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How We Invented the Airplane
by ORVILLE WRIGHT
OUR FIRST INTEREST [in the problem of flight] began when we were children. Father brought home to us a small toy actuated by a rubber string which would lift itself into the air. We built a number of copies of this toy, which flew successfully.... But when we undertook to build a toy on a much larger scale it failed to work so well. The reason for this was not understood by us at the time, so we finally abandoned the experiments. In 1896 we read in the daily papers, or in some of the magazines, of the experiments of Otto Lilienthal, who was making some gliding flights from the top of a small hill in Germany. His death a few months later while making a glide off a hill increased our interest in the subject, and we began looking for books pertaining to flight. We found a work written by Professor Marey on animal mechanism which treated of the bird mechanism as applied to flight, but other than this, so far as I can remember, we found little.
In the spring of 1899 our interest in the subject was again aroused through the reading of a book on ornithology. We could not understand that there was anything about a bird that would enable it to fly that could not be built on a larger scale and used by man. At this time our thought pertained more particularly to gliding flight and soaring. If the bird's wings would sustain it in the air without the use of any muscular effort, we did not see why man could not be sustained by the same means. We knew that the Smithsonian Institution had been interested in some work on the problem of flight, and, accordingly, on the 30th of May 1899, my brother Wilbur wrote a letter to the Smithsonian inquiring about publications on the subject. Several days later we received a letter signed by R. Rathbun, assistant secretary.
Among the reprints of the Smithsonian sent to us and mentioned in the letter was the Problem of Flying and Practical Experiments in Soaring, by Otto Lilienthal; Story of Experiments in Mechanical Flight, by S. P. Langley; and, I think, a paper by Pettigrew, as well as a copy of Mouillard's Empire of the Air. We sent for copies of Chanute's Progress in Flying Machines, Langley's Experiments in Aerodynamics, and the Aeronautical Annuals of 1895, 1896, and 1897. On reading the different works on the subject we were much impressed with the great number of people who had given thought to it—among these some of the greatest minds the world has produced. But we found that the experiments of one after another had failed. Among these who had worked on the problem I may mention Leonardo da Vinci, one of the greatest artists and engineers of all time; Sir George Cayley, who was among the first of the inventors of the internal-combustion engine; Sir Hiram Maxim, inventor of the Maxim rapid-fire gun; Parsons, the inventor of the turbine steam engine; Alexander Graham Bell, inventor of the telephone; Horatio Phillips, a well-known English engineer; Otto Lilienthal, the inventor of instruments used in navigation and a well-known engineer; Thomas A. Edison; and Dr. S. P. Langley, secretary and head of the Smithsonian Institution. Besides these there were a great number of other men of ability who had worked on the problem. But the subject had been brought into disrepute by a number of men of lesser ability who had hoped to solve the problem through devices of their own invention which had all of them failed, until finally the public was led to believe that flying was as impossible as perpetual motion. In fact scientists of the standing of Guy-Lussac, the great French scientist and engineer, and Professor Simon Newcomb, one of the greatest of the American scientists and mathematicians, had attempted to prove that it would be impossible to build a flying machine that would carry a man. Admiral Melville, chief engineer in the United States Navy, a little later, in 1901, or 1902, published an article in which he pointed out the difficulties of building a flying machine to carry a man, and stated that the first flying machine would be more expensive than the most costly battleship.
After reading the pamphlets sent to us by the Smithsonian we became highly enthusiastic with the idea of gliding as a sport. We found that Lilienthal had been killed through his inability to properly balance his machine in the air. Pilcher, an English experimenter, had met with a like fate.
We found that both of these experimenters had attempted to maintain balance merely by the shifting of the weight of their bodies. Chanute, and I believe all the other experimenters before 1900, used this same method of maintaining the equilibrium in gliding flight. We at once set to work to devise a more efficient means of maintaining the equilibrium....
The first method that occurred to us for maintaining the lateral equilibrium was that of pivoting the wings on the right and left sides on shafts carrying gears at the center of the machine, which, being in mesh, would cause one wing to turn upward in front when the other wing was turned downward. By this method we thought it would be possible to get a greater lift on one side than on the other, so that the shifting of weight would not be necessary for the maintenance of balance. However, we did not see any method of building this device sufficiently strong and at the same time light enough to enable us to use it.
