterwards a little and progressing without beating its wings, repeating the same performance time after time.”

Da Vinci, too, had some notion as to the need for balancing a machine while in the air, and did not seem—like most others of the early pioneers—to imagine that once a man had launched himself from a height he would be able to control his craft by instinct. He wrote, indeed, suggesting the position of a pilot in a flying machine, that “he should be free from the waist upwards, in order that he might keep himself in equilibrium, as one does in a boat.”

He realised, too, a fact that the modern airman always bears in mind; and that is the value of flying high. Da Vinci wrote in this regard: “Safety lies in flying at a considerable height from the ground, so that if equilibrium be temporarily upset there may be time and space for regaining it.”

Among the machines Da Vinci planned was an ornithopter, or craft with arched wings which would flap like those of a bird; and a helicopter, or apparatus in which revolving screws are used to draw it up into the air. He devised mechanism by which a man might move two wings, shaped like those of the bird, and thus imitate natural fight. These wings were planned ingeniously, so that they would contract on the up-stroke and expand when forced downward. In one of his notebooks, too, he made a sketch of a helicopter machine which was to have a lifting propeller 96 feet in diameter, and to be built of iron with a bamboo framework. He made paper helicopters, or whirling screws, and sent them spinning into the air; and to him, also, was due the first suggestion for the use of a parachute.

Fig. 2.—Besnier’s Apparatus.

From this time, until the beginning of the nineteenth century, men still strove to fly, but all of them failed to see a vital point: that they must learn gradually to balance themselves in the air, even as the young birds have to do. So those who were not killed were badly injured, and those who persisted in experiments were looked upon either as madmen or fools. Some, however, were not so foolish as they seemed. They brought forward schemes so as to attract the attention of kings and those in high places; and this was particularly the case in France, during the reigns of Louis XIV. and Louis XV. But the notoriety they won was short-lived. The day came when they needed to make good their claims—when they were called upon to fly; and then they met death, disablement, or disgrace, and were forgotten quickly. Of the devices suggested many showed ingenuity; and some were quaint, in view of what we know of flight to-day. In the machine, for instance, designed by an experimenter named Besnier—who was a locksmith by trade—there were four lifting planes, closing on the up-stroke and opening on the down, and these the operator was to flap by the use of his hands and feet ([Fig. 2]). A rather similar idea was suggested as long ago as 1744, by the inventor De Bacqueville; his plan was to fix four planes or wings to his hands and feet, and then propel himself through the air by vigorous motions of his arms, and kickings of his legs ([Fig. 3]). He made a flight from a balcony overlooking a river, but finished his trial ingloriously by falling into a barge. Such schemes, indeed, were doomed to failure; and they are only interesting because they show how, even in those far-off days, men were ready to risk their lives in attempts to conquer the air.

Fig. 3.—De Bacqueville (1744).

CHAPTER II
THE WORK OF SCIENTISTS

Sir George Cayley’s forecasts—A steam-driven model which flew—The shape and curve of planes.

So passed the haphazard stage of flight; and now history moves to a second and more important period, that in which men of science were attracted to the problem. They worked upon theories, and made experiments with models; they studied the shape which Nature has given the birds; they sifted false notions and showed where error lay. But they did not fly. They were merely clearers of the ground, gathering information and classifying it, and paving the way for those daring workers who were to follow them—men who, by putting science to the test, were willing to risk their lives.

Fig. 4.—Sir George Cayley’s
suggestion for an
Arched Plane.

To England goes the distinction of the first practical attempts to solve the problems of flight; and it is the work of Sir George Cayley, an eminent scientist and engineer, that next merits attention. In a series of articles, published in Nicholson’s Journal during the years 1809-10, he forecasted many of the principles that go to the making of a modern-type aeroplane. He advised the construction of machines with fixed, outstretched wings like those of a bird; but he did more than this, for it is admitted generally he was first to point out that, to increase their lifting power as they were moved through the air, these wings should not be flat, but should be curved from front to back, or arched upward ([Fig. 4]). How important this suggestion was, subsequent experimenters were to show. Sir George Cayley realised also that a tail-plane, carried at the rear of a machine, would give it equilibrium, and might be moved up and down to control ascent or descent; and he used a rudder upon models, to steer them from side to side. He advised the use of steam engines as a motive power, and of revolving propellers to drive a craft through the air. But, like many another man, he was before his time. He built experimental craft—one, a model glider, which would sail down gracefully from the top of a hill; and another, a far larger machine, which would bear a man through the air, for a distance of several yards, if he ran forward with it against the wind. But the difficulty of obtaining a sufficiently light and practical motor, either of steam or other power, was an obstacle that proved insurmountable. One light engine, which Sir George Cayley planned, was to be driven by a series of gunpowder explosions in a cylinder; but the suggestion came to no practical issue.

This scientist did not write or work in vain. He compiled data which was invaluable, and interested and encouraged other men—even those, indeed, who in due course made the conquest. One of the first to work upon Sir George Cayley’s theories was an experimenter named Henson. He planned an ambitious machine weighing about a ton. It was to have planes of canvas stretched over a rigidly trussed frame of bamboo rods and hollow wooden spars; and these planes were to contain 4500 square feet of lifting surface, and be driven by screws operated by a steam engine of 30 h.p. ([Fig. 5]).

But this craft did not take practical shape, although in its appearance and many of its details it bore a resemblance to machines which ultimately were to fly. In the specification of the patent he took out for his invention, Henson indicated that it was for

“Improvements in locomotive apparatus and machinery for conveying letters, goods, and passengers from place to place through the air.”

Fig. 5.—Henson’s proposed Machine.

Explaining his theories in this same specification he wrote:

“If any light and flat or nearly flat article be projected or thrown edgewise in a slightly inclined position, the same will rise into the air till the force exerted is expended, when the article so thrown or projected will descend; and it will readily be conceived that, if the article so projected or thrown possessed in itself a continuous power or force equal to that used in throwing or projecting it, the article would continue to ascend so long as the forward part of the surface was upwards in respect to the hinder part.”

Had Henson been able to carry out his ideas, it is almost certain that this experimental machine would have been wrecked in its tests, and probably several more after it, seeing that he would have had to learn to control them when in flight, and remembering also that, even with aircraft as they are built to-day, many details have to be studied and improved before a successful model is evolved.

All such work, of course, entails heavy expense. It was, indeed, the cost of experiments which prevented many an early inventor from building a full-sized machine. The designing and construction of a man-carrying craft, and the employment of skilled workmen and mechanics, to say nothing of repairs that may have to be made during a series of tests, represent an expenditure that may amount to thousands of pounds. As a rule, the inventor is not a man of wealth; and so far as flying was concerned, at any rate in the early days,—and to a more limited extent even at the present time,—people with money thought the difficulties so great that they would not advance funds for the carrying out of trials. So men with ideas had to do the best they could, and this resolved itself generally into writing and lecturing, and endeavouring to interest the public. But the public was not easily interested; ordinary folk did not believe that men would ever fly, while many people declared that it was going against Nature for us to try to imitate the birds, and that nothing but mischief would come of so doing.

Henson, failing to make definite progress with his scheme for a man-carrying craft—despite the fact that a company was floated to assist him—co-operated with another enthusiast named Stringfellow in a plan which was not so elaborate. They began to experiment with a series of models driven by tiny and most ingenious steam engines built by Stringfellow; and so cleverly did he construct them that the Aeronautical Society awarded him a prize of £100. The model which won him this recognition was a little plant which, while it weighed only 13 lbs., without water or fuel, would develop one horse-power.

What, by the way, is meant by a horse-power? The answer is as follows: in the early days of engineering, when it was found necessary to establish some well-recognised unit of power, a large number of experiments were carried out with horses, which were made to raise a weight from the ground by means of an arrangement of pulleys and ropes. The experiments showed this: that a horse can exert sufficient power to raise 33,000 lbs., or about 15 tons, to a height of 1 foot in the space of one minute. This, therefore, was called “one horse-power.”

In Stringfellow’s days, it must be remembered, there was no petrol engine; an engine so extremely light for the power that it will give, and with its liquid fuel and oil carried conveniently in tanks—an engine which, as Sir Hiram Maxim puts it, will give one horse-power of energy “for the weight of a barn-door fowl.”

The question of motive-power was, indeed, the great obstacle for the pioneers. When a man builds an aeroplane he must drive it through the air; and to drive it through the air he requires an engine. But he knows that his planes, owing to the small density or sustaining power of the air through which they pass, will raise only a limited load. And the machine itself, even if it is built of wood and canvas, represents an appreciable weight; to say nothing of that of the pilot. So, if his engine is heavy in proportion to the power it gives, and its fuel weighty, he may be prevented altogether from rising from the ground; or if he does rise, he may be able only to carry sufficient fuel for a flight of a short distance.

Fig. 6.—Henson and Stringfellow’s Model.

