Like many of the American war-winning fighter aircraft of World War 2 (1939-1945), the Republic P-47 "Thunderbolt" was the subject of many experiments, modifications, and offshoots to help extract additional power and performance from the excellent airframe. The P-47D model became the definitive wartime production model and the promising, yet-developmentally troubled, P-47M was limited to just 130 examples before the company moved on the follow-up P-47N - which was given extended fuel stores to better cope with long ranges of the Pacific Theater. More radical conversions were still had between these more notable forms and the XP-47H was a late-war attempt to turn the "Jug" into an inline-engined fast fighter.
The XP-47H was born from two P-47D-15-RA production airframes ("Razorback" models) set aside specifically to test the new Chrysler XI-2220-11 16-cylinder inverted-Vee liquid-cooled inline engine promising up to 2,500 horsepower. These aircraft were pulled from Republic's production line in Evansville, Indiana, a facility set up to help offset the heavy industrial need for Thunderbolts in the American war effort. The H-model more or less retained the form and function of the P-47D but the new, and utterly complex, Chrysler engine installation meant that the rather basic fuselage of the P-47D would need to undergo considerable modification to accept the powerplant.
As a test bed, the fighter was stripped of all of its armament and "military" equipment. Unlike the "open-nosed" air-cooled radial piston engine fitted to the original D-models, the XP-47H was given an all-new forward section shaped around the liquid-cooled inline engine. The nose was very pointed thanks to the spinner which was streamlined with the general shape of the aircraft. The engine drove a four-bladed propeller unit and also caused the nose section to extend noticeably forward of the cockpit - limiting the pilot's forward vision. Under the nose was seated a cooling radiator air scoop designed to draw air as the aircraft reached speed and this gave the revised Thunderbolt a deeper side profile than normal and made a large aircraft appear even larger.
All other physical qualities of the D-model were retained including the elliptical wing mainplanes, single-finned tail unit, and tail-dragger undercarriage (retractable). The pilot sat at midships underneath a heavily-framed canopy which slid back on side rails. The raised fuselage spine of the Razorback Thunderbolts limited views to the critical rear of the aircraft - later remedied by the introduction of a bubble-style canopy design during the war.
The Chrysler inline proved more trouble than it was ultimately worth and delays incurred on that project naturally delayed the XP-47H program. As such, the H-model's prototype did not go airborne until July of 1945 and even then the intended axial flow supercharger tied to the engine was not in a ready state so a General Electric CH-5 turbosupercharger unit was substituted in its place.
With the program slowly progressing, engineers were optimistic for a maximum speed of around 490 miles per hour - making the H-model one of the fastest piston-engined fighters of the war. However, testing soon revealed that the XP-47H was a dead-end project - doomed by its troublesome engine, spotty development successes, and the end of the war in the Pacific come August 1945. During testing, the H-model recorded a maximum speed of 414 miles per hour, far short of the expected performance gains - and this without weaponry or military equipment fitted.
The project was eventually dropped by Republic despite the high investment already put into the fighter.
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