Subject: Number Twenty-One in the Series--the Curtiss XP-21

From: [email-masked] (Joseph F Baugher)
Date: 29 Sep 92 13:03:57 GMT

>From Joseph F Baugher <[email-masked]>

The Curtiss XP-21 is yet another example of the infuriatingly 
inconsistent designation system used by the USAAC during the 1920s and 
early 1930s.  

The history of the XP-21 begins with the Curtiss P-3 pursuit.  The P-3 
was an attempt to adapt the Curtiss P-1 single-seat biplane fighter to 
a radial engine.  The last P-1A of the series (Ser.  No 26-300) had 
been modified as the XP-3A with the replacement of the original 
liquid-cooled Curtiss D-12 by a 410 hp Pratt and Whitney R-1340-3 
air-cooled radial engine.  This airplane flew for the first time in 
April 1928, and became the prototype for the P-3A series, of which 
only five examples were built (Ser Nos 28-189/193).  

In 1930, XP-3A Ser No 26-300 and P-3A Ser No 28-189 were used as 
flying test-beds for the new 300 hp Pratt and Whitney R-985 Wasp 
Junior engine.  These planes were then redesignated XP-21.  This new 
designation was intended to identify a particular test configuration 
and was not intended to indicate a new prototype.  The first flight of 
an XP-21 took place in December 1930.  Tests did not convince the Army 
that there was any intrinsic superiority of the radial engine as a 
powerplant for the Hawk.  Consequently, XP-21 Ser No 28-189 was later 
fitted with a D-12 engine and became a standard P-1F.  However, XP-21 
Ser No 26-300 continued on as a testbed and became XP-21A when it was 
fitted with an improved 300 hp R-975 Wasp Junior 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