Henson and Stringfellow built in 1845 a model which weighed about 30 lbs. ([Fig. 6]); and although its stability was not perfect, it was an interesting machine—a forecast of the monoplane of the future. Here one saw the lifting planes take shape; the body between the wings; the tail-planes at the rear; and, above all, a suggestion of the means by which machines would be driven through the air: the fitting to the model, that is to say, of revolving propellers or screws. When an inventor has fitted an engine to an aircraft, means must be devised for using its power to drive the machine through the air; and to make the wings flap like those of a bird, has been found so complicated, owing to the mechanism necessary to imitate natural movements, that much of the power is wasted. Inventors such as Henson and Stringfellow, realising this difficulty, made wings that were outstretched and immovable, like those of a bird when it is soaring, and relied upon screw propellers—which they set spinning at great speed by means of their engines—to thrust their craft forward through the air.

Fig. 7.

In an early and simple form, the aerial propeller was as shown in [Fig. 7]. Here are two curved blades, so shaped that, when the propeller is made to revolve quickly, these blades will act powerfully upon the air. What the propeller does is to screw itself forward through the air, as one might revolve a corkscrew and drive it into a cork, or force a gimlet into a piece of wood. Each time you twist the gimlet for instance, as you drive it inwards, it forces itself a certain distance through the wood; and in a like manner the air-propeller, each time it revolves, tends to bore its way through the air ([Fig. 8]) and so push, or draw with it, the flying machine to which it is attached. But with air, seeing that its density is small, it is necessary to use a large screw, and to turn it fast, before power can be obtained.

Fig. 8.

In 1845, Stringfellow, who was now working alone—Henson having abandoned the tests and gone abroad—met with a definite success. He obtained actual flights with a steam-driven model in the form of a monoplane, weighing 8½ lbs. These tests attracted attention among scientists, but they led to nothing else—that is to say, no full-sized machine was the result. But Stringfellow’s model interested many people in the problems of flight. It showed, indeed, although in miniature, that a flying machine could be built and driven through the air; and so this patient experimenter did not labour in vain.

Following Stringfellow, upon the list of those who forged links in the aerial conquest, came Francis Herbert Wenham. His interest in flying, as with many other men, was aroused by watching the birds. Wenham, an engineer by profession, made a voyage up the Nile; and his study of the movement of birds, as they flew near his yacht, caused him to take up aviation in earnest, and carry out experiments for the Aeronautical Society. Wenham was interested largely in the lifting power of planes, and sought efficient shapes. He recommended the building of arched surfaces, so arranged that they had considerable span, but were narrow from front to back; and he suggested also that they should, when fitted to a machine, be placed one above another. Thus Wenham was the inventor of the biplane, as we know that craft to-day.

In explaining this point he wrote:

“Having remarked how thin a stratum of air is displaced between the wings of a bird in rapid flight, it follows that, in order to obtain the necessary length of plane for supporting heavy weights, the surfaces may be superposed, or placed in parallel rows with an interval between them” ([Fig. 9]).

Fig. 9.—Superposed Lifting Planes.

To illustrate his theory, he built a model which had six long, narrow planes, arranged one above the other, rather like the slats of a Venetian blind. Wenham’s experiments were highly important, because they cleared a great deal of ground, and removed many misunderstandings. By showing that a long, narrow plane was more efficient—would, that is to say, carry a greater load through the air than one which was deep from front to back, owing to the fact that it is the front section of an inclined plane that provides the most “lift”; and by illustrating how, in a full-sized machine, such a row of planes could be arranged one above another, Wenham directed men’s thoughts towards a definite goal. By his work, and chiefly by his sifting of data, an outline was obtained of that aeroplane of the future which was actually to fly.

While Wenham was experimenting, an inventor named Penaud, in France, testing a series of models, made one which was driven by the twisting of elastic, and flew quite well. Penaud’s work in this respect is interesting, because small elastic-driven machines, such as he designed, were used afterwards in demonstration, and are flown to-day. For a miniature aeroplane, elastic is an ideal motive force—light and yet providing ample power, and with only one disadvantage: it unwinds itself rapidly, and then the model must descend.

In experiments of permanent value, after the discoveries of Wenham, important work was that of Horatio Phillips. Like Wenham, he devoted his attention mainly to a study of lifting planes, and tested many shapes and curves. Sir George Cayley, it may be remembered, had suggested a curved and not a flat plane; but Phillips went one better than this, for in 1881 he devised a plane with what has been termed a dipping front edge.

Fig. 10.—The Phillips Wing-Curve.

The shape and curve of a plane, is of vital importance. A machine may be built, and an engine and propellers fitted, but the question is: Will the planes support through the air the load they have been given to carry? Phillips made many experiments, and in the end he produced a wing-shape which he patented. He pointed out that an advantage might be gained in lifting effect if the main curve or camber was situated near the front edge of the plane, and not in the centre ([Fig. 10]). The theory Phillips worked upon was this—and it is interesting if it can be expressed clearly. Taking a plane curved as he recommended, with this “hump” towards the front, and forcing it through the air as would be the case were an aeroplane in flight, the rush of wind which meets the edge of the plane is split into two currents—one sweeping above and one below. The air current below the plane, following its curve, is thrust downward, and in being so thrust down imparts a lift to the plane; while the current thrown above the plane—rushing up and over the “hump” which, as has been shown, is situated close to the front edge—will sweep rearwards in such a way that there is a partial vacuum or air space between the fast-moving wind current and the curved-down section of the plane behind the “hump.” The value of such a vacuum is this: it has a raising effect upon the surface of the plane, which is thus not only pushed up from below, but drawn from above.

Fig. 11.—Suction above a Cambered Surface.

How a vacuum is caused, by air passing over such an arched surface as Phillips recommended, may be shown in a simple experiment. Take a sheet of paper and curve it in the way shown in [Fig. 11], allowing the rear portion to hinge in such a way that it will move freely up and down. Then, if the sheet of paper is held between the finger and thumb and one blows across the top edge, the hinged flap at the rear will be found to raise itself—drawn up by the influence of the vacuum, such as Phillips describes.

Apart from his theory as to the dipping front edge of a plane, Phillips agreed with a suggestion made by Wenham; and this was that a plane, in order to be most effective in its “lift,” should be narrow from front to back. This theory meant that, as a plane moved forward, it was the curving front section which gripped and acted up the air; and that, if the plane was carried too far towards the rear, its lifting influence fell away, while the surface that was superfluous acted as so much resistance to the machine’s progress through the air.

Fig. 12.—Phillips’s Experimental Craft.

In furtherance of his views, Phillips built the strange-looking machine which is seen in [Fig. 12]. It resembled, more than anything else, a huge Venetian blind; and he adopted this form so as to introduce as many narrow planes as possible. There were, as a matter of fact, fifty in the machine, each 22 feet long and only 1½ inch wide. The craft, as can be seen, was mounted on a light carriage which, having wheels fitted to it, ran round and round upon a railed track. A steam engine was used as motive power, driving a two-bladed propeller at the rate of 400 revolutions a minute. The machine was so arranged on its metals that, although the rear wheels could raise themselves and show whether the planes exercised a lift, the front one was fixed to its track—thus preventing the apparatus from leaping into the air, overturning, and perhaps wrecking itself. Tests with the machine were successful. The lifting influence of the planes, when the engine drove them forward, was sufficient to raise the rear wheels from the track; and they did so even when a weight of 72 lbs., in addition to that of the apparatus, had been placed upon the carriage. In his main object, then, Phillips succeeded; and that was to show the lifting power of his planes. But his apparatus had not the makings of a practical aeroplane. He gained for himself, nevertheless, a name that has lived and will live. Even to-day, in discussing the wing-shape of some machine, draughtsmen will speak of the “Phillips entry.” Other workers did not pin themselves exactly to his shapes or theories, but these paved the way for a series of further tests.

Science was forging link by link indeed the chain that would lead to an ultimate conquest. Sir George Cayley suggested an arched plane; Wenham devised a machine in which narrow planes should be fitted one above another; and Phillips laid down the rule for a curve or camber of special shape, which should exercise most “lift” when thrust through the air. But still men lacked many things; all the links in the chain were far from being in their place; and one of the greatest flaws was that no man, even supposing he was able to build a machine that would fly, had learned as yet to balance that machine when it was in the air.

CHAPTER III
FIRST FRUITS OF STUDY

The building of large machines—Sir Hiram Maxim’s costly work—A steam-driven French craft which flew—Professor Langley’s research in America.

Of the way research next tended, it may be said that it was the first putting into practice of the theories science had laid down; for now, having an idea as to the shape of planes, and knowing that these planes could be made to carry a load through the air, there were engineers who began to build man-carrying, power-driven machines. In so doing, however, they may be said to have tried to run before they could walk. What they did was to provide the world with powerful flying craft before there were men who could handle them.

