The Lend-Lease Fighter

Development of Bell's P-63 Kingcobra

by Randy Wilson

Copyright © 1998 by the Confederate Air Force and Randy Wilson. All rights reserved.

Often referred to as a P-39 with an uprated engine and laminar flow wings, Bell’s P-63 Kingcobra was really a new and larger design which, unfortunately, copied the basic layout of its predecessor.

[Author's note: the next three paragraphs were not originally published due to space limitations]

In early 1941, even before the first P-39 had been blooded in combat, lessons learned from the air war in Europe caused Bell to propose an improved version of the Airacobra to the U.S. Army Air Corps. Two projects were put forth and approved for prototype testing, the XP-39E and the XP-63. Both projects featured new laminar flow wings of greater span and a more powerful Allison V-1710 engine with a second, auxiliary supercharger for better performance at altitude.

Three XP-39E prototypes were built from modified Airacobra airframes but proved to be little, if any improvement over the original. The XP-63 started with a completely redesigned and larger airframe, which shared little but the general layout and appearance with the P-39. Key points in common were the Allison V-12 engine mounted behind the cockpit, 37mm cannon in the nose and automotive style doors on each side of the pilot’s compartment.

Two P-63 prototypes were ordered, with a third airframe intended for static load testing. The first XP-63 flew on December 7, 1942 but was badly damaged the next month after a failure of the landing gear. The second prototype flew in February 1943 but was lost a few months later due to an engine failure. Flight testing was finally completed with the third airframe, and the first production P-63A was delivered to the U.S. Army Air Forces in October 1943.

At the same time the P-63 was being designed, North American’s Allison powered P-51 fighter was re-engined with a Rolls-Royce Merlin engine, which resulted in a dramatic increase in performance and range at high altitude. This was primarily due to the Merlin’s excellent two-stage mechanical supercharger but North American was also able to find space for 269 gallons of fuel internally in what became the Mustang, the first true Allied long-range escort fighter.

The Allison V-1710 engine which powered the P-39, P-63 and other fighters was designed from the beginning to use a turbosupercharger to boost its power at altitude, and when so fitted, as in the P-38 Lightning, gave excellent service. However, when the decision was made to reserve the limited supply of turbosuperchargers primarily for heavy bombers, all but the P-38 were forced to rely on Allison’s mechanical supercharger, which was found wanting in power above 12,000 feet. Allison’s answer to this problem was the P-63A’s 1,325 horsepower V-1710-93 engine, which featured a second, auxiliary supercharger with an automatic hydraulic drive. All subsequent production P-63s had versions of this two-stage supercharger, but their performance never matched the Merlin-powered Mustang.

When the P-39 was designed in the late 1930s, streamlining and small size and weight were one of the few ways to ensure a fast and maneuverable fighter. With the fuselage occupied by the pilot, the mid-engine and its cooling system, plus the 37mm cannon and ammunition, the only space left for fuel was in the wings. With the same general layout, the P-63 suffered the same limitation, thus most P-63As held only 100 gallons of fuel, and early on pylons were added under the fuselage and later the wings for external fuel tanks or bombs. Thus development of the Kingcobra moved toward a ground attack fighter-bomber, where a heavy ordnance load counted more than long range.

A total of 1,725 P-63As were built by Bell between October, 1943 and December of 1944. Most were armed with the 37mm cannon and two 0.50 caliber machine guns in the nose, plus two more 0.50 caliber guns in pods under the wings. Many could also carry two 500 pound bombs, while later production P-63As could also mount three air-to-ground rockets under each wing. Maximum loaded weight was 10,500 pounds and the top speed at 25,000 feet over 400 mph.

The designation P-63B was reserved for a Merlin-engined variant which was never built, thus the next production model Kingcobra was the P-63C, powered by an Allison V-1710-117 engine with water injection for greater war emergency power. Rated the same as the A model’s engine for normal use, the Dash 117 engine could be boosted from the usual 55 inches of manifold pressure to 78 inches for very short periods using water injection. Internal fuel capacity was slightly increased to 107 gallons, and deliveries of the first of 1,227 P-63Cs began in January of 1945.

One P-63D was built, featuring a sliding bubble canopy, longer span wings and 1,425 horsepower Dash 109 engine. While its performance was an improvement over the earlier Kingcobras, it was still behind the North American Mustang as a high-altitude and long-range fighter and was not developed further. The longer wings, however, were used on the thirteen P-63Es, which reverted to the automotive style pilot’s compartment but retained the more powerful engine. Two (some sources say only one) E model airframes were completed with a much enlarged vertical fin and rudder under the designation P-63F. The Ghost Squadron’s P-63 is one of these very rare F models.

One other E series aircraft served as the XP-63H, powered by a turbocompound V-1710-127 engine, which had not only the two-stage supercharger but an exhaust driven gas turbine which fed power mechanically back to the engine. At 29,000 feet, this engine still delivered 1,550 horsepower, and at low altitudes, with special fuel, its output was an amazing 2,900 horsepower!

How then did the Kingcobra perform in combat with the U.S. Army Air Forces? It didn’t – the only American use of P-63s as fighters were a few hundred employed as transition trainers in Advanced Training Units. Most, about 2,397, Kingcobras were provided to the Soviet Union under Lend-Lease, ferried by U.S. and Soviet pilots via Alaska and then Siberia. As with the P-39, the Soviets used the P-63’s 37mm cannon for attacks on tanks and other armored targets and seemed to have good luck with them in air-to-air combat. However few details have been published about the later.

The French were also provided with 300 P-63Cs late in the war, although some sources suggest the actual number delivered was less than two hundred. Kingcobras operated with French forces until about 1951, seeing their last combat in Indochina. No wonder the P-63 is often called the Lend-Lease Fighter – but the most unusual service that the Kingcobra performed in World War II was that of a manned aerial gunnery target, in what has been called Operation Pinball.

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