The Bell Aircraft Corporation's X-14 jet-powered VTOL (vertical-rising) airplane was designed to take off vertically in a conventional horizontal position, shift to forward flight and land vertically, eliminating the need for a runway. Powered by two British-made Armstrong-Siddely jet engines, the X-14 differed from the so-called "tail sitter" VTOL airplanes because it could operate without the help of ground handling equipment to position it for takeoff.
Built under a US Air Force contract, the X-14 used a planar array of diverter vanes to vector the exhaust of two Armstrong Siddeley ASV8 Viper engines (1,750 lb thrust each) at the center of gravity. These thrust diverter vanes were located behind the engines direct the powerful jet blast toward the ground to lift the airplane into the air. The vanes could be rotated to direct the exhaust from vertical to nearly horizontal. For forward flight, the pilot re-directs the thrust toward the rear of the airplane.
The first hovering flight of the X-14 was made 19 February 1957 at the Bell Aircraft Niagara Falls, NY, airport plant by Bell test pilot David W. Howe. Subsequent hovering and forward flights proved the contention of Bell engineers that vertical-rising flight from a conventional horizontal position was practicable.
The X-14, which was an experimental airplane, had a wing span of 34 feet and a length of 25 feet. It was eight feet tall at the tail. The 25 ft fuselage and tail were from a Beech T-34; the 34 ft span wing was from a Beech Bonanza. The lack of a ejection seat limited hover testing to very low and very high altitudes. The gross weight was originally only 3,100 lb.
Bell Aircraft developed the first American jet VTOL in 1954 with its own funds to explore the directed-thrust principle and as a result of this development program received an Air Force contract to design and build the X-14. The original prototype was turned over to the Smithsonian Institution in Washington D.C.
Because normal control surfaces, such as elevators, rudder and ailerons, have no effect during hovering and at slow forward speeds, the X-14 was equipped with compressed air nozzles at wing tips and tail to provide necessary directional control. The ejected air positions the aircraft during hovering and slow speed forward flight just as the conventional airplane control surfaces provide directional control during normal flight. Bell engineers devised this technique for use on the company's first experimental VTOL, which was powered by two Fairchild J-44 turbojet engines. For vertical takeoff, the jet engines were rotated to a vertical position and returned to the horizontal position for level flight.
The landing gear had to be lengthened when the phenomenon of suck-down was first discovered. Engine gyroscopic effects and exhaust gas reingestion were also encountered. First hover flight was achieved on 17 February 1957; first transition was made on 24 May 1958. The Viper engines were replaced with higher power GE J85 engines when it was transferred to NASA in 1960. It was eventually fitted with a digital fly-by-wire control system and continued flying as a V/STOL testbed until 1981.
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