CHAPTER VIII
Having traced the growth of winged models from their earliest beginning to the time when they proved the possibility of mechanical flight, we may now study the evolution of larger machines, designed to carry human beings. Considering first the aëroplane, we may follow the two general methods advocated by various inventors for launching a man safely in the air, both of which led to success. The first of these may be called Henson’s method, the second Lilienthal’s, coupling them with the names of their distinguished pioneer exponents. Henson in 1842 proposed that the pilot should mount a full-power machine, run along a smooth course, and glide into the air without previous experience in the art of navigating. Lilienthal recommended careful preliminary training on a glider, by which the novice should acquire sufficient skill in parrying the wind to qualify him to manage a dynamic machine, under its more complex conditions of control. Others, more cautious still, contended that automatic equilibrium should be secured before a rider risked his bones on the aërial bronco; while still others thought the uncertain beast should be tethered to some point in the sky, say a balloon or taut wire, or the end of a pole; so that however he bucked, or reared, he should not fall over on his rider.
We have noticed in the first chapter some picturesque man-flights, usually deplorable or tragic; and always fruitless for lack of scientific method in experimentation and report to the world. There can be no doubt that such flights were accomplished, mainly, of course, by the aid of gravity; but the difficulty is to ascertain the exact nature of any given performance, the specifications of the apparatus, and the principles of equilibrium and control. Gradually, however, the experimenters improved both in the construction of man-carrying devices and in the manner of imparting their results to their colleagues, or successors; and so the flying enterprise began to assume a progressive aspect, attended with that scientific dignity which invests secure and continuous advance in any branch of knowledge. Little of value, however, can be gleaned from any such flights made prior to the middle of the nineteenth century. From that time forward observers and inventors made definite and fairly methodical efforts to develop the art of gliding and soaring in the air, the first fruit of which was to hasten the advent of the modern aëroplane.
A French novelist and aëronautic writer, G. de la Landelle, relates an amazing adventure in the art of soaring, which may have some foundation in fact, though savoring strongly of fiction. An experienced sailor, Captain Le Bris, having observed the albatross soaring without wing-beat, determined to imitate the fascinating flight of that limber-winged spirit of the sea. To such end he built the bird shown in Fig. 38, a ninety-pound albatross, with arched wings fifty feet across and articulated to the boat-like body. In this the brave aviator would stand upright, turn the wings and tail to maintain his balance, and steer grandly through the sky. Placing this long-winged creature across a cart driven by a peasant, he stood erect and headed against a breeze; the wings set low to prevent lifting till an opportune moment, and the bird held down to the car by a rope which the captain could quickly release. When the horse was a-trot, and the wind blowing freshly, Le Bris raised the front edges of the wings. Thereupon the albatross tugged upward, and the mooring rope was slipped, but accidentally whipped around the driver’s waist. The horse galloped away with the cart; the bird, with the exultant sailor on its back, soared 300 feet into the air, and incidentally carried up the peasant, dangling at the end of the rope and howling with fright. Noting the distress of his passenger, the kindly captain sailed close to earth, so that the peasant might disembark and run to his horse, meaning then to hie away for a long cruise in the clouds. But with this change of weight the vessel seemed not to navigate well; so she was brought skimming to land, with no mishap save a slight damage to the advancing wing, which broke as it touched the ground.
Fig. 38.—Le Bris’ Aëroplane, 1855.
Having repaired the great bird’s wing, Captain Le Bris next made a launching from the arm of a derrick, 30 feet above the ground, overlooking a quarry 70 feet deep. The attendant swains stood open-mouthed, wondering whether this madman would overleap the clouds, or promptly butt out his brains on a jagged rock. When the wind blowing from the quarry seemed to float him in perfect poise, he tripped the suspension hook, and headed for the precipice on even keel. He was now happily launched, and keen for an aërial journey; but after passing the brink, he seemed to encounter an eddy which tilted his craft forward. The vessel dipped and rose; the captain plied his levers, turning now the tail, now the pinions. He crossed safely over the invisible breakers, and reached the quiet air of the quarry on level wing. But now his forward speed was lost, the great bird sank rapidly and crashed upon the rocky bed below. The wary seaman anticipating a bump, sprang upward to soften his fall; but a lever rebounding from the shock, hit one of his legs and broke it.
Some twelve or thirteen years later, in 1867, Le Bris, aided by a public subscription at Brest, built a second albatross, with which he made a number of small flights, sometimes riding it himself, and sometimes replacing his weight by ballast. On one occasion the loaded bird, held by a light line, rose 150 feet and advanced against the wind. Suddenly the sailors holding the line observed it slacken, and saw with amazement the long-winged creature soar forward 600 feet, as stately and serene as its living prototype. Presently encountering a sheltered and quiet region of air before some rising ground, it settled softly to earth in perfect equipoise. But on a subsequent launching from the same favorable ground, the dumb creature pitched forward and plunged to the earth where it lay shattered and torn in a hopeless tangle. Le Bris looked on the wreck in despair, surveying sadly the remains of his once cherished bird; then sat upon the débris a long time, his head between his hands, his heart broken, his mind tortured with anguish. Impoverished, chagrined, derided, he now must abandon the albatross business. Five years later this intrepid sailor of sea and air was killed by some ruffians, in 1872, while a constable in his native place, and after a period of honorable service to the state in the Franco-Prussian War.
The story is more romantic than instructive, for want of exact data. To give the experiments their proper value to others, fuller details of the mechanism should be furnished, and adequate measurements of the speed and direction of the aërial currents. At one time the sailing was even, at another, rough, though outwardly the conditions appeared the same. Apparently the successful flights occurred when the bird was launched to windward from rising ground, that is, when the current had an upward slant, to exert a propulsive effort. This species of soaring has been observed frequently in nature, and has been imitated both with models and with man-carrying gliders. Nevertheless Le Bris’ experiments were very remarkable for the time, and, if adequately reported, might have proved to be of much interest and value to aëronautical science.
