North American XB-21
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The North American XB-21 (manufacturer's model designation NA-21)<ref name="USAF"/> and sometimes referred to by the name "Dragon",<ref>Jones 1962, p. 65.</ref> 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,<ref name="Boeing">Yenne 2005, pp. 64–65.</ref> the NA-21 prototype was constructed at North American's factory in Inglewood, California,<ref name="DD">Donald 1997, p. 696.</ref> where work on the aircraft began in early 1936.<ref name="Baugher">Baugher, Joe. "North American XB-21." American Military Aircraft, 1 August 1999. Retrieved: 29 July 2011.</ref> The NA-21 was a mid-wing monoplane of all-metal construction, powered by two Pratt & Whitney R-2180-A Twin Hornet radial engines,<ref name="Baugher"/> which were fitted with turbosuperchargers for increased high-altitude performance.<ref name="DD"/>
Flown by a crew of six to eight men,<ref name="USAF"/> the XB-21 featured a remarkably strong defensive armament for the time,<ref name="DD"/> including as many as five .30-calibre M1919 machine guns.<ref name="USAF">"Factsheets: North American XB-21." National Museum of the United States Air Force. Retrieved: 16 July 2017.</ref> These were planned to be fitted in hydraulically powered<ref name="Reuter">Reuter 2000, p. 38.</ref> nose and dorsal turrets, in addition to manually operated weapons installed in waist and ventral positions.<ref name="DD"/> Up to Template:Convert of bombs could be carried in an internal bomb bay, with Template:Convert of bombs being able to be carried over a range of Template:Convert.<ref name="DD"/>
Testing and evaluation
Undertaking its maiden flight on 22 December 1936 at Mines Field in Los Angeles, test flights indicated a number of minor problems.<ref name="TwoD">Rusinek 2005</ref> 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.<ref name="USAF"/>
During the course of flight testing, the gun turrets proved troublesome, their drive motors proving to be underpowered, and issues with wind blast through the gun slots were also encountered.<ref name="Reuter"/> As a result of these problems, the XB-21's nose turret was faired over, while the dorsal turret was removed.<ref name="USAF"/>
The XB-21 proved to have superior performance over its competitor,<ref name="TwoD"/> but price became the primary factor distinguishing the Bolo and the XB-21.<ref name="Baugher"/> On this account, the modified B-18 was declared the winner of the competition, Douglas quoting a price per aircraft of US$64,000, while North American's estimate was US$122,000 per aircraft, and an order was placed for 177 of the Douglas aircraft, to be designated B-18A.<ref name="Baugher"/><ref name="USAF"/>
Despite this, the US Army Air Corps found the performance of the XB-21 to have been favorable enough to order five pre-production aircraft, to be designated YB-21.<ref name="USAF"/> However, soon after this contract was awarded, it was cancelled, and none of the YB-21s were ever built, leaving the XB-21 as the sole example of the type ever constructed.<ref name="USAF"/> Operated by North American Aviation, the XB-21 served as a research aircraft until its retirement.<ref name="Boeing"/>
Although the XB-21 failed to win a production contract, it was the first of a long line of North American Aviation medium bomber aircraft, and provided experience and knowledge that assisted in the development of the North American NA-40,<ref>Yenne 2006, p. 87.</ref> which, developed into the B-25 Mitchell, would become one of the Army's standard medium bombers of World War II.<ref>Donald 1997, p. 697.</ref>
Specifications (XB-21)
See also
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References
Notes
Bibliography
- Donald, David, ed. The Complete Encyclopedia of World Aircraft. London: Orbis, 1997. Template:ISBN.
- Jones, Lloyd S. U.S. Bombers, B1-B70. Fallbrook, California: Aero Publishers, 1962. Template:ASIN.
- Reuter, Claus. Development of Aircraft Turrets in the AAF, 1917–1944. New York: S.R. Research & Publishing, 2000. Template:ISBN.
- Rusinek, Ed. "A Tale of Two Dragons." North American Aviation Retirees Bulletin, Winter 2005.
- Yenne, Bill. The American Aircraft Factory in World War II. St. Paul, Minnesota: Zenith Press, 2006. Template:ISBN.
- Yenne, Bill. The Story of the Boeing Company. St. Paul, Minnesota: Zenith Press, 2005. Template:ISBN.
Further reading
External links
Template:North American Aviation aircraft Template:USAF bomber aircraft Template:Good article