Subject: Number Seventy-Six in the Series--Bell XP-76

From: [email-masked]
Date: 1 Jun 93 14:36:48 GMT

>From [email-masked]

One of the persistent criticisms of the Bell P-39 Airacobra was that 
its high-altitude performance was rather poor in comparison to that of 
its competitors.  The Bell P-76 was a proposed advanced version of the 
Airacobra that would be equipped with a more powerful engine, a 
laminar flow wing, and other refinements that would help to correct 
some of these deficiencies.  

The P-76 project began its life as the XP-39E, which was a 1941 
project to flight-test the experimental Continental I-1430-1 
inverted-Vee supercharged liquid cooled engine.  The company 
designation for this project was Model 23.  The first two machines 
were ordered on April 10, 1941, with a third machine being added on 
October 17, 1941.  As called for in the contract, three production 
P-39Ds were taken off the line and modified to XP-39E standards.  
Serials were 41-19501, 41-19502, and 42-7164.  

The Continental engine was not yet ready when the XP-39E airframes 
were completed, and the 1325 hp Allison V-1710-47 engine had to be 
installed in its place.  The carburetor air intake was relocated and 
the wing-root radiator intakes were enlarged.  The XP-39E featured 
laminar-flow wings with square-cut tips, the wing span and gross area 
being increased to 35 feet 10 inches and 236 square feet respectively.  
Each of the three examples of the XP-39E that were built tested 
different configurations for the vertical tail surfaces--the first 
being rounded and tapered, the second being cut-off square and rather 
short, and the third being rather similar to that of the P-51.  
Armament was the same as that of the P-39D.  

Empty and loaded weights of the XP-39E were 6936 lbs and 8918 lbs 
respectively.  During tests, a maximum speed of 386 mph at 21,680 feet 
was attained.  An altitude of 20,000 feet could be reached in 9.3 
minutes.  

The XP-39E was considered by the Army as being sufficiently different 
from the stock P-39 that it was considered worthy of a new pursuit 
designation--it was redesignated XP-76 on February 24, 1942.  The Army 
felt sufficiently confident in the new aircraft that they ordered no 
less than 4000 production P-76s from Bell, all of which were to be 
manufactured at Bell's new plant in Atlanta, Georgia.  Less than three 
months later, the USAAF was to have second thoughts about the wisdom 
of its decision.  Even though the XP-76 had proven itself to be faster 
than the P-39D, the new design was considered to be inferior to the 
basic Airacobra in other respects, and the order for the P-76 was 
cancelled in its entirety on May 20, 1942, freeing up the Bell-Atlanta 
plant for license manufacture of the B-29 Superfortress.  

Even though no production ensued, the XP-39E/XP-76 did provide some 
valuable basic data which proved useful for the P-63 Kingcobra 
project.  

Sources: 

  War Planes of the Second World War, Fighters, Volume Four, William 
  Green, Doubleday, 1964.  

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

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

  P-39 Airacobra in Action, Ernie McDowell, Squadron/Signal 
  Publications, 1980 

  Fighters of the United States Air Force, Robert F. Dorr and David 
  Donald, Temple Press Aerospace, 1990.  

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