Republic XP-47H Thunderbolt
In early 1940, Chrysler had been busy watching the results of air combat over Europe for the previous few months and recognized that there would soon be demand for far more powerful power plants. So they began development of a massive new liquid-cooled engine to meet that perceived requirement. This became the Chrysler XIV-2220, which promised a rather impressive, for 1940 certainly, 2,500hp.

In 1943, two P-47D-15-RE airframes (serials 42-23297/23298) were selected for testing with the new experimental 2300 hp Chrysler XIV-2220-1 sixteen-cylinder inverted Vee liquid-cooled engine. These aircraft were redesignated XP-47H. The liquid-cooled Chrysler engine with its large under-fuselage radiator radically changed the appearance of the Thunderbolt, and increased overall length to 39 feet 2 inches. With the increased power and improved streamlining, a maximum speed of 490 mph was anticipated.

So, it wasn’t until late-July 1945 that the first flight by the Chrysler engined aircraft took place. And in a short test program that only apparently ran for a few months, the XP-47H showed that it would need a whole lot more work before it would ever be close to being a reliable service aircraft.

There are also some discrepancies in the sources as to just how successful the XP-47H was performance wise, with some saying it did indeed achieve the hoped for speed of 490mph, while others say that it actually proved inferior to the then current models of P-47 Thunderbolt already in service at the time!

In any case, the Chrysler XIV-2220 engine never achieved production and the advent of jet propulsion killed any further USAAF interest in the development of even faster piston-engined fighters. Consequently, no further work was undertaken on the XP-47H project.




Republic XP-47J Thunderbolt
The fastest version of the Thunderbolt was the XP-47J, which was proposed in November 1942 as a lighter-weight version of the Thunderbolt designed to explore the outer limits of the design's basic performance envelope. The XP-47J was fitted with a 2800 hp Pratt and Whitney R-2800-57(C) housed inside a close-fitting cowling and cooled by a fan. The ventral intake for the CH-5 turbosupercharger was separated from the engine cowling and moved aft. The four-bladed propeller was fitted with a large conical-shaped spinner. The wing structure was lightened and the armament was reduced from eight to six 0.50-inch machine guns. The contract was approved on June 18, 1943.

The XP-47J was a completely new airframe and not a conversion of an existing P-47D. The serial number was 43-46952. The XP-47J flew for the first time on November 26, 1943. On August 4, 1944, it attained a speed of 504 mph in level fight, becoming the first propeller-driven fighter to exceed 500 mph. At one time, it was proposed that the J model would be introduced onto the production line, but the advent of the even more advanced XP-72 resulted in plans for the production of the P-47J being abandoned before any more could be completed.

A proposal to adapt the XP-47J to use contrarotating propellers with an R-2800-61 engine was dropped.

Maximum speed of the XP-47J was 507 mph at 34,300 feet, range was 765 miles at 400 mph, 1070 miles at economical cruising speed. An altitude of 15,000 feet could be reached in 4.5 minutes. Service ceiling was 45,000 feet. Weights were 9663 pounds empty, 12,400 pounds normal loaded, 16,780 pounds maximum. Wingspan was 40 feet 11 inches, length was 33 feet 3 inches, height was 14 feet 2 inches, and wing area was 300 square feet.

Republic XP-72
The Republic XP-72 was Alexander Kartveli's proposal for a replacement for his fabulously successful P-47 Thunderbolt. It was evolved in parallel with the XP-69 escort fighter project.

The XP-69 was a completely new design, whereas the XP-72 was a more-or-less straightforward progressive development of the P-47 Thunderbolt. The XP-72 was the first fighter to be designed around the huge 28-cylinger Pratt & Whitney R-4360 Wasp Major, the most powerful piston engine produced during World War 2. The engine was close-cowled and was fan-cooled. The Wasp Major was to have driven a pair of three-bladed Aeroproducts contrarotating propellers. The wing and tail of the P-47D were to be retained, but the airframe was enlarged and strengthened. The turbosupercharger was still located aft of the cockpit as it was in the P-47, but the turbosupercharger intake was moved to a position just underneath the cockpit rather than in the extreme nose. The lower fuselage was modified to allow for the larger air intake for the turbosupercharger. The XP-72 was to have been fitted with a bubble-type canopy, similar to that used by the late production blocks of the P-47D. Compressibility recovery flaps were fitted. Armament was to consist of six wing-mounted 0.50-inch machine guns, and two 1000-pound bombs were to be carried on underwing shackles.

The greater promise displayed by the XP-72 caused the USAAF to cancel the XP-69 project in favor of the XP-72. Two XP-72 prototypes were ordered on June 18, 1943. Serial numbers were 43-36598 and 43-36599.

XP-72 Ser No 43-36598 flew for the first time on February 2, 1944. Power was provided by a 3450 hp Pratt & Whitney R-4360-13 Wasp Major air-cooled radial engine. Since delivery of the planned Aeroproducts contrarotating six-bladed propeller had been delayed, the first XP-72 was equipped with a single four-bladed propeller as a temporary stop-gap measure. Nevertheless, the performance was excellent, a maximum speed of 490 mph being reached in flight tests. The second XP-72 (43-36599) flew for the first time on June 26, 1944. It was fitted with the Aeroproducts contrarotating propellers, which had finally been delivered. Unfortunately, the second XP-72 was written off in a takeoff crash early in its test flight program.

In spite of the loss of the second prototype, the USAAF was so impressed with the performance of the XP-72 that they ordered one hundred P-72 production variants. These P-72s were to have the R-4360-19 engine and were to be provided with an optional choice of four 37-mm cannon as an alternative for the six 0.50-in machine guns. It was anticipated that speeds in excess of 500 mph would be attained.

However, the changing character of the war created a greater need for long-range escort fighters than for high-speed interceptors, and the USAAF rapidly lost interest in the XP-72 project. The order for the one hundred P-72s was cancelled. The advent of jet-powered fighters which promised even more spectacular performance was undoubtedly also a factor. The surviving XP-72 (43-36598) is thought to have been scrapped at Wright Field at about the time of V-J Day.

Specification of Republic XP-72:

Powerplant: One 3450 hp Pratt & Whitney R-4360-13 Wasp Major air-cooled radial engine. Performance: Maximum speed was 490 mph at 25,000 feet. Normal range was 1200 miles at 300 mph and maximum range was 2520 miles at 315 mph with two 125 Imp. gall. drop tanks. Initial climb rate was 5280 feet per minute, and climb rate at 25,000 feet was 3550 feet per minute. An altitude of 15,000 feet could be reached in 3.5 minutes, 20,000 feet in 5 minutes. Service ceiling was 42,000 feet. Weights were 11,476 pounds empty, 14,433 pounds normal loaded, 17,490 pounds maximum. Dimensions were wingspan 40 feet 11 inches, length 36 feet 7 inches, height 16 feet 0 inches, and wing area 300 square feet.











(Text from here - https://www.crouze.com/baugher/ )