Another Frenchman alert to the glory of aërial motion was L. P. Mouillard, the poet-farmer of Algeria. From boyhood he studied the birds with unabated interest and pleasure. He would journey miles to attend the “morning prayer” of the starlings in the forest of Baba-Ali; noting, just before sunrise, how their melodies suddenly hushed, and the forest seemed to bound upward, and heaven filled with the music of innumerable wings. He would time the shadow of the high bird of passage riding the hurricane from continent to continent. He saw the tyrant eagle fold his wings in mid air and plunge a thousand feet in ferocious swoop after the swift-fleeing duck or rabbit. He loved to watch the great tawny vulture on the mountain top shake the dew from his vast plumes, straddle the morning wind, and all day long, with never a beat of those grand pinions, soar godlike through immensity, the marvel and delight of the nether world. When the electric wind of the desert, blowing from Central Africa, brought the big scavengers and noble birds of prey, he sat on the ground scrutinizing their majestic flight and planning to imitate it. He would lie in ambush where the silent-rowing owl darted at dusk through the timber, fierce and swift as the eagle; a dreadful thing, with its night piercing eyes, its big ears and beak, its horrid talons, its sudden shriek startling the forest with ominous echoes. No feature escaped him, and least of all an aërodynamic one.
For thirty years he continued these studies. He would bring home the birds, lay them on their backs and mark their contour on paper, measure their projected area, weigh and compare them. He formulated curious conclusions about sailors and rowers, the functions of tail and quill feathers, weight and wing-spread, bulk, agglomeration of mass, resistance and velocity. He notes that only massive birds soar well, the broad-winged ones requiring a moderate wind, the narrow-winged ones requiring a gale, and sailing with perfect ease in a tempest; and he concludes that man may imitate both types. His book[24] is replete with charming anecdotes, observations and quaint theories, interesting alike to ornithology and aviation.
But Mouillard did more than theorize; he built soaring machines and soared a little. His third and best glider, illustrated in Fig. 39, was a tailless monoplane made of curved agave sticks screwed to boards, and covered with muslin. The aviator, standing in the open space C, harnessed the plane on with straps looped round his legs and shoulders, and fastened to the points D D. His forearms, passing under straps, rested on the board, enabling him to tilt the whole by shifting his weight. In order to vary the dihedral angle between the wings, they were hinged together and actuated by rods running from the man’s feet to the ends of the boards, hardly as far out as the center of wind pressure, thus apparently stressing his legs like a wishbone.
Fig. 39.—Mouillard’s Aëroplane.
He now sent the home folks away from the farm, buckled on his wings and walked along the prairie road waiting for a breeze. The road was raised five feet above the plain and bordered by ditches ten feet wide. His wings felt light; he ran forward to test their lift, and he thought to amuse himself by jumping the ditch. The result is thus expressed in his own words:[25]
“So I took a good run across the road and jumped at the ditch. But, oh, horrors; once across the ditch my feet did not come down to earth; I was gliding on the air, and making vain efforts to land; for my aëroplane had set out on a cruise. I dangled only one foot from the soil, but, do what I would, I could not reach it, and I was skimming along without the power to stop. At last my feet touched the earth; I fell forward on my hands; broke one of my wings, and all was over; but goodness, how frightened I had been! I was saying to myself that if even a light wind-gust occurred, it would toss me up 30 to 40 feet into the air, and then surely upset me backward, so that I would fall on my back. This I knew perfectly, for I understood the defects of my machine. I was poor, and I had not been able to provide myself with a more complete aëroplane. All’s well that ends well. I then measured the distance between my toe marks, and found it to be 138 feet.
“Here is the rationale of the thing. In making my jump I acquired a speed of 11 to 14 miles per hour, and just as I crossed the ditch I must have met a puff of rising wind. It probably was traveling some 8 to 11 miles per hour, and the two speeds added together produced enough pressure to carry my weight.”
He repaired his wing and repeated the test a few days later. A violent wind gust came; picked him up from the earth, and whelmed him over. In his alarm he allowed his “wish-bone” to spread, and the wings to fold up like those of a butterfly at rest, pinching him between them like a nut in a nutcracker. One wonders whether the overwheeling vultures witnessed this gentleman’s flight with any sense of humor.
After mature reflection, Mouillard concluded that he should give his aëroplane a rudder, and flex the wings, in order to insure adequate control. But here he halted, being a poor man unskilled in the art of construction. He had reached the limit of his endowments. He had observed faithfully and described charmingly the wonderful flights of various birds; but he must leave to his technical successors the pleasure of imitating or excelling those extraordinary maneuvers—leave them the pleasure, the sacrifice, the long years of toil and danger, accompanied perhaps by indiscriminate applause or derision.
In the meantime another distinguished disciple of the birds was energetically at work in Germany. No less ardent than Le Bris, or Mouillard, Otto Lilienthal was far better equipped and circumstanced. He was a graduate of the Potsdam Technical School, and a student for three years in the Berlin Technical Academy. He was engaged in practical construction ten years in various machine shops at Berlin. After 1880 he operated a flourishing machine factory of his own. From boyhood he with his brother Gustavus had carefully studied the flight of birds, and had made numerous experiments in aviation. On moonlight nights in their little home place of Anclam, in Pomerania, the boys would run downhill, flapping their home-made wings, like Dædalus and Icarus, but with no other danger than discovery and teasing by their neighbors. At Potsdam and Berlin they continued to experiment and to construct wings of increasing size and power. Thus Otto Lilienthal reached early manhood thoroughly trained by his long courses in the technical schools and shops, brimming with well pondered ideas, strengthened by continuous observation and experiment, and in financial circumstances which permitted him to devote time and money to the unremunerative pursuit of aviation. To this may be added that his mature years were cast in a time when the allied sciences could aid him far more than they had aided his predecessors of the preceding generation.
