From: jfb@ihlpl.att.com (Joseph F Baugher)
Newsgroups: sci.military
Subject: Third in the series--The Curtiss P-3 Hawk
Keywords: radial engine, racers, experiments
Date: 23 Aug 92 22:16:22 GMT
Organization: AT&T Bell Laboratories -  Naperville, Illinois


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

The P-3 was an attempt to adapt the Curtiss P-1  Hawk  airframe  to  a
radial engine.  Like the Navy, the USAAC was initially undecided as to
whether it preferred radial or in-line engines for its fighters.   The
radial  engine  had  been successfully applied to the Boeing P-12, and
the  Army  wanted  to  determine  if  the  radial  engine   could   be
successfully applied to the Curtiss Hawk as well.

The designation XP-3 had originally been reserved  for  P-1A  Ser  No.
26-300 which was to be fitted with the new experimental 390 hp Curtiss
R-1454 air-cooled radial engine.  However,  this  engine  had  already
been tested in other aircraft and had been found to be unsatisfactory.
Consequently, the XP-3  designation  was  cancelled  before  this  new
engine could be installed.

In October 1927, P-1A Ser No 26-300 was fitted instead  with  the  new
410 hp Pratt and Whitney R-1340-1 Wasp air-cooled radial engine.  This
aircraft was redesignated XP-3A No. 1 (factory designation Model 34N).
This  aircraft  was originally delivered to the Army uncowled, but the
plane was used by the Army to test some early NACA cowling designs for
radial engines.

The lighter engine installation gave the XP-3A an improved  climb  and
ceiling  performance  as compared  with  the P-1 series.  The Army was
sufficiently impressed that they ordered 5 P-3As on December 27, 1927.
Serials were 28-189/193.  Deliveries began in October 1928.  Power was
provided by the 450 hp Pratt and Whitney R-1340-3 (SR-1340B).  Maximum
speed  was  171 mph at sea level, 168 mph at 5000 feet.  Initial climb
rate was 1742 feet per  minute.   Service  ceiling  was  23,000  feet.
Weights  were  2024  pounds  empty,  2730 pounds gross.  Range was 342
miles.  Armament was two 0.30-cal machine guns mounted  in  the  upper
fuselage,  synchronized  to fire through the propeller arc.  The P-3As
were originally delivered to the Army completely uncowled, but  narrow
Townend rings were soon added.  These rings did little to increase the
speed over that of the original uncowled XP-3A.

The designation of XP-3A 26-300 was changed to XP-21 when it  was used
to test-fly the 300-hp R-985-1 Wasp Junior in December 1930.  This new
designation was used to identify a particular test  configuration  and
not  a new prototype.  However, this engine had only half the power of
service fighters of the period, and the project was not successful.  A
later  engine  change  to  the  300  hp Pratt and Whitney R-975 radial
changed the designation of 26-300 to XP-21A.

The designation XP-3A No. 2 was applied to a production P-3A  (Ser  No
28-189)  which  was  used  for test work for the development of a NACA
cowling with fuselage faired to match the cowl. The XP-3A  No.  2  was
fitted  with a tight cowling and large spinner, and was entered in the
1929 National Air Race Free-for-All.  It came in second  at  186  mph,
when  the  Army  raced  against  civilians  for  the  last time.  This
airplane was later redesignated XP-21 No. 2 when it was fitted with  a
Pratt  and  Whitney  R-985-1 Wasp Junior engine of 300 hp.  28-189 was
later brought up to standards of P-1F following a change to  D-12  (V-
1150-3) engine.

Tests with the P-3 and the XP-21 failed to convince the  Army  of  any
intrinsic  superiority  of  the radial engine for the Hawk, and it was
decided that the Hawk line of Army fighters  was  to  stick  with  the
liquid-cooled engine.

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
Newsgroups: sci.military