Thomas Morse XP-13 Viper USAF.jpg
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 American 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

The XP-13, powered by the Curtiss H-1640-1 Chieftain engine
The XP-13, powered by the Curtiss H-1640-1 Chieftain engine

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.


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


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

Specifications (XP-13 (Chieftain engine))

Data from William Green; Gordon Swanborough (1994). The Complete Book of Fighters: An Illustrated Encyclopedia of Every Fighter Aircraft Built and Flown. Salamander. ISBN 978-0-86101-643-3.

General characteristics



See also

Related lists


  1. ^ The Complete Book of Fighters Editors: William Green & Gordon Swanborough (Barnes & Noble Books New York, 1998, ISBN 0-7607-0904-1)
  2. ^ a b "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. ^ a b c Dorr and Donald 1990, p.43
USAAS/USAAC/USAAF/USAF fighter designations 1924–1962, and Tri-Service post-1962 systems