Chapter V - Gliding at Kitty Hawk
One must look at a map of North Carolina to get an idea of the isolation of the long strip of sandy beach that separates the Atlantic Ocean from Albemarle, Pamlico, and Roanoke Sounds. At the time the Wrights went there, no bridges connected this beach with any part of the North Carolina mainland or even with nearby Roanoke Island, site of Sir Walter Raleigh’s “Lost Colony.” At one point on the beach was the Kitty Hawk life-saving station, and alongside it a government weather bureau. About a mile back from the ocean was the hamlet of Kitty Hawk which, though it had a post office, was little more than a settlement, with only about a score of dwelling houses, most of them as widely scattered as in an ordinary farming community. Four miles south was the Kill Devil life-saving station.
It was not surprising that when Wilbur Wright, on September 9, 1900, reached Elizabeth City, North Carolina, the nearest railroad point to his destination, the first persons he chanced to ask about Kitty Hawk had never heard of the place. Then he met one Israel Perry, formerly a resident of Kitty Hawk, who lived the year round on his little flat-bottomed schooner. As no other boatman showed any interest in making the trip, Wilbur booked passage with “Captain” Perry, despite the boat’s dirty, forbidding appearance. After loading parts of the glider and other goods that had been shipped from Dayton, he set out with Perry on the morning of September 10 for the forty-mile voyage to Kitty Hawk. Wilbur noticed that the small boat they used to go from the wharf out to where the schooner was anchored was leaking badly and he asked if it was safe.
“Oh,” Perry assured him, “it’s safer than the big boat.” That didn’t inspire too much confidence in what was in store, and Wilbur soon learned that any misgivings he felt were amply justified. Toward the middle of the afternoon they met a strong head wind that forced them to seek a smooth water haven in North River where they anchored to await better weather. By that time Wilbur had worked up a good appetite; but he discovered that neither the food nor the kitchen met even minimum standards of cleanliness and he made excuses, as politely as he could, for not eating. All he had with him against hunger was a small jar of jelly his sister Katharine had slipped into his suitcase.
The weather was not favorable for continuing the voyage until the afternoon of the second day, and the boat reached a wharf, where there was a small store, on Kitty Hawk bay, at about nine o’clock that night. Not knowing where else to go, Wilbur stayed aboard until the next morning. A small boy named Baum agreed to guide him to the home of William J. Tate, about a quarter of a mile away. By the time Wilbur arrived there, on that morning of September 12, it was just forty-eight hours since he had tasted food other than his little supply of jelly.
After introducing himself, and in response to “Bill” Tate’s inquiries about how he enjoyed his trip, Wilbur spoke of his back being sore from lying on deck and how his arm ached from holding on when the boat rolled. Then it came out that he had been unable to bring himself to eat the food provided on the Perry schooner.
“You mean to tell me,” asked “Bill” Tate, greatly concerned, “that you’ve eaten no victuals for two days?”
Here was a situation that called for quick action in a hospitable home. It was after the Tates’ breakfast hour but Mrs. Tate soon had a fire in the kitchen stove and prepared a great platter of ham and eggs that the guest seemed to relish.
Then Wilbur inquired if it would be possible for him to obtain board and lodging there for the week or more until his brother “Orv” arrived.
Tate went into an adjoining room to ask his wife. As the door was ajar, Wilbur could hear what was said. Mrs. Tate was a bit alarmed. Here was a man able to devote time and money for weeks at a time to sport. Doubtless he must be a person of great wealth, accustomed to every luxury. Would he be satisfied with the best they could offer?
Wilbur stepped to the door, explaining that he could not help overhearing their conversation, and said it must be understood that if he were accepted as a paying guest he would not expect any extra frills, but would greatly appreciate the courtesy.
“This fellow’s a real gentleman,” thought Tate, and by way of settling the question, without waiting to hear any more from his wife, he said to Wilbur:
“You must be tired. Why don’t you come into our spare bedroom and take a nap?”
