Martin XB-51

B-51
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Type	Bomber
Manufacturer	Glenn L. Martin Company
Maiden flight	1949-10-28
Status	Cancelled in 1951
Number built	2
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.

Specifications (XB-51)

General characteristics

• 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

Performance

• Maximum speed: 645 mph (1,040 km/h)
• Range:
  
• 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)

Armament

• Guns: 8× 20 mm (0.787 in) cannon with 1,280 rounds
• Rockets: 8× High Velocity Aerial Rockets (HVAR)
• Bombs: 2,000 (900 kg)

External links

• USAF Museum: XB-51

Related content

Comparable aircraft

• English Electric Canberra

Designation sequence

• 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

Related lists

• List of attack aircraft
• List of bomber aircraft
• List of military aircraft of the United States