The Airplane - Jay Spenser [90]
This engine weighed just under 200 pounds (90 kilograms) and developed 12 hp. The brothers had calculated they needed 8 hp to fly, so this engine actually provided a 50 percent power margin. That they could fly on so little installed power attests to their engineering.
If the Wright 1903 Flyer’s engine was a bit crude, the opposite was true of its propellers. The brothers were in fact the first people ever to realize that an airplane’s propeller is a rotating wing; as such, it needs to be an efficiently cambered airfoil, not a glorified paddle.
Casting about for available insights to help them create their propellers, they looked to maritime practice only to discover that a ship’s screws were designed by trial and error. There being no existing body of scientific theory for them to draw upon, and lacking the time and funding to pursue comprehensive empirical studies, they realized there was only one alternative: they must think it all out, develop their own propeller theory, and then use it to develop their own propellers through calculation.
“What at first seemed a simple problem became more complex the longer we studied it,” Orville later wrote. “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.”3
The brothers did what they always did: they talked it through, arguing points of interest day after day and sometimes well into the evening. Anytime a new thought struck or idea took shape, one brother presented it to the other and a lively discussion ensued. These often ended with each brother having taken the other’s position.
After several months of thrashing it all out, the dynamics of propellers were no longer a mystery. “When once a clear understanding had been obtained,” explained Orville, “there was no difficulty in designing suitable propellers, with proper diameter, pitch, and area of blade, to meet the requirements of the flyer.”4
Hand-crafted out of laminated spruce, these two-bladed pusher propellers were 8 feet (2.44 meters) in diameter. They had greater pitch near the hub, where they passed more slowly through the air, gradually flattening out to a mild camber at their tips. The Wrights had scored an aerodynamic bull’s-eye, these propellers being within a few percentage points of optimal.
But that wasn’t the end to their ingenuity. The Wrights drove these propellers via bicycle chains mounted on sprocket gears. By changing the gear diameters, they could select for a different number of propeller rotations per minute despite an engine that ran at only one speed. And to balance the thrust, they gave one of the chain drives a half twist so that the propellers rotated in opposite directions.
Whereas chauffeurs such as Langley and Voisin applied power as soon it was available, the Wrights added it last. As true airmen, they taught themselves to fly and achieved control around all three axes before proceeding to powered experiments.
Germany pioneered gasoline engines but then ignored airplanes to concentrate on dirigible engines. Great Britain, a producer of fine automobiles and their engines, likewise showed no interested in aero propulsion. That left the French to single-handedly create Europe’s first airplane engines, and they did a fine job of it.