By the next day Wilbur was at work. The cloth covering for the glider – white French sateen of extra good quality – had already been shaped and sewed at Dayton, except at the ends, to permit fitting it over the framework. But now he had to make changes in the covering, because the glider was going to be smaller than originally planned. The longest timbers, for the wing spars, that he had been able to find in either Norfolk or Elizabeth City were only sixteen feet long instead of the eighteen-foot length he desired. Thus it was necessary to cut out strips from the middle of the lengths of cloth for both upper and lower wings. For resewing the cloth where necessary, Wilbur borrowed Mrs. Tate’s machine. But all the rest of the work of assembling the glider was done at a tent Wilbur set up, about half a mile from the Tate home, at a spot where there were a few trees and a view of the bay. He dragged the crates, containing various parts and tools, to the tent and hoped to have everything in readiness when Orville arrived. But the heat was intense, the job of carrying water to the camp used up much energy, and when Orville got there on September 28, Wilbur told him regretfully that much work on the glider was still to be done.
Orville’s trip had been uneventful. Indeed, though he came on a better boat than Israel Perry’s, he had struck such a calm sea that his voyage from Elizabeth City took two days, the same as Wilbur’s. For the first five days after Orville’s arrival, both brothers stayed at the Tate home. Then they established themselves in camp. One end of their tent, twelve by twenty-two feet, was tied to a tree for anchorage. The tree was headquarters for a mocking bird that sometimes joined in the harmony when Orville twanged at a mandolin he had brought from home.
Not many visitors came to the camp from near-by Kitty Hawk. One reason for this that the camp was considered dangerous after news got about that the Wrights used a gasoline stove. “Bill” Tate was favorably impressed, though with an acetylene lamp, intended for a bicycle, that the Wrights used for lighting. He said he had notion to install such a system of gas lighting in his house.
It was necessary to carry water about one thousand feet over the sand. Orville volunteered to do the cooking – and he continued to do so during all their experiments at Kitty Hawk. But he always felt that he had the better of the bargain, for the dish-washing job was Wilbur’s. As it was impossible to obtain fresh bread, Orville learned to make biscuits and without the use of milk. They were good biscuits, too – better, his father afterward insisted, than anyone else could make. To simplify operations, Orville always mixed at one time enough flour and other dry ingredients to last for several days, as biscuits had to be baked three times daily.
Working together, the brothers soon had the glider assembled. When completed it weighed about fifty-two pounds. Though the main spars were only sixteen feet long, the “bows” at the end of each wing surface bought the total span to 165 square feet instead of 200 as intended. A space eighteen inches wide at the center of the lower surface where the operator would lie, with feet over the rear spar, was left free of covering. The apparatus had no rear vanes or tail of any kind; but it had two important features never used by previous experimenters. One was the front rudder, or “elevator,” the rear edge of which was about thirty inches from the nearest edge of the wings; the other was the wing warping. By an ingenious arrangement of the trussing, the wings could be twisted into a helicoidal warp from one end to the other, thus exposing one wing to the air at a greater angle than the other. This was to be used for bringing the machine back to the level if it was tipped up sidewise by a gust of wind.
The Wrights’ first surprise at Kitty Hawk was that the winds were not what they had counted on. United States Weather Bureau reports had led them to think they would have winds of about fifteen miles an hour almost every day. But now it dawned on them that fifteen miles an hour was simply the daily average for a month. Sometimes the wind was sixty miles an hour, and the next day it would be entirely calm. It now began to look as if they might frequently have to wait a few days for suitable conditions, which meant that their experiments would require more time than they had expected.
