The Wrights' Propeller Blade Had A Completely New Pitch.

Unfortunately, they found there was none. Marine screws were designed by varying size and pitch until a propeller was produced that could supply the required performance. What was more unsettling, ship screws operated roughly at an efficiency of 50 percent, whereas Orville and Wilbur calculated that a 66 percent efficiency rate was needed to thrust their flyer into the skies. Thus, they set about to devise a workable theory of propeller action - something that had never been done.

"What at first seemed a simple problem became more complex the longer we studied it," Orville recalled. "With the machine moving forward, the air flying backward, the propellers turning sidewise, and nothing standing still, it seemed impossible to find a starting point from which to trace the various simultaneous reactions…After long arguments, we found ourselves in the ludicrous position of each having been converted to the other's side…"

Heated discussions on propellers filled the Wrights' parlor for many evenings. What they finally decided was that a propeller was actually a vertically moving wing that provided the thrust of the flying machine through the air. Thrust depended on the shape of the propeller blade; its pitch (or angle it strikes the air); the speed at which it turns; the speed at which the machine travels forward; and the speed of the air advancing through the rotating blades.

How the Wrights designed their propellers is still not completely known to this day. In December, they began analyzing the thrust of a fan 28 inches in diameter, driven by a one horsepower motor. By February of 1903, they were working with a propeller 8 feet in diameter. By March they had designed propeller blades with a predicated efficiency of 66 percent. Using two propellers instead of one, they decided, would increase power, and running them in opposite directions would eliminate any twisting effect on lateral control.

By June they were confident they come up with propellers that were efficient enough to do the job. Writing to George Spratt, Orville reflected that confidence. "(We) soon discovered, as we usually do, that all the propellers built heretofore are all wrong, and then built a pair…based on our theory, which are all right! Isn't it astonishing that all these secrets have been preserved for so many years just so that we could discover them!!"

This "Kitty Hawk Moment" is brought to you by EAA, whose Countdown to Kitty Hawk program, presented by Ford Motor Company, includes an exact flying reproduction of the Wright Flyer. It is the centerpiece of EAA's national tour during 2003, which will conclude with a five-day celebration at Kitty Hawk, North Carolina, where the Wright flyer will fly again at exactly 10:35 a.m. on Dec. 17, 2003, commemorating 100 years of powered flight.