page_title: Thomas-Morse XP-13 Viper
section_title: Design and development
hierarchical_section_title: Thomas-Morse XP-13 Viper / Design and development
caption_attribution_description: PictionID:41898525 - Title:Ray Wagner Collection Image - Catalog:16_000808 Thomas-Morse XP-13 29-453 - Filename:16_000808 Thomas-Morse XP-13 29-453.tif - - Ray Wagner was Archivist at the San Diego Air and Space Museum for several years and is an author of several books on aviation --- ---Please Tag these images so that the information can be permanently stored with the digital file.---Repository: San Diego Air and Space Museum
context_page_description: 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.
context_section_description: 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) 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.
  In the end, the Army decided against production, Thomas-Morse was acquired by Consolidated Aircraft, and the prototype was lost to an inflight fire.
caption: The XP-13, powered by the Curtiss H-1640-1 Chieftain engine
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