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 The United States Army (USA) is the land warfare, land military branch, service branch of the United States Armed Forces. It is one of the eight Uniformed services of the United States, U.S. uniformed services, and is designated as the Army o ...

in 1929, but they did not adopt it.

Design and development

Thomas-Morse XP-13 - Ray Wagner Collection Image (16573609412)

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 The Thomas-Morse MB-3 was an open-cockpit biplane fighter primarily manufactured by the Boeing Company for the U.S. Army Air Service in 1922. The MB-3A was the mainstay fighter for the Air Service between 1922 and 1925. Development In March 1918 ...

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 The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraf ...

had a corrugated

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

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 The Curtiss H-1640 Chieftain was an unusual American 12-cylinder radial aero engine designed and built by the Curtiss Aeroplane and Motor Company in the mid-1920s.Gunston 1989, p. 46 Design and development The H-1640 was an air-cooled 12 cylin ...

-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 radialGunston 1986, p.46.) 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 The Consolidated Aircraft Corporation was founded in 1923 by Reuben H. Fleet in Buffalo, New York, the result of the Gallaudet Aircraft Company's liquidation and Fleet's purchase of designs from the Dayton-Wright Company as the subsidiary was ...

, and the prototype was lost to an inflight fire.

Variants

;XP-13 :Prototype, serial number 29-453 with 600 hp (448 kW) Curtiss H-1640-1 Chieftain hex engine ;XP-13A :The XP-13 modified with a 525 hp (391 kW) Pratt & Whitney SR-1340-C enclosed in a

NACA cowling The NACA cowling is a type of aerodynamic fairing used to streamline radial engines installed on airplanes. It was developed by Fred Weick of the National Advisory Committee for Aeronautics (NACA) in 1927. It was a major advance in aerodynamic ...

, along with a revised

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

and

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adve ...

"The American Fighter", Enzo Angellucci and Peter Bowers, (Orion Books ), 1987 ;XP-14 :This designation was used for a proposed Curtiss version of the Viper with the Curtiss H-1640-1 Chieftain hex engine

Operators

; *

United States Army Air Service The United States Army Air Service (USAAS)Craven and Cate Vol. 1, p. 9 (also known as the ''"Air Service"'', ''"U.S. Air Service"'' and before its legislative establishment in 1920, the ''"Air Service, United States Army"'') was the aerial war ...

Specifications (XP-13 (Chieftain engine))

References

;Notes ;Bibliography * Dorr, Robert F. and David Donald. ''Fighters of the United States Air Force''. London:Temple, 1990. . * Gunston, Bill, ''World Encyclopedia of Aero Engines''. London: Guild Publishing, 1986.

External links