Developments in Airplane Design
Early attempts were made to build flying machines according to the principle of bird flight, but these failed; it was not until the beginning of the 20th cent. that flight in heavier-than-air craft was achieved. On Dec. 17, 1903, the Wright brothers produced the first manned, power-driven, heavier-than-air flying machine near Kitty Hawk, N.C. The first flight lasted 12 sec, but later flights on the same day were a little longer; a safe landing was made after each attempt. The machine was a biplane (an airplane with two main supporting surfaces, or wings) with two propellers chain-driven by a gasoline motor.
The evolution of the airplane engine has had a major effect upon aircraft design, which is closely associated with the ratio between power load (horsepower) and weight. The Wright brothers' first engine weighed about 12 lb (5.4 kg) per horsepower. The modern piston engine weighs about 1 lb (0.4 kg) or less per horsepower, and jet and gas-turbine engines are much lighter. With the use of jet engines and the resulting higher speeds, airplanes have become less dependent on large values of lift from the wings. Consequently, wings have been shortened and swept back so as to produce less drag, especially at supersonic speeds. In some cases these radically backswept wings have evolved into a single triangular lifting surface, known as a delta wing, that is bisected by the fuselage of the plane. Similar alterations have been made in the vertical and horizontal surfaces of the tail, again with the aim of decreasing drag.
For certain applications, e.g., short-haul traffic between small airports, it is desirable to have airplanes capable of operating from a runway of minimum length. Two approaches to the problem have been tried. One, the vertical takeoff and landing (VTOL) approach, seeks to produce craft that take off and land like helicopters, but that can fly much faster. The other approach, short takeoff and landing (STOL), seeks to design more conventional aircraft that have reduced runway requirements. The lessened lift associated with swept-back wing designs increases the length of runway needed for takeoffs and landings. To keep runway lengths within reasonable limits the variable-sweep, or swing, wing has been developed. A plane of this type can extend its wings for maximum lift in taking off and landing, and swing them back for travel at high speeds.
A proposed variant of the swing wing, in which one wing sweeps to the rear and another forward, produces an arrangement that causes a minimum shock wave at supersonic speeds. It is thought that if this modification were applied to supersonic transport (SST) designs it would somewhat lessen their objectionable noise levels. No solution has been proposed to lessen their high fuel consumption, however. Recent developments in fan-jet engines, in which a turbine powers a set of vanes that drive air rearward to augment thrust, have made supersonic flight possible at low altitude. Much research has also gone into reducing the noise and air pollution caused by jet engines.
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