Almost as soon as they began their trials of the glider, the brothers got another surprise. According to the Lilienthal tables of air pressure, their machine of 165 square feet needed a wind of only from seventeen to twenty-one miles an hour to support it as a kite with a pilot aboard. But they found that much stronger winds were needed to lift it. Since suitable winds would not be plentiful, their plan of practicing by the hour aboard the glider while flying it as a kite would have to be postponed. Instead, they flew it as a kite, loaded with about fifty pounds of chain, but with no man aboard. They held it with two ropes, and operated the balancing system by cords from the ground. Though the results were promising, inspiring confidence in the system of maintaining equilibrium, the brothers knew that only by actual gliding experience could they confirm what the kite experiments had indicated as being true.
One thing that puzzled them was that the machine appeared to be greatly deficient in lifting power as compared with calculated lift of curved surfaces of its size. In wondering what might be the cause of this wide discrepancy between expected and actual lifts, the Wrights considered the possibility it might be because the curvature of the wings was less than that used by Lilienthal. Or could it be that the cloth covering was too porous and permitted some of the lifting power of the wind to be lost? They wondered, too, if the Lilienthal tables they had followed, relating to air pressure on wind surfaces, could be in error.
They next determined to try gliding on the side of a hill. That meant toting their machine four miles south of their camp to a great sand dune about one hundred feet high, called Kill Devil Hill. On their first day at the hill, the wind was about twenty-five miles an hour. As they lacked previous experience at gliding they decided to wait for less of a blow to fourteen miles an hour, and they made about a dozen glides. “Bill” Tate was there and assisted them.
In making these glides, the machine was only two or three feet from the soft, sandy ground, and though the brothers repeatedly made landings while moving at a speed of twenty miles an hour, neither operator nor machine was harmed. The slope of the hill toward the northeast was about 9 ½ degrees, or a drop of approximately one foot in six. After moving at a rate of about twenty-five to thirty miles an hour with reference to the wind, or ten to fifteen miles over the ground, the machine, while keeping its course parallel to the slope, increased its speed, thus indicating that it could glide on a slope less steep.
Their control of the machine was even better than they had dared to expect. They got quick response to the slightest movement of the front elevator, which promised to be satisfactory in maintaining fore and aft balance. At first, they fastened the warping mechanism, to make it inoperable, and had only the elevator to manipulate, for they feared that, inexperienced as they were, if they tried to use both, then they might be unsuccessful with either. But even without the use of the warping mechanism it was possible to make glides of five to ten seconds before the sidewise tilt of the machine forced a landing. Before making the last three or four flights the Wrights loosened the warping wires to permit the sidewise control to be used.
When these experiments of 1900 ended, instead of the hours of practice in the air the Wrights had hoped to have, they had flown the machine as a kite with a man aboard barely ten minutes, and had had only two minutes of actual gliding.
Now that the experiments for that year were ended and they had no further use for the glider, the brothers weighed the machine with sand and left it on the hill. When “Bill” Tate saw that they were through with the glider he asked if he might have it, and they gladly gave it to him. Mrs. Tate used the sateen that covered the wings to make dresses for her two small daughters. She noted that it appeared to be unusually good fabric, more closely woven and better than she had seen in the stores. Some of her neighbors, when they saw the dresses she made of it, remarked that it seemed too bad to use such excellent material on a kite.
Though the amount of practice was less than they had expected, all the Wrights learned in that season of 1900 seemed to confirm the correctness of certain opinions held at the beginning. Their method of warping or twisting the wings to maintain lateral balance was better than dependence on either the dihedral angle or shifting the weight of the operator; better than any method yet tried. And their front elevator had been highly satisfactory as a means for directing the machine up and down. Before leaving Kitty Hawk they decided that their next experiments would be with a glider large enough to be flown as a kite, with an operator aboard, in winds ordinarily to be counted on.
When the brothers set to work on their glider for the experiments of 1901, they decided to make it of the same general design as the first one, and with the same system of control. But they carried out their plan to give it considerably more area, to provide greater lifting power. Another change they made was to increase the curvature of the wings to conform to the shape on which Lilienthal had based his tables of air pressures. It had wings of about seven-foot chord (the straight line distance between the front and rear edges) with a total span of twenty-two feet, and weighed ninety-eight pounds. After a section twenty inches wide had been removed from the middle of the lower wing, and the rear corners of the wings rounded off, the total lifting area was 290 square feet, as compared with 165 in the previous glider. The front elevator, with its rear edge about two and one half feet away from the front edge of the wings, had a four-and-one-half foot chord and an area of eighteen square feet.
