Martin XB-51
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| XB-51 | |
|---|---|
 First prototype, 46-685 during testing |
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| Type | Bomber |
| Manufacturer | Glenn L. Martin Company |
| Maiden flight | 28 October 1949 |
| Status | Cancelled in 1952 |
| 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, 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.
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[edit] Design and development
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 slots, 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 further 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 "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 (1,800 kg) bombload. Eight 20 mm cannon 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 behind 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 were their own design.[4]
[edit] Testing
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.
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 Towards the Unknown as the "Gilmore fighter",[5] then continuing its aerodynamic and weapons-handling tests until it crashed during takeoff on 25 March 1956.[3]
[edit] 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: 3× General Electric J47-GE-13 turbojets
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)
- Thrust/weight: 0.28
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)
[edit] See also
Comparable aircraft
Related lists
[edit] References
[edit] Notes
- ^ Knaack, Marcelle Size. Post-World War II bombers, 1945-1973. Washington, DC: Office of Air Force History, 1988. ISBN 0-16-002260-6.
- ^ a b c Winchester 2005, p. 144.
- ^ a b c d e f g Winchester 2005, p. 145.
- ^ Tuttle, Jim. Eject! The Complete History of U.S. Aircraft Escape Systems. St. Paul, Minnesota: MBI Publishing Company, 2002. ISBN 0-7603-1185-4.
- ^ Winchester 2005, p. 144. Note: Although the XB-51 did not receive an official name, "Panther" had been suggested by the company.
[edit] Bibliography
- Andrade, John M. U.S. Military Aircraft Designations and Serials since 1909. Earl Shilton, Leicester: 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, CA: Aero Publishers, 1962, second edition 1974. ISBN 0-8168-9126-5.
- Winchester, Jim. "Martin XB-51." Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft. Kent, UK: Grange Books plc., 2005. ISBN 1-84013-309-2.
[edit] External links
- USAF Museum: XB-51
- Several photographs of the Martin 234 XB-51 46-685
- Toward The Unknown at the Internet Movie Database
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