| XB-51 | |
|---|---|
 First prototype,46-685 during testing | |
| General information | |
| Type | Bomber |
| Manufacturer | Glenn L. Martin Company |
| Status | Canceled in 1952 |
| Primary user | United States Air Force |
| Number built | 2 |
| History | |
| First flight | 28 October 1949 |
| Retired | 25 March 1956 |
TheMartin XB-51 was an Americantrijetground-attack aircraft. It was designed in 1945 and made its maiden flight in 1949. It was originally designed as a bomber for theUnited States Army Air Forces under specification V-8237-1 and was designatedXA-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 theEnglish Electric Canberra which — built by Martin — entered service as theMartin B-57 Canberra.
This unorthodox design, first flying on 28 October 1949, was fitted with threeGeneral 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) thrustRocket-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]
The main landing gear consisted of dual wheel sets in tandem in the fuselage, similar to theBoeing B-47 Stratojet, with outrigger wheels at the wingtips (originally proved on a modifiedMartin 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 rotatingbomb bay, a Martin trademark; bombs could also be carried externally up to a maximum load of 10,400 lb (4,717 kg), although the specified basic mission required only a 4,000 lb (1,814 kg) 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. AShort-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]
In 1950, theUnited States Air Force issued a new requirement based on earlyKorean War experience for a night intruder/bomber to replace theDouglas A-26 Invader. The XB-51 was entered, as well as theAvro Canada CF-100 andEnglish 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, aload 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 emergencyforward airfields.
While the XB-51 was not selected for procurement, it was decided that Martin would build 250 Canberras under license, under the designationB-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 filmToward 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]
Data fromU.S.Standard Aircraft Characteristics[6]
General characteristics
Performance
Armament
Aircraft of comparable role, configuration, and era
Related lists
| International | |
|---|---|
| Other | |