One of the most interesting and ambitious designs was that of Sir Hiram Maxim; and it was one to which he devoted years of labour and large sums of money. He is said, indeed, to have expended £20,000 upon aerial research. After a number of experiments with plane shapes, following the theories of Phillips, he began to build a very large machine, which he set upon a miniature railway as Phillips had done, using the same precaution of a check-rail to prevent it from rising more than a certain distance in the air. His apparatus, when built at Baldwin’s Park, Kent, weighed 8000 lbs.: it was, in fact, the largest machine ever built. The span of its planes was 105 feet, and they offered a total supporting surface of 6000 square feet.

Fig. 13.

A. Elevating Plane; B.B. Outriggers; C.C. Operating Wires;
D.D. Position for ascending; E.E. Position for descending.

The inventor employed the suggestion made by Wenham, and fitted his lifting planes one above the other; while he used a horizontal plane in front of the machine to act as an elevator. This plane could be tilted up and down; and the idea was that, when it was tilted upward as the machine ran forward upon its rails, it would exercise such a lifting influence that the front of the craft itself would be raised, and so cause the main-planes to assume a steeper angle to the air; and the result of the planes being inclined thus more steeply would be to give them a greater lift, and so induce the whole machine to raise itself from the ground. This system is explained in [Fig. 13], and is important because such lifting planes, for rising or descending, have now come into general use.

Sir Hiram Maxim employed another controlling surface which has become a feature of present-day aircraft, and this was an upright plane, which could be swung from side to side, and by which his craft was to be steered. Such a rudder-plane is illustrated in [Fig. 14]. By this means, as will be shown later, practically all aeroplanes are steered to-day. The action of the aerial rudder, when it is moved from side to side, is like that of swinging the rudder of a ship; but for the same reason that propellers have to be made large—owing to the small density of the air—so an aeroplane rudder needs to be a comparatively large plane, in proportion to the size of the craft, before it will exercise an adequate turning influence.

Fig. 14.

A. Vertical steering rudder; B.B. Outriggers; C.C. Operating wires;
D.D., E.E. Positions assumed in turning.

To drive his machine Sir Hiram used two specially-built and lightened steam engines, which developed a total of 360 h.p., and yet weighed only 640 lbs.; that is to say, they gave one h.p. of energy for each 1¾ lb. of weight. But they were only suitable for purposes of experiment. Sir Hiram himself wrote:

“The quantity of water consumed was so large that the machine could only remain in the air for a few minutes, even if I had had room to manœuvre and learn the knack of balancing it in the air. It was only too evident to me that it was no use to go on with the steam engine.”

The engines drove two canvas-covered wooden screws, each 18 feet in length, and the general appearance of the machine is indicated by [Fig. 15]. In these trials, although it was always captive, the aeroplane demonstrated much that its inventor had set himself to prove. In Sir Hiram Maxim’s own words, it showed that it had “a lifting effect of more than a ton, in addition to the weight of three men and 600 lbs. of water.” He adds: “My machine demonstrated one very important fact, and that was that very large aeroplanes had a fair degree of lifting power for their area.”

Fig. 15.—The Maxim Machine.

So unmistakably did this craft show its lifting power, that—in one fierce effort to rise—it broke a check rail which kept it upon its metals, with the consequence that it became unmanageable, swerved sideways, and was wrecked. At this stage Sir Hiram, having no faith in the future of such steam engines as he was using, and having spent a large sum of money, was compelled to relinquish his tests. His trouble was that he was, as the saying goes, “before his time.” The machine was too ambitious and too large. That it would have lifted itself into the air was proved; but there was no man living who could have controlled it. To put in charge of such a craft a man who knew nothing of the navigation of the air, would have been like placing a novice at the levers of a 60-mile-an-hour express. Picture such a huge aircraft in the hands of a man who had never flown. It would rise, it is true; but how could one who was not an expert so adjust the angle of its lifting plane that it would glide smoothly from the ground and not rear itself upward and fall with a crash? A machine is struck by wind-gusts, too, when it is aloft; and there is the delicate art of making a descent, without damaging one’s craft by a rough contact with the ground. Besides, it would have been unlikely that this machine, being purely experimental, would have been perfectly balanced as it flew: it might have shown a tendency to slip sideways when in the air, or dive steeply. All of which goes to show this: that the inventor might have wrecked one costly machine after another before he obtained a practical model, even were he lucky enough to escape with his life. Sir Hiram Maxim’s machine, while it settled problems as to weight-lifting and power, lacked the man who could fly it; and so did others of these man-lifting craft which were built before their time. A child must learn to walk before it can run, and must learn to crawl before it can walk. And what had not been realised, at this stage of the conquest, was that there must be some stage between building a model and a full-sized, motor-driven machine: some step, in a word, by which a man might learn, without too great a risk of death, to balance himself when in the air.

While Sir Hiram Maxim in England was devoting time and money to the quest, there was another skilled engineer, a Frenchman, who was working at the problem, and also by means of large machines. This was Clement Ader, one of the European pioneers of the telephone, and he experimented for many years. One of his first machines had wings like those of a bird, and these the would-be flier was to operate by his own muscular power. But this failed, seeing that men are not provided with sufficient power, by their unaided efforts, to wing their way through the air in a flapping flight. As Giovanni Borelli, a seventeenth century writer, quaintly puts it: “It is impossible that men should be able to fly craftily by their own strength.”

PLATE I.—THE LANGLEY MACHINE.

This craft, a double monoplane, was launched from a platform over the river Potomac, loaded with a weight equivalent to that of a man. The trials were unsuccessful; but recently—after a lapse of many years—the Langley machine has been tested again, and has proved its ability to fly.

Ader next turned to steam-driven craft, and built a series of queer, bat-like machines, which he called “Avions,” one of which is illustrated in [Fig. 16]. Its wings were built up lightly and with great strength by means of hollow wooden spars, and had a span of 54 feet, being deeply arched. The whole machine weighed 1100 lbs., and was thus far smaller and lighter than Maxim’s mighty craft. To propel it, Ader used a couple of horizontal, compound steam engines, which gave 20 h.p. each and drew the machine through the air by means of two 4-bladed screws. The craft was controlled by altering the inclination of its wings, and also by a rudder, the pilot sitting in a carriage below the planes. In 1890, after its inventor had spent a large sum of money, the machine—which, unlike those of Phillips and Maxim, ran upon wheels and was free to rise—did actually make a flight, or rather a leap into the air, covering a distance of about fifty yards. But then, on coming into contact with the ground again, it was wrecked. Ader’s experiments were regarded by the French Government as being so important that he received a grant equalling £20,000 to assist him in continuing his tests; and this goes to show how, even from the first, the French nation was—by reason of its enthusiasm and imagination—able to appreciate what its inventors were striving to attain, and eager to encourage them in their quest. For just an opposite reason—because, that is to say, it had not this imagination nor intuition—England neglected her experimenters, or merely regarded their efforts with an amused tolerance, as though they were children playing with toys.

Fig. 16.—Ader’s “Avion.”

Ader’s greatest success came in 1897. With an improved machine, he obtained a flight through the air of nearly 300 yards; and this goes down to history as being the first ascent by a power-driven aeroplane having a man on board. Ader’s name will never be forgotten, and one of his machines is exhibited, as a relic beyond price, at the Institute of Arts and Science in Paris. But the flight ended in damage to the machine, as the other had done. A wind gust threatened to overturn the craft, its engines were shut off, and it descended so heavily that it was wrecked. Through constant difficulties in regard to motive power, and the heavy cost of his experimental work, Ader was unable to make a definite success, or produce a machine which could be called a practical craft. In his case again, as in that of Maxim, there was a great and apparently insurmountable defect. The aeroplane would rise; its engines and propellers would drive it through the air; but the steersman had not his machine under control: he had not, in a word, learned to fly. The prospect, therefore, was unpromising, because one machine after another might share the same fate—rising into the air, flying a hundred yards or so, and then over-balancing and crashing to earth: thus, in fact, might thousands of pounds be squandered.

But this stage of putting into practice what science had taught, although disheartening for those who passed through it, was still of value; it made a stepping-stone to the next. One of the men who thus laboured, without himself seeing his work brought to the goal of success, was Professor S. P. Langley, an American scientist connected with the Smithsonian Institution, and a man of original ideas and great resource. He made a methodical investigation of the action of lifting planes and the shape of propellers, using a large revolving table so that he could test the latter while they were moving through the air. Then he began building models which took a double monoplane form, as indicated by [Fig. 17], with wings set at dihedral or upturned angle. This uptilting of the wings was to give the models stability while in flight: and the fixing of planes at the dihedral angle was tested, by later experimenters, in regard to full-sized machines. But while it gave an undoubted stability when a craft was flying under fair conditions, it was declared by some experts to be a disadvantage in gusty winds. There seemed also a risk that a machine so built might slip sideways when upon a turn. But in some machines to-day a modified dihedral angle is used, and with satisfactory results.

