POWER PLANT: Three × General Electric J-47-GE-13 turbojet engines, rated at 2,700 kp each
PERFORMANCE: 645 mph
COMMENT: In early 1945, USAAF issued requirement for a new attack bomber for low-level bombing and close support as a successor to the Douglas A-26 Invader. Martin Company proposed its design and won the competition with designation, XA-45. Soon later USAAF revised its requirement for better close-support bombing. Martin accepted the new requirement and was received contract for two prototypes, the project was redesignated XB-51. The first XB-51 made its first flight on Oct 1949. The aircraft was powered by three jet engines: one at the extreme tail with an intake at the base of the tailfin, and two underneath the forward fuselage in pods. The innovative, variable incidence wings were swept at 35° and with 6° anhedral. The main landing gear consisted of dual sets of wheels in tandem in the fuselage with outrigger wheels at the wingtips. Crew provision was for a pilot under a “fighter”-type bubble canopy and for an operator/navigator in a compartment located lower than and to the rear of the cockpit. It became the fastest ground support bomber at the time. Although test flights were satisfying Martin XB-51 never went into production. Noteworthy is the fact that the design can be traced back to a German WWII-project Messerschmitt Me P.1102/105 that was to be powered by three Heinkel-Hirth HeS-109-011 turbo-engines, one in the extreme tail and two in pods under the extreme forward fuselage and provided with variable-sweep wings, too (Ref.: 24)
POWER PLANT: Two General Electric J35-GE-3 turbojet engines, rated at 1,835 kp each
PERFORMANCE: 507 mph
COMMENT: USAAF leaders in the Air Material Command began to consider the possibilities of jet-propelled bombers as far back as October 1943. At that time, Douglas Aircraft was just beginning to design a promising twin-engine bomber designated the XB-42 “Mixmaster”. Reciprocating engines powered this aircraft but they were buried in the fuselage, leaving the laminar flow-airfoil wing clean of any drag-inducing pylon mounts or engine cowlings. The airframe appeared ideally suited to test turbojet propulsion. Douglas confirmed the feasibility of the concept and the USAAF amended the XB-42 contract in March 1944 to include the development of two turbojet-powered XB-43 prototypes, reduced from an initial order of 13 test aircraft. The Douglas design team convinced the Army that modifying the XB-42 static test airframe into the first XB-43 was a relatively straightforward process that would save time and money compared to developing a brand new design. Douglas replaced the two Allison V-1710 engines with a pair of General Electric J35 turbojets, then cut two air intakes into each side of the fuselage, aft of the pressurized cockpit. Removing the propellers and drive shafts freed enough space for two long jet exhaust ducts. Without any propellers present, there was no chance of striking the blade tips on the runway, so the entire ventral fin/rudder unit of the earlier XB-42’s full four-surface cruciform tail was omitted. Douglas compensated for the loss of yaw stability by enlarging the dorsal fin/rudder unit. The end of World War II caused a general slowdown within the aviation industry and General Electric was late delivering the engines. So America’s first turbojet bomber finally flew for the first time on 17 May 1946. Douglas Aircraft was keen to mass-produce the new bomber and the USAAF considered ordering 50, but these plans never became realized. The USAAF was already moving ahead with a new bomber, the North American XB-45 “Tornado”, designed from the outset for turbojet power and promising a quantum leap in every category of performance (Ref.: 24).
POWER PLANT: Two Allison V-1710-125 liquid-cooled engine, rated at 1,325 hp each, each driving one of the twin three-bladed propellers
PERFORMANCE: 410 mph at 23,440 ft
COMMENT: The XB-42 was developed initially as a private venture; an unsolicited proposal was presented to the USAAF in May 1943. This resulted in a contract for two prototypes and one static test airframe, the USAAF seeing an intriguing possibility of finding a bomber capable of the Boeing B-29 “Superfortress” range without its size or cost. The aircraft mounted a pair of Allison V-1710-125 liquid-cooled V-12 engines behind the crew’s cabin, each driving one of the twin propellers. Air intakes were in the wing leading edge. The landing gear was tricycle and a full, four surface cruciform tail was fitted, whose ventral fin/rudder unit prevented the coaxial propellers from striking the ground. The pilot and co-pilot sat under twin bubble canopies, and the bombardier sat in the extreme front behind a plexiglass nose. Defensive armament was two 0.50 in machine guns each side in the trailing edge of the wing, which retracted into the wing when not in use. These guns were aimed by the copilot through a sighting station at the rear of his cockpit. The guns had a limited field of fire and could only cover the rear, but with the aircraft’s high speed it was thought unlikely that intercepting fighters would be attacking from any other angle. The first XB-42 was delivered to the Army Air Force and flew at on 6 May 1944. Performance was excellent, being basically as described in the original proposal: as fast or even faster than the de Havilland “Moquito” but with defensive armament and twice the bomb-load. The end of World War II allowed the Air Force to consider possibilities with a little more leisure. Although with the second prototype additional Westinghouse 19XB-2A jet engines were mounted under the wings to enhance performance (XB-42A) it was decided to wait for the development of better jet bombers rather than continue with the XB-42 program (Ref.: 24).