The North American XB-21 (manufacturer's model designation NA-21) was a prototype bomber aircraft developed by North American Aviation in the late 1930s, for evaluation by the United States Army Air Corps. Evaluated against the Douglas B-18 Bolo, it was found to be considerably more expensive than the rival aircraft, and despite the ordering of a small number of evaluation aircraft, only the prototype was ever built.
Design and development
North American Aviation's first twin-engined military aircraft, the NA-21 prototype was constructed at North American's factory in Inglewood, California, where work on the aircraft began in early 1936. The NA-21 was a mid-wing monoplane of all-metal construction, powered by two Pratt & Whitney R-2180-A Twin Hornet radial engines, These were planned to be fitted in hydraulically powered nose and dorsal turrets, in addition to manually operated weapons installed in waist and ventral positions. Modifications resolving these resulted in the aircraft being re-designated NA-39, and, accepted by the US Army Air Corps as the XB-21. The aircraft, which had been assigned the serial number 38-485, was evaluated early the following year in competition against a similar design by Douglas Aircraft, an improved version of the company's successful B-18 Bolo. which, developed into the B-25 Mitchell, would become one of the Army's standard medium bombers of World War II.
Specifications (XB-21)
thumb|The XB-21 prototype undergoing maintenance