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 Mitchell medium bomber.

NA-40
Role Attack bomber
National origin United States
Manufacturer North American Aviation
First flight January 1939
Primary user United States Army Air Corps
Number built 1
Developed from North American XB-21
Developed into North American B-25 Mitchell

Design and development
NA-40 prototype front view, showing constant dihedral wing discarded early in development of the successor B-25 design

The Air Corps issued a circular (number 38-385) in March 1938 describing the performance they required from the next bombers — a payload of 1,200 lb (540 kg) with a range of 1,200 mi (1,900 km) at more than 200 mph (320 km/h).[1] Several American aircraft companies responded with submissions: Bell Model 9 with two engines, Boeing-Stearman Model X-100 with Pratt & Whitney R-2180 radials, Douglas Model 7B with Pratt & Whitney R-1830 Twin Wasp radials, Martin Model 167F[1] and North American submitted their NA-40 design. The NA-40 had benefited from the North American XB-21 (NA-39) of 1936, which was the company's partly successful design for an earlier medium bomber that had been initially accepted and ordered, but then cancelled. However, the company's experience from the XB-21 contributed to the design and development of the NA-40. The single NA-40 built flew first at the end of January 1939. It went through several modifications to correct problems. These improvements included fitting 1,600 hp (1,193 kW) Wright R-2600 "Twin Cyclone" radial engines, in March 1939, which solved the lack of power.[1]

In March 1939, North American delivered the substantially redesigned and improved NA-40 (as NA-40B) to the United States Army Air Corps for evaluation.[1] It was in competition with other manufacturers' designs produced - the Bell had not been built - Douglas 7B, Stearman XA-21, and the Martin Model 167F[2] but failed to win orders. The aircraft was originally intended to be an attack bomber for export to the United Kingdom and France, both of which had a pressing requirement for such aircraft in the early stages of World War II.

Despite the loss of the 7B in an accident injuring a French observer in January, the French had ordered the 7B and a revised version (as the DB-7). Unfortunately, the NA-40B was destroyed in a crash on 11 April 1939 while undergoing testing. Although the crash was not considered due to a fault with the aircraft design, the U.S. Army ordered the DB-7 as the A-20 Havoc.[3][4]

The Air Corps issued a specification for a medium bomber in March 1939 that was capable of carrying a payload of 2,400 lb (1,100 kg) over 1,200 mi (1,900 km) at 300 mph (480 km/h)[5] NAA used the NA-40B design to develop the NA-62, which competed for the medium bomber contract. No YB-25 was available for prototype service tests. In September 1939, the Air Corps ordered the NA-62 into production as the B-25, along with the other new Air Corps medium bomber, the Martin B-26 Marauder "off the drawing board".

Variants
North American NA-40B prototype side
NA-40
A twin-engined, five-seat bomber to meet 1938 USAAF requirement for an attack bomber, it was powered by two 1,100 hp (820 kW) Pratt & Whitney R-1830-56C3G radials. Wingspan was 66 ft (20.12 m), and length 48 ft 3 in (14.71 m). First flown on 29 January 1939, it proved to be underpowered and unstable.[6][7]
NA-40B
The NA-40B (also known as the NA-40-2) was a modification of the NA-40 prototype with two 1,600 hp (1,193 kW) Wright R-2600-A71-3 radials and numerous minor changes. It first flew in revised form on 1 March 1939, but crashed on 11 April 1940.[6]
NA-40-3 through NA-40-7
Proposed export versions, not built.[8]

Specifications (NA-40B)

Data from Baugher[1]

General characteristics

  • Crew: 5
  • Length: 47 ft 10 in (14.58 m)
  • Wingspan: 66 ft (20 m)
  • Wing area: 559 sq ft (51.9 m2)
  • Empty weight: 13,961 lb (6,333 kg)
  • Gross weight: 19,741 lb (8,954 kg)
  • Powerplant: 2 × Wright R-2600-A71-3 Twin Cyclone 14-cylinder radial engines, 1,275 hp (951 kW) each at 12,000 feet

Performance

  • Maximum speed: 309 mph (497 km/h, 269 kn) at 14,000 ft (4,300 m)

Armament

  • Guns: 3x 0.30 in (7.6 mm) flexible machine guns (nose, turret and ventral/waist)
  • Bombs: designed for 2,100 lb (950 kg)

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

Notes
  1. Baugher, Joe. "North American NA-40." American Military Aircraft: US Bomber Aircraft, 6 March 2000. Retrieved: 24 May 2015.
  2. Baugher, Joe. "Douglas Model 7B." American Military Aircraft: US Bomber Aircraft, 2000. Retrieved: 28 May 2015.
  3. Parker 2013, pp. 77–79, 83, 88, 92.
  4. Borth 1945, pp. 70, 92, 244.
  5. Baugher, Joe. "North American B-25 Mitchell." American Military Aircraft: US Bomber Aircraft, 6 March 2000. Retrieved: 24 May 2015.
  6. Dorr Wings of Fame Volume 3, p. 124.
  7. "North American". Aerofiles, 2009. Retrieved: 12 December 2011.
  8. McDowell, Ernest (1978). B-25 Mitchell In Action. Squadron/Signal Publications, Inc. p. 3. ISBN 0-89747-033-8.

Bibliography
  • Borth, Christy. Masters of Mass Production. Indianapolis, Indiana: Bobbs-Merrill Co., 1945.
  • Donald, David, ed. The Complete Encyclopedia of World Aircraft. London: Orbis, 1997. ISBN 0-7607-0592-5.
  • Dorr, Robert F. "North American B-25 Variant Briefing". Wings of Fame, Volume 3, 1996. London: Aerospace Publishing. ISBN 1-874023-70-0. ISSN 1361-2034. pp. 118–141.
  • Jones, Lloyd S. U.S. Bombers, B1-B70. Fallbrook, California: Aero Publishers, 1962. ASIN B0007FFBSO.
  • Norton, Bill. American Bomber Aircraft Development in World War 2. Hersham, Surrey, UK: Midland Publishing, 2012. ISBN 978-1-85780-330-3.
  • Parker, Dana T. Building Victory: Aircraft Manufacturing in the Los Angeles Area in World War II. Cypress, California: Dana Parker Enterprises, 2013. ISBN 978-0-9897906-0-4.
  • 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.
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