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Martin XB-51
The Martin XB-51 was an American "tri-jet" ground attack aircraft. It was designed in 1945 and made its maiden flight in 1949. It was originally designed as a bomber for the United States Army Air Forces under specification V-8237-1 and was designated XA-45. The "A" ground attack classification was eliminated the next year, and the XB-51 designation was assigned instead. The requirement was for low-level bombing and close support. The XB-51 lost out in evaluation to the English Electric Canberra which entered service as the B-57.
==Design and development==
The resulting unorthodox design, first flying on 28 October 1949, was (unusually for a combat aircraft) fitted with three engines, General Electric J47s in this case: one at the extreme tail with an intake at the base of the tailfin, and two underneath the forward fuselage in pods.〔 The innovative, variable incidence wings, swept at 35° and with 6° anhedral, were equipped with leading-edge slats, full-width flaps and spoilers instead of ailerons. The combination of variable incidence adjustment and slotted flaps allowed for a shorter takeoff run.〔 Four 954 lb (4.24 kN) thrust Rocket-Assisted Take Off (RATO) bottles with a 14-second burn duration could be fitted to the rear fuselage to improve takeoff performance. Spectacular launches were a feature of later test flights.〔Winchester 2005, p. 144.〕
The main landing gear consisted of dual sets of wheels in tandem in the fuselage, similar to the B-47 Stratojet, with outrigger wheels at the wingtips (originally proved on a modified B-26 Marauder named "Middle River Stump Jumper"〔Winchester 2005, p. 144.〕). The B-51 was a large but aerodynamically "clean" design which incorporated nearly all major systems internally.〔 The aircraft was fitted with a rotating bomb bay, a Martin trademark; bombs could also be carried externally up to a maximum load of 10,400 lb (4,700 kg), although the specified basic mission only required a 4,000 lb (1,814 kg) bombload.〔("Pivoting Bomb-bay Door Permits Accurate Drops at High-Speeds." ) ''Popular Mechanics'', February 1954, p. 126.〕 Eight 20 mm (.79 in) cannons mounted in the nose would have been installed in production aircraft.〔
Crew provision was for a pilot under a "fighter"-type bubble canopy and a SHORAN (short-range navigation and bombing system) operator/navigator in a compartment located lower than and to the rear of the cockpit (only a small observation window was provided).〔Winchester 2005, p. 145.〕 Both crew members were provided with a pressurized, air-conditioned environment, equipped with upward-firing ejection seats.〔Winchester 2005, p. 145.〕 The XB-51 was the first Martin aircraft equipped with ejection seats, these being of their own design.〔Tuttle, Jim. ''Eject! The Complete History of U.S. Aircraft Escape Systems''. St. Paul, Minnesota: MBI Publishing Company, 2002. ISBN 0-7603-1185-4.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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