North American XB-21

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.

XB-21
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

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

Data from [1][5]

General characteristics

  • Crew: Six to eight
  • Length: 61 ft 9 in (18.82 m)
  • Wingspan: 95 ft 0 in (28.96 m)
  • Height: 14 ft 9 in (4.50 m)
  • Wing area: 1,120 sq ft (104 m2)
  • Empty weight: 19,082 lb (8,655 kg)
  • Gross weight: 27,253 lb (12,362 kg)
  • Max takeoff weight: 40,000 lb (18,144 kg)
  • Powerplant: 2 × Pratt & Whitney R-2180-A Twin Hornet turbosupercharged radial engines, 1,200 hp (890 kW) each
  • Propellers: 3-bladed

Performance

  • Maximum speed: 220 mph (350 km/h, 190 kn) at 10,000 feet (3,000 m)
  • Cruise speed: 190 mph (310 km/h, 170 kn)
  • Range: 1,960 mi (3,150 km, 1,700 nmi) with 2,200 pounds (1,000 kg) of bombs
  • Combat range: 600 mi (970 km, 520 nmi) with 10,000 pounds (4,500 kg) of bombs
  • Service ceiling: 25,000 ft (7,600 m)
  • Time to altitude: 10 minutes to 10,000 feet (3,000 m)

Armament

  • Guns: Five .30-calibre machine guns, mounted in single turrets in the nose and dorsal positions, and single manually operated mounts in the waist and ventral positions.
  • Bombs: Up to 10,000 pounds (4,500 kg) in an internal bay.

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

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

Bibliography
  • Donald, David, ed. The Complete Encyclopedia of World Aircraft. London: Orbis, 1997. ISBN 0-7607-0592-5.
  • Jones, Lloyd S. U.S. Bombers, B1-B70. Fallbrook, California: Aero Publishers, 1962. ASIN B0007FFBSO.
  • Reuter, Claus. Development of Aircraft Turrets in the AAF, 1917–1944. New York: S.R. Research & Publishing, 2000. ISBN 1-894643-08-9.
  • 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. ISBN 0-7603-2300-3.
  • Yenne, Bill. The Story of the Boeing Company. St. Paul, Minnesota: Zenith Press, 2005. ISBN 0-7603-2333-X.

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