Fig. 17.—Langley’s Steam-driven Model.

Professor Langley’s models, tested over the river Potomac, flew many times for distances of half a mile. One, weighing 25 lbs., flew for appreciably more than half a mile, and at a speed of 20 miles an hour; and with another, which was slightly larger and weighed 30 lbs., a three-quarters of a mile flight was obtained. This model measured a little more than 12 feet across its wing tips, and was about 16 feet long. The miniature steam engine which drove it, developing 1½ h.p., weighed about 7 lbs., and operated a couple of two-bladed propellers which were fitted behind the main wings, and turned in opposite directions at the rate of 1200 revolutions a minute.

So successful were Professor Langley’s models that the United States War Department became interested; and the result was that an official grant was made for the building, according to the Professor’s plans, of a machine of man-carrying size. But with this craft, which weighed 830 lbs., and was driven by a 52 h.p. engine—and is shown in [Plate I]—there was a record of failure: launched from the roof of a house-boat over the Potomac, it fell several times into the water; and ultimately, and largely owing to the heavy cost of tests with such large machines, the trials had to be abandoned.

But that the Langley machine would have flown, had it been launched more carefully, has been demonstrated recently, and in a remarkable way. On June 28th, 1914, obtaining permission to make tests with the actual Langley machine, which had been preserved as a relic. Mr. Glenn Curtiss fitted the craft with floats, and drove it across the surface of the water at Hammondsport, New York, using the same engine that had been in the machine during its early and unsuccessful trials. After skimming the water for a short distance the monoplane rose, flying steadily and well, and vindicating its constructor’s theories, although he himself was dead.

CHAPTER IV
OTTO AND GUSTAV LILIENTHAL

How two German schoolboys built wings which they tested on moonlit nights—The beginnings of a great and patient quest—Otto Lilienthal’s theories and study of the birds.

Much of the ground has now been cleared, and—apart from such a story as may be told merely from facts and figures, and is apt to prove unsatisfying—we have striven to show the inner meaning of this great quest: how each of these pioneers, although he may have seemed to spend money in vain, and build models only to meet with failure, was really playing a useful part; was in fact—although he himself did not realise it—forging one of the links in the chain.

It has been shown how men passed from an ill-judged, haphazard stage; how science threw upon the problem the clear, cold light of wisdom; and then, further encouraged by the data that was to hand, how there were engineers who were ready to build large machines and demonstrate that, even in a crude and early form, an apparatus with curved planes would lift itself from the ground.

But still there remained this problem: how were men to learn to balance themselves when in the air? And, in considering the equilibrium of the aeroplane, it must be remembered that the air in which a machine must fly is a disturbed and turbulent sea. So, even were a man to build himself a craft which would, without the need of a hand upon its levers, balance itself accurately when in still air, there would still be the problem of the wind gusts; there would, that is to say, still be the risk of a machine being struck by an air-wave, particularly when flying near the ground, and being thrown out of its balance and dashed to earth.

Fig. 18.—Flow of the wind over hills.

As waves roll across the surface of the sea, so in the aerial ocean are there breakers and eddies and many dangers unknown; and men cannot see, but only feel them. The air does not flow in regular streams over the earth’s surface; could we follow its movements with our eyes, we should see that it is full of whirls and eddies, with currents of warm air flowing upward, streams of cool air moving downward; and with all the obstructions on the face of the earth, such as hills and woods, causing an interruption and a disturbance in the air flowing over them ([Fig. 18]). The face of a cliff, for instance, will deflect a current upward, leaving a partial void at its summit; and into this void the air will rush in the form of a whirling eddy.

The man who would learn to fly has to launch himself into a treacherous, quickly-moving element; and one which, to add to his perils, he cannot see. The rower in a boat, who sets out upon a stormy sea, can watch the flow of the waves and turn the prow of his vessel to a breaker that threatens him. But the aerial navigator moves in a medium that is invisible; gusts that rush upon him are unseen; he is unaware of their onslaught until his craft heels before the shock. This risk, from the sudden sweeping up of an air-wave, was put clearly by Wilbur Wright when he wrote:

“A gust, coming on very suddenly, will strike the front of a machine and will throw it up before the back part is acted on at all. Or the right wing may encounter a wind of very different velocity and trend to the left wing.”

In the aerial sea a machine will pitch and roll as does a ship upon the water; and the man who would fly must learn to check his craft, should it threaten to overturn; must be ready instantly with some system of controlling gear so as to correct the influence of each driving gust. And his task is made the harder because his machine, when struck suddenly by a gust, may fall towards the earth at any angle. On the road, when one learns to ride a bicycle, the machine will topple to one side or the other; but a craft in the air may fall forward or backward as well as from side to side, or partly forward and partly backward—or may slip and dive at any possible angle, either forward or backward or upon either side. A pioneer wrote, after his first experience in learning to fly:

“It is rather like trying to steer a motor-car along an exceptionally greasy road; you seem to slip all ways at once; and to slip so quickly also that, unless you make the right balancing movements without an instant’s delay, you find your machine has gone beyond control.”

If he were to succeed, if he were to fly like a bird, then a man had to learn this art of balancing himself in the air. Futile it was, as has been shown, to build some powerfully-engined machine that no one could control; futile also, and perilous as well, to make a pair of wings and jump from a tower. Another way must be found, or the quest abandoned and admitted hopeless. Here was the need; and here too, as we shall tell, came the man; a man who was not famous, who worked without reward and struggled to find time for his experiments; who died before he could see the final triumph; yet who won a fame that cannot die, and whom men call “the father of the aeroplane.”

To Germany one turns in telling the story of this man’s work. He was an engineer, Otto Lilienthal by name, and from the days of his boyhood he and his brother Gustav, living in Anklam, a small German town, were builders of model aeroplanes and students of the flight of birds. When the boys were thirteen and fourteen years of age respectively, they designed a flying machine; and in describing it afterwards, Gustav Lilienthal wrote:

“Our wings consisted of beech veneer with straps on the under sides through which we pushed our arms. It was our intention to run down a hill and to rise against the wind like a stork. In order to escape the gibes of our schoolmates, we experimented at night-time on the drill-ground outside the town; but there being no wind on these clear, star-lit summer nights, we met with no success.”

But they were not discouraged, and continued to build simple, easily-constructed machines—from each of which, although it would not fly, they learned a useful lesson. One, for instance, they made with wings of goose feathers, sewn upon tape and fixed to wooden spars. These wings, when finished, they fastened upon hoops which were strapped to the operator’s chest and hips; and he could, by means of a lever and a stirrup arrangement, beat the wings up and down by movements of his legs. This machine they hung from a beam in an attic in their house; but although the wings did flap, and actually showed some tendency to lift, the apparatus was soon consigned to a lumber-room, and they were busy with plans for another.

What impressed Otto Lilienthal was the fact that, even when provided by Nature with a perfect flying apparatus, the birds of the air had to learn to use it. They could not just leap upward and “ride the wind” as men had tried to do; they needed to take their first fluttering flights—beating their wings anxiously and often falling back to earth, because they did not know as yet how to use these wings. Particularly did Lilienthal study the flight of storks. He obtained young birds from neighbouring villages, and fed them in his garden with meat and fish while he watched their efforts to learn to fly, and studied that marvellous piece of mechanism—the wing Nature had given them. Writing of his observations in a book he afterwards prepared, called Birdflight as the Basis of Aviation, Lilienthal describes the antics of young storks upon the lawn behind his house:

“When the actual flying practice begins, the first attention is devoted to the determination of the wind direction; all the exercises are practised against the wind, but since the latter is not so constant on the lawn as on the roofs, progress is some-what slower. Frequently a sudden squall produces eddies in the air, and it is most amusing to watch the birds dancing about with lifted wings in order to catch the wind which changes from one side to another, all round. Any successful short flight is announced by joyful manifestations. When the wind blows uniformly from an open direction over the clearing, the young stork meets it, hopping and running; then turning round, he gravely walks back to the starting-point and again tries to rise against the wind.

“Such exercises are continued daily: at first only one single wing-beat succeeds, and before the wings can be raised for the second beat, the long, cautiously placed legs are again touching ground. But as soon as this stage is passed, i.e. when a second wing-beat is possible without the legs touching the ground, progress becomes very rapid, because the increased forward velocity facilitates flight, and three, four, or more double beats follow each other in one attempt, maybe awkward and unskilled, but never attended by accident, because of the caution exercised by the bird.”

