From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Thirteenth in the series--The Thomas-Morse XP-13 Viper
Keywords: Another casualty of the Chieftain engine
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Wed, 9 Sep 1992 16:54:37 GMT


From Joseph F Baugher <jfb@ihlpl.att.com>


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.

Sources:

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

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

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

Joe Baugher       AT&T Bell Laboratories    2000 North Naperville Road 
		  Naperville, Illinois 60566-7033.   (708) 713-4548


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