Berliner-Joyce XP-13 Viper

Last revised June 7, 1998

The XP-13 Viper was the last fighter built by the Thomas-Morse Aircraft Corporation of Ithaca, New York. The Thomas-Morse Aircraft Corporation had started life in early 1917 when the Thomas Brothers Aeroplane Company merged with the Morse Chain Works. The Thomas-Morse outfit built the well-known S-4 fighter-trainer of World War 1, which never actually served in combat, but became a very popular participant at postwar air shows. They also designed and developed the MB-3, the first American fighter of indigenous design to enter service. However, under the bizarre military procurement policy of the early 1920s, Boeing actually obtained the bulk of the production contracts for the MB-3. During the 1920s, Thomas-Morse specialized in the construction of all-metal designs, observation planes, and racers, although a few unsuccessful fighter projects were attempted. Like lots of other companies, Thomas-Morse found that firm military orders were hard to come by.

The XP-13 (named "Viper" by the company) was created for the new 600 hp Curtiss H-1640-1 Chieftain twelve-cylinder 2-row air cooled engine. Thomas-Morse's experience with the manufacture of all-metal aircraft stood them in good stead in the design of the Viper. The fuselage had an all-metal structure covered by a corrugated aluminum-sheet skin. The wing was of wooden construction with fabric covering, but the ailerons were made of corrugated metal sheet. Tail surfaces were of metal and fabric, but the control surfaces were covered with corrugated sheet metal.

The Viper was delivered to the USAAC for evaluation in early 1929. The aircraft was tested at Wright Field in June 1929 as P-559, then purchased by the Army and designated XP-13. The serial number was 29-453. Performance was satisfactory, but the Chieftain suffered with insurmountable cooling problems. Similar problems had been encountered with Curtiss-built fighters powered by this engine. The XP-13 had an empty weight of 2262 lbs and a gross weight of 3256 lb. The maximum speed was 172.5 mph at sea level, 169.9 mph at 5000 feet. The XP-13 could climb to 5000 feet in 3 minutes, and the service ceiling was 20,800 feet. The XP-13 was not fitted with any armament.

Because of the insoluble overheating problems, the Chieftain engine was abandoned. The XP-13 prototype then had a new engine installed in September 1930, a 525 hp Pratt and Whitney SR-1340-C enclosed in a NACA cowling, along with a revised fin and rudder. The designation was changed to XP-13A. The change to a new engine resulted in even better performance. The XP-13A had an empty weight of 2224 lbs and a gross weight of 3194 lb. Maximum speed was 188.5 mph at 5000 feet. The XP-13A could climb to 5000 feet in 3.5 minutes, and service ceiling was 24,150 feet. A USAAC performance report of 1930 described the XP-13A as having a "comfortable feel" in all aerobatics and that it "makes a wonderfully smooth slow roll". However, by then the opportunity was lost. and the Army never ordered the aircraft into production. The Viper caught fire during its last test flight and was destroyed in the resulting crash.

A second Viper was to have been built by Curtiss under the designation XP-14. However, the failure of the Chieftain engine was to cause this project to be cancelled before any aircraft could be built.

The failure of the XP-13 to win a contract was catastrophic for the Thomas-Morse company. In August, 1929, the Thomas-Morse company was taken over by the Consolidated Aircraft Company of Buffalo, New York. The Thomas-Morse company disappeared as a separate entity shortly thereafter.


  1. United States Military Aircraft Since 1909, Gordon Swanborough and Peter Bowers, Smithsonian Institution Press, 1989.

  2. The American Fighter, Enzo Angellucci and Peter Bowers, Orion Books, 1987.

  3. General Dynamics Aircraft and their Predecessors, John Wegg, Naval Institute Press, 1990.