Lilienthal was fascinated by the mechanism of the bird’s wing. He and his brother built one machine after another to determine the exact amount of lifting effort that a man could obtain by imitating the wing-beat of a bird. One such apparatus is illustrated in [Fig. 19]. This had a double set of wings; a wide pair in the centre and narrower ones in front and at the rear. These wings beat alternately, by movements of the operator’s legs; and the machine was suspended by a rope and pulleys from a beam, being counterbalanced by a weight. The tests showed this: that, after some practice in working the wings, a man could raise with them just half the weight of himself and of the machine; but the muscular effort proved so great that he could only maintain this rate of wing-beating for a few seconds. Here, incidentally, a fact may be mentioned: the energy a man can produce, at all events for a prolonged effort, has been estimated at about a quarter of a horse-power; and this—in tests so far made—has been insufficient for the purpose of wing-flapping flight. Lilienthal himself thought that, with some perfect form of apparatus, a man might fly with an expenditure of 1·5 h.p. of energy; but other experimenters have put the minimum power necessary, even if mechanism could be devised, at 2 h.p. And another fact must be remembered: even had Lilienthal been able, with such a machine, actually to raise himself in the air, he would still have had the problem of balancing himself, in addition to the working of his wings.

Fig. 19.

Fig. 20.—Lilienthal Kite.

After many tests such as these, carried out over a number of years, during which the brothers grew from boys to men, Lilienthal decided that no good results could be obtained unless a machine was made to move forward through the air, instead of seeking to rise straight upward. By such forward motion if rapidly made, and with a suitably shaped wing or surface, he calculated that a definite support might be obtained from the air, and without any great output of energy. The value of forward motion is seen when a large bird seeks to rise. The first few flaps are heavy and laboured; but after this, as soon as it begins to travel forward, the wings exercise a lifting influence apart from their beat; and, as the bird flies faster, so its wing-beats become less violent. An instance of the need for a bird to move forward when it begins to fly, is provided in the case, say, of a sparrow imprisoned in a chimney: even if the chimney is wide, and there is plenty of room for the bird to fly straight upward and escape, it has not the power to lift itself vertically for any appreciable distance, because it cannot obtain the lifting assistance of a leap forward through the air; it is in fact a prisoner within the chimney.

Lilienthal studied the gliding or soaring flight of many birds; that form of flight in which, with its wings outstretched and held almost motionless, a bird such as the falcon will hover in the air, using no apparent effort and yet supporting itself with ease; diving, rising again, and wheeling in a perfect mastery of the medium in which it moves. Lilienthal built and flew kites, to which he gave curved wings in imitation of those of birds ([Fig. 20]). With one of these he obtained, although only for a few moments, an actual gliding flight. The incident is described by his brother Gustav:

“It (the kite) was held by three persons, one of whom took hold of the two lines which were fastened to the front cane and to the tail respectively, whilst the other two persons each held the line which was fastened to each wing. In this way it was possible to regulate the floating kite, as regards its two axes. Once, in the autumn of 1874, during a very strong wind, we were able to so direct the kite that it moved against the wind. As soon as its long axis was approximately horizontal the kite did not come down, but moved forward at the same level. I held the cords controlling the longitudinal axis, and my brother and my sister each one of the cords for the adjustment of the cross-axis. As the kite maintained its lateral equilibrium, they let go the cords; the kite then stood almost vertically above me and I also had to free it. After another thirty steps forward my cords got entangled in some bushes, the kite lost its balance, and in coming down was destroyed. Yet, having gained another experience, we easily got over the loss.”

From kites, in quest of a curved surface which should give a maximum lift with a minimum resistance to its own passage through the air, Lilienthal embarked upon a series of tests with wing shapes; setting these up in the wind upon suitable recording machines, and noting patiently the data that could be procured. There are many problems to be considered when planning a wing for flight. If it is given a deep curve or camber from front to back this may, while exercising a powerful lift, offer too high a resistance as it passes through the air, and thus waste the energy needed to propel the craft; or, if its front edge is dipped too sharply, this may cause the air to act upon its upper surface, and send a machine diving headlong to the ground. The planning of a successful wing becomes a compromise, having for its object a surface which shall give the greatest lifting influence with the least resistance. Lilienthal, after much experiment and the examination of the wings of many birds, decided that the curve, camber, or upward arch of a plane should measure, at its maximum depth, about one-twelfth of whatever width the plane might have from front to back.

CHAPTER V
GLIDING FLIGHT

How a man may use gravity as a motor—Theory of the “glider”—The craft Lilienthal built—A problem of balance—The centres of gravity and pressure.

Up to this point in his research Lilienthal had moved more or less upon the lines of other experimenters. Had he continued to follow in their footsteps, he would have planned some large and impracticable machine—and perhaps gone no further. But although he desired to test the lifting power of the planes he had built, Lilienthal had always in mind this vital fact—that a man must learn to balance himself in the air before he can hope to fly. His own words, in summing up this problem, were: “stability first; propulsion afterwards”; and by this he meant a man must acquire the art of handling a craft in the air, before he dares to fit a motor and attempt power-driven flight.

But if a man used neither wing-beats nor a motor to drive him through the air, how was such practice to be obtained? Lilienthal solved the problem—and made his name immortal—by devising a system in which he used the force of gravity as his motor. His plan was this: first he would build a pair of large, light wings—so light in fact that, even with the woodwork that was in them and with the additional weight of a balancing tail, he could raise them to his shoulders and run forward. With these wings he would go to the summit of a sloping hill and face what wind might be blowing—as he had seen the young storks do. Then he would run forward with his wings, so as to obtain the lifting influence necessary before they could act upon the air. And then, when the wind was sweeping under his curved wings, he would raise his legs from the ground and seek to soar or glide; his own weight, and that of his machine, providing a gravity motor or downward pulling influence, while the sustaining power of his planes, resisting this drag, would send him gliding through the air, only a few feet from the ground, at an angle which tended gradually earthward.

Fig. 21.

Paper glider, in which the cardboard weight (A.) should be 3/10 inch wide, and 1/16 inch thick, slightly arch planes upward (B.B.). Turn up a little flap at each end (C.C.). An eighth inch is sufficient. Hold between finger and thumb (the cardboard weight uppermost); then allow to dive, as indicated by the dotted line.

This power of a weighted plane to glide, even when no motive power is attached to it, may be demonstrated quite simply by the little paper model seen in [Fig. 21]. If, when you have made this, you allow it to flutter from your hand without any weight attached, the model plunges, dips, and dives; it has no forward motion, therefore it has no stability or poise. But when you gum the small cardboard weight to its fore-plane, the action of the model is changed. By the use of this tiny strip of cardboard you have, so to say, given it an engine; you have provided it with means whereby it can obtain forward motion, and so glide through the air. When you hold it as shown in the sketch, with the weighted fore-plane tilted downward, and release it without a jerk, the tendency for the model is to fall to the ground as it did before. But now there is the weight to reckon with: this pulls the model forward and downward, tending to fall more quickly, of course, than the paper by itself would do. But there is also the plane behind the falling weight to be taken into consideration: jerked forward and downward through the air, this begins to exercise a sustaining influence, and so resists the falling movement of the weight. Still the weight, actuated by the force of gravity, pulls downward. But the plane refuses to fall sheer to the ground; and yet the weight must have its way. So, as in most situations of this kind, there is a compromise. The falling weight pulls; the plane resists; and in a flash the model starts upon a graceful glide. Its plane is fulfilling its task of bearing it through the air; and the weight is carrying out its mission also, in causing the glide to tend earthward. So, pulled down by its weight and yet partly sustained by its plane, the model will pass across a room; and if its plane and its weight are in a nice adjustment, one may see a pretty manœuvre before it reaches the floor. As it is swept faster through the air, owing to the increasing drag of the weight, the plane of the model acquires a greater lifting influence; and the moment comes when this “lift,” reaching a maximum, checks altogether the descending movement, and causes the model actually to ascend. Up indeed it goes, for a second, in a sudden swerve. But this ascending impulse is soon checked; gravity cannot be denied. The model loses speed; and, as it loses speed, so does its plane lose lift. Hence the weight is again the predominating partner; it pulls down the fore-plane, converts the rise into a fall, and brings the model with another dive to the floor.

But here, at all events, is a demonstration of this theory of gliding flight—one that can be carried out without a motor. Of course such flying has its restrictions: a man must start from the summit of a hill, and the glide is in the form of a descent towards the ground below; but still he is passing through the air; and above all—and this proved the advantage of the scheme for such a pioneer as Lilienthal—there is no need, during any such glide, to pass high above the ground. The operator may, in fact, if the side of his hill slopes gently, skim within only a few feet of its surface; and this means that, should he lose his balance at first, as he may expect to do, he will not share the fate of those who leapt from towers, but will be able to alight without mishap.

Fig. 22.—Lilienthal Glider.

