TYPE: Fighter, fighter bomber

ACCOMMODATION: Pilot only

POWER PLANT: One Allison V-1710-35 liquid-cooled Vee engine with single-stage supercharger, rated at 1,150 hp

PERFORMANCE: 360 mph at 15,000 ft

COMMENT: The Bell P-39 “Airacobra” was one of the main American fighter aircraft in service when the United States of America entered the World War II. Designed by Bell Aircraft, it had an innovative layout, with the engine installed in the center fuselage, behind the pilot, and driving a tractor propeller via a long shaft. It was also the first fighter fitted with a tricycle undercarriage.  Although its mid-engine placement was innovative, the P-39 design was handicapped by the absence of an efficient turbo-supercharger, limiting it to low-altitude work. The XP-39 made its maiden flight on 6 April 1938 achieving 390 mph at 20,000 ft, reaching this altitude in only five minutes. A production order was placed and by the time of the Pearl Harbor attack, nearly 600 P-39s had been built. When P-39 production ended in August 1944, Bell had built 9,558. Most important variants were Bell P-39N and P-30Q, if which 4,773 have been built. The “Airacobra” saw combat throughout the world, particularly in the Southwest Pacific, Mediterranean and Russian theaters. But the “Airacobra” found itself outclassed as an interceptor and the type was gradually relegated to other duties. It often was used at lower altitudes for such missions as ground strafing (Ref.: 23).

TYPE: Fighter, fighter bomber

ACCOMMODATION: Pilot only

POWER PLANT: One Chrysler XI-2220-11 inverted-Vee in-line engine, rated at 2,500 hp

PERFORMANCE: 414 mph

COMMENT: While the production of the Republic P-47 Thunderbolt had been emerging in ever-mounting quantities, Republic’s engineers had been investigating other ways in which the Thunderbolt could be improved. Two P-47D-15-RAs were assigned for testing the Chrysler XI-2220 engine, a 16 cylinder inverted-Vee liquid-cooled unit which transmitted its power to a propeller shaft by way of gears located midway along the crankshaft. The design was such as to produce an extremely finely-streamlined cowling of low frontal area, despite the engine’s ability to produce 2,500 hp. The converted aircraft were designated Republic XP-47H and remembered to a pre-war project, the Republic XP-69. Extensive redesign of the P-47 airframe was necessary to install the XI-2220-11 engine, with which was associated a General Electric CH-5 single-stage turbosupercharger in a modified installation in the rear fuselage. The first flight was not made until July 1945 and in one of the 27 flights a top speed of 414 mph had been recorded. The second XP-47H flew briefly after the war ended (Ref.: 9).

TYPE: Fighter, fighter bomber

ACCOMMODATION: Pilot only

POWER PLANT: One Pratt & Whitney R-2800-57 Double Wasp radial engine plus one General Electric CH-5 turbosupercharger, rated at 2,800 hp at 32,500 ft

PERFORMANCE: 505 mph at 34,500 ft

COMMENT: In 1942 studies made by Republic culminated in proposals for a “lightweight” P-47 with an improved engine installation. Construction of two prototypes was authorized, but within a few weeks it became clear to Republic and the USAAF that the more radical development of the P-47 powered by a 3,000 hp Pratt & Whitney R-4300 Wasp Major, than proceeding as the Republic P-72 held greater promise than the P-47J within a similar timescale, and work on the latter project was limited to a single XP-47J. This sole prototype had a lightened wing structure, a more powerful variant of the R-2800 radial engine, driving a four-bladed propeller with a large spinner and a fan to assist the flow of cooling air through a narrow annulus around the spinner. A separate intake scoop beneath and behind the engine cowling provided air for the General Electric CH-5 supercharger in the rear fuselage. The first flight was made in November 1943, and on August 1944 a speed of 505 mph was recorded, at 34,450 ft. This was the highest known speed achieved up to that time in level flight by a propeller driven aircraft and established the XP-47J as one of the few such aircraft to have broken through the 500-mph “barrier” (Lit.: 9).

TYPE: Interceptor, Fighter, Fighter-bomber

ACCOMMODATION: Pilot only

POWER PLANT: One Pratt & Whitney R-2800-53 engine, rated at 2,000 hp

PERFORMANCE: 414 mph

COMMENT: In 1940 the Curtiss Aircraft Company proposed a new design for the eventual replacement for the Curtiss P-40. The new aircraft, the Curtiss XP-60, went through a long series of prototype versions with different engines. Installation of the British Rolls-Royce Merlin engines led to the development of the XP-53, soon redesignated XP-60. Delayed deliveries of the Merlin engines necessitated the installation of Wright (XP-63C) as well as Chrysler (XP-60B) engines. To improve the performance of the XP-60C the engine was changed again, this time a Pratt & Whitney R-2800 with contra-rotating propellers was installed. During its first flight the results were generally satisfactory. Changing the contra-props into a four-bladed propeller led to the XP-60E. But the performance was poorly, too,  and further work on this design was abandonded. (Ref.: 8)