North American XB-21

{{Infobox aircraft

|name= XB-21

|image= North American XB-21 4.jpg

|image_border= yes

|caption=

|type= Medium bomber

|national_origin= United States

|manufacturer= North American Aviation

|designer=

|first_flight= 22 December 1936

|introduction=

|retired=

|status=

|primary_user= United States Army Air Corps

|more_users=

|produced=

|number_built= 1

|program cost=

|unit cost= US$122,000

|developed_from=

|variants=

|developed_into= North American NA-40

}}

The North American XB-21 (manufacturer's model designation NA-21) and sometimes referred to by the name "Dragon",Jones 1962, p. 65. 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,Yenne 2005, pp. 64–65. the NA-21 prototype was constructed at North American's factory in Inglewood, California,Donald 1997, p. 696. where work on the aircraft began in early 1936.Baugher, Joe. [http://www.joebaugher.com/usaf_bombers/b21.html "North American XB-21."] American Military Aircraft, 1 August 1999. Retrieved: 29 July 2011. The NA-21 was a mid-wing monoplane of all-metal construction, powered by two Pratt & Whitney R-2180-A Twin Hornet radial engines, which were fitted with turbosuperchargers 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 guns.[https://web.archive.org/web/20140925024834/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2491 "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 {{convert|10000|lb}} of bombs could be carried in an internal bomb bay, with {{convert|2200|lb}} of bombs being able to be carried over a range of {{convert|1900|mi|km}}.

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.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, an improved version of the company's successful B-18 Bolo.

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,Yenne 2006, p. 87. which, developed into the B-25 Mitchell, would become one of the Army's standard medium bombers of World War II.Donald 1997, p. 697.

Specifications (XB-21)

File:North American XB-21 6.jpg

{{Aircraft specs

|ref=

|prime units?=imp

|genhide=

|crew=Six to eight

|capacity=

|length m=

|length ft=61

|length in=9

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|span m=

|span ft=95

|span in=0

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|height m=

|height ft=14

|height in=9

|height note=

|wing area sqm=

|wing area sqft=1120

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|empty weight kg=

|empty weight lb=19082

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|gross weight kg=

|gross weight lb=27253

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|max takeoff weight lb=40000

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|eng1 number=2

|eng1 name=Pratt & Whitney R-2180-A Twin Hornet

|eng1 type=turbosupercharged radial engines

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|eng1 hp=1200

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|prop blade number=3

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|max speed kmh=

|max speed mph=220

|max speed kts=

|max speed note=at {{convert|10000|ft}}

|cruise speed kmh=

|cruise speed mph=190

|cruise speed kts=

|cruise speed note=

|stall speed kmh=

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|stall speed note=

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|range km=

|range miles=1960

|range nmi=

|range note=with {{convert|2200|lb|kg}} of bombs

|combat range km=

|combat range miles=600

|combat range nmi=

|combat range note=with {{convert|10000|lb|kg}} of bombs

|ferry range km=

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|ferry range nmi=

|ferry range note=

|endurance=

|ceiling m=

|ceiling ft=25000

|ceiling note=

|g limits=

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|glide ratio=

|climb rate ms=

|climb rate ftmin=

|climb rate note=

|time to altitude=10 minutes to {{convert|10000|ft}}

|lift to drag=

|wing loading kg/m2=

|wing loading lb/sqft=

|wing loading note=

|fuel consumption kg/km=

|fuel consumption lb/mi=

|power/mass=

|more performance=

|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 {{convert|10000|lb}} in an internal bay.

|avionics=

}}

References

=Notes=

=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. [https://web.archive.org/web/20081121215312/http://www.aiaa-myaerospace.org/rhtp/stories/rusinek_tale.pdf "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}}.