This, then, was Lilienthal’s plan; he would build a machine with wings and a tail, stand facing the wind as the storks had done, then seek to glide through the air in the manner of a soaring bird. The idea underlying his scheme was that he hoped, by a series of such gliding flights, to learn the adjusting movements he knew would be necessary to preserve his balance in the air. The gliding craft Lilienthal built, as illustrated in [Fig. 22], has become an historical machine. The framework of its wings and the supports of its tail were of willow, and the wings and tail, to give them their grip upon the air, were covered with a smoothly stretched fabric. Then the whole structure was braced and tightened; and though it weighed less than 50 lbs., it was strong enough to bear its operator though the air. Lilienthal could raise the apparatus upon his shoulders—passing his head through the aperture between the planes, which will be noted in the sketch—and walk or run forward; and to hold the machine, as he carried it thus, he gripped two wooden rods. The tail was flexible, being allowed an automatic movement, thus giving the craft a certain natural stability. The main wings had a span of 24 feet, and the machine measured 18 feet from front to tail. The wings were cambered, according to the curve Lilienthal had decided most efficient, and contained about 180 square feet of lifting surface. In giving them this area, Lilienthal was relying upon experiments he had made; these showed that, as his machine glided through the air, each square foot of its surface should bear a weight equal to about 1 lb.

Although enthusiastic, Lilienthal was not impatient: he had the priceless gift of judgment, allied to common-sense. So, when he had his glider built, he made no wild nor dangerous tests. He contented himself, in fact, with a leap from a springboard no more than 3 feet high; and this height he increased gradually to 8 feet. By such humble beginnings, and without risking his life, he proved that his glider would sustain his weight in the air; or, to be more precise, that its wings would exercise a lift sufficient to permit him to glide rather than fall to the ground. So now he began more elaborate tests, seeking hills which had gently-sloping sides, so that he might glide down them. But with many the difficulty was this: the winds near the surface, being broken and disturbed, blew fitfully and in gusts, while what Lilienthal needed was a steady, uniform wind. At length he found favourable conditions at some gravel-pits at Südende; and here, on the brink of a pit, he built a shed and housed his gliders.

PLATE II.—SANTOS-DUMONT’S FIRST FLIGHTS.

Here, actually in the air, and with its pilot clearly visible at the controls, is seen the craft in which—at Bagatelle in 1906—the airman flew a distance of 230 yards.

Now, patient and assiduous, he began to teach himself the art of aerial balance. Raising his wings to his shoulders he would face the wind—which in his first tests he did not care to be blowing at more than ten or fifteen miles an hour. Then, running against the wind to increase the pressure beneath his wings, he would raise his legs and begin to glide, moving forward and at the same time downward. How he appeared when in flight is indicated by Fig. 23.

Fig. 23.—Lilienthal gliding.

His first tests were brief, for the reason that his craft would either dip too sharply, or incline its planes steeply and so check its forward speed. In either event the result was the same: the glide came to an end. But Lilienthal’s caution saved him from being injured in an involuntary descent. It must be remembered he was always moving close to the earth; therefore he had only a short distance to fall. To safeguard himself still further he fitted below his machine a shock absorber, which came into contact with the ground first and lessened the force of any impact.

But the difficulties of preserving his balance were great, as he had foreseen; for not only did his glider dip down, or rear itself up, but also—under the influence of wind-gusts—threatened to slip sideways. It was Wilbur Wright, lecturing afterwards upon problems of aerial equilibrium, who said crisply:

“The balancing of a gliding or flying machine is very simple in theory; it merely consists in causing the centre of pressure to coincide with the centre of gravity; but in actual practice there seems to be an almost boundless incompatibility of temperament between the two, which prevents their remaining peaceably together for a single instant.”

Fig. 24.—Centres of gravity and pressure.

Here, in a sentence, is the problem. As a cambered plane is moved in flight, the air-pressure upon it is not disposed equally over the surface, but tends to locate itself at a spot to the front of the middle line of the plane. When a plane is at a normal inclination to the air, indeed, this centre of pressure, as it is called, is at a point upon the surface about one-third of the distance between the front and rear edges. As to the centre of gravity, the second factor in the problem, this may be explained best, perhaps, by a practical illustration. Take a small sheet of cartridge paper, cut to represent the plane of a flying machine, and lay this along the blade of a knife. By moving it to and fro and adjusting its equilibrium, you will be able to make it rest upon the knife-edge without falling forward or backward; this point at which it balances itself represents its centre of gravity. Here, then, are the forces: the centre of pressure, which is the thrust of the air, and the centre of gravity, which is the pull of the earth seeking to drag down a machine when in flight. These two forces must, as we have been told, be made to coincide. In the next illustration ([Fig. 24]) the problem is made clearer. In diagram A is seen a plane A.B. which is moving through the air in the direction indicated by the arrow. The two forces—that is to say, the centre of pressure (C.P.) and the centre of gravity (C.G.)—coincide with each other: therefore the plane is in equilibrium. But now suppose a gust of wind strikes the plane. This tends to tilt it upward; and the result is that the centres of pressure and gravity show that “boundless incompatibility of temperament” of which Wilbur Wright complained. The impact of the gust, making the plane rear up, throws the centre of pressure farther back along its surface, as is shown in diagram B. The plane is at once out of balance. Or it may be argued that, as it passes through the air, the wind pressure under the plane is suddenly lessened. This would cause its front edge to drop; whereupon the centre of pressure would, as is seen in diagram C, move immediately forward upon the plane—and so throw it out of balance again.

This is the problem of the man who would navigate the air. He launches himself in a treacherous, unstable element: constantly, beneath his wings, the air pressure changes and varies in its strength; constantly is he losing his balance—and as constantly must he regain it. Imagine a man walking a tight-rope, and seeking incessantly to keep himself in equilibrium, and you have a notion of what the first man faced when he strove to fly. And his case, really, was worse than that of the tight-rope walker. The latter is concerned mainly with the danger of falling to one side or the other; he need not trouble himself unduly with the problem of his fore and aft stability. But the aerial acrobat may fall forward or backward, or from side to side. Hence his trick, once he masters it, is the more skilful.

The art, as has been shown, is to bring together these centres of gravity and pressure; and it can be done in either of two ways. One is to alter the centre of gravity should the machine begin to fall, and the other to move the centre of pressure. Lilienthal, and others of the early gliders, adopted the plan first mentioned; they shifted the centre of gravity. But others who followed them, and notably the Wright brothers, finding that they needed to build larger craft, made use of movable planes by which they could shift the centre of pressure; but this, of course, will be dealt with in its place.

To alter the centre of gravity of a machine it is necessary to move in some way the weight it carries—to shift the load forward or backward, say, or from side to side. In Lilienthal’s glider the load was the weight of his own body, and he learned to move this when wind-gusts struck his craft. His body, as he passed through the air in flight, hung free from the shoulders below the wings of his machine; he was therefore able to swing himself forward or backward, or from side to side. And this he did, counteracting the rolling movements of his machine, and seeking always to prolong the glide. Should his craft be struck by a sudden gust, for example, and heel to one side, he swung the weight of his body towards the rising wing; should he dive abruptly, or threaten to rise at an acute angle, he was ready with a movement of his body to check the falling tendency and restore the machine to an even keel. But the point to be considered is this: all these movements, when a craft is in flight, have to be made with a lightning rapidity. There is not an instant to lose; not a fraction of a second to be wasted while a man thinks what he is to do. His balancing, if he would glide through the air with wings, must be instinctive—instantaneous; as, indeed, is the balancing of the birds. Here, then, is the difficulty: to learn to make these balancing movements with sufficient quickness; and this Lilienthal found to be the stumbling-block. Time after time, while gliding close to the ground, his machine lost its balance and, before he could correct the slip or dive, had come to earth. But these falls did not hurt him, nor did they damage his machine; so he was able, like the storks, to try again and again.

It is not easy to realise this difficulty of learning to fly. The first airmen found their rate of thinking too slow. For all earthly actions they could think quickly enough; but when they came to pass through the air they found the sending of a command from their brains to their limbs was not done fast enough. They found they could not rely upon thinking what to do when a craft threatened to fall. They had to practise until they acquired the power of making a balancing movement without thinking at all; they learned, that is to say, to keep their equilibrium by sub-conscious movements—or, to use a simpler word, by “instinct”; to balance themselves as they passed through the air, like a man balances himself when he rides a bicycle, without giving the action a thought.

Lilienthal probed all these difficulties, and saw that—as with other problems—it was not so much brilliant daring that would bring him success, as a painstaking course of practice, along right and sensible lines. So, whenever the weather was favourable and the wind not too high, he made his running leaps down the sides of hills, being content as a rule, in all his early trials, if he remained only a second or so in the air. Here, indeed, was another difficulty of learning to fly. No experience was possible unless a machine was in flight; and yet, in making his first tests, Lilienthal had to be content with a second’s practice here and a second there; to be glad in fact if, after a whole month’s work, he had been for one clear minute in the air.

