Originally posted by SunTracker
P47 performance is directly related to engine thrust. Lets not forget, that a souped-up P47 hit 504mph in July 1944 in level flight.
That was the XP-47J, fitted with a 2,800 hp C-series R-2800 engine. This prototype was abandoned for Republic's 3,600 hp XP-72A.
Designed specifically to defeat the Fw 190, the XP-47J was Republic's effort at an "air superiority" fighter. Weight was reduced (so was the armament, reduced from 8 to 6 guns) 9,663 pounds (empty), power was increased by 800 hp, and a "high activity" paddle-blade prop was employed to more efficiently use the added power.
Factory test data reveals a climb rate of 4,900 fpm at sea level, and a startling 4,400 fpm climb rate at 20,000 feet. The XP-47J, flying with full internal fuel and ballast installed to simulate a full ammo load, reached 30,000 feet in 6 minutes, 45 seconds!
This prototype was fully fitted for combat, it was not stripped down. It included guns, ammo ballast, armor and a full set of radios. It was not, however, fitted with underwing pylons (as were no other P-47s when the XP-47J rolled out in November of 1943).
Ultimately, the engine and prop combination were fitted to a P-47C-5, which exceeded 480 mph during test runs. Eventually, the data from this program resulted in the P-47M, the fastest, best climbing P-47 to see combat duty in the war. There were plenty of hotrodded Jugs prior to the M model as P&W tech reps had been assisting crew chiefs in tuning the R-2800s for sustained over-boost use. During 1943, both Republic and Pratt & Whitney had done extensive durability testing with R-2800 engines over-boosted to as much as 3,600 hp. Later C-series engines were tested at boost settings producing 3,600+ hp for 250 hours without failure. They determined that while engine life was greatly shortened, there was little risk of catastrophic engine failure from over-boosting to 72 in/Hg for short durations. Consequently, many P-47s were rigged in the field (primary mods being to the wastegates) for this power output. Johnson stated without ambiguity, that his P-47 could pull 72" MAP,
without water injection! Johnson related that crew chief Pappy Gould and a P&W rep named Ron Dempsey explained that they could rig Johnson's Jug for 72" MAP with a kit fabricated locally. Johnson asked what the benefit would be and he was told that he could expect to see major increases in climb, acceleration and speed. Johnson said, "go ahead". Johnson stated that the result was a 470 mph P-47D-5 (serial 42-8561, named "Lucky"). Johnson's P-47 was certainly not the only Jug to be so modified. According to Gould, that most, if not all P-47s in the 61st FS of the 56th FG was field modified in the same way.
What many don't realize or understand was that unauthorized field modifications were the rule, not the exception, throughout the AAF. Modified canopys (some P-47s razorbacks also sported Malcolm Hoods), Spitfire mirrors, custom fuel blends (almost all fuels were blended locally), modified wastegates and turbo regulators to name just a few. Johnson's P-47 had every seam sanded smooth, and gaps filled with autobody filler. Then it was polished as smooth as glass. Pappy Gould described some of his own tricks, which included gasket-matching, smoothing and polishing of exhaust ports and stacks. Exercising extreme care in matching and aligning intake plumbing. Redundent sealing throughout the turbo ducting. Rejetting carbs and carefully cleaning up venturis. Reshaping cylinder baffling to improve engine cooling. Almost no aircraft remained truly "factory stock".
My regards,
Widewing