This was a much larger machine than anyone had ever tried to fly. The Wrights knew it could not be controlled simply by shifting the pilot’s weight, as others had done, but they had faith in their own operable front elevator and believed they could manage it. If their calculations were correct, it would be supported in a wind of seventeen miles an hour, with the wing surfaces at an “angle of incidence” of only three degrees. (“Angle of incidence,” now more often called “angle of attack,” has been defined as the angle at which the plane presents itself to the air in advancing against it.)
As it would be impractical to keep so large a machine with them in the tent, as they had done with the smaller glider, the brothers built near Kill Devil Hill a rough frame shed, twenty-five feet long, sixteen feet wide, and seven feet high at the eaves. Both ends of the building except the gable parts were made into doors, hinged above. When open, doors provided an awning at each end of the building. For living quarters they still used a tent. By driving a pipe ten or twelve feet into the sand they got a water supply.
Though the great stretch of sandy waste seemed too desolate for anyone to bother about owning, yet it was all under the ownership of one person or another and the Wrights took the precaution to obtain permission to erect their buildings.
This year they were to have company in camp. Octave Chanute, with whom they had been in correspondence for about a year, stopped in Dayton in June, 1901, at their invitation, to get better acquainted. When he learned that the Wrights had carried on their experiments in 1900 without the presence of a doctor in camp, and were intending to do so again, he told them he thought that was too risky, considering the kind of work and the isolation of the experiment ground. He said he knew a young man in Coatesville, Pennsylvania, George A. Spratt, “an amateur” in aeronautics, who had some medical training. Spratt had never seen any gliding experiments, and Chanute thought he would be eager for the opportunity. If the Wrights would board him at camp, Chanute said, he would be glad to pay Spratt’s traveling expenses to Kitty Hawk and would consider himself “compensated by the pleasure given to him.” Chanute also proposed that they have in camp with them E. C. Huffaker, of Chuckey City, Tennessee, who was building a glider that Chanute was financing, and the Wrights consented. Thus there were four regularly in camp that season, and for a time Chanute himself was with them as a guest.
The new machine was completed and ready for trial on the afternoon of July 27. Since it was designed to be flown in a wind of seventeen miles, and there was but thirteen miles of wind on that way, the brothers took the machine to the big Kill Devil Hill for its first trial. After five or six short turning-up flights they made a glide of 315 feet in nineteen seconds. Although several flights on this first day of experiments in 1901 exceeded the best made the year before, yet it was soon evident that in several respects the machine was not as good as the first one. It was found that the wings with a camber of one to twelve – the camber recommended by Lilienthal, and used by Chanute and others – was not so good as the camber of one to twenty-two, used by the Wrights in 1900. (Camber of one to twenty-two means that the length of the chord, the straight-line distance between the front and rear edges of the wings, is twenty-two times the distance from the chord to the deepest part of the wing curve.) This was demonstrated by the fact that the 1901 machine could not glide on a slope as nearly level as had the earlier machine. The Wrights found, too, that a machine with wings of one to twelve camber was not so easily controlled fore and aft as when the wings were of one to twenty-two camber. They decided therefore to reduce the camber of the wings to make them more like the earlier machine. When they resumed their gliding, after the camber had been reduced (one to eighteen), the control of the machine appeared to be good as it was the year before, and they then made flights in winds of twenty-two to twenty-seven miles an hour, without accident. Though most of these flights the lateral control was highly effective, in a few others – the wing warping appeared to have no effect at all.