CHAPTER VI
“THE BIRD MAN”

Construction of an artificial hill—The building of larger craft—Peril of gusty winds—The accident which caused Lilienthal’s death.

So determined was Lilienthal to obtain the best conditions for his gliding that, finding no natural slope to meet his purpose, he ordered the construction of an artificial hill. This was built at Gross-Lichterfelde, near Berlin, and was 50 feet high and had gently sloping sides from which, at any direction of the wind, he could make a soaring flight. On the top of the hill, which is illustrated in [Fig. 25], Lilienthal had a roomy chamber, and in it he stored his craft. In this illustration, also, the airman may be observed standing upon the hilltop, ready for a trial. By means of dotted lines, and representations of machines in flight, it is possible to show how he glided through the air.

In the upper of the two flights shown, profiting by a day when there were rising currents in the wind, Lilienthal had allowed himself to be lifted, for a moment or so, to a point in the air actually higher than that from which he started. Then, in order to obtain forward speed, he dived, only to incline his wings more steeply again, and allow the wind to bear him upward. In this way, by exercising skill in the balancing of his machine, he was able to prolong a glide, and under favourable conditions to traverse, before touching ground, a distance through the air of nearly 1000 feet.

Fig. 25.—Lilienthal’s artificial hill.

In the second of the glides shown in [Fig. 25], Lilienthal is making a swift, low flight—one of those during which he was never far from the ground, and with which he contented himself in early tests. On glancing again at this sketch it will be noted that the upper of the craft shown has two main sustaining wings, placed one over the other in the girder construction already described. It is in fact a biplane, whereas the lower machine is a monoplane—such a craft as was illustrated in [Fig. 22]. It was when Lilienthal became expert at balancing himself in the air that he built a machine on the biplane principle. His reason for doing so was that he required more surface in the sustaining wings, so that they might carry him farther through the air. What he wanted to do in each of his glides was to remain in the air as long as possible, and thus gain a maximum of experience. The difficulty, as explained, was to obtain enough practice. In five years, for instance, although assiduous in his experiments, Lilienthal was not more than five hours in the air.

Fig. 26.—Lilienthal’s
Biplane Glider.

Thus it was that he built a biplane, each of the wings being 18 feet in span, and containing 100 square feet of surface. The craft is shown in [Fig. 26]. Lilienthal did with it what he expected he would be able to do; he increased materially the length of his glides. But there were drawbacks in the use of this machine, and one introduced an element of danger. With the monoplane, so soon as he made balancing movements by instinct, Lilienthal found he could control his craft quite well; it was small, and responded quickly when he threw the weight of his body from side to side. But the biplane, being considerably larger, and having more surface upon which the wind could act, was sluggish in its response to his controlling movements. In the case of both monoplane and biplane, Lilienthal relied merely upon the weight of his body to counteract falling movements. In the biplane, therefore, although it required a greater leverage to restore its balance, he was unable to increase the correcting influence. This difficulty, in the use of a large machine, was faced subsequently by the Wrights, and how they solved it will be shown.

Lilienthal recognised the position, of course, and saw there might be peril in the use of a biplane; but he was content, none the less, to rely upon his skill. In each glide he made he became more expert; instead of allowing his machine to slip to the ground when struck by a gust, he restored its equilibrium by an instantaneous movement of his body: he was, in fact, like a man who had learned to ride a bicycle—balancing himself without pausing to think what he should do. But Lilienthal, in his navigation of the air, was facing a danger the cyclist has not to fear. He was braving dangerous wind-gusts; and he did not know, and had no means of knowing, with just what strength these gusts would strike his craft. Also—and this too was a danger no man on earth need fear—he had empty air below him should he fall. The peril grew greater as his skill increased, because he soared higher, and left greater distances between him and the ground below. In another way, also, he courted greater risk; and this was through gliding in stronger winds. At first, when he was unskilled, he had cared only to brave a wind of a velocity, say, of 10 or 15 miles an hour. But soon, feeling his balancing power grow greater, he ventured into the air when there was a wind of from 20 to 25 miles an hour.

In regard to this question of the strength of the wind, uncertainty often exists. What, for example, is a “stiff breeze”? What is a “strong wind”? And at what velocity must the wind blow before it is called a gale? Such questions are often asked, and the table below should prove instructive:

Fig. 27.—Lilienthal combating a wind-gust.

In gliding in a breeze, say of 25 miles an hour, Lilienthal had to face this danger, and it is one all airmen meet: whereas the average strength of a wind may be maintained at 25 miles an hour, there is no assurance that there will not be a sudden and heavy gust of a greater force than this. Sometimes, when the wind is uncertain, there will come a gust which has double the force of the normal pressure; and such a gust, sweeping unexpectedly against an aircraft, threatens to blow it over and send it headlong to the ground. Thus Lilienthal, having no more control over his machine than could be brought to bear by movements of his body, was running a considerable risk when he soared in gusty winds—particularly if using the biplane form of craft. Sometimes, when struck by a gust, his glider would heel and assume a dangerous position in the air such as is illustrated in [Fig. 27]. Here the craft threatens to fall backwards and partly sideways; and the operator can be seen throwing his body and legs forward, in a quick effort to check this overturning impulse.

One incident, indicating the risks Lilienthal ran, should be mentioned: he was gliding 50 feet high one day, in a fresh wind, when one of the wooden arm supports, which he gripped while in flight, broke suddenly and threw his craft out of balance. The machine, before he could right it, fell heavily to the ground; but, thanks to the shock-absorber below the wings, Lilienthal escaped with nothing worse than bruises.

He had set himself to master this art of balance, and master it he did, and was ready to risk his life in so doing. In the year 1896 he was bold enough to glide from hills 250 feet high; and from such a height he would come sweeping through the air, often traversing before alighting a distance of 750 feet. Sometimes, too, on a day when the wind was high, he would stand upon the hilltop and allow the wind pressure under his wings to raise him in the air; then, throwing his weight forward, he would start his craft on a downward glide. Frequently, when experimenting in strong winds, he would find himself higher than his starting-point, and would hang almost motionless for a moment or so, soaring in the air. But such hovering flight, though he practised assiduously, he found difficult to maintain. He could not keep his machine poised in an ascending current of wind; he had not that instinct of the birds which enables them to profit instantly by each rising gust, and hold themselves in it as they allow it to bear them upward. Soaring flight has a fascination for those who study the navigation of the air; but no man, as yet, has been able to indulge in it for more than the briefest space of time. It is only possible to hover thus, without effort or the use of a motor, when the forces that govern a machine are exactly in balance; that is to say, the power of gravity which is pulling downwards must be balanced perfectly by the strength of the wind, which is blowing under the planes of the machine and tending to force it upward. Should the wind fail in its thrust, then the craft will move forward and downward; should the wind blow more strongly, then it will drive the machine backward, and tend to throw it out of equilibrium. Some birds, profiting by the skill they have in the minute adjustment of their wings, are able to hover over a given spot at will, remaining motionless in the air, without flap or visible effort.

But Lilienthal, although he never attained such proficiency as might enable him to soar indefinitely above the hill from which he sprang, was always confident that some perfect glider would be invented, and men thus be able to imitate the birds. It was when writing upon this problem of soaring flight that he expressed the thought:

“It is not to be wondered at that birds are able to perceive the slightest variations in the movements of the air, because the whole of their body surface acts as an organ for this sensation; the long and widely extended wings constitute a sensitive feeling lever, and minute sensibility will be particularly concentrated in the follicles from which the feathers issue, just as is the case with our finger-tips.... Should it ever become possible for man to imitate the splendid sailing movements of birds, he will not require to use steam engines or electro-motors for the purpose; a light, properly shaped, and sufficiently moveable wing, and the necessary practice in its manipulation is all that will be required of him. He should, unconsciously, be able to draw the greatest advantages from whatever wind may be blowing, by properly presenting the wings.”

When three years of gliding lay behind him, Lilienthal thought he could go little farther in this research. He was able to balance himself in the air; he could glide in high winds; but always, seeing that he had no motive power with which to drive his craft, he must start from a hilltop and descend to the ground. Now he sought longer and bolder flight; and so he and his brother discussed the building of an engine which might propel a glider through the air. No petrol motor, unfortunately for Lilienthal, was then available; so he planned to construct a carbonic acid motor, and make this drive his craft by flapping the ends of its wings.

During the summer of 1896 he was busy with plans for this motor, while still continuing his flights; but in August he decided to cease gliding for a while, and await a test of the power-driven craft. So on Sunday, August 9th, he said he would travel out to Stollen, make one or two final flights, and pack up his machine. His brother Gustav was to have accompanied him as usual, but had a mishap with his bicycle, and so remained behind. What happened is described, in few but expressive words, by Gustav Lilienthal:

“Our families, whom we had intended to take with us, remained at home, and my brother drove out, accompanied by a servant. He intended to make some change on the rudder, but at the very first glide, the wind being uncertain, the apparatus, when at a considerable height, lost its balance. Unfortunately my brother had not fitted the shock-absorber, and the full shock of the fall took effect, so that the apprehension of our uncle was fulfilled. My brother fell, a victim to the great idea which—although at that time so little recognised—is now acknowledged in its full bearing by the whole civilised world.”