A short time afterward, one evening when I returned home with my sister and Miss Harriet Silliman, who was at that time a guest of my sister's in our home, Wilbur showed me a method of getting the same results as we had contemplated in our first idea without the structural defects of the original. He demonstrated the method by means of a small pasteboard box, which had ... the opposite ends removed. By holding the top forward corner and the rear lower corner of one end of the box between his thumb and forefinger and the rear upper corner and the lower forward corner of the other end of the box in the like manner, and by pressing the corners together, the upper and lower surface of the box were given a helicoidal [spiral ] twist, presenting the top and bottom surfaces of the box at different angles on the right and left sides.
From this it was apparent that the wings of a machine of the Chanute double-deck type, with the fore-and-aft trussing removed, could be warped in like manner, so that, in flying, the wings on the right and left sides could be warped so as to present their surfaces to the air at different angles of incidence and thus secure unequal lifts on the two sides....
We began the construction of a model embodying the principle demonstrated with the paper box within a day or two. This model consisted of superposed planes each measuring five feet from tip to tip and about thirteen inches from front to rear. The model was built and, as I remember it, was tested in the latter part of July 1899.... I was not myself present....
[Experiments with this five-foot apparatus, more a model glider than a kite, were confined to one day.]
According to Wilbur's account of the tests, the model worked very successfully. It responded promptly to the warping of the surfaces, always lifting the wing that had the larger angle. Several times ... when he shifted the upper surface backward by the manipulation of the sticks attached to flying cords, the nose of the machine turned downward as was intended, but in diving downward it created a slack in the flying cords, so that he was not able to control it further. The model made such a rapid dive to the ground that the small boys present fell on their faces to avoid being hit, not having time to run....
We felt that the model had demonstrated the efficiency of our system of control. After a little time we decided to experiment with a man-carrying machine embodying the principle of lateral control used in the kite model already flown. From the tables of Lilienthal we calculated that a machine having an area of a little over 150 square feet would support a man when flown in a wind of sixteen miles an hour. We expected to fly the machine as a kite and in this way we thought we would be able to stay in the air for hours at a time, getting in this way a maximum of practice with a minimum of effort. In September of 1900 we went to Kitty Hawk, North Carolina, and there assembled the machine, most of the parts of which we had made at Dayton.
From the United States Weather Bureau reports we had found that Kitty Hawk was one of the windiest places in the country, and that during the month of September it had an average wind in the neighborhood of 16 miles an hour. We wrote to the Weather Bureau man at the Kitty Hawk station, telling him of the nature of the experiments we wished to conduct and asking him in regard to the suitability of the ground in that neighborhood. We received a very favorable report from him, and also from the postmaster at Kitty Hawk, to whom he had shown our letter.
[The machine] had two superposed surfaces measuring eighteen feet from tip to tip and about five feet from front to rear. The surfaces were spaced five feet apart and were connected at the extreme forward edge by six upright posts, and at about one foot from the rear edge by another row of uprights or struts. The struts were connected to the surfaces by means of flexible joints. The ribs were made of thin strips of ash, slightly bent near their forward extremities. These ribs were bound to the forward spar on the spar's upper side, so that the spar and curvature given to the ribs produced a [wing] curvature of about one-eighteenth to one-twentieth of the chord [the straight-line distance from front to rear edge of wing]. The spars were enclosed in a sheath formed by sewing a strip of cloth over them, resulting in the elimination of all sharp angles or corners. The ribs were enclosed likewise.
Both the forward and the rear rows of uprights were trussed by wires much like the Chanute glider. The machine thus had two systems of rigid trusses laterally; but, unlike the Chanute machine, it was not rigidly trussed from front to rear. On the contrary, a flexible cable was connected to the upper surface at the extreme outer upright in the rear, passed diagonally downward through a pulley on the lower surface at the outermost forward upright, thence across to a pulley in a corresponding position on the lower plane on the opposite side of the machine, and then diagonally upward to a connection to the upper surface at the outermost rear upright. Another flexible cable was attached to the upper surface at its forward edge at the outermost upright on the one side, passed diagonally downward and backward and crossing the first-mentioned flexible cable to a pulley at the rear of the lower surface, then across to a pulley at the rear of the lower surface at the opposite side, and then up to the connection of the forward upright to the upper surface. A cradle in which the operator lay was connected to the cable running along the forward edge of the lower surface, so that when the cable was pushed to the right the upper rear corner of the machine was pulled downward and forward and the corresponding part on the opposite side of the machine was allowed to move upward and rearward. In this manner a helicoidal warp was imparted to the surfaces.