The Wrights now made the discovery that in free flight, when the wing on one side of the machine was presented to the wind at a greater angle than that on the other side, the wing with the greater angle, instead of rising as it was expected to do, sometimes descended. The explanation was that the greater angle of the wing at one side gave more resistance to forward motion and thus reduced the speed on that side. This decrease in speed more than counter-balanced the effect of the larger angle of the wing in producing lift. (The Wrights had not discovered when flying the glider as a kite, because, when held by ropes, the wing always maintained equal air speeds, even when their resistances were unbalanced.)
It was evident to the brothers that their present method of controlling equilibrium was not yet complete. Something was needed to maintain equal speeds at the two wing tips. The idea occurred to them that the addition of a vertical fin attached to the machine at some distance in the rear of the wings might be the solution of the problem. But the test of such a fin had to be left until another season.
The behavior of the glider in these various flights forced the Wrights to give thought to another scientific problem, that regarding the center of air pressure on curved surfaces. Contrary to the teachings of scientific books on the subject, it was becoming more and more evident that the travel of the center of pressure on a cambered surface is not always in the same direction as the travel on a plane surface. When the angle of attack on a plane surface is decreased, the center of pressure moves toward the front edge; but on a cambered surface this is true only when larger angles are being decreased. When the angle of attack on a cambered surface is decreased from, say, thirty degrees to twenty-five degrees, the center of pressure moves forward, as it does on a plane surface; but when a certain angle (between twelve and fifteen degrees) is reached, then the movement of the center of pressure moves toward the rear so long as any further decrease is made in the angle of attack. The Wrights proved this by a series of experiments with a single surface from their plane. Knowledge of the phenomenon of this reversal of center of pressure was of great importance to them in their later work of designing aeroplanes.
Scientific problems were not the only ones to perplex the Wrights. A sore trial were the mosquitoes and sandfleas, particularly numerous and aggressive in that summer of 1901. As Orville Wright recalled in later years, there were times when he thought while fighting mosquitoes through the night, that if he could just survive until morning he would pack up and return home. Those mosquitoes might have caused a long postponement of the conquest of the air.
By the time they left Kitty Hawk on August 20, the brothers had satisfied themselves that a glider of large surfaces could be controlled almost as easily as a smaller one, provided the control is by manipulation of the surfaces themselves instead of by movements of the operator’s body. So far as they knew, judging from figures previously published, they had broken all records for distance in gliding. Chanute, who had witnessed part of the 1901 experiments, insisted that the results were better than had ever been attained before. All that was encouraging. But, on the other hand, if most of the supposedly scientific information available was worthless, then their task was even more formidable than they had expected. With no dependable previous knowledge to guide them, who were they to determine how man should fly? Wilbur seemed much discouraged. Possibly he had entertained hopes of actually flying, though he had always disclaimed having such an idea. He was ready to drop the experiments altogether. On the way home, Wilbur declared his belief: Not within a thousand years would man ever fly!
Chanute urged the brothers not to drop their experiments, arguing that if they did it would be a long time before anyone else would come as near to understanding the problem of how to work toward its solution. Without knowing it, Chanute made a great contribution to aviation history, for the Wright brothers heeded his repeated admonitions against ceasing their efforts. Without the proddings of Chanute they might not have gone on.
Chanute performed another great service for aeronautics when he, as president of the Western Society of Engineers, invited Wilbur Wright to address that body at a meeting in Chicago, September 18, 1901, on the subject: Some Aeronautical Experiments.
Wilbur shrank from the idea of making such a talk and would hardly have done so except to oblige his friend. He cautioned Chanute, though, not to make the speech a prominent feature of the program, because, he said, he made no pretense of being a public speaker. Chanute did nevertheless plan to use the announcement of the talk as a means to help make the meeting to be a big success. He wanted to know if it would be all right to make the occasion “Ladies’ Night.” Wilbur decided he would already be as badly scared as a man could be and the presence of women would not make the situation much worse. But he insisted on one thing, that he must not be expected to appear in formal evening dress.
