Martin XB-51

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The Martin XB-51 was an American trijet 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 — built by Martin — entered service as the Martin B-57 Canberra.

Design and development

File:Twin XB-51.jpg
Martin's two XB-51 prototypes, seen low over the runway on a high-speed pass

This unorthodox design, first flying on 28 October 1949, was fitted with three General Electric J47 engines — an unusual number for a combat aircraft — two underneath the forward fuselage in pods, and one at the extreme tail with the intake at the base of the tailfin.[1] The innovative, variable incidence wings, swept at 35° and with 6° anhedral, were equipped with leading edge slats and full-width flaps. Spoilers gave most of the roll control and undersized ailerons provided feel for the pilot.[2] The combination of variable incidence and slotted flaps gave 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.[1]

File:Martin XB-51 rocket-assisted take off 061026-F-1234S-013.jpg
Testing RATO

The main landing gear consisted of dual wheel sets in tandem in the fuselage, similar to the Boeing B-47 Stratojet, with outrigger wheels at the wingtips (originally proved on a modified Martin B-26 Marauder named "Middle River Stump Jumper"[1]). The XB-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 Template:Cvt, although the specified basic mission required only a Template:Cvt bombload.[4] Eight 20 mm cannon mounted in the nose would have been installed in production aircraft.[3]

There were two crew in a shared cockpit. A pilot sat forward under a fighter-type bubble canopy. A Short-Range Navigation (SHORAN) navigation and bombing system operator sat lower down and to the rear, with only a small observation window.[3] The cockpit was a pressurized, air-conditioned environment, equipped with upward-firing ejection seats.[3] The XB-51 was the first Martin aircraft equipped with ejection seats, these being of their own design.[5]

Operational history

File:XB-51.jpg
46-685 on approach

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 Douglas A-26 Invader. The XB-51 was entered, as well as the Avro Canada CF-100 and English Electric Canberra; the XB-51 and Canberra emerged from these as the favorites.

Test flights showed the XB-51 to be highly maneuverable at low altitudes and substantially faster than the Canberra and faster than most fighter aircraft of the era.[3] However, the XB-51's endurance was significantly lower than that of the Canberra and this factor was decisive in its cancellation. In addition, a load limiting factor of only 3.67 g (36 m/s2) meant that the general strength of the airframe was relatively low and would prevent tight turns while fully loaded. Additionally, the tandem main gear plus outriggers of the XB-51 were thought unsuitable for the requirement to fly from emergency forward airfields.

While the XB-51 was not selected for procurement, it was decided that Martin would build 250 Canberras under license, under the designation B-57. Furthermore, Martin's rotating bomb bay would be incorporated into production variants of the B-57. A "Super Canberra", incorporating other XB-51 features, such as swept wings and tail-planes, was also proposed. This aircraft – although it promised much better speed and performance than the B-57 – never reached the prototype stage, mainly because the many changes would have taken too long to implement and test, before it could be put into production.[1]

Flights by the XB-51 prototype, 46-685, continued, for general research purposes, following the project's official cancellation by the USAF. A second prototype, 46-686, which first flew in 1950, crashed during low-level aerobatics on 9 May 1952, killing pilot Major Neil H. Lathrop. 46-685 continued to fly, including an appearance in the film Toward the Unknown as the "Gilbert XF-120" fighter.[note 1] 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)

File:Martin XB-51 3-view line drawing.png
3-view line drawing of the Martin XB-51

Data from U.S.Standard Aircraft Characteristics[6]

General characteristics

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Armament

  • Guns: 8 × 20 mm M24 cannon (0.79 in) cannon with 1,280 rounds
  • Rockets: 8 × High Velocity Aerial Rockets (HVAR) or
  • Bombs: Up to 10,400 lb (4,720 kg) carried internallyScript error: No such module "Check for unknown parameters".

See also

Aircraft of comparable role, configuration, and era

Related lists

References

Notes

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  1. ↑ 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.

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Citations

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  1. ↑ a b c d Winchester 2005, p. 144.
  2. ↑ The Martin XB-51, Air Force Legends Number 201, Scott Libis, published by Steve Ginter 1998, Template:ISBN, p.5
  3. ↑ a b c d e f g 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. Template:ISBN.
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "citation/CS1".

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Bibliography

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  • Andrade, John M. U.S. Military Aircraft Designations and Serials since 1909. Earl Shilton, Leicester, UK: Midland Counties Publications, 1979. Template:ISBN.
  • 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. Template:ISBN.
  • Mikesh, Robert C. 'B-57 Canberra At War 1964-1972. London: Ian Allan, 1980. Template:ISBN.
  • Winchester, Jim. "Martin XB-51." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc., 2005. Template:ISBN.

External links

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