In order to circle to the left, we moved the cradle slightly to the left, thus turning the tail slightly to the left and imparting an increased angle to the right wing and a smaller angle to the left wing. This caused the machine to tilt so that the left wing was lower than the right wing, which, of course, in turn, caused the machine to slide somewhat to the left. This side movement of the machine tended to cause the vertical rudder to strike the air at a greater angle than was necessary to compensate for the difference in resistance of the right and left wings.
This tendency caused the tail to lag behind in this lateral movement just as the feather of an arrow causes the feathered end to lag behind when the arrow is dropped sidewise. Thus the lateral movement of the main aeroplane sidewise, as the result of tipping, became combined with the rotary movement about its vertical axis, due to the vane-like action of the tail, and the machine proceeded on a circular course. But as the speed of the outside wing increased, and that of the inside wing decreased, by reason of the fact that the inner wing was traveling in a smaller circle than the outside wing, there was a tendency to tilt too much and this was corrected by gradually moving the cradle toward the high wing, thus increasing the angle on the low wing and decreasing the angle of the high wing and also setting the rudder over toward the high wing. This was done gradually, but only sufficiently to prevent the low wing from sinking lower and not enough to bring it back to the level. The machine then continued to circle to the left, with the vertical tail set over somewhat to the right, so that the machine turned in the opposite direction to that in which a ship would have turned with the ship's rudder set over to the right.
When it was desired to stop circling, a sudden movement of the cradle toward the high side gave the wings an increased warp and brought the machine up to the level. Then on setting the cradle back to its central position, thus restoring the wings and tail to their central positions, the machine proceeded in a straight line, with the wings level.
The horizontal rudder, or elevator, was attached to a framework about four feet forward of the lower main plane. This elevator was pivoted about one-third back from its front edge. To the forward edge of the elevator were attached two springs which extended horizontally forward to the framework which supported the elevator. The rear edge of the elevator could be raised or lowered by means of two arms extending from the operator and connecting to the rear edge of the elevator through links. Thus when the rear edge of the elevator was raised, the springs referred to prevented the front edge from moving downward to a like angle, and as a result a curvature was given to the elevator on its upper side. When the rear edge of the elevator was moved downward a curvature on the under side was produced....
We attempted to fly the machine as a kite with a man on board a number of times, but were successful in keeping it up only when the wind was about twenty-five miles or more an hour. It failed to perform in lifting as had been calculated from the Lilienthal tables of air pressure. However, when flown in the strong winds, it responded promptly to the warping of the wings, so that the side with the greater angle would rise above the side with the lower angle and the machine would go sidling off toward the lower side, but the low side was brought up again by reversing the angles of the wing tips.
We also made a number of tests of it flown without an operator in which we attempted to measure the lift, the drift, and the center of pressure.
Before leaving camp for the year we carried it to the Kill Devil Hill, four miles from Kitty Hawk, and made about a dozen free flights, gliding down the side of the hill on the air.... The experiments were concluded near the end of October....
Although we were highly pleased with the performance of the machine, in so far as lateral control was concerned, we were disappointed with its lifting ability. We did not know whether its failure to lift according to the calculations made previous to our going to Kitty Hawk was due to the construction of our machine, or whether the tables of air pressure, at that time generally accepted, were incorrect. As a result we wrote to Mr. Chanute soon after our return from Kitty Hawk, giving him an account of the experiments just made, and asking his opinion as to the cause of the failure of the machine to lift, according to calculations. He suggested that it might have been due to the peculiar shape of wing curvature which we had used, and recommended that if we took up experiments again we use ribs having curvature used by Lilienthal....
In order to try to satisfy our own minds as to whether the failure of the 1900 machine to lift according to our calculations was due to the shape of the wings or to an error in the Lilienthal tables, we undertook a number of experiments to determine the comparative lifting qualities of planes as compared with curved surfaces and the relative value of curved surfaces having different depths of curvature. This was done by mounting the two surfaces to be compared at the extremities of the arms of an acute V-shaped structure made of wood. The V was pivoted on a vertical bearing at its point, the V lying in a horizontal plane. The surfaces were mounted vertically on the V, with their lifts opposed to each other. In this way we attempted to determine which had the greater lift by the amount one surface could push the other from the normal position. The surfaces while so mounted were exposed to the wind. The experiments were so crudely carried out that close measurements were not possible. But the results of these experiments confirmed us in the belief already formed that the accepted tables of air pressure were not to be altogether relied upon.
Excerpted from How We Invented the Airplane by Orville Wright, Fred C. Kelly. Copyright © 1988 Dover Publications, Inc.. Excerpted by permission of Dover Publications, Inc..
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Posted February 13, 2014