Flightline: 151 - Martin XB-51 Dragon
The Martin XB-51 was designed as a low-level bombing and ground support, but lost out to the English Electric Canberra for a USAF contract.
What became the XB-51 originated in 1945 with USAAF specification V-8237-1, which called for a replacement for the A-26 Invader.; three companies responded with designs: Curtiss' XA-43, Convair's XA-44 and Martin's XA-45. The following year, the USAAF did away with the A "Attack" designation, and Curtiss & Convair dropped out, with the former reworking their design as the XF-87 Blackhawk twin-engined fighter, while Convair dropped the XA-44 in favor of the XB-46 instead. Martin pushed on with their design however, which was now designated the XB-51.
Cutaway drawing of the XB-51, showing internal structures and components. | Illustration: Glenn L. Martin Company
The XB-51 (though never official, the name "Dragon" appears occasionally) had many unusual and innovative features, including the three J47 engines being installed in two pods under the middle fuselage and the third in the tail, a swept, variable incidence wing which had leading edge slats and slotted flaps for a shortened takeoff roll and spoilers for roll control, landing gear that consisted of tandem main wheels supplemented by wingtip-mounted outriggers, and the first appearance of Martin's rotating bomb bay, which would go on to appear in most of the company's other products of the 1950s. The XB-51 was designed to carry a maximum load of 10,400lbs of bombs internally, and would also have been armed with eight 20m cannon. The aircraft had a crew of two, seated in tandem beneath a fighter-style canopy and on ejection seats of Martin's own design.
The "Middle River Stump Jumper", a Martin XB-26M Marauder modified to test the landing gear for the XB-48 and XB-51. | Video: USAAF
Dummy bombs mounted on the rotating bomb bay of an XB-51. | Photo: Glenn L. Martin Company
The first of 2 XB-51s flew on 28 October 1949, and quickly proved to be a fast and nimble aircraft, although short ranged (common with early jets) and was somewhat fragile, with a load limit of 3.67g, which would have limited maneuvering with a full load of weapons and fuel. Provisions were made for up to four disposable JATO bottles to improve takeoff performance.
One of the XB-51s testing the JATO system. | Photo: USAF
The two XB-51s perform a low-level, high-speed pass. | Photo: USAF
As a result of US experiences in the Korean War, the USAF issued a new requirement for a night intruder/bomber (although it was still replacing the A-26....), with the XB-51 now competing against the Avro Canada CF-100 and English Electric Canberra. Despite being faster than the Canberra, the XB-51 was not selected as the USAF judged it to be too fragile, as well as the outrigger gear set-up being unsuitable for rough-field service. Martin was awarded the license contract for the Canberra as consolation, with the newly minted B-57 Canberra modified with the same tandem cockpit setup and rotating bomb bay as the XB-51
An XB-51 coming in to land in a rare color photo of the plane. | Photo: USAF
The XB-51s continued to fly even after the type was canceled, with both participating in general research projects. The second prototype crashed on 9 May 1952 during a low-level aerobatics routine, leaving the first to fly on alone. Marked as the fictional "Gilbert XF-120", the plane appeared in 1956's Toward the Unknown, although it had crashed on 25 March 1956 while en-route to Eglin AFB to shoot additional footage, bringing an end to the XB-51's time aloft.
Screen capture of the XB-51, marked as the XF-120, flying in formation with an F-100 Super Sabre in Toward the Unknown. | Image: Warner Brothers Films