In this speech Wilbur boldly declared that the best sets of figures obtainable regarding air pressure against airplane surfaces appeared to contain many serious errors. Orville, at the shop in Dayton, was a little alarmed about that part of the speech. What if something about their own work had been wrong and the figures compiled by various scientists should finally be proved correct? Certainly it was no small responsibility for anyone so little known as Wilbur or he to denounce publicly the work of eminent scientists, dignified by preservation in books long regarded as authoritative. It would be both presumptuous and risky to brand supposedly established facts as untrue unless the person doing so could be unassailably sure of his ground.
In this cautious state of mind Orville rigged up a little wind-tunnel for the purpose of making a series of tests. This tunnel consisted simply of what appeared to be an old starch box, not more than eighteen inches long, that was lying in the shop. In it he placed a hastily constructed apparatus, a main part of which was simply a metal rod pivoted in the manner of a weather vane. Without attempting to give technical details of the method used, it may be said that a curved surface was balanced against a plane surface in an air current passing though the box. As Orville had provided the box with a glass top he could measure the angles to the wind at which the curved surface and the plane surface of equal area produced equal pressure.
The experiments with this crude apparatus lasted only one day. They were conclusive enough so far as they went, indicating errors in published figures relating to air pressure on curved surfaces. But as Orville was later to learn, the published errors were greatest in regard to wing surfaces set at a small angles, such as would be used in flying, and he had tested thus far only larger angles. With the tests thus incomplete, Orville and Wilbur decided on the latter’s return from Chicago, that it might be prudent to stay on the safe side and omit from the published record of Wilbur’s speech the more severe part of his criticism of available figures. They would wait until further wind-tunnel experiments could give more detailed knowledge. Consequently, when Wilbur’s speech appeared in the December, 1901, issue of the Journal of the Western Society of Engineers, it was a bit less startling than the one he had actually delivered – though, even after the deletions, there still remained strong hints that accepted tables of figures might be wrong. And the record of the speech was treated as of great importance. It has probably been reprinted and quoted as often as any other article ever written on the subject of flying.
The Wrights were not sure they would ever build another glider. But their curiosity, their passion for getting at truth, had not been too much aroused for them to quit studying the problem of air pressures. They decided to build another wind-tunnel, less crude than the one Orville had hastily used, of an open-ended box about sixteen inches square on the inside by six feet long. In one end would come a current of air and the draft thus created would be “straightened,” as well as made uniform, by having to pass through a set of small pigeon-holes. It would have been a great convenience to use an electric fan for sending the air into the tunnel. But the Wrights had no electric current in their shop – still lighted by gas – and the fan was driven by a one-cylinder gas engine they had previously made. They attached the fan to a spindle that had held an emery wheel. A new measuring device, or balance, was built of wire intended for bicycle spokes, and pieces of hacksaw blades. These experiments were now done with much more refinement than as first, and the measurements were for both “lift” and “drift.” But as each curved surface measured was balanced against the pressure on a square plane, exposed at ninety degrees to the same air current, it was not necessary to know the precise speed of the air current.
During that autumn and early winter of 1901, the brothers tested in the wind-tunnel more than two hundred types of wing surfaces. They set these at different angles, starting with the angle at which the surface begins to lift, and then at 2 ½ degree intervals, up to twenty; and at five degree intervals up to forty-five degrees. They measured monoplane, biplane, and triplane models; also models in which one wing followed the other, as used by Langley in his experiments. They measured the lift produced by different “aspect ratios” – that is, the ratio of the span of the wing to its chord. They found that the greater the span in proportion to the chord the more easily the wing may be supported. They measured thick and thin surfaces. One surface had a thickness of nearly one-sixth of its chord.
Among other things, these experiments proved the fallacy of the sharp edge at the front of an airplane wing and the inefficiency of deeply cambered wings as then generally advocated by others. Sometimes they got a result so unexpected that they could hardly believe their own measurements – as, for example when they discovered that, contrary to all previously published figures by students of the subject, a square plane gave a greater pressure when set at thirty degrees than at forty-five degrees.
