Martin XB-51

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.

XB-51
First prototype, 46-685 during testing
Role Bomber
Manufacturer Glenn L. Martin Company
First flight 28 October 1949
Retired 25 March 1956
Status Canceled in 1952
Primary user United States Air Force
Number built 2
Unit cost
US$12.6 million for the program[1]

Design and development
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.[2] 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.[3] The combination of variable incidence and slotted flaps gave a shorter takeoff run.[4] 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]

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"[2]). The B-51 was a large but aerodynamically "clean" design which incorporated nearly all major systems internally.[4] 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 required only a 4,000 lb (1,814 kg) bombload.[5] Eight 20 mm cannon mounted in the nose would have been installed in production aircraft.[4]

Crew was a pilot under a "fighter"-type bubble canopy and a Short-range navigation and bombing system (SHORAN) operator/navigator in a compartment located lower than and to the rear of the cockpit (only a small observation window was provided).[4] Both crew members were provided with a pressurized, air conditioned environment, equipped with upward-firing ejection seats.[4] The XB-51 was the first Martin aircraft equipped with ejection seats, these being of their own design.[6]

Operational history
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 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.[4] 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.[2]

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. 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.[4]

Specifications (XB-51)

Data from U.S. Standard Aircraft Characteristics[7]

General characteristics

  • Crew: 2
  • Length: 85 ft 1 in (25.93 m)
  • Wingspan: 53 ft 1 in (16.18 m)
  • Height: 17 ft 4 in (5.28 m)
  • Wing area: 548 sq ft (50.9 m2)
  • Airfoil: NACA 63A010[8]
  • Empty weight: 30,906 lb (14,019 kg)
  • Gross weight: 57,874 lb (26,251 kg)
  • Max takeoff weight: 62,452 lb (28,328 kg)
  • Powerplant: 3 × General Electric J47-GE-13 turbojet engines, 5,200 lbf (23 kN) thrust each

Performance

  • Maximum speed: 644 mph (1,036 km/h, 560 kn)
  • Range: 1,075 mi (1,730 km, 934 nmi)
  • Ferry range: 1,444 mi (2,324 km, 1,255 nmi)
  • Service ceiling: 41,750 ft (12,730 m)
  • Rate of climb: 6,600 ft/min (34 m/s)
  • Wing loading: 105.6 lb/sq ft (516 kg/m2)
  • Thrust/weight: 0.27

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 internally
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gollark: Yes, you said that.

See also

Aircraft of comparable role, configuration and era

Related lists

References

Notes
  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.
  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. Winchester 2005, p. 144.
  3. The Martin XB-51, Air Force Legends Number 201, Scott Libis, published by Steve Ginter 1998, ISBN 0-942612-00-0, p.5
  4. Winchester 2005, p. 145.
  5. "Pivoting Bomb-bay Door Permits Accurate Drops at High-Speeds." Popular Mechanics, February 1954, p. 126.
  6. Tuttle, Jim. Eject! The Complete History of U.S. Aircraft Escape Systems. St. Paul, Minnesota: MBI Publishing Company, 2002. ISBN 0-7603-1185-4.
  7. "Standard Aircraft Characteristics: XB-51" (PDF). US Air Force. 11 July 1952. Retrieved 8 June 2017.
  8. Lednicer, David. "The Incomplete Guide to Airfoil Usage". m-selig.ae.illinois.edu. Retrieved 16 April 2019.

Bibliography
  • 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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