The Boys' Book of Model Aeroplanes / How to Build and Fly Them: With the Story of the Evolution of the Flying Machine

by Francis A. Collins

PLATE XVIII.

A Good Model Excepting that its Vertical Rudders Are Too Large.

“We began our first active experiments at the close of this period, in October, 1900, at Kitty Hawk, North Carolina. Our machine was designed to be flown as a kite, with a man on board, in winds of from fifteen to twenty miles an hour. But, upon trial, it was found that much stronger winds were required to lift it. Suitable winds not being plentiful, we found it necessary, in order to test the new balancing system, to fly the machine as a kite without a man on board, operating the levers through cords from the ground. This did not give the practice anticipated, but it inspired confidence in the new system of balance.”

“The machine of 1901 was built with the shape of surface used by Lilenthal, curved from front to rear, with a slight curvature of ⁴¹⁄₁₂ of its cord. But to make doubly sure that it would have sufficient lifting capacity when flown as a kite in fifteen or twenty mile winds, we increased the area from 165 square feet, used in 1900, to 308 square feet, a size much larger than Lilenthal, Chanute, or Pilcher had deemed safe. Upon trial, however, the lifting capacity again fell short of calculation, so that the idea of securing practice while flying as a kite, had to be abandoned. Mr. Chanute, who witnessed the experiments, told us that the trouble was not due to poor construction of the machine. We saw only one other explanation—that the tables of air pressure in general use were incorrect.”

“We then turned to gliding—coasting down hill in the air—as the only method of getting the desired practice in balancing the machine. After a few minutes’ practice we were able to make glides of 300 feet, and in a few days were safely operating in twenty-seven mile winds. In these experiments we met with several unexpected phenomena. We found that, contrary to the teachings of the books, the center of pressure on a curved surface traveled backward when the surface was inclined, at small angles, more and more edgewise to the wind. We also discovered that in free flight, when the wing on one side of the machine was presented to the wind at a greater angle than the one on the other side, the wing with the greater angle descended, and the machine turned in a direction just the reverse of what we were led to expect when flying the machine as a kite. The larger angle gave more resistance to forward motion, and reduced the speed of the wing on that side. The decrease in speed more than counterbalanced the effect of the larger angle. The addition of a fixed vertical vane in the rear increased the trouble, and made the machine absolutely dangerous. It was some time before a remedy was discovered. This consisted of movable rudders working in conjunction with the twisting of the wings.”

“The experiments of 1901 were far from encouraging. We saw that the calculations upon which all flying-machines had been based were unreliable, and that all were simply groping in the dark. Having set out with absolute faith in the existing scientific data, we were driven to doubt one thing after another, till finally, after two years of experiment, we cast it all aside, and decided to rely entirely upon our own investigations. Truth and error were everywhere so intimately mixed as to be indistinguishable. Nevertheless, the time expended in preliminary study of books was not misspent, for they gave us a good general understanding of the subject, and enabled us at the outset to avoid effort in many directions in which results would have been hopeless.”

“To work intelligently, one needs to know the effects of a multitude of variations that would be incorporated in the surfaces of flying-machines. The pressures on squares are different from those on rectangles, circles, triangles, or ellipses; arched surfaces differ from planes, and vary among themselves according to the depth of curvature; true arcs differ from parabolas, and the latter differ among themselves; thick surfaces differ from thin, and surfaces thicker in one place than another vary in pressure when the positions of maximum thickness are different; some surfaces are more efficient at one angle, others at other angles. The shape of the edge also makes a difference, so that thousands of combinations are possible in so simple a thing as a wing.”

PLATE XIX.