From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Twentieth in the Series--The Curtiss YP-20
Keywords: redesignations
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Mon, 28 Sep 1992 16:51:26 GMT


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

It is a gross understatement to say that the designation  scheme  used
by  the  Army  for  its pursuit aircraft during the late 1920s and the
early 1930s was bizarre and inconsistent.  Sometimes, an  experimental
change  in  powerplant in an existing pursuit design would call for an
entirely new designation.  On other occasions, it would call only  for
a  new  version  letter in the existing designation.  And sometimes it
would call for no redesignation at all.  Often,  an  existing  pursuit
airframe would be taken off the production line, experimentally fitted
with a new engine, given a new designation, and then would revert back
to  the  old  designation  when  the  engine  was removed.  No example
typified the eccentricities of the designation system  more  than  the
gyrations which produced the Curtiss YP-20.

The history of the YP-20 can be said to start back with the first Army
production  contract  for  the Curtiss P-6 Hawk.  The designation P-11
had been reserved by the Army for a version of the P-6 powered by  the
600  hp  Curtiss  H-1640  Chieftain two-row twelve-cylinder air-cooled
engine.  Three P-11s had been ordered (Ser  Nos  29-267,  29-268,  and
29-374)  by  the Army at the same time that the original P-6 order had
been issued.  However, in tests with  other  airframes  the  Chieftain
engine  had  proven  itself  to  be  completely  unsatisfactory, being
subject to chronic overheating problems.  The Chieftain engine project
was  cancelled  while  the P-11 airframes were still on the production
line. The three P-11 airframes were  then  used  for  other  purposes.
29-267  and  29-368  were  fitted  with  Conqueror  engines  and  then
delivered to the Army as standard P-6s.  However, 29-374 was  to  have
an entirely different fate.

In October 1930, Ser No 29-374 was fitted with  a  650  hp  Wright  R-
1870-9  Cyclone  radial  engine.   The  fin  and  rudder  were changed
slightly by raising the division between the rudder balance areas  and
the top of the fin by half a rib space.  The aircraft was redesignated
YP-20, continuing the rather bizarre practice of  giving  new  pursuit
designations  to  existing  airframes  which  had  been experimentally
fitted with different kinds of engines.  A large set  of  wheel  pants
was  briefly  fitted to the YP-20 in the interest of attaining greater
speed.

The YP-20 had a maximum speed of 187 mph at sea level and 184  mph  at
5000  feet.   The  initial  climb  rate  was  2600 feet/minute, and an
altitude of 5600 feet could  be  attained  in  2.3  minutes.   Service
ceiling was 26,700 feet.  Weights were 2477 lbs empty, 3323 lbs gross.
The YP-20 was armed with two 0.30-cal  machine  guns  mounted  in  the
upper  fuselage  decking,  synchronized  to fire through the propeller
arc.

In June, 1931, the  YP-20  participated  unsuccessfully  in  a  flyoff
against  a  standard  P-6,  a standard Boeing P-12, and the Conqueror-
powered XP-22.  The high speed of the XP-22 won it a production  order
for 46 production examples under the designation YP-22.

After the tests were over, Ser No 29-374 was fitted with  a  V-1570-23
Conqueror engine and with the new nose, belly radiator, and single-leg
undercarriage first tried out on the XP-22.  With these  changes,  Ser
No.  29-374  was  redesignated XP-6E, and became the prototype for the
famed P-6E version of the Hawk.  After  having  proven  out  the  P-6E
concept,  the  aircraft was fitted with a turbosupercharger and became
the P-6F.

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.  

  Curtiss Aircraft: 1907-1947, Peter M. Bowers, Naval Institute Press, 
  1987.

  "The Curtiss Army Hawks", Peter M. Bowers, Aircraft in Profile, 
  Doubleday, 1969.


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


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