After careful research for the most efficient form of alar surface, Lilienthal resolved to imitate the birds. First he would build a pair of arched wings, and learn to coast down the atmosphere, balancing and steering like a stork in the gusty and treacherous current. He would thus acquire the pilot’s skill, and ascertain the towline power required to sustain a given weight. Then he would add a suitable propelling mechanism, test it cautiously, and acquire the mastery of dynamic flight. Incidentally, perhaps, he would learn to ride all over creation without motive power; for he was convinced that certain great birds soar without muscular effort, and that man could acquire this delightful art in favorable weather. To strengthen the plausibility of that doctrine, he announced his discovery that the general trend of the wind is three and a half degrees upward, a fact inexplicable and almost incredible to his illustrious confrère of the Smithsonian Institution.[26] Such was Lilienthal’s ample program; more, indeed, than he would live to accomplish, though possibly not beyond his power of achievement, if he could have lived to enjoy the hale long years of his illustrious countryman aëronaut, Count Von Zeppelin.
In the year 1891 Lilienthal made his first series of trials in sailing flight. His glider was the bird-shaped apparatus shown in [Plate XVI], made of willow wood covered with waxed sheeting. It weighed about 40 pounds, and spread 107 square feet of surface. Taking this in his arms he first ran 24 feet along a raised board and jumped off, gliding through still air. Then, elevating the board to a height of six feet, he repeated the run, jump and glide, always landing very softly. Thus he became “king of the air in calm weather,” a title still creditably sustained by his numerous successors of the present day; for as yet no one “mounts the whirlwind and directs the storm.”
Next he went to some little mounds in a field beyond Werder, and jumped from these, gradually lengthening his flights till he attained a range of nearly 80 feet. As he was now gliding in light winds, he found it necessary to add a vertical rudder, in order to preserve his balance easily, and keep his bow toward the direction of the wind. His complete apparatus was, therefore, a birdlike affair, with two rigid wings and a double tail for steering vertically and horizontally. He found also that he could fly longer and alight more softly when the wind was blowing—an obvious possibility.
Encouraged by this experience Lilienthal explored the country about Berlin for sailing ground where he could make long glides, whatever the direction of the wind. Such a region he found near Rathenow, where the Rhinow hills, covered with grass and heather, slope gently upward from the flat plowland to a height of over 200 feet. This he thought an ideal coasting ground; for he felt the aërial currents very smooth, and he could always select clear land sloping ten to twenty degrees toward the wind. Here in the summer of 1893, with a new and improved glider, he made many flights, finally ranging from 200 to 300 yards, steering up and down, or to right and left at will; sometimes pausing in mid air, and several times returning to the starting point. This was more than coasting; for a mere coaster never maintains, nor returns to, his original level. It was a fair start at true soaring, the ideal locomotion. A glorious sport it was, sailing like an eagle high over the landscape and over the heads of the astonished spectators.
The new machine resembled its predecessors in form and maneuver; but differed in dimensions. It was a birdlike craft with parabolically arched wings and a double tail. It measured 7 meters across, spread 14 square meters of surface, weighed with the rider 200 pounds, and in calm air could sail down a slope of 9°, at a speed of 9 meters per second. This was very efficient sailing, the work of gravity being hardly two horse power. With the man lying prone, as eventually planned, the economy would be still greater.
PLATE XVI.
LILIENTHAL’S MONOPLANE GLIDER.
(Courtesy W. J. Hammer.)
LILIENTHAL’S BIPLANE GLIDER.
(Courtesy W. J. Hammer.)
PILCHER’S MONOPLANE GLIDER.
The craft was thought also to possess stability; and this it had, in a measure, about those two axes corresponding to the two rudders; but the control about the third axis, effected by dangling the legs to right or left, was extremely crude and primitive. It was in keeping with his adage: “to contrive is nothing; to construct is something; to operate is everything.” If he had contrived more intelligently, he would have operated more easily, and avoided those wild and dangerous dancings in space. A more scientific adage would read: “To design effectually is everything, to construct is routine, to operate is play.”
The marvel is that Lilienthal, the observant, the technically trained, the practically skilled, should operate for three years, then patent, an aërial glider having two rudders, but lacking the third rudder, or torsional wing, now so commonly used throughout the world. But doubtless he contemplated a device for preserving the lateral balance without shifting his weight; for he acknowledged the economic advantage of lying prone on the machine, and stated that this might be done after some important improvements in the apparatus had been made.
Having executed nearly two thousand flights with his monoplane, Lilienthal in 1895 built a two-surface glider. He found this still easier to control, and now thought he had sufficiently acquired the art of sailing to justify his undertaking the next and more difficult art of imitating the rowing flight of birds. He had constructed a ninety-pound engine, of two and a half horse power, to actuate the wings of his glider; but, before applying this motor, he went to the Rhinow Hills for a little further experience in sailing. Previously he had remained in the air twelve to fifteen seconds; but he wished to exceed this record.
On the 9th of August, 1896, he made a long glide to prove the effectiveness of the horizontal rudder, and then wished to undertake a second flight of the greatest duration feasible. No intimation had he that this sail would prove disastrous. Giving the timepiece to his assistant, he set forth on a level course, but suddenly dipped forward and plunged headlong to earth through a height of fifty feet. He was dragged out from the débris with a broken spine, from which he died the following day.
