The Airplane - Jay Spenser [67]
French pioneer Robert Esnault-Pelterie developed an advanced but only marginally successful monoplane in 1907. This machine featured roll control (via downward-only wing warping) and yaw control but no pitch control. A fascinating machine, the R.E.P. (taking its name from his initials) flirted with steel-tube construction, cantilever wings, and hydraulic brakes before World War I.
Ultimately, Europe’s experimenters were groping in the dark when it came to flight control.
Wilbur Wright read a book about ornithology and another addressing the mechanics of birds’ flight. He visited rocky outcroppings overlooking a river and studied soaring hawks by the hour, but they were too distant to betray useful insights. As for small birds in the Wrights’ Dayton neighborhood, they flew too quickly for study.
Beginning an intellectual journey, the brothers speculated that birds control their direction of flight by shifting their weight and drawing in a wing to temporarily reduce lift on one side, thus tilting them to that side. Then one day in West Dayton, Wilbur saw a pigeon perform such a display of aerial artistry that these theories went out the window.
Wilbur realized that birds turn by twisting their wingtips to temporarily generate more lift on one side than the other. No shifting of weight, no readjustment of relative wing area, just a dynamic change in each wing’s pitch or angle of incidence that affected how big a bite of the air it took from one moment to the next.
Here, then, was how an airplane also should turn. One wing should temporarily create more lift and the other less to tilt the machine into a bank that would end with an opposite application of control forces. But how to achieve this?
The Wrights toyed with the idea of building a glider employing shafts meeting at central gears to mechanically pivot the wings to opposite orientations. Seeing no way to keep the weight sufficiently low, however, they abandoned the concept.
Then one day Orville returned home to find Wilbur brimming with triumphant excitement. He held forth a small, empty cardboard box that had come off the bicycle shop’s supply shelf from which he had removed its two narrow ends. Imagining two parallel long sides also gone, it roughly approximated the wings of a Chanute-style biplane glider.
Holding the corners of each end between finger and thumb, Wilbur gave this box a helical twist. The parallel “wings” distorted, angling up on one side and down on the other. Here was the solution to the control problem.
Wilbur’s idea was wing warping. By leaving intact a Chanute biplane glider’s lateral trussing but removing its fore-and-aft trussing and then installing adjustable tensioning cables for the latter, a glider could be built whose wings could be dynamically adjusted in flight. On one side, they would take on a greater angle of attack; on the other, they would flatten out. With more lift on one side, the glider would turn.
On a windy day in July 1899, Wilbur—accompanied by two small boys—went to a field in Dayton to test a biplane kite built to this formula. It had superimposed wings spanning 5 feet (1.5 meters) and a trailing fixed surface. To control it, Wilbur held two sticks, each secured at both ends with long cords.
Holding the kite aloft, the boys released it at Wilbur’s signal. It rose into the wind, and Wilbur tried out his wing warping. The kite obediently tilted one way or the other on command. Mechanically achieved roll control had been demonstrated.
The demands of the highly seasonal bicycle business preempted further work until August 1900. Wilbur, who at that point was more interested in flight than his brother, worked up the design and set to work constructing a man-carrying glider. Unable to find spruce in Dayton’s lumber yards sufficiently long to serve as wing spars, he built what he could. The spars he would obtain in North Carolina.
From replies to his query letters, Wilbur had settled on Kitty Hawk