From: Joseph F Baugher <jfb@ihlpl.att.com>
Subject: Number Thirty-Seven in the Series--the Curtiss YP-37
Keywords: Liquid-cooled Hawk
Organization: AT&T Bell Laboratories -  Naperville, Illinois
Date: Fri, 13 Nov 1992 17:39:31 GMT


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


In early 1937, the USAAC expressed an interest in seeing how much the 
performance the P-36 could be improved if its radial engine were 
replaced by the new turbosupercharged Allison V-1710 liquid-cooled 
engine.  On February 16, the USAAC placed an order with Curtiss for a 
single P-36 airframe powered by this new engine.  

In response to this USAAC request, Curtiss's chief designer Donovan 
Berlin fitted a 1150 hp Allison V-1710-11 turbosupercharged engine to 
the original Model 75 prototype airframe.  He positioned the three 
Prestone cooling radiators immediately behind the engine.  In order to 
balance the aircraft and to make room for the radiators, the pilot's 
cockpit was moved quite far aft.  Except for the cockpit relocation 
and the V-12 liquid-cooled engine, the XP-37 was otherwise identical 
to the P-36.  

The modified Model 75 prototype was redesignated Model 75I by Curtiss 
and was delivered to the Army as a new airframe.  It was designated 
XP-37 with Army serial number 37-375.  The XP-37 flew for the first 
time in April 1937 and was delivered to the army in June.  

The XP-37 attained a maximum speed of 340 mph at 20,000 feet and a 
service ceiling of 35,000 feet.  An altitude of 20,000 feet could be 
reached in 7.1 minutes.  Gross weight was 6350 lbs.  The aircraft was 
equipped with what was the standard USAAC armament of the time--one 
0.30-in and one 0.50-in machine gun mounted in the fuselage and 
synchronized to fire through the propeller arc.  

Almost from the first, the XP-37 aircraft ran into trouble.  The 
supercharger was extremely unreliable, and the performance of the 
aircraft fell short of expectations.  In addition, the positioning of 
the cockpit that far aft on the fuselage resulted in extremely poor 
visibility, especially during takeoffs and landings.  

The XP-37 was retired to an Army mechanics' school in August 1941 with 
a total of only 152 hours of flying time.  

Although the new engine/supercharger combination was quite troublesome 
in the XP-37, the Army was nevertheless impressed by the potential of 
the design, and on December 11, 1937 they ordered 13 service test 
YP-37s.  Serials were 38-472/484.  These used Allison V-1710-21 
engines fitted with improved B-2 superchargers, revised nose contours, 
a 25-inch increase in fuselage length aft of the cockpit, and most of 
the aerodynamic improvements worked out on the XP-37.  The first one 
of these flew in June of 1939.  However, the YP-37s continued to 
suffer with the same supercharger problems of the X-model and did not 
live up to their potential.  All but one of the YP-37s were out of 
service or retired to mechanics' schools by early 1942.  The 
highest-time aircraft had only 212 hours.  The last active example 
(38-474) was transferred to the National Advisory Committee for 
Aeronautics (NACA) for research in August 1942.  It survived until 
January 1946.  

The YP-37 was powered by a 1000 hp Allison V-1710-21.  Wing span was 
37 feet 3 1/2 inches, length was 32 feet 11 1/2 inches, and wing area 
was 236 square feet.  Weights were 5592 lbs empty, 6700 lbs gross.  
Maximum speed was 340 mph at 10,000 feet.  An altitude of 20,000 feet 
could be attained in 8 min 30 sec.  Service ceiling was 34,000 feet.  

In the meantime, the USAAC had already held a competition for a new 
fighter in January 1939, and had chosen another Berlin design, the 
Model 75P which was also derived from the P-36.  This was eventually 
to emerge as the famous P-40.  All further work on the P-37 was 
abandoned.  

Sources: 

  Curtiss Aircraft, 1907-1947, Peter M Bowers, Naval Institute Press, 
  1979 

  The Curtiss Hawk 75, Aircraft in Profile No.  80, Profile 
  Publications, Ltd.  1966 

  War Planes of the Second World War, Fighters, Volume Four, William 
  Green, Doubleday, 1961.  

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

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