The machine on which the father of aërial gliding made his last flight is shown in [Plate XVI]. Of the hazardous nature of its construction Mr. Chanute thus writes: “The two surfaces were kept apart by two struts, or vertical posts, with a few guy wires, but the connecting joints were weak, and there was nothing like trussing. This eventually cost his most useful life. Two weeks before that distressing loss to science, Herr Wilhelm Kress, the distinguished and veteran aviator of Vienna, witnessed a number of glides by Lilienthal with his double-decked apparatus. He noticed that it was much wracked and wabbly, and wrote to me after the accident: ‘The connection of the wings and the steering arrangement were very bad and unreliable. I warned Herr Lilienthal very seriously. He promised me that he would soon put it in order, but I fear that he did not attend to it immediately.’”
It will be observed that Lilienthal gave fair attention to the merits of both the monoplane and the biplane, the two familiar types in lively competition at the present hour. The first he found in Nature; the second he could have found in England, as the developments principally of Wenham and of Phillips. His example and prestige did much to promote the biplane; but he seems to have had no very decided preference for either. Though he found his biplane very satisfactory, he thought of returning to the monoplane.
In April, 1896, he wrote:[27] “I am now engaged in constructing an apparatus in which the position of the wings can be changed during flight in such a way that the balancing is not effected by changing the position of the center of gravity of the body. In my opinion this means considerable progress, as it will increase the safety. This will probably cause me to give up again the double sailing surfaces, as it will do away with the necessity which led me to adopt them.” He thus seems to have studied the two types impartially, and to have invented a means for balancing the machine without shifting the center of mass.
Lilienthal had given a powerful and permanent impulse to aviation, both by his writings and by his practical experience in the air. He first showed quantitatively the advantage of arched wings, by carefully derived tables of wind pressure; then he mounted the wings himself and taught the world, by bold and frequent flight, the art of aërial gravity sailing. The two remaining achievements, dynamic and soaring flight, he was to undertake as promptly as possible. If his life had been spared, no doubt he would have contributed much to the advancement of these arts, both by example and by direct effort; for he was in the prime of life, full of energy and daring, highly equipped, and ardently devoted to his favorite science. He began his studies in aviation at the age of thirteen and died at the age of forty-eight years.
Among the admirable traits of the father of sailing flight must be mentioned his scientific liberality and esprit de corps. Though he patented his invention he did not conceal, or withhold, his discoveries when he could publish them properly. These discoveries were made at a great sacrifice of time and means, and must have appeared to him valuable trade secrets; yet he published all his scientific data, his theories, and observations; he encouraged his confrères in various countries to witness and emulate his experiments, to share intimately his laboriously developed knowledge of aviation, to join hands with him in hastening the advent of practical flight. Such is the esprit de corps which has ever prevailed among truly scientific men, as distinguished from the mercenary and commercial; such are the unselfish investigators whom the world delights to honor, both for their genius and for their liberal contributions to the common and permanent possessions of humanity.
Before his death Lilienthal had the pleasure of knowing that competent disciples were emulating him in doctrine and practice. One of the earliest and cleverest of these was Percy S. Pilcher, Assistant Lecturer in Naval Architecture and Marine Engineering at the University of Glasgow. In the summer of 1895 he built the glider shown in [Plate XVI]. This, like Lilienthal’s, was a double-tailed monoplane arched fore and aft; but, better than his for manual control, it was straight from tip to tip, like the designs of Henson, Penaud, and other predecessors. This improvement was introduced to prevent side gusts from rocking the craft so readily as they do the V-shaped gliders. His best sailer, the Hawk, shown in the figure, had wings curved one in twenty, about one third from their front edge.[28] Sometimes he sailed downhill; again he was towed or launched, like a kite, by means of a cord, running through five-fold multiplying gear, and drawn by running boys, or a horse. In both cases he controlled the machine to his own satisfaction, making in 1897 smooth downhill glides of 700 feet length, from an elevation of 70 feet.[29] He had also visited Lilienthal, but only after achieving success at home.
Having acquired some skill in sailing, Mr. Pilcher began work on a power machine. This was to be propelled by a screw actuated by an oil engine, and was to be mounted on wheels backed by stiff springs. Having observed his speed of descent in gliding, he computed that two tow-line horse power would float him and his machine, weighing together 220 pounds. A like result was obtained when he was flown as a kite. He was, therefore, on the straight road to achieving human flight on a screw-propelled, wheel-mounted monoplane. If he had been more cautious he might have been the first person to achieve human flight in a practicable type of dynamic machine; for he seems to have equaled, if not excelled, his German master in aëroplane design. But like the master he provided inadequately for the structural strength of his glider, and braved too far the dangers of gusty weather. One stormy day, September 30, 1899, wishing to please several persons who had come a long distance to see him, he made two trial flights in a gentleman’s park near Rugby. The second of these proved fatal. The spectators heard a cracking noise, saw the tail break, and the whole craft plunge headlong to the ground. Poor Pilcher was mortally hurt and died thirty-four hours later, without ever regaining consciousness. He was then in his thirty-third year.
Had this talented young Briton and his German tutor both lived, there would doubtless have been a pleasant race and rivalry between them; for the pupil was forming opinions and plans sufficiently divergent from those of his master and friend. He did not approve Lilienthal’s high wings and low center of gravity, nor his V-shape for lateral equilibrium, nor his flapping wing tips for propulsion, nor his method of launching the dynamic machine. Fortunately both published their ideas and experiments, leaving to their successors the task of judging the merits of their designs, and of adding any improvements that might still be required in order to achieve final success.
