North American XB-21

XB-21
Role	Medium bomber
National origin	United States
Manufacturer	North American
First flight	22 December 1936
Primary user	United States Army Air Corps
Number built	One
Unit cost	$122,000 USD[1]

The North American XB-21, also known by the manufacturer's model designation NA-21, 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 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, company test flying indicated a number of minor problems.^[7] Modifications resolving these resulted in the aircraft being re-designated NA-39, and, accepted by the U.S. Army Air Corps as the XB-21. The aircraft, which had been assigned the serial number 38-485,^[1] 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 the fly-off, 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 $64,000 USD, while North American's estimate was $122,000 USD per aircraft,^[1] and an order was placed for 177 of the Douglas aircraft, to be designated B-18A.^[5]

Despite this, the 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]

Legacy

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 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 (170 kn; 310 km/h)
• Range: 1,960 mi (1,703 nmi; 3,154 km) with 2,200 pounds (1,000 kg) of bombs
• Combat range: 600 mi (521 nmi; 966 km) with 10,000 pounds (4,500 kg) of bombs
• Service ceiling: 25,000 ft (7,620 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

	Aviation portal
	United States Army portal

Aircraft of comparable role, configuration and era

• Breguet 693
• Bristol Blenheim
• Douglas B-18 Bolo
• Martin Model 146
• PZL.37 Łoś
  

Related lists

• List of bomber aircraft
• List of military aircraft of the United States
  

References

Notes

1. ^ ^{a b c d e f g h i j} "Factsheets: North American XB-21." National Museum of the United States Air Force. Retrieved: 21 May 2010.
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

• 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 1-8946-4308-9.
• 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.

External links

• XB-21 at Aero-Web.org