|Manufacturer||Glenn L. Martin Company|
|Status||Cancelled in 1951|
|Unit cost||US$12.6 million for the program|
The Martin XB-51 was a ground attack aircraft designed to a 1945 United States Army Air Forces requirement, and originally 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 resulting design, first flying on October 28, 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. The wings, swept at 35° and with 6° anhedral, were equipped with variable incidence, leading-edge slots, full-width flaps and spoilers instead of ailerons. The main landing gear was dual sets of wheels in tandem in the fuselage, similar to the B-47 Stratojet, with outrigger wheels at the wingtips. 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 (1,800 kg) bombload.
In 1950, the United States Air Force issued a new requirement based on early Korean war experience for a night intruder/bomber to replace the A-26 Invader. The XB-51 was entered, as well as the Avro Canada CF-100 and the English Electric Canberra. The Canberra and XB-51 emerged as the favorites. The XB-51 was a highly maneuverable aircraft at low level, and substantially faster than the Canberra. However, its load limiting factor of only 3.67 g (36 m/s²) restricted tight turns, and the XB-51's endurance was substantially poorer than the Canberra's; this latter proved to be the deciding factor. Additionally, the tandem main gear plus outriggers of the XB-51 was thought unsuitable for the requirement to fly from emergency forward airfields. The Canberra was selected for procurement and the XB-51 program ended. Martin did not end up the loser, however, for they were selected to build the 250 Canberras ordered under the designation B-57A.
Flight testing for research purposes continued after program cancellation. The second prototype crashed on May 9, 1952 during low-level aerobatics. The other aircraft continued to fly, including appearing in the film Towards the Unknown, until it crashed on takeoff on March 25, 1956.
- Crew: 2
- Length: 85 ft 1 in (25.9 m)
- Wingspan: 53 ft 1 in (16.2 m)
- Height: 17 ft 4 in (5.3 m)
- Wing area: 548 ft² (50.9 m²)
- Empty weight: 29,584 lb (13,419 kg)
- Loaded weight: 55,923 lb (25,366 kg)
- Max takeoff weight: 62,457 lb (28,330 kg)
- Powerplant: × , 5,200 lbf (23 kN) each
- Maximum speed: 645 mph (1,040 km/h)
- Combat: 1,075 mi (1,730 km)
- Ferry: 1,613 mi (2,596 km)
- Service ceiling: 40,500 ft (12,300 m)
- Rate of climb: 6,980 ft/min (35.5 m/s)
- Wing loading: 102 lb/ft² (498 kg/m²)
- Guns: 8× 20 mm (0.787 in) cannon with 1,280 rounds
- Rockets: 8× High Velocity Aerial Rockets (HVAR)
- Bombs: 2,000 (900 kg)
- Knaack, MS (1988). Post-World War II bombers, 1945-1973. Office of Air Force History. ISBN 0-16-002260-6.
- A- sequence: XA-42 - XA-43 - A-44 - XA-45
- B- sequence: XB-48 - YB-49 - B-50 - XB-51 - B-52 - XB-53 - B-54
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