XP-13 Viper

The XP-13 Viper was a prototype biplane fighter designed by the Thomas-Morse Aircraft Corporation and delivered to the United States Army in 1929.

This aircraft was one of several designs by Thomas-Morse designed and 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 by it the "Viper", it was officially purchased by the Army in June of 1929 and designated "XP-13".

The XP-13 fuselage had a corrugated aluminum skin built over metal frame; the flying surfaces were also metal-framed, but covered with the traditional fabric. While designed to use the 600hp Curtiss H-1640-1 Chieftain engine, 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 of 1930 it was replaced with a Pratt & Whitney SR1340C Wasp of 450hp. Ironically, the weaker engine actually resulted in a speed increase of 15 mph, at least partly because of the weight savings.

In the end, the Army decided against production, Thomas-Morse was acquired by Consolidated Aircraft, and the prototype was lost to a fire that broke out during flight.

The designation XP-14 was used for a proposed Curtiss version of the Viper.

References

• Lloyd S. Jones, U.S. Fighters (Aero Publishers, Inc., 1975) pp. 46-47 ISBN 0-8168-9200-8
• National Museum of the USAF page, with photo

Designation sequence

• 1924-1948 USAAC/F:
  • Pursuit: XP-10 - P-11 - P-12 - XP-13 - XP-14 - XP-15 - P-16 - XP-17

Related lists

• List of military aircraft of the United States
• List of fighter aircraft