Martin XB-51
Description
Role	ground attack
Crew	two; pilot and navigator in tandem
First flight	April 17, 1950
Manufacturer	Martin
Dimensions
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
Weights
Empty	29,584 lb	13,419 kg
Loaded	55,923 lb	25,366 kg
Maximum takeoff	62,457 lb	28,330 kg
Powerplant
Engines	3 × General Electric J47-GE-13 turbojets
Thrust	5200 lb	23 kN
Performance
Maximum speed	645 mph	1038 km/h
Combat range	1075 miles	1,730 km
Ferry range	1613 miles	2,596 km
Service ceiling	40,500 ft	12,300 m
Rate of climb	6980 ft/min	2,130 m/min
Avionics
Avionics
Armament
Guns	8 × 20 mm cannon with 1280 rounds
Bombs	4 × 1600 lb (730 kg) bomb internally, or 2 × 2000 lb (900 kg) bombs externally. Maximum bombload 10,400 lb (4,700 kg).
Rockets	8 × High Velocity Aerial Rockets (HVAR)

The Martin XB-51 was a ground attack aircraft designed to a 1945 United States Army Air Force 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.

External link

• USAF Museum: XB-51