The North American XB-21 (manufacturer's model designation NA-21) and sometimes referred to by the name "Dragon", was a prototype

bomber aircraft A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped from an aircraf ...

developed by

North American Aviation North American Aviation (NAA) was a major American aerospace manufacturer that designed and built several notable aircraft and spacecraft. Its products included: the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the F ...

in the late 1930s, for evaluation by the

United States Army Air Corps The United States Army Air Corps (USAAC) was the aerial warfare service component of the United States Army between 1926 and 1941. After World War I, as early aviation became an increasingly important part of modern warfare, a philosophical r ...

. Evaluated against the

Douglas B-18 Bolo The Douglas B-18 Bolo is an American heavy bomber which served with the United States Army Air Corps and the Royal Canadian Air Force (as the Digby) during the late 1930s and early 1940s. The Bolo was developed by the Douglas Aircraft Company f ...

, 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,Yenne 2005, pp. 64–65. the NA-21 prototype was constructed at North American's factory in

Inglewood, California Inglewood is a city in southwestern Los Angeles County, California, in the Los Angeles metropolitan area. As of the 2020 U.S. Census, the city had a population of 107,762. It was incorporated on February 14, 1908. The city is in the South Bay ...

,Donald 1997, p. 696. where work on the aircraft began in early 1936.Baugher, Joe
"North American XB-21."
''American Military Aircraft,'' 1 August 1999. Retrieved: 29 July 2011. The NA-21 was a mid-wing

monoplane A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

of all-metal construction, powered by two

Pratt & Whitney R-2180-A Twin Hornet The Pratt & Whitney R-2180-A Twin Hornet was a radial engine developed in the United States by Pratt & Whitney. It had two rows of seven cylinders each. Applications * Douglas DC-4E The Douglas DC-4E was an American experimental airliner ...

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

s, which were fitted with

turbosupercharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

s for increased high-altitude performance. Flown by a crew of six to eight men, the XB-21 featured a remarkably strong defensive armament for the time, including as many as five .30-calibre

M1919 machine gun The M1919 Browning is a .30 caliber medium machine gun that was widely used during the 20th century, especially during World War II, the Korean War, and the Vietnam War. The M1919 saw service as a light infantry, coaxial, mounted, aircraft, and ...

s."Factsheets: North American XB-21."
National Museum of the United States Air Force. Retrieved: 16 July 2017. These were planned to be fitted in hydraulically poweredReuter 2000, p. 38. nose and dorsal turrets, in addition to manually operated weapons installed in waist and ventral positions. Up to of

bombs A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanic ...

could be carried in an internal

bomb bay The bomb bay or weapons bay on some military aircraft is a compartment to carry bombs, usually in the aircraft's fuselage, with "bomb bay doors" which open at the bottom. The bomb bay doors are opened and the bombs are dropped when over th ...

, with of bombs being able to be carried over a range of .

Testing and evaluation

Undertaking its

maiden flight The maiden flight, also known as first flight, of an aircraft is the first occasion on which it leaves the ground under its own power. The same term is also used for the first launch of rockets. The maiden flight of a new aircraft type is alwa ...

on 22 December 1936 at

Mines Field Los Angeles International Airport , commonly referred to as LAX (with each letter pronounced individually), is the primary international airport serving Los Angeles, California and its surrounding metropolitan area. LAX is located in the W ...

in Los Angeles,

test flight Flight testing is a branch of aeronautical engineering that develops specialist equipment required for testing aircraft behaviour and systems. Instrumentation systems are developed using proprietary transducers and data acquisition systems. D ...

s indicated a number of minor problems.Rusinek 2005 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 The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated as ...

, an improved version of the company's successful

B-18 Bolo The Douglas B-18 Bolo is an American heavy bomber which served with the United States Army Air Corps and the Royal Canadian Air Force (as the Digby) during the late 1930s and early 1940s. The Bolo was developed by the Douglas Aircraft Company f ...

. 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. As a result of these problems, the XB-21's nose turret was faired over, while the dorsal turret was removed. The XB-21 proved to have superior performance over its competitor, but price became the primary factor distinguishing the Bolo and the XB-21. 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. 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. 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. Operated by North American Aviation, the XB-21 served as a research aircraft until its retirement. 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 The North American NA-40 was an American prototype bomber aircraft developed by North American Aviation in the late 1930s for evaluation by the United States Army Air Corps. Although unsuccessful, it led directly to the North American B-25 Mitchel ...

, which, developed into the

B-25 Mitchell The North American B-25 Mitchell is an American medium bomber that was introduced in 1941 and named in honor of Major General William "Billy" Mitchell, a pioneer of U.S. military aviation. Used by many Allied air forces, the B-25 served in ...

, would become one of the Army's standard medium bombers of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

.Donald 1997, p. 697.

Specifications (XB-21)

References

Notes

Bibliography

* Donald, David, ed. ''The Complete Encyclopedia of World Aircraft''. London: Orbis, 1997. . * Jones, Lloyd S. ''U.S. Bombers, B1-B70''. Fallbrook, California: Aero Publishers, 1962. . * Reuter, Claus. ''Development of Aircraft Turrets in the AAF, 1917–1944''. New York: S.R. Research & Publishing, 2000. . * 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. . * Yenne, Bill. ''The Story of the Boeing Company''. St. Paul, Minnesota: Zenith Press, 2005. .

External links

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