The XB-51 was completed with 3 x General Electric J47-GE-13 turbojet engines of 5,200lbs thrust each. These included a water-alcohol thrust quality which was used to support short/quick take-off actions beyond the normal thrust power output of the turbojets. Also, 4 x rocket pods could be installed at the rear of the fuselage for 14-seconds of take-off assistance (Rocket-Assisted Take-Off = "RATO"), each canister producing 954lbs of additional thrust each. The engines were protected in armor against ground-based artillery fire (FlaK type) and their combined output power gave the airframe a maximum speed of 645 miles per hour with a cruising speed of around 530 miles per hour. Ferry range was out to 1,600 miles with an operational service ceiling of 40,500 feet (hence the cockpit pressurization for the crew).
Dimensions included a wingspan of 53 feet, a length of 85 feet and a height of 17.3 feet. Empty weight was listed at 29,590lb with a Maximum Take-Off Weight of 62,560lb.
Proposed armament for the XB-51 line was to include 8 x 20mm cannons with a total of 1,280 x 20mm projectiles carried. All of the cannon were to be fitted in the nose assembly and used for strafing runs against land-based or naval targets. An internal bomb bay was nestled in the fuselage complete with a rotary-style delivery system and cleared to carry up to 10,400lbs of internal stores. This would have included conventional drop bombs or 8 x 5" High-Velocity Aerial Rockets (HVAR). Aiming systems for the aircraft included an A-1-B gun-bomb rocket sighting device with radar ranging capability. All gun actions would be recorded on an onboard camera and a rear-facing camera would record the ground for damage assessment during strafing/bombing rungs. Still another camera was installed for high-altitude attack work or general reconnaissance. The XB-51made use of the SHORAN (SHOrt RAnge Navigation) bombing system already proven in the Korean War (1950-1953) through the Douglas A-26/B-26 Invader light bombers and Boeing B-29 Superfortress heavy bombers. The SHORAN system used the AN/APN-3 radar set and K-1A bombing computer in conjunction with a pair of AN/CPN-2/2A ground stations for improved bombing effectiveness over that seen in World War 2 (1939-1945).
The prototype XB-51 aircraft were assigned serial numbers 46-685 and 46-686. Its original attack-minded approach begat the little-known, short-lived "XA-45" designation before the bomber-minded classification was introduced to produce the "XB-51" designation. The original USAAF requirement was met by submissions from Martin as well as Avro Canada (the CF-100) and English Electric (the Canberra). While the XB-51 proposal was favored ahead of the two competing types for its inherent speed and agility, it eventually lost out to the British Canberra for its vastly superior operational range which was highly coveted. The Canberra was procured by the now-renamed USAF as the "B-57" and was, ironically, produced in 250 examples by Glenn L. Martin Company facilities.
Despite the XB-51 program setback, the prototypes continued in flight testing after their formal, potential USAF run had ended. Both prototypes were then lost in separate crashes - the second during maneuvers in May of 1952 and the first on a flight to Elgin AFB during March of 1956. Such ended the short-lived tenure of the Martin XB-51.
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