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The Northrop XA-13 was the first of a series of attack aircraft based on the Northrop Gamma, one of the first aircraft produced by the newly founded Northrop Corporation in 1932. The Northrop Gamma was designed as a special purpose and mail-carrying aircraft, and was produced in a number of custom-built versions for different customers, using a variety of different engines.
The Northrop Gamma was a low winged monoplane, with its cockpit placed half way back along the fuselage. The wing had a straight central section, while the outer sections were at an upwards angle, while the undercarriage was contained in streamlined trousers, with the bottom third of the wheels exposed.
Northrop soon realised that the Gamma had better performance than the standard US Army Air Corps attack aircraft, the Curtis A-12 Shrike, and decided to produce a military prototype. The resulting Gamma 2C was completed in May 1933. It retained the same wing and undercarriage as the civilian Gammas and was powered by a 735hp Wright SR-1820-F2 nine-cylinder radial engine. The biggest change was to the cockpit – the centrally located cockpit of the normal Gamma was replaced with a two-seat cockpit, covered by a greenhouse canopy, which was moved forward to place the pilot just behind the wing leading edge. The Gamma 2C was armed with four wing-mounted 0.30in machine guns, and one rear mounted gun that could be fired in the normal way from the rear cockpit or down through a ventral hatch. Maximum bomb load was 1,100lb, carried on racks under the wings and central fuselage.
In July 1933 the Gamma 2C began tests at Wright Field. It was returned to Northrop for modifications in February 1934, and then after these changes had been made was purchased on 28 June 1934 by the Army Air Corps, and given the designation XA-13. The main change made to the XA-13 was the replacement of the trapezoidal vertical tail surface of the Gamma 2C with a triangular version with rounded corners.
The Gamma 2C/ XA-13 was the first of a sizable family of military aircraft. The first order came in 1934, and was for a light bomber version for the Chinese government. After examining a second prototype, the Gamma 2F, on 24 December 1934 the US Army followed suit, ordering 110 aircraft, with the designation A-17. In 1935 the XA-13 was given a new engine, and became the XA-16. Finally, after Northrop had become the El Segundo Division of Douglas a sizable export market was found for the Northrop attack aircraft, this time as the Douglas 8A.
Engine: Wright SR-1820-F2
Power: 735hp
Span: 48ft
Length: 29ft 2in
Height: 9ft 2in
Empty Weight: 3,600lb
Gross Weight: 6,463lb
Maximum Speed: 207mph
Cruising Speed: 198mph
Climb rate: 1,300ft/min
Ceiling: 21,750ft
Range: 1,100 miles
Guns: Five 0.30in machine guns
Bomb load: 1,100lb
Suggested Reading
McDonnell Douglas: v.1, Rene J. Francillon (Amazon.co.uk)
McDonnell Douglas: v.1, Rene J. Francillon (Amazon.com)