These wind-tunnel experiments in the bicycle shop were carried on for only a little more than two months, and were ended before Christmas, 1901. The Wrights discontinued them with great reluctance; but, after all, they were still in the bicycle business, still obliged to give thought to their means for earning a living, and with no idea that this scientific research could ever be financially profitable. In those few weeks, however, they had accomplished something of almost incalculable importance. They had not only made the first wind-tunnel in which miniature wings were accurately tested, but were the first men in all the world to compile tables of figures from which one might design an airplane that could fly. Even today, in wind-tunnels used in various aeronautical laboratories, equipped with the most elaborate and delicate instruments modern science can provide, the refinements obtained over the Wrights’ figures for the same shapes surfaces are surprisingly small. But it is doubtful if the difficulties and full values of the Wrights’ scientific researches within their bicycle shop are yet appreciated. The world knows they were the first to build a machine capable of sustained flight and the first actually to fly; but it is not fully aware of all the tedious, grueling scientific laboratory work they had to do before flight was possible. Important as was the system of control with which the Wrights’ name has been connected, it would not have given them success without their wind-tunnel work which enabled them to design a machine that could lift itself.
The Wrights had a double reason for making sure of their figures. With little money to spend on a hobby, it was much cheaper to rectify mistakes on paper than after the idea was put into material form. They knew that if they should decide to go on to further gliding attempts, they could not afford to spend much more on apparatus built according to unreliable data.
After compiling their own tables of figures, the Wrights gave copies of them to their friend Chanute and others interested in the problem of aerodynamics. Chanute well knew that the Wrights now had knowledge of aeronautics far beyond that of anyone else in the world, and he felt that for them to go on with their experiments was almost a duty. He much regretted, in the interest of science, he said, that they had reached a stopping-place, for he was sure further experiments on their part promised “important results.”
Chanute might well have felt pride in the effectiveness of his insistence that the Wrights should go on experimenting, as well as in the results of his invitation to Wilbur to make that Chicago speech. Except for that speech and its daring statements that Orville thought needed more confirmation, there probably would have been no wind-tunnel experiments marked one of the great turning points in the long history of attempts at human flight.
It still remained for the Wrights to put their new knowledge to actual test in gliding, and they set out on August 25, 1902, for their third stay at Kitty Hawk. But not until September 8, were they able to begin the work of assembling their new glider, for the camp, battered by winter gales, needed much repairing; and they decided to build an addition to it for living quarters. They did not have their machine for its first trial until September 19.
This new glider was of not much greater lifting area than that of the previous year, though the wing span had been increased from twenty-two to thirty-two feet. But since the wind-tunnel experiments had demonstrated the importance of the “aspect ratio,” the total span was now about six times the chord instead of three. One minor change also may be noted. In the earlier gliders, the wing-warping mechanism had been worked by movement of the operator’s feet; but now in this 1902 glider it was done by sidewise movement of one’s hips resting on a “cradle.” The most noticeable change was the addition of a tail, consisting of fixed twin vertical vanes, with a total area of a trifle less than twelve square feet. Its purpose was to correct certain difficulties encountered in some flights with the 1901 machine. When the wing surface at the right and left sides were warped to present different angles toward the wind, the wing that had the greater angle, and therefore the more resistance, tended to lag behind, and then the slower speed offset what otherwise would have been the greater lifting power of that wing. The tail was expected to counter-balance that difference in resistance of the wing tips. If the wing on one side tended to swerve forward, on a vertical axis, then the tail, more exposed to the wind on that same side, should, it was thought, stop the machine from further turning.
Entirely apart from any advantages to be gained from the use of the tail, the first trials of the new machine were highly encouraging for another season. It was soon evident that by disregarding all tables of air pressure used by their predecessors and building according to the figures obtained from their wind-tunnel experiments, the Wrights had made a big advance toward flight. Because of the knowledge they now had, not possessed by any previous experimenter, of how the wings should be shaped, this 1902 machine was of just about twice the “dynamic efficiency” of any other glider ever built; it could have been flown with probably less than half the power required for any other glider.
