XB-21
North American XB-21 4.jpg
Role Medium bomber
National origin United States
Manufacturer North American Aviation
First flight 22 December 1936
Primary user United States Army Air Corps
Number built 1
Developed into North American NA-40

The North American XB-21 (manufacturer's model designation NA-21)[1] and sometimes referred to by the name "Dragon",[2] 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,[3] the NA-21 prototype was constructed at North American's factory in Inglewood, California,[4] where work on the aircraft began in early 1936.[5] The NA-21 was a mid-wing monoplane of all-metal construction, powered by two Pratt & Whitney R-2180-A Twin Hornet radial engines,[5] which were fitted with turbosuperchargers for increased high-altitude performance.[4]

Flown by a crew of six to eight men,[1] the XB-21 featured a remarkably strong defensive armament for the time,[4] including as many as five .30-calibre M1919 machine guns.[1] These were planned to be fitted in hydraulically powered[6] nose and dorsal turrets, in addition to manually operated weapons installed in waist and ventral positions.[4] Up to 10,000 pounds (4,500 kg) of bombs could be carried in an internal bomb bay, with 2,200 pounds (1,000 kg) of bombs being able to be carried over a range of 1,900 miles (3,100 km).[4]

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.[7] 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.[1]

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.[6] As a result of these problems, the XB-21's nose turret was faired over, while the dorsal turret was removed.[1]

The XB-21 proved to have superior performance over its competitor,[7] but price became the primary factor distinguishing the Bolo and the XB-21.[5] 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.[5][1]

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.[1] 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.[1] Operated by North American Aviation, the XB-21 served as a research aircraft until its retirement.[3]

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,[8] which, developed into the B-25 Mitchell, would become one of the Army's standard medium bombers of World War II.[9]

Specifications (XB-21)

The XB-21 prototype undergoing maintenance
The XB-21 prototype undergoing maintenance

Data from [1][5]

General characteristics

Performance

Armament

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

Notes

  1. ^ a b c d e f g h i "Factsheets: North American XB-21." National Museum of the United States Air Force. Retrieved: 16 July 2017.
  2. ^ Jones 1962, p. 65.
  3. ^ a b Yenne 2005, pp. 64–65.
  4. ^ a b c d e Donald 1997, p. 696.
  5. ^ a b c d e Baugher, Joe. "North American XB-21." American Military Aircraft, 1 August 1999. Retrieved: 29 July 2011.
  6. ^ a b Reuter 2000, p. 38.
  7. ^ a b Rusinek 2005
  8. ^ Yenne 2006, p. 87.
  9. ^ Donald 1997, p. 697.

Bibliography

Further reading