The Airplane - Jay Spenser [69]
At least that’s what was supposed to happen, and it had worked in kite tests. Now, however, incomprehensible things sometimes occurred when Wilbur attempted to bring up a low wing or turn one way or the other. The glider would tilt as commanded but then rotate alarmingly the other way. Slipping sideways out of control, it would crash to the sand, resulting in splintered wood, consternation, and the need for repairs.
Talking it through in camp, the brothers correctly diagnosed the problem. During warping, the side of the glider generating greater lift was also experiencing greater drag even as the opposite side experienced reduced lift and drag. Moreover, the wings on the outside of a turn must travel farther and thus fly faster than the inboard wings. Since the amount of lift and drag is proportional to the speed with which a wing passes through the air, this disparity was accentuated in turns.
The net result was forces working in opposition. Even as lift rolled the glider into a turn around the longitudinal axis, drag was wrenching it out of the turn by yawing it the other way around the glider’s vertical axis. Trying to bring the low wings up using warping also risked commanding them to too high an angle of attack for their reduced airspeed, causing them to stall and lose their remaining lift.
That explained the odd behavior and crashes, which scuttled the brothers’ hopes for an easy solution to the controllability problem. The flying season again having come to a close, the Wrights left Kitty Hawk thoroughly dispirited. In addition to the vexing control issues, their gilder was generating far less lift overall than it should have. On the long train trip home, the brothers discussed abandoning their research, although they knew they could not. The challenge was simply too fascinating.
Instead, they spent the closing months of 1901 learning from their wind tunnel.
In September 1902, the Wrights returned to Kitty Hawk armed with new knowledge and many crates containing the parts of a large new glider. Assembled in eleven days, the Wright 1902 Glider was longer, narrower, and had wings of a flatter camber. Wingspan was 32 feet (9.75 meters), chord 5 feet (1.52 meters), and weight 112 pounds (51 kilograms).
The 1902 machine featured the same wing warping mechanism as the previous year’s glider. However, this system was no longer actuated by the feet. Instead, the pilot would bank by shifting his hips to the desired side in a wooden cradle.
For the first time, there was a tail. Mounted on struts aft of the wings were two fixed vertical vanes that the brothers hoped would cure the previous year’s control issues. By resisting side-to-side swings, they believed, this vertical stabilizer would help the glider track through turns without experiencing as great a disparity in airspeed from one side to the other.
From the outset, the 1902 machine flew long distances. Demonstrating lower drag and higher lift, it closely matched the brothers’ computed expectations. However, they also found that wind gusts from the side lifted the glider’s upwind wings, upsetting its course through the air.
The brothers addressed this sensitivity by revising the glider’s diagonal trussing so as to give its wings a slight downward arch as viewed from the front. Accomplished at their camp, this rigging change made the glider’s wingtips droop 4 inches (10 cm) relative to the center of the wings.
Thus revised with anhedral, the glider became relatively insensitive to side gusts. Anhedral also eliminated what little lateral stability there