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Aviation History
1928
1928 - 1159.PDF
DECEMBER 20, 1928 " At Kitty Hawk (which took these young enthusiasts two or three days to reach from Dayton, Ohio), they found that in a wind of 25 m.p.h. the machine flew at an angle of about 20° ; and in order to fly the machine as a kite at small angles, they had to fly it"without an operator on board and manipulate the controls by cords from the ground. They made a long series of actual measurements of lift and drift of the machine under various loads. These were probably the first full-scale measurements taken of lift and drift, and revealed the first discrepancies in existing tables, the lift being far less than they had been led to expect. They assumed that the depth of curvature of 1 in 22 was insuffi- cient, and they decided that the second glider which they intended to build in the winter at Dayton, and take to Kitty Hawk the following summer, should have the recognised Lilienthal curve of 1 in 12. " Owing to the difficulty of flying the machine as a kite with one of them on board, they took the machine to Kill Devil Hill, which rises from the flat sand to a height of more than 100 ft., and they made short glides lying full length on the lower wing in order to save head resistance. The slope of the hill was a drop of 1 in 6. " The following year they brought their second glider to 27 m.p.h. They were, however, unable to fly the machine as a kite with the operator on it, owing to the poor lift, in spite of the fact that the second glider was nearly twice the area of the first. "They discovered, on this second glider, that the pressure was inclined forward of the perpendicular, and this confirmed Lilienthal's discovery ; but the measurements for lift and drift observed by the Wrights differed greatly from those given by Lilienthal. " They also discovered that their method of lateral balance, by changing the angle of the tips of the wings, acted in the reverse manner when gliding to the way in which it acted when flying as a kite. "On September 18, 1901, Wilbur read his classic paper before the Western Society of Engineers. All their work up to that time is described in that paper with the clearness and accuracy only possible from the pen of a master scientist. So clearly is their work set out, that the paper has been used to show that the Wrights published their invention of warping control before applying for their patent, and were therefore entitled to no reward. " Having discovered, contrary to the teaching of the books, that the centre of pressure of a curved surface travelled back- m m Mr. Wilbur Wright flying one of the early Wright biplanes —the first practi- cal development of the 1903 Kitty Hawk experi- mental machine —at Le Mans, in August, 1908. Efi m m m m m Kill Devil Hill. The new machine was 308 sq. ft., and the camber of the wings was the Lilienthal curve of 1 in 12. On the first glide the machine turned downwards and landed after going only a few yards. On successive glides the operator lay farther and farther back on the machine until, after several short glides, the machine flew on an undulating glide for 300 ft. No one save the operator knew that it required all the power of the elevator to keep the machine from diving or running high up into the air and then stalling. "After several very dangerous glides of this character, they came to the conclusion that the trouble was due to the deep curvature, 1 in 12, and it was suspected that this induced a reversal of the centre of pressure at small angles. To test this, they took the upper surface off the machine and attached it by two cords to its front edge. They then found that in a light wind, the surface flew at a large angle ; in a moderate wind it flew straight; and in a strong wind it pointed down- wards. This confirmed their suspicion that the centre of pressure travelled backwards when the angle-became small, and would produce diving unless sufficiently guarded against. They therefore rebraced the surfaces so as to restore the original curve of 1 in 22. With this curve they now suc- ceeded in making a large number of glides in winds up to wards when the surface was inclined at small angles, and that measurements and formula; published by different investigators were contradictory, they found it necessary to test everything for themselves." Up to this time, they had taken up" flying mostly as a sport : now they entered upon the serious scientific side of it. " A wind tunnel was built in which they tested about 50 various shaped model surfaces at intervals of 2|°, and they made tables of all the measured results. The third glider was constructed by calculation from these tables. " In the autumn of 1902, this third glider was taken to Kill Devil Hill, where they made nearly 1,000 gliding flights, several of which covered distances of over 600 ft. " On this machine a vertical rudder was installed, adjusted simultaneously with the warping of the wings, so that by automatically" turning the rudder towards the side of the machine where the wing was at the greatest angle, the warping was made to function correctly, both when gliding and when flying as a kite. " They now returned home to Dayton and built the first power machine. They were obliged to build their own engine, because no suitable engine was available. They had also to design and make the propellers. This entailed a 1C65
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