Contemporary with Pilcher, Mr. Octave Chanute and Mr. A. M. Herring, in America, were emulating the work of Lilienthal. Mr. Chanute was an experienced civil engineer, who had previously written a history of aviation, and experimented with numerous flying models; Mr. Herring, his employee for the time, was a mechanical engineer who had assisted in Langley’s experiments, and previously had flown a Lilienthal glider, and had made researches in the science of mechanical flight. On June 22, 1896, accompanied by two assistants, they went into camp among the sand dunes, on the southern shore of Lake Michigan, to study the art of navigating an aëroplane without artificial motive power. Mr. Chanute thought that the maintenance of equilibrium under all circumstances was at that time the most important problem of aviation; and that until automatic stability was secured, it would be premature and dangerous to apply a motor. He wished to evade, for he did not relish, Lilienthal’s way of balancing by shifting the body and kicking wildly at the stars. His main purpose, therefore, was to acquire the pilot’s science; but secondarily he would learn much about the architecture of gliders, the behavior of air currents, the elements of propulsion and sustentation.
PLATE XVII.
CHANUTE’S FIVE DECK GLIDER.
HERRING IN CHANUTE BIPLANE.
HERRING’S COMPRESSED-AIR BIPLANE.
(Courtesy Carl Dientsbach.)
They made some flights with a Lilienthal monoplane; but, finding this unsafe and treacherous, they discarded it in favor of a multiple-wing glider designed by Chanute, which after many empirical modifications in the placement of the sustaining surfaces, assumed the form shown in Plate XVII. This glider resembled the Lilienthal biplane in having the surfaces vertically superposed, the rider below them, and the rudder in the rear; but it was a five-decker whose wings, on either side, could swerve fore and aft, so as to bring the center of lift always over the center of gravity, in order to prevent excessive rearing or plunging. This glider was found very tractable in a twenty-mile wind, and in a thirteen-mile breeze would sail down a slope of one in four.
After further study, the five-decker was replaced by a three-decker; which presently was deprived of its obtrusive and unessential lower surface, thus assuming the familiar form shown in Plate XVII. As will be observed, this was a radically new and elegant design, consisting of two superposed arched surfaces held together by vertical posts and diagonal wires, like a Pratt truss. It was, in fact, the renowned “Chanute glider” which has been copied by so many succeeding designers of biplanes.
The Chanute glider weighed 23 pounds, spread 135 square feet, and readily carried a total weight of 178 pounds at 23 miles an hour. It was provided, as shown, with side planes and a double rudder, and this latter was elastically connected to the main body to insure steadiness of flight, on the principle of the elastic wing margins used by D. S. Brown in 1874. This craft was found easy to manipulate in launching, sailing and landing, a two-inch shift of the pilot’s weight equivalencing a five-inch shift on the Lilienthal monoplane. It was steady at a speed of twenty to forty miles an hour through the air, even when the wind was blowing seventeen miles an hour overground. The angle of descent was 7.5° to 11°, depending on the speed and trend of the wind. The work of gravity expended in maintaining steady flight was at the rate of two horse power for the 178 pounds, a good showing with the rider vertical.
Summer passed before Mr. Chanute could perfect the invention for automatic stability by means of swerving wings; but otherwise the gliding experiments were very satisfactory. The strong and simple biplane evolved during those few weeks of fruitful study, though not an original creation, having been foreshadowed theoretically and experimentally, in the work of Wenham,[30] Stringfellow, Lilienthal, Phillips, and Hargrave, was nevertheless an important contribution to the science of aviation, by reason of its strength and simplicity of design, its efficiency, its stability, and, best of all for that day, its record for good flights and safety. All who could appreciate it understood that the addition of a light motor would transform it to a dynamic flyer, navigable at least in mild weather. The most eager, perhaps, was Mr. Herring; for he had not only mastered this glider, but some years previously had flown successfully rubber-driven models very much resembling it in design. These two aviators, therefore, came to a parting of the ways, Chanute still pursuing automatic stability, Herring impatiently heading for dynamic flight by the shortest route available. Had they continued together on a practical course, they might, ere the close of the century, have anticipated at least the early flights of the French aviators, if they could have constructed or purchased an adequate motor.
After some further development of the aërial glider to adapt it to power flight, Mr. Herring began the construction of a dynamic aëroplane. He had previously built very light steam and gasoline engines,[31] and deemed the latter best for a perfected flyer, though preferring steam or compressed air in a first experimental test.
When seen by the present writer in October, 1898, at St. Joseph, Mich., Mr. Herring was about to launch himself in the compressed-air driven biplane shown in [Plate XVII]. It was essentially a powered Chanute-Herring glider, steadied by a double tail, and controlled by shift of the pilot’s weight, the tail being elastically attached. The writer then suggested that both a glider and a dynamic aëroplane should be controlled entirely by steering and balancing surfaces, on the principle set forth in his paper of 1893; and, in particular, indicated that the lateral balance should be controlled by changing the inclination of the wings on either side, while the double tail should be used to steer and steady the aëroplane sidewise and vertically; in other words, that a torque about each of the three rectangular axes of the machine should be secured from impactual pressure, thus obviating the need for shifting the pilot’s weight. Mr. Herring, while making no objection to this proposal, intimated that he had a device for insuring control without shifting the pilot’s weight, but believed the most important effort for the moment should be to make a short flight with the machine as it stood, for the purpose of enlisting capital, then to add the controlling devices at leisure. He expected to remove the wheels shown in the figure, hold the aëroplane against a stiff breeze from Lake Michigan, start the propellers, strike a soaring attitude, and fly forward for a few seconds against the wind.
The successful accomplishment of such a flight covering an overland distance of seventy-three feet in eight or ten seconds, against a wind of thirty miles an hour, was reported in the Chicago Evening News, of November 17th of that year; but the present writer has not been able to ascertain the reporter’s name, or that of any other witness to the event, which, if true, is well worthy of verification and detailed record.
