Bell XP-52
The Bell XP-52 and subsequent XP-59 were World War II fighter aircraft design projects by the American Bell Aircraft Corporation. Both projects featured a twin-boom layout with a rear-mounted engine driving pusher contra-rotating propellers. When the XP-59 project was cancelled the designation XP-59A was used as a cover for a secret jet fighter prototype, which would enter production as the P-59 Airacomet. XP-52. The XP-52 design was begun by the Bell Company in 1940, separate from the R-40C competition, under the Air Material Command designator MX-3. The short fuselage carried a piston engine in the  rear, driving a pair of contra-rotating propellers in a pusher configuration. The wings were swept back at an angle of 20 degrees, with a horizontal stabilizer mounted behind the propeller on twin booms running back from the wings. The fuselage was unusually streamlined, being round and barrel-shaped, with the forward-located pilot's cockpit fully faired-in to its lines and the nose ending in a round air intake which was ducted back internally to the engine. The undercarriage was a tricycle arrangement, with the main wheels retracting into the tailbooms. Propulsion was to be provided by the  experimental Continental XIV-1430-3 inverted V-12 engine. The XP-52 was cancelled in October 1940 because the XIV-1430 engine ran into technical difficulties. Bell submitted a similar design to the US Navy as the Model 19, but this too was never built. XP-59. Although generally similar in layout to the XP-52, the XP-59 was slightly larger and heavier, and was to be powered by a Pratt and Whitney R-2800-23 engine of . Two prototypes were ordered in February 1941. On 3 October 1941 the contract for Bell's first jet fighter was signed. The prototype was designated the XP-59A and it  would enter production as the P-59 Airacomet. The original XP-59 was cancelled on November 25, 1941 because Bell itself was pre-occupied with development of the Bell P-63 Kingcobra.