In this amazing machine they could even beat the birds. They measured the angle with reference to the horizontal, at which the hawks soared, and saw that they themselves could glide at a smaller angle – as small as 5-1/3 degrees; the best the hawks could do was 6 degrees.
Altogether the Wrights made more than one thousand gliding flights in September and October 1902. Several glides were of more than six hundred feet, and a number were against a thirty-six-mile-an-hour wind. No previous experimenter had ever dated to try gliding in so stiff a wind. That the Wrights were successful of such feats gave proof of the effectiveness of their devices for control. Some of their flights lasted more than a minute and at times it was possible to soar in one spot without any descent. So impressive were such exhibitions that Bill Tate’s brother Dan solemnly offered the opinion: “All she needs is a coat of feathers to make her light and she will stay in the air indefinitely.”
About one time in fifty, however, the machine behaved in a manner quite mysterious. It would turn up sidewise and come sliding to the ground in spite of all the warp the operator could give to the wing tips. At one trial the lateral control would work perfectly and then the next time, under conditions that seemed to be about the same, it was impossible to prevent one wing end from striking the sand with a kind of spinning movement that the brothers called “well-digging.”
This new problem, that had not occurred in their previous gliders, came from the fact that the machine had a tail. Those “well-digging” accidents were tailspins – though that term did not come into use until several years afterward. But even after it was evident that the tail had something to do with the machine’s peculiar behavior, neither brother was prepared to explain why. Then one night Orville drank more of his customary amount of coffee. Instead of going to sleep as usual the moment he got into bed, he lay awake for several hours. Those extra cups of coffee may have been important for the future of practical flight for, as he tossed about, he figured out the explanation of the phenomenon caused by the tail. Here it is, as he eagerly gave it to Wilbur, and to their brother Lorin, who was visiting them, at breakfast the next morning:
When the machine became tilted laterally it began to slide sidewise while advancing, just as a sled slides downhill or a ball rolls down an inclined plane, the speed increasing in an accelerated ratio. If the tilt happened to be a little worse than usual, or if the operator were a little slow in getting the balance corrected, the machine slid sidewise so fast that this movement caused the vertical vanes to strike the wind on the side toward the low wing instead of on the side toward the high wing, as it was expected to do. In this state of affairs the vertical vanes did not counteract the turning of the machine about a vertical axis, caused by the difference of the warped wings on the right and left sides; on the contrary, the vanes assisted in the turning movement, and the result was worse than if there were no fixed vertical tail.
If his explanation was sound, as Orville felt sure it was, then, he said, it would be necessary to make the vertical tail moveable, to permit the operator to bring pressure to bear on the side toward the higher wing. (This is the form of the Wright system of control that came into general use – the independent control of aileron and rudder.)
Wilbur promptly saw that the explanation was probably correct and nodded approvingly. And he immediately made a suggestion. A particular relation existed, he said, in the desired pressures on the tail, no matter whether the trouble was due to difference of resistance of the wing tips or on account of sliding. Whatever the reason, it was desirable to get rid of the pressure on the side of the low wing, to which a greater angle of incidence must be imparted in restoring lateral balance, and bring pressure on the side of the tail toward the high wing where there must be a reduced angle. So why not have the mechanism that controlled the wing warping and that which moved the tail operated in conjunction? Then the pilot, instead of having to control three things at once, would need to attend to the front elevator and the wing-warping device. The brothers at once attached the wires controlling the tail to those that warped the wings – and they also changed the tail from two vertical fins to a single vertical rudder.
After the changes in the 1902 glider, the Wrights had their machine in about the form pictured and described in the drawings and specifications of their patent, applied for on the 23rd of the next March.
With all their accurate data for making calculations, and a system of balance effective in winds as well as in calms, the brothers believed that they now could build a successful power-flyer.
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