Republic XP-47J Superbolt

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Brief Summary
The XP-47J represents one of the fastest propeller planes built during the Second World War only really being surpassed in maximum top speed of a propeller aircraft after the war by the likes of planes such as the Soviet Tu-95 and the American XFY-1 Pogo.



As the P-47 begun service in 1942 there were already plans made to improve upon the design as it begun making it’s way into the skies in Europe from the production lines in the United States, two P-47’s were set aside to experiment in two directions. The first direction involved changing the engine with a liquid cooled engine, designated the XP-47H the second direction involved the reduction of weight and modifications of the engine being designated the XP-47J.

The first and main difference when it comes to a standard jug P-47’s and the XP-47J is the engine with the Pratt & Witney R-2800 57(C) being added which had a standard output of 2100hp and a war time emergency output of 2800hp and unlike the P-47’s air intake cooling the XP-47J was cooled by a tight cowling fitted to enclose the engine and be cooled by an intake fan and a new chin scoop. Inlets had also been fitted to provide additional air for the turbo supercharger and the exhaust system was altered so that it could be vented out the ventral ports for an additional boost.

As this plane was meant to test what the limits of what can be done to the P-47 the armaments were reduced to 6 50 cal browning’s with 267 rounds each, the rear fuel tank and radio equipment were removed to give more aerodynamics alongside the plane being unable to use any ordinance.

A contra-rotating propeller was initially proposed but delays meant it was shelved and eventually planned to be used later on another prototype. As the plane was a modified P-47-D Razor back it’s conversion took a small amount of time and was ready by November 1943 only 5 months after it was contracted to be built.

The plane’s wingspan was 40’10 feet or 12.4m and the length of 33’3 feet or 10.1m, the empty weight of the aircraft was 9663lb or 4383kg and was designed for a standard weight of 12400lb of weight (5625kg), the ceiling for this aircraft was 44500feet or 13716m high and the planes cruise speed was 400mph (644km/h), the fuel capacity was 287 US gallons ( 1086L)

The weight modifications in all saved about 1000lb (roughly 300kg) of weight from the standard P-47D alongside it’s beast of an engine meant that by July 1944 tests were seen to see just how far the plane could be pushed after the addition of a new propeller and the General Electric CH-5 Turbocharger.

With the changes all set in August 1944 a test flight for the maximum speed of the aircraft was set out and the test pilot reportedly measured a top speed of 505mph or 812.7km/h, recorded on the 5th of August with the test flight most likely being on the 4th, with it’s top speed it beats out any other propeller plane of it’s era with the closest plane to it being the British Vickers Supermarine Spiteful which achieved an impressive 483mph or 777km/h with it’s 2375hp Griffon engine. Both planes were designed and tested around the same time showcasing the what the maximum potential speeds of propeller aircraft of their era were capable of.

Tests of the aircraft’s climb rate also showcased it could climb up to 30,000 feet or 9144m in six minutes 45 seconds, to be noted though none of these speeds were achieved later on when the USAAF took control of the plane however they still managed a 484mph or 779km/h maximum speed which although less than the initial tests still put’s it slightly ahead of the Spiteful overseas.

For all it’s speed and power the plane suffered a lot of issues that prevented it’s acceptance into service the main one among these was that only after 10 hours of flight testing the engine would be so worn out that it would need replacing whilst a second prototype that was planned never came to be limiting the plane to the single prototype.

The prototype would of received the contra-rotating propeller however Pratt and Whitney never solved the issues with that alongside Republics growing interest with the XP-47J project with them wanting to move onto newer and fresher ideas after their ideas of the limitations of the P-47 were tested.


Although initially planned to be able to slide into the production line with ease it became apparent only about 30% of the aircraft was the same as the P-47’s in production therefore would take more time to get the XP-47J up to speed with the production needed during the war. The P-47D was proven and successful in combat so there was no real reason for changes to the XP-47J.

Republic fell out of favour about a month after they received the XP-47J in July 1943 and would propose and produce their next project of a next generation fighter the XP-72 Ultrabolt, this plane would suffer the same fate as a lot of the late propeller planes in that the limits of what could be achieved with such a plane had been met and the jet age was beginning to catch up and dethrone the age of the propeller plane.


After all is said and done the XP-47J did help out it’s siblings one of which mounted the same engine being the P-47M with 130 of them being built.

Throughout it’s run the top speed had changed multiple times especially after the USAAF took over the plane with it’s 9th of December 1944 test stating the planes top speed of 484mph (779km/h) at 25350 feet (7727m), whilst the official summary report says the plane’s maximum speed is 507mph (816km/h) and a climb rate of 4900fpm (24.9m/s), lastly Republic’s test report on January 27th 1945 states the top speed is 502mph (808km/h). this is all most likely to do with how problematic the engine and exhausts were with the plane with constant issues in test flights.




Crew: 1
Length: 10.1m (33’3 feet)
Wingspan: 12.4m (40’10 feet)
Height: 4.3m (14’2 feet)
Wing Area: 300 square feet (27.87 square meters)
Empty Weight: 4383kg (9663lb)
Standard Weight: 5625kg (12400lb)
Maximum Weight: 7615kg (16788lb)
Engine: Pratt & Whitney R-2800-57(C) 2100hp standard, 2800hp war time emergency power
Service limit: 13715m (44997 feet) (8.52mi)
Maximum range: 1722km (1070mi)
Maximum speed: 813km/h (505mph)
Cruise Speed: 644km/h (400mph)
Rate of climb: 24.9m/s (4900feet/m)
Armaments: 6x .50 calibre Browning Heavy Machine guns (three per wing) (267 rounds per gun (1602 rounds overall)
Hardpoints: None


Republic P-47 Thunderbolt variants - Wikipedia.


I don’t play the american tt but I like it. +1

I guess maybe researchable tree at 6.7 BR in rank 4. and after P-51H-5

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