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Thomas-Morse XP-13
Role Fighter
Manufacturer Thomas-Morse
Designer B. Douglas Thomas[1]
Introduction June 1929
Primary user United States Army Air Service
Number built 1[2]

The XP-13 Viper was a prototype biplane fighter aircraft designed by the United States company Thomas-Morse Aircraft Corporation. The airplane was delivered to the United States Army in 1929 but they did not adopt it.

Design and development[edit | edit source]

This aircraft was one of several B. Douglas Thomas designs built in hopes of a production contract from the Army, following the successful Thomas-Morse MB-3 of 1919. Financed by the company, and named the "Viper", it was officially purchased by the Army in June 1929 and designated "XP-13".

The XP-13 fuselage had a corrugated aluminum skin built over a metal frame; the flying surfaces were also metal-framed, but covered with the traditional fabric. While designed to use the 600 hp Curtiss H-1640-1 Chieftain engine, (a novel 12-cylinder two-row air-cooled radial with the rear cylinders directly behind the front cylinders rather than staggered as normal in a two-row radial[3]) for which the XP-13 incorporated a complex system of baffles to direct cooling air over the engine, the engine simply would not stay cool enough, and in September 1930 it was replaced with a Pratt & Whitney SR1340C Wasp of 450 hp. Ironically, the lower-power engine actually resulted in a speed increase of 15 mph, at least partly because of the weight savings.[4]

In the end, the Army decided against production, Thomas-Morse was acquired by Consolidated Aircraft, and the prototype was lost to an inflight fire.

Variants[edit | edit source]

Prototype, serial number 29-453 with 600 hp (448 kW) Curtiss H-1640-1 Chieftain hex engine[2]
The XP-13 modified with a 525 hp (391 kW) Pratt & Whitney SR-1340-C enclosed in a NACA cowling, along with a revised fin and rudder[5]
This designation was used for a proposed Curtiss version of the Viper with the Curtiss H-1640-1 Chieftain hex engine

Operators[edit | edit source]

 United States

United States Army Air Service

Side view of P&W-powered XP-13A variant showing corrugated aluminum skin.

Specifications (XP-13 (Chieftain engine))[edit | edit source]

Data from "The Complete Book of Fighters" cover Editors: William Green & Gordon Swanborough (Barnes & Noble Books New York, 1998, ISBN 0-7607-0904-1), 608 pp.

General characteristics

  • Crew: 1
  • Length: 23 ft 6 in (7.16 m)
  • Wingspan: 28 ft 0 in (8.53 m)
  • Height: 8 ft 5 in (2.56 m)
  • Wing area: 189 ft² (17.6 m²)
  • Empty weight: 2,262 lb (1,026 kg)
  • Loaded weight: 3,256 lb (1,477 kg)
  • Powerplant: 1 × Curtiss H-1640-1 Chieftain 12-cyliner two-row air-cooled radial engine, 600 hp (448 kW)


  • Maximum speed: 150 knots (172 mph, 277 km/h) (at sea level)
  • Cruise speed: 113 knots (130 mph, 209 km/h [6])
  • Range: 168 NM (193 mi, 312 km [6])
  • Service ceiling: 20,775 ft (6,300 m)
  • Rate of climb: 1,700 ft/min[6] (8.6 m/s)



See also[edit | edit source]

References[edit | edit source]

  1. The Complete Book of Fighters Editors: William Green & Gordon Swanborough (Barnes & Noble Books New York, 1998, ISBN 0-7607-0904-1)
  2. 2.0 2.1 "U.S. Army Aircraft 1908-1946" by James C. Fahey, 1946, 64pp.
  3. Gunston 1986, p.46.
  4. "U.S. Fighters", by Lloyd S. Jones, (Aero Publishers, Inc. ISBN 0-8168-9200-8, 1975) pp. 46-47
  5. "The American Fighter", Enzo Angellucci and Peter Bowers, (Orion Books ISBN 0-517-56588-9), 1987
  6. 6.0 6.1 6.2 Dorr and Donald 1990, p.43
  • Dorr, Robert F. and David Donald. Fighters of the United States Air Force. London:Temple, 1990. ISBN 0-600-55094-X.
  • Gunston, Bill, World Encyclopedia of Aero Engines. London: Guild Publishing, 1986.

External links[edit | edit source]

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