In following the votaries of passive flight, as represented by Lilienthal and his school, we have overlooked the great man-carrying bird of Clément Ader, one of the most prominent and successful aviators of that active period. If the reports be true, Ader may justly claim to be the first person to navigate the air in a dynamic flying machine. However, it must be observed that his achievements did not at first arouse in France a great pitch of exultation and enthusiasm. There seemed at the time to be some skepticism as to the practicability of his device. But later cordial reparation was made by placing it on the Stand of Honor at the Aëronautical Salon, held in the Grand Palais, at Paris, in December, 1908.
Clément Ader set out in life with the fixed determination to make a fortune, then to build a practical flying machine. Adopting the profession of electrical engineer, he quickly accumulated enough capital, as he thought, to realize his early ambition. He next visited Africa to study at close range the great soaring birds that Mouillard had described with so much admiration and vivacity. Going to Algeria he disguised himself as an Arab, and, with two Arab guides, journeyed to the interior where he watched the great soaring vultures, which he enticed with bits of meat to perform before him their marvelous maneuvers, wheeling in wide circles, and without wing beat, from earth to sky.
After several years of study of the anatomy and flight of birds, Ader began, at the age of forty-two years, to construct an aëroplane. His first machine was a birdlike monoplane mounted on skids, or wheels, and driven by a 40-horse-power steam engine actuating a screw, placed forward. The total weight was 1,100 pounds, the spread 46 feet, the length 21 feet. The Eole, as he called it, received its first open-air test on the morning of October 9, 1890, in the grounds surrounding the Chateau d’Armainvilliers, near Gretz, a portion of the course being so prepared that the trace of the wheels would be visible. When everything was ready for the trial, Ader mounted the machine, in presence of a few friends, ran quickly over the ground, urged by the propeller thrust, then rose into the air and sailed 150 feet. Such is the report of the witnesses to what is claimed as the first flight of a human being in a power-driven flying machine.
Subsequently this bold inventor built Eole No. 2, which, by special permission of the War Department, he tested on a prepared track, 2,400 feet long, on the Satory Camp. Over this course he ran his machine several times, and on one occasion flew 300 feet; but on alighting broke one of the wings.
Ader, now having spent one and a half million francs on his experiments, placed the Eole on exhibition in order to raise money for their continuation. In this venture also he was successful, being presently subventioned by the French War Department to build an aëroplane for its use. His subsequent labors are concisely set forth in Automobilia and Flight for February, 1909, as follows:
“Under these new conditions the workshop in the Rue Pajou was abandoned for larger premises in the Rue Jasmin, where the construction of the Avion was commenced in May, 1892, all persons engaged with the construction being under a military vow of secrecy. The motor was built first, and tested before a commission composed of army officers and some of the leading technicians of France. It was found to develop 30 horse power for a total weight of 32 kilogrammes; and even now, though seventeen years old, is regarded as a chef d’œuvre. In the spring of 1897 the Avion was ready to make flights. Like its predecessors it was modeled on the form of a bat; but, although the wings could not be flapped, they could be folded, and could be advanced or retarded horizontally.
“Everything appearing satisfactory, Ader informed the military commission that he was ready to undergo tests; the committee met at the workshops in the Rue Jasmin on August 18, 1897; were pleased with the machine, and ordered flights to be made immediately at Satory. It was not, however, until October 12th that a flight was attempted on the carefully guarded military ground, and in the presence of General Mesnier. The apparatus covered a distance of 1,600 yards, and although it did not fly, for this distance it is certain that on several occasions it completely left the ground. Ader declared that according to whether the wings were carried forward or to the rear, it was the front or the rear wheels only which left the ground. The pressure in the generator at this moment varied between 3 and 4 atmospheres. On increasing it to 6 or 7 atmospheres none of the wheels touched.
“Satisfied with the results of the test, General Mesnier called the commission together for further trials on the following day, October 14, 1897. Unfortunately it was a rough, squally morning, that would have prevented many a modern aviator from bringing a machine into the open. But as the officers had been brought together specially for this purpose, a flight was attempted.
“‘After several revolutions of the propellers, and a few yards covered at a moderate speed, we were off at a high rate of travel,’ wrote Ader, who was at the wheel on this memorable occasion. ‘The pressure was about 7 atmospheres. Almost immediately the vibrations of the rear wheel ceased, and, directly after, those of the front wheels were no longer felt, showing that we had entirely left the ground. Unfortunately the wind had increased in strength, and I had some difficulty in keeping to the line that had been marked out. I increased the pressure to 9 atmospheres, and immediately the speed increased considerably, the vibrations ceased again, showing that we had once more left the ground. Under the influence of the wind the aëroplane had a constant tendency to drift to the right, away from the circular track that had been marked for it. Finally, with the wind broadside on, the machine was in a rather dangerous position, for it was being still more rapidly driven out of its course. I increased the pressure still more and put the rudder hard over to the left, with the result that for a few seconds the machine worked back towards the track and still maintained itself in the air. But it was impossible to struggle against the wind, and finding that the machine was being carried towards some artillery sheds, and somewhat unnerved by the speed at which the ground appeared to be rushing past, I stopped the engine; there was a shock, and I was on the ground.’
“Ader was uninjured, but his machine was rather badly smashed. It had certainly flown, but with such difficulty in the face of the wind that the army commission was evidently little inclined to report favorably upon it. Several weeks passed without any communication being received from the War Department; then it became apparent to Ader that the Government had no longer faith in his invention. This was proved early in the following year by an official communication to the effect that no further funds could be allotted to this work. Discouraged at the abandonment after forty years’ labor and the expenditure of about two million francs, Ader commenced the destruction of his machines. The earlier ones were destroyed, but the Avion, the one which had appeared before the army commission, was saved and sent to the Museum of the Arts et Métiers in Paris.”
