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XB-51
Martin XB-51 46-585 in flight.jpg
First prototype, 46-685 during testing
Role Bomber
Manufacturer Glenn L. Martin Company
First flight 28 October 1949
Retired 25 March 1956
Status Cancelled in 1952
Primary user USAF (NACA)
Number built 2
Unit cost
US$12.6 million for the program[1]

The Martin XB-51 was an American "tri-jet" ground attack aircraft designed to a 1945 United States Army Air Forces requirement. It was originally designed as an attack aircraft by the Air Force 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 developmentEdit

Twin XB-51

Both prototypes taking off in formation

Martin XB-51 rocket-assisted take off 061026-F-1234S-013

Testing RATO

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.[2] The innovative wings, swept at 35° and with 6° anhedral, were equipped with variable incidence, 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.[3] 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.[2]

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"[2]). The B-51 was a large but aerodynamically "clean" design which incorporated nearly all major systems internally.[3] 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.[4] Eight 20 mm (.79 in) cannons mounted in the nose would have been installed in production aircraft.[3]

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).[3] Both crew members were provided with a pressurized, air-conditioned environment, equipped with upward-firing ejection seats.[3] The XB-51 was the first Martin aircraft equipped with ejection seats; the ejection seats being of their own design.[5]

Operational historyEdit

XB-51

A shot of 46-685 on approach from the archives of the National Museum of the U.S. Air Force

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 (its "turn-of-speed" was faster than most fighter aircraft of the era[3]). 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. Furthermore, the rotating bomb bay was incorporated in the B-57. A proposed B-57 Super-Canberra also included XB-51 features, such as swept wing and tailplane. In the end it was never built, mainly because it was a new design and would have taken too long to put in production, although it promised much better speed and performance.[2]

Flight testing for research purposes continued after program cancellation. The second prototype, 46-686, which first flew in 1950, crashed on 9 May 1952 during low-level aerobatics. The first prototype, 46-685 continued to fly, including appearing in the film Toward the Unknown as the "Gilbert XF-120" fighter.[6] The surviving prototype was en route to Eglin AFB to shoot additional footage when it crashed during takeoff following a refueling stop in El Paso, Texas, on 25 March 1956.[3]

Specifications (XB-51)Edit

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: 3 × General Electric J47-GE-13 turbojets

Performance

  • Maximum speed: 645 mph (1,040 km/h)
  • Range: 1,075 mi (1,730 km)
  • Ferry range: 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)
  • Thrust/weight: 0.28</ul>Armament
  • Guns: 8 × 20 mm (0.79 in) cannon with 1,280 rounds
  • Rockets: 8 × High Velocity Aerial Rockets (HVAR)
  • Bombs: 2,000 (907 kg)
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See alsoEdit

ReferencesEdit

NotesEdit

  1. Knaack, Marcelle Size. Post-World War II bombers, 1945-1973. Washington, DC: Office of Air Force History, 1988. ISBN 0-16-002260-6.
  2. 2.0 2.1 2.2 2.3 Winchester 2005, p. 144.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Winchester 2005, p. 145.
  4. "Pivoting Bomb-bay Door Permits Accurate Drops at High-Speeds." Popular Mechanics, February 1954, p. 126.
  5. Tuttle, Jim. Eject! The Complete History of U.S. Aircraft Escape Systems. St. Paul, Minnesota: MBI Publishing Company, 2002. ISBN 0-7603-1185-4.
  6. A few seconds of test flight footage of an XB-51 also appeared in the 1951 Tales of Tomorrow episode "Plague From Space". Note: Although the XB-51 did not receive an official name, "Panther" had been suggested by the company.

BibliographyEdit

  • Andrade, John M. U.S. Military Aircraft Designations and Serials since 1909. Earl Shilton, Leicester, UK: Midland Counties Publications, 1979. ISBN 0-904597-22-9.
  • Boyne, Walter. "Attack, The Story of the XB-51, Martin's Phantom Strike Ship!" Airpower, Volume 8, No. 4, July 1978.
  • Jones, Lloyd S. U.S. Bombers, B-1 1928 to B-1 1980s. Fallbrook, California: Aero Publishers, 1962, second edition 1974. ISBN 0-8168-9126-5.
  • Mikesh, Robert C. 'B-57 Canberra At War 1964-1972. London: Ian Allan, 1980. ISBN 0-7110-1004-8.
  • Winchester, Jim. "Martin XB-51." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc., 2005. ISBN 978-1-84013-809-2.
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External linksEdit

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