The Northrop XP-56 was an experimental single-seat aircraft with an unusual configuration. The project was born out of an earlier prototype model called the Northrop N2B. It was designed around the Pratt & Whitney X-1800 engine and had a pusher configuration with dual contra-rotating propellers. The US Army commissioned Northrop to begin design work on 22 June 1940, and after reviewing the blueprints the Army placed an order for a prototype in September 1940.
Problems beset the XP-56 from the outset. Firstly Pratt & Whitney decided to discontinue the X-1800 engine, meaning Northrop had to adjust the design to accommodate a more powerful, but also larger and heavier substitute. The alteration also delayed the construction by a full five months.
Due to the radical tailless design of the XP-56 Northrop decided it would be wise to construct a simplified test aircraft first. This they called the Model N-1M. Successful flight trials were conducted using this aircraft and the results were fed back into the XP-56′s design. Following the success of the N-1M, and the promise of even higher performance from the the XP-56, the army requested a second prototype to be built.
The Northrop XP-56 wasn’t just unconventional in its design. It was also different in its materials and construction. As aluminium was in short supply due to the war effort, Magnesium was used for the airframe and skin. Lightweight and relatively strong, magnesium was a good substitute for the design. However there wasn’t much experience in working with the metal, especially in aircraft construction. In order to build the aircraft Northrop hired Vladimir Pavlecka to develop the heliarc welding technique used for joining magnesium alloy.
Engine runs of the first finished Northrop XP-56 prototype were conducted in March 1943, unfortunatley excessive propellor shaft flex caused the engine to fail. It took Pratt & Whitney five months to send a replacement.
Taxi tests of the aircraft showed up some serious stability issues in the yaw axis. Engineers first thought this was due to uneven wheel brakes and a considerable amount of time and money was spent trying to rectify the problem, including replacing the manual hydraulic brake system. At the end of September 1943 the Northrop XP-56 flew for the first time. It immediately became apparent that the yaw instability came not from the wheels, but from aerodynamic instability caused by the lack of a suitably sized vertical stabilizer. The small upper stub was therefore replaced by a much larger upper vertical stabilizer.
After a series of test flights the first XP-56 prototype was destroyed when a tire blew out during a high-speed (130 mph) taxi run across Muroc Dry Lake. The pilot, John Myers was lucky to escape with his life. He credited his survival to the fact he always wore a polo player’s helmet!
The second prototype was completed in 1944. It featured a number of alterations, including a re-positioning of the center-of-gravity slighty further forward, an even larger vertical stabilizer, and redesigned rudder control linkages. After its first flight the pilot reported that he had difficulty getting the aircraft’s nose of the ground at speeds below 160 mph (257 km/h). He also noted that the aircraft was extremley sensitive around the yaw axis. Further flights showed that the nose heaviness disappeared after the undercarriage had been retracted. However during subsequent flights the XP-56 failed to achieve the sorts of speed that were expected of it. On its tenth flight the pilot reported some rather alarming characteristics, including extreme tail heaviness, lack of power, and excessive fuel consumption. It was the final nail in the XP-56′s coffin. It was deemed to unsafe to fly and the project was abandoned.
Besides, by 1946 the US Army Air Forces were becoming increasingly interested by shiny and new jet-powered aircraft designs.