The last aëroplane, or Avion, weighed 1,100 pounds, spread 270 square feet, and was driven by a 40-horse-power steam engine actuating twin screws projecting before the bird-shaped flyer. The engine weighed but 7 pounds per horse power—quite a remarkable achievement for that day.
In following the votaries of passive flight, as represented by Lilienthal and his school, we have overlooked the great dynamic aëroplane of Mr. Maxim, one of the most prominent aëroplane builders of that active period. Having in 1889 made elaborate experiments on the atmospheric resistance of sustaining surfaces, and on the thrust of screw propellers, he proceeded to build the gigantic aëroplane shown in [Plate XVIII], the greatest flyer thus far known to history. It was a twin-screw multiplane mounted on a platform forty feet long by eight feet wide, and having four wheels running along a track eight feet wide and half a mile long. Above the rails of this track were guard rails to prevent the flyer from rising more than three inches during the tests. The whole machine weighed 3.5 tons, spread 5,500 square feet of surface, and, at a speed of 40 miles an hour, lifted more than a ton, in addition to the weight of the three men and 600 pounds of water. Its propelling plant comprised a naphtha tubular boiler, and a compound steam engine of 350 horse power actuating twin screws 17 feet 10 inches in diameter which gave a thrust approximating 2,000 pounds. These screws were made of American yellow pine, covered with canvas and painted, then smoothly sandpapered to reduce the friction; for Maxim, like certain French aviators, erroneously imagined that a polished surface has less air friction than a dead even surface. The framework was composed of seamless steel tubing stayed with steel wire. The aëroplane was to be steered right and left by a rudder, and up and down by horizontal planes, one fore, another aft, and its lateral stability was to be secured by side planes set at a dihedral angle. A meritorious feature for that day were the superposed arched surfaces whose framing was smoothly covered below and above by skillfully stretched fabric, causing the air to flow evenly without wasteful eddies.
PLATE XVIII.
MAXIM’S AËROPLANE.
(Courtesy W. J. Hammer.)
LANGLEY’S LARGE AËROPLANE.
(Courtesy Smithsonian Institution.)
Many runs along the track were made to test the working of this great apparatus before trusting it to launch forth in free flight. Dynamometers gave independently the thrust of the screws, and the lift of the wings on the front and rear axles. The ascensional planes for controlling the fore and aft equilibrium were tested during the run, as also the practical operation of the propelling plant. During the trials of 1893 the machine frequently lifted clear of the lower track, and flew forward resting against the guard rails above the wheels. Finally, on a gusty day, the lift against the upper track caused this to give way, whereupon the machine rose into the air with Mr. Maxim and his assistant, then toppled over on the soft earth, suffering some damage to its framework. Here the experiments were discontinued for lack of funds, having indeed demonstrated that a large weight can be carried in dynamic flight, but having proved little as to the feasibility of controlling an aëroplane in launching, in free flight, and in landing.
Compared with the work of his contemporaries this achievement of Mr. Maxim was herculean, both in construction and expenditure, the cost being reported as nearly one hundred thousand dollars. It raised high hopes for aviation. It proved conclusively not only that a flying machine could be made to lift a pilot, but that it could carry hundreds of pounds additional weight. It still holds the world’s record for magnitude of machine and cargo. But it had two great defects; it was improperly balanced and it was inadequately powered; for, as Mr. Maxim says, “the quantity of water consumed was so large that the machine could not have remained in the air but a few minutes, even if I had had room to maneuver and learned the knack of balancing in the air.”[32] These defects, however, would soon be remedied by the work of others, and particularly by the costly experiments of the automobilists, who were rapidly developing a light gasoline motor suitable for aviation.
The inventors thus far noticed had developed most of the important features of the present-day flying machines, but had not provided adequate mechanism for preserving a steady lateral balance. The present writer had proposed the combination of a double rudder and torsional wings to steer and control a flyer, and had published a paper setting forth its general principle and describing a specific device; but inventors had little need for a third rudder till they encountered the dangers of dynamic flight in gusty weather. The paper referred to was presented to the Third International Conference on Aërial Navigation, in August, 1893, under the title, Stability of Aëroplanes and Flying Machines, and was published with the proceedings of the conference.[33] It discusses mainly the question of automatic stability and steadiness; but recommends personal control during the experimental period. It concludes as follows:
“We have been considering the question of automatic stability, in so far as it may be secured in the construction of the craft itself,[34] apart from a pilot, or special equilibrating devices. The application of the latter would give exercise to an infinite amount of ingenuity, and would, perhaps, best be left to the fancy of the individual inventor. One curious design, however, occurs to me, which, since I have not seen it described elsewhere, may be worth a moment’s notice.
“Suppose a Phillips’s machine (see [Plate XIV]) to be provided with a double tail, and to have a vertical fin extending longitudinally along its entire length, well above the center of gravity. These would steady its flight and promote stability. Suppose also that its sustaining slats were pivoted, so that a pilot could at pleasure change their inclination on the right and left side independently. He could then set the engine for a desired speed, sweep forward along the earth with the sustainer slats horizontal, and at will mount into the air, by giving the slats an upward inclination. Once in the air he could raise or lower the machine by slightly changing the angle of the slats; he could wheel to right or left by giving one set of slats a little different slope from the other; he could arrest all pitching, rocking and wheeling by a slight counter movement of the sustainers. It would be necessary, of course, to preserve a rapid forward motion, for it is a peculiarity of the compound aëroplane that, if it comes to a standstill in the air, it will drop plumb down with a frightful plunge until it acquires headway.”
