POWER FOR THE AIRPLANE
Going back to the four forces that govern the flight of a plane, we find thrust pulling the plane forward. Thrust is the force that keeps the plane in the air; without it the airplane could not leave the ground for sustained flight. Thrust is created by the propeller. The propeller blades function in the same manner as the wings. Just as the wing of a plane bites into the air to cause lift, the propeller blades, patterned after wing camber, bite into the air to create thrust. Their action on the air is similar to a screw biting its way into wood.
The propeller is whirled by the engine. Without the engine to whirl it the propeller is useless, for without thrust we would have no lift. That makes the engine the governing factor in flight. Weight also is a serious force in flight, and the Wrights and Curtiss found from the beginning that the four-cycle gasoline engine would give greater power for its weight than would a steam or electric engine.
The principle of the airplane engine is the same as the one used in the automobile engine. However, weight always has been a problem to aircraft designers. The automobile engine always has been too heavy for use in a plane. When the Wrights built their first plane, automobile engines weighed 25 to 35 pounds per horsepower. The Wrights built one that weighed 13 pounds per horsepower and produced 12 horsepower. They used this engine in 1903 to power their first plane. Since that time all practical airplanes have been powered with gasoline engines, designed specifically for use in heavier-than-air machines. Since the first flight, engineers constantly have strived to produce engines with greater power and less weight per horsepower. How well they have succeeded is proved by the progress of the airplane.
It was in 1905 that the Wright Brothers had first offered to the Army a license to use their patents; but nothing came of it. Reports coming from Dayton during the next two years, concerning their flying activities, caused the newspapers to publish a number of articles about them.
Theodore Roosevelt, then our President, was a diligent reader, and several articles about the Wrights attracted his attention. One day he clipped one of these articles from a newspaper and scribbled across it one word: “Investigate!” He passed it along to his Secretary of War, William Howard Taft. In a short time the almost forgotten Wright Brothers had a call from Brigadier General James Allen, U. S. Army Signal Corps. In the autumn of 1907 Wilbur Wright appeared in Washington to confer with the War Department.
A few months later, in July, 1907, an aëronautical division was established in the Office of the Chief Signal Officer of the Army. In December of that year the Army asked for bids on the construction of an airplane. The specifications called for a machine that could carry a weight of 350 pounds. It had to be able to remain in the air continuously for one hour with two passengers. During the flight the machine was required to remain under perfect control and to be capable of being steered in all directions. Its speed should be 40 miles per hour. The machine had to be built so that it could be taken apart and packed for transportation in army wagons. Then it had to be reassembled and put in flying condition in one hour.
By this time inventors everywhere were working on flying machines, but the Wright Brothers were the only ones who put in an appearance with an airplane for the Army trials in September, 1908.
Unfortunately the trial was a failure. The huge crowd gathered at Fort Meyer, Virginia, was horrified to see a propeller fly off and the machine crash, killing Lieutenant Tom Selfridge, the Army observer, and injuring Orville Wright. Tom Selfridge thus became the first American air martyr, and the future dimmed for the Wright Brothers and the airplane.