At the moment his machine lost balance, Lilienthal was more than 100 feet in the air. Striking the ground with great violence, he sustained injuries which were almost immediately fatal. In his work, to which he sacrificed his life, he had met with no encouragement or recognition. He suffered the fate of pioneers; his theories were so far ahead of his time that folk did not grasp their significance. Little interest seems to have been taken in his glides; there was no sensation; there were no crowds. Nobody, in fact, realised what he was doing, or appreciated the vast importance of these seemingly simple tests. But in the years that followed, when other men came to grips with the problem as Lilienthal had done, when they were able to use the data he had compiled and to profit by his experiences in actual flight, then this pioneer came into his own.

His work, summarised, may be said to lie in this: he provided a stepping-stone to power-driven flight. He showed men that they should learn to balance themselves in the air before, and not after, they had built themselves costly craft. How his example acted as a spur upon others, and how the work he had begun was carried to its triumph, will be the purpose of our next chapters to show.[1]

CHAPTER VII
WILBUR AND ORVILLE WRIGHT

How two American engineers followed up Lilienthal’s work—Their biplane glider and its ingenious control—First experiments and successes.

For those who might care to study them, Lilienthal had written papers and essays as explanations of his work, and when the news of his death was flashed round the world, inventors were induced to turn to these teachings and read for themselves what he had done. Among those who were interested were two young Americans, unknown then, but now world-famous—Wilbur and Orville Wright. Living in Dayton, Ohio, they were the sons of Milton Wright, a prominent church worker of that city, and they carried on a bicycle store and engineer’s shop. Both were born engineers—keen, clever, patient, and enthusiastic in their work; and they had discussed many times—before they read of Lilienthal’s death—the problem of building an aeroplane. Now this interest was re-awakened; and as Wilbur Wright himself said:

“The brief notice of his (Lilienthal’s) death which appeared in the telegraphic news at that time, aroused a passive interest which had existed from my childhood, and led me to take down from the shelves of our home library a book on “Animal Mechanism” by Professor Marey, which I had already read several times. From this I was led to read more modern works, and as my brother soon became equally interested with myself, we passed from the reading to the thinking, and finally to the working stage.”

What the Wrights first set themselves to do was to investigate previous data. They wanted to prove, if they could, whether this data was sound or badly reasoned: they needed a firm and definite basis of their own before they would build any large machine. So they tested the theories of their predecessors and made experiments, particularly as to the sustaining power of surfaces of various shapes and curves. To this end they built and flew kites, studying the lift they exercised; then they decided to build a light gliding machine, such as Lilienthal had used. But there was a drawback to be faced in all such practical work, and the Wrights saw it clearly; this was to get a sufficient amount of actual flying. It was Wilbur who wrote:

“It seemed to us that the main reason why the problem had remained so long unsolved was that no one had been able to obtain any adequate practice. It would not be considered at all safe for a bicycle rider to attempt to ride through a crowded city street after only five hours’ practice, spread out in bits of 10 seconds each over a period of five years; yet Lilienthal, with this brief practice, was remarkably successful in meeting the fluctuations and eddies of the wind gusts.”

They made up their minds to build a glider with ample wing-surface, so that it would be sustained in light breezes, and to take the machine to where they might be sure of a steady wind, and there fly it as a kite; allow it, that is to say, to ascend into the air at the end of a rope, and hold it steady against the wind while the operator practised his balancing movements.

Fig. 28.—The 1900 Wright Glider (operator’s position).

Their first glider was a biplane, with 165 square feet of lifting surface, as illustrated in [Fig. 28]; several of its features need explanation. First there is the position of the operator; he can be seen lying prone across the centre of the lower plane. This attitude was adopted by the Wrights to minimise wind-pressure. Should a man be upright in his machine, they calculated that his body would, as the glider passed through the air, offer an appreciable resistance; while, in lying flat, he would offer scarcely any resistance at all.

A small horizontal plane will be noted in front of the main-planes; this was to govern the rising and descending of the machine. The Wrights came to the conclusion that any body-moving method for controlling their craft, such as Lilienthal had adopted, would not be sufficiently powerful in a wind. Lilienthal, it will be remembered, had found his control weaken when he used a machine of large surface. So the Wrights decided that, instead of altering the centre of gravity of their machine when gusts struck it, they would leave the centre of gravity immovable and shift the centre of pressure upon their planes. This was done partly by the elevating plane, as it came to be called. Tilted upward, this had the effect of raising the front of the glider, and causing the centre of pressure to travel backward upon the planes. Tilted down, it made the planes dip forward, and brought the centre of pressure nearer their front edge. When he wanted to rise, the pilot raised the elevator; when he wished to glide earthward, he inclined it down. Here, indeed, was the method such as was described in [Fig. 13], when dealing with the machine Sir Hiram Maxim built; and this system of the lifting plane is worthy of special mention. In one way or another, fitted in front of the planes or behind them, it is the recognised method for controlling the rise or descent of an aeroplane.

Apart from governing the ascending or descending movement, there was the question of preventing a machine from slipping sideways; and this the Wrights solved ingeniously. They saw, of course, that when their glider lurched to one side or the other, they would need some power to tilt it back again. So they devised a system by which the plane-ends of their machine—being made flexible—might be warped, or caused to shift up and down. This action the operator controlled, as he lay across the lower plane, by a movement of cords, and its operation is shown in [Fig. 29]. The effect upon the machine may be described thus: should a wind-gust tilt down one plane-end, the “warp” upon that side of the machine was drawn down also, and the effect of this—seeing that it caused the plane to assume a steeper angle to the air and exercise a greater lift—was to raise the plane-ends that had been driven down by the gust. By a system of connecting the control cords, this balancing influence was made to act with double force; when one wing warped down, the other moved up; and, in this way, while the side of the machine tilted down was made to rise, the other plane-ends, which had been lifted, were made to descend. A dual righting influence was thus obtained. This system, which imitates the flexing movements made by a bird, was an important device; the Wrights patented it—combining the movement with an action of the rudder—and brought cases at law to enforce their rights.

Fig. 29.—The Wright Wing-warp.

In the summer of 1900, with their first machine, the brothers went for experiments to Kitty Hawk, North Carolina. They had chosen this lonely settlement, located on a strip of land that divides Albemarle Sound from the Atlantic Ocean, because they hoped it would provide them with a strong, steady wind; there were also, fairly close to the settlement, suitable sand-hills for gliding.

Upon the first day of their trials the wind was blowing at nearly 30 miles an hour, and they allowed the glider to rise as a kite. Flown in this way, it bore the weight of a man; but they were disappointed at the position it assumed when in the air. Its planes set themselves at an angle which was too steep, and it seemed to give less lifting power than they had expected. They tested their system of control, and found that the wing-warping for sideway balance acted extremely well, proving quicker and more certain than would the shifting from side to side of the operator’s body. The elevating plane was also efficient.

Fig. 30.—Launching the Wright Glider.

Then they took the glider to the sand-hills. At first the wind was too high, but after waiting a day it dropped to 14 miles an hour, and they were able to make nearly a dozen glides down the side of a slope which had a drop of 1 foot in 6. It had been their idea, in building the machine, that the operator should run before gliding, as Lilienthal had done, and only lie upon the plane when the speed was sufficient to give the surfaces their lift. But in practice they found a better method than this. Two assistants, as illustrated in [Fig. 30], took the machine by its plane-ends and ran forward with it, the pilot assuming beforehand his position upon the plane; then, when they had gained a pace sufficient for the machine to soar, they released their hold and it glided forward. Beneath the glider, under the centre of the lower plane, there were two wooden skates or runners, and these took the weight of the machine when it alighted, and allowed it to slide forward across the ground before coming to rest. By the use of these landing skids, and by steering at as fine an angle as possible, the Wrights found they could touch ground, even at 20 miles an hour and lying across the machine, without injury either to themselves or the craft.

The first glides were short, and all close to the ground; but they bore out the tests when the machine had been flown as a kite, and showed that the elevating plane and wing-warp would do their work. The Wrights were, indeed, astonished at the celerity with which the glider responded to the fore-plane.

Writing afterwards of this first visit to Kitty Hawk, Wilbur summarised the experiments thus:

“Although the hours and hours of practice we had hoped to obtain finally dwindled down to about two minutes, we were very much pleased with the general results of the trip, for setting out as we did with almost revolutionary theories on many points and an entirely untried form of machine, we considered it quite a point to be able to return without having our pet theories completely knocked on the head by the hard logic of experience, and our own brains dashed out into the bargain.”