The Republic XP-72 was Alexander Kartveli's proposal for a replacement for his fabulously successful P-47 Thunderbolt. In the 18 months it saw operational service over the Russian Front, it proved itself to be a worthy successor to the P-47. Its armament of 4 37mm M-9 cannon and 4,000 pound bombload made it a formidable ground attack aircraft while its speed and agility made it feared in air combat, capable of taking on early jets such as the Me-262 and He-162 on equal terms. A popular fighter, the F-72 remained in US service until 1956 and it was widely exported after WW2. Examples of the type remained in foreign service into the late 1970s with the last aircraft of this type being phased out of Chilean Air Force service in 1981.
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. It drove 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 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 consisted of six wing-mounted 0.50-inch machine guns, and two 1000-pound bombs were to be carried on underwing shackles.
The XP-72 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.
Republic F-72A Thunderstorm
By the time the first production aircraft were delivered in September 1945, the USAF had changed its designation system so that Fighters were labeled in the F-series rather than P-series. Thus, the F-72A was identical to the XP-72 except it had the R-4360-19 engine delivering 3,500 horsepower. The new engine combined with the contra-rotating props gave the F-72A a maximum speed of 516 mph at 30,000 feet, putting it into the same league as the much-vaunted German Me-262. It was much more agile than the twin-engined German fighter and its machine guns were better suited to high-speed dogfights where firing opportunities were fleeting and the slow-firing 30mm German cannon had only limited value. The F-72A quickly became known as the “Jetslayer”, one subtle advantage being that it looked very similar to the older P-47.
Specification of Republic F-72A:
Powerplant: One 3500 hp Pratt & Whitney R-4360-19 Wasp Major air-cooled radial engine. Performance: Maximum speed was 516 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. Armament was six 0.5 inch machine guns and up to 2,000 pounds of bombs or rockets
Republic F-72B Thunderstorm
The F-72B was the first fighter-bomber version of the F-72 and was provided with an optional choice of four 37-mm M-9 cannon as an alternative for the six 0.50-in M-3 machine guns. Bombload was increased to a maximum of 4,000 pounds. The aircraft retained the 3500 hp Pratt & Whitney R-4360-19 engine. Performance was identical to that of the F-72A. Production of the F-72B was strictly limited by the availability of the R-4360 engine, most supplies having been absorbed by the B-36 program.
Republic F-72C Thunderstorm
A further development of the F-72B, the C-model standardized on the armament of four 37mm M-9 cannon but had the 3,800 hp R-4360-41 engine. Weight was reduced by deleting some armor. These modifications boosted the speed of the aircraft to 525 miles per hour, making the F-72C one of the fastest piston-engined fighters ever to see service. The first C-models were delivered to units just in time to see combat over the Russian Front