Design and development
Both prototypes taking off in formation
Testing RATOThe 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 "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. 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.[
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: 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
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)
