Thomas-Morse XP-13 Viper
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.
|Designer||B. Douglas Thomas|
|Primary user||United States Army Air Service|
Design and developmentEdit
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.
- 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
- This designation was used for a proposed Curtiss version of the Viper with the Curtiss H-1640-1 Chieftain hex engine
Specifications (XP-13 (Chieftain engine))Edit
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.
- 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 sq ft (17.6 m2)
- Empty weight: 2,262 lb (1,026 kg)
- Gross 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 kn (172 mph, 277 km/h) (at sea level)
- Cruise speed: 113 kn (130 mph, 209 km/h) 
- Range: 168 nmi (193 mi, 312 km) 
- Service ceiling: 20,775 ft (6,300 m)
- Rate of climb: 1,700 ft/min (8.6 m/s) 
- The Complete Book of Fighters Editors: William Green & Gordon Swanborough (Barnes & Noble Books New York, 1998, ISBN 0-7607-0904-1)
- "U.S. Army Aircraft 1908–1946" by James C. Fahey, 1946, 64pp.
- Gunston 1986, p.46.
- "U.S. Fighters", by Lloyd S. Jones, (Aero Publishers, Inc. ISBN 0-8168-9200-8, 1975) pp. 46–47
- "The American Fighter", Enzo Angellucci and Peter Bowers, (Orion Books ISBN 0-517-56588-9), 1987
- Dorr and Donald 1990, p.43
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