The succeeding paragraph disclosed a specific contrivance embodying the principle just given. This showed two levers rotating drum shafts for actuating wires adapted to change the impact angles of the wing surfaces. Accordingly this much of the mechanism of control, together with the broad device of the torsion wings, has been the common property of inventors since the publication of that paper. Furthermore, the combination of torsional wings and a double rudder, either fixed or movable, has been public property since that date.[35]
Little was said about the manner of manipulating the double rudder and torsional wings; for the rules of manipulation would vary in different machines, depending upon structural design and external conditions. For example, if the proposed fin and vertical rudder were ample and suitably placed, the lateral balance could be controlled by merely twisting the wings, without touching the vertical rudder; but if the fin and rudder were not adequate, the lateral poise would be controlled by twisting the wings and working the vertical rudder conjunctively. A novice might prefer leaving the rudders fixed and controlling the poise in short flights by twisting the wings by means of a single lever having two independent movements, one to rotate the wings oppositely, the other to rotate them identically.
The principle of control expressed in italics had been set forth also in a preceding paragraph. Having proposed means for securing both stability and steadiness about each of the three axes of an aëroplane, the text continued:
“These ends could probably be attained very well by mounting two compound aëroplanes on a long backbone,[36] somewhat after the manner of the Hargrave cellular kites, and adding a compound rudder to the whole.” ... “If the inclination of the sustainers, front and back, could be altered independently, it might be feasible for a pilot to preserve the equilibrium of the machine even when its center of gravity was frequently shifted, as by the moving of passengers to and fro.”[37]
At that date, 1893, an inventor doubtless could have secured a broad claim on a mechanism embodying the torsion-wing-and-double-rudder mechanism of control. But in those days aviation was pursued largely as a liberal study by scientific men who wished to hasten the advent of practical flight, by presenting important physical measurements and principles which could be freely employed by all. Accordingly the three-rudder system of control seems not to have been claimed by an inventor much before the close of the nineteenth century. Since then it has been patented in one form or other by many practical aviators, some endeavoring to claim the whole broad contrivance, others claiming more restricted devices.
The static principle of the torsion wing is a familiar one in elementary mechanics. It is this: a torque of given magnitude and direction has the same effect on a rigid body whatever its point of application. The longitudinal torque, or moment, may therefore be exerted by the wings, by suitable rudders, by forward planes, by any auxiliary planes, or fins, however placed or moved for the purpose. Accordingly there seems to be an unlimited variety of concrete patentable devices available to the inventor for securing impactual torque about the longitudinal axis, or either of the other two axes. But in planning such devices it is well to remember that the moment of a couple increases with its arm, so that in a wide aëroplane the wing tips may best furnish the torque; while in a high short-winged machine, vertical planes, fins, or rudders may give the desired longitudinal moment. Obviously such vertical guiding or controlling surfaces may be so placed as to tilt the machine toward the center of curvature of its path, at the same time opposing the centrifugal force, and exerting a torque about the vertical axis tending to steer the flyer along its path.[38]
The principle of projectile stability is another consideration of some importance in aviation, or more generally in all submerged navigation, whether of air or water. A submerged body has projectile stability if its nose tends always to forerun its centroid, and follow a steady course. A dart is a good example; a fish, a torpedo. Thus if a torpedo-shaped homogeneous solid be hurled in any manner through a fluid, obliquely or even tail foremost, it promptly turns its nose to the front and proceeds steadily along an even course; but if the body has not true dynamical balance, it may oscillate or gyrate, or flit about in the most erratic manner.
Projectile stability in a flyer, as in an arrow, may be attained by playing the centroid in or near the line of forward resistance, and well ahead of the side resistance. The reasons for this are manifest. If, however, this arrangement be neglected, a special damping, or controlling, device is required to preserve headlong and steady motion. In particular, the objections to placing the centroid too low were emphasized in the above quoted paper as follows:
“I have mentioned the advantage of placing the center of mass below the center of surface; this has also its objections. While the stability against inversion is increased, the stability against rocking is sacrificed. The aëroplane so constructed may not easily overturn; but it will sway to and fro with a pendular motion. This, when lateral, is very objectionable, when fore and aft it is fatal to uniform progress, as we shall see in studying the longitudinal stability of flying machines. We shall then see that the center of mass cannot be lowered with impunity.”
Of the various flyers and models thus far studied, some manifest fairly good, others very imperfect projectile stability. Many inventors have been more alert to the gravitational stability and safety of the parachute than to the kinetic stability and keen, direct flight of the arrow. Some of the most pretentious machines imitated the thistle down more nearly than the dart or swallow. But the exigencies of actual flight would easily rectify such imperfections of design.
Tractional balance also is a property of some importance in fluid navigation. This requires that the line of propulsive thrust coincide with the line of fluid resistance. It is a property, however, that inventors readily apprehend, and usually provide for.
In general a flyer is subject to four forces: weight, thrust, air pressure and inertia. When these balance about any axis the craft has equilibrium about that axis; when they balance about the three axes the craft is completely balanced, and preserves its orientation in flight. Devices for preserving this complete balance have already been described; as also provision for propulsion and sustentation, launching and landing safely.
Thus at the close of the nineteenth century all the essential principles and contrivances of pioneer flight were worked out, except one—a suitable motor. This was the real problem of the ages. The rest was easy by comparison. A light enduring motor, if available to the old time inventors, would have brought dynamic flight centuries ago. That only could have baffled Da Vinci, Cayley, Henson, Wenham and the long line of pioneer aviators. Eventually, of course, steam engines had come, endowed with ample power; but costly to build and wasteful to operate. The light automobile engine appeared in the latter nineties; promptly thereafter followed the dynamic flyer, the snow-winged herald of the twentieth century.