Le P40 - en anglais 2
The P-40 did not follow the normal design procedure for a new military airplane.
Rather, the P-40 prototype was a conversion of an existing U.S. Army model, the
Curtiss P-36A. It was the 10th P-36A airframe fitted with an Allison V-1710 V12 liquid-
cooled engine replacing the Pratt & Whitney R-1830 "Twin-Wasp" air-cooled radial.
P-36A The Allison V-12, built by a division of General Motors, allowed a smaller frontal region
than the radial engines which reduced drag. This engine was also used inthe P-38,
P-39, and P-51A. With the standardization of the Allison V-1710,
the P-36 design was reworked to incorporate this engine, this resulted in three
new designations of XP-37, YP-37, and XP-40.
The XP-37 which was equipped with a General Electric turbo-supercharger,
and featured numerous other modifications, including a rearward positioned cockpit.
The XP-37 showed at Army a top speed of 340 mph at 20,000 feet.
XP-37 Thirteen YP-37s were built for service evaluation, but differed little from the XP-37.
The plane was lengthened 25 inches and the skin was Alclad which allowed a polished
metal finish. Both the XP-37 and the YP-37 suffered from troubles with the turbo-
supercharging system; the problems of supercharging the Allison was never fully solved
until 1944.
YP-37 With increasingly ominous signs of an approaching war, development of this fighter was
abandoned in favor of a less complex and more direct conversion of the P-36 for the
Allison engine, the XP-40. With the promise from Allison that an internal supercharger
could be fitted to the V-1710, the 10th P-36A was used. The armament would be the
same as the P-36A; one .30 caliber Browning M-2 with 500 rounds on the top left of
the engine cowling and one .50 caliber Browning M-2 with 200 rounds on the top right
of the cowling. Provisions were made to carry six 20 lb bombs. Fuel capacity would be
158 U.S. gallons and since the prototype would consist largely of a preexisting design,
the cost was a real bargain. Although from the firewall back the P-36 and XP-40 look
virtually the same, much more was considered than just mounting the Allison on the
P-36. The liquid-cooled Allison required many systems (coolant radiators and tanks)
not needed by an air-cooled engine. These along with gun mountings, air induction
systems, weight and balance and maintenance considerations had to be woven into
the new design.
Because the 1150 HP V-1710-19 did not have a turbo and an intercooler (this affected
high altitude performance), the radiator was mounted externally far aft below and
behind the cockpit (similar to the later North American P-51).
The initial XP-40
The XP-40 made its first flight on October 14, 1938 and was accepted by the Army on the 16th. The XP-40 showed at Army a top speed of 342 mph at 11,000 feet.
Although there had been wind tunnel tests, air flow and cooling problems showed up
in flight tests. Various fixes were tried which lead to the radiator being moved forward
under the engine.
Final version of the XP-40 In January 1939 the XP-40 competed against the Bell XP-39 and the twin-engine Lockheed XP-38 with turbos (it crashed after continuing its delivery flight past Wright Field to set a new coast-to-coast speed record). The XP-40 won the competition and the Army immediately ordered 524 production models (the army ordered later ordered models of both the P-38 and P-39). The first production P-40 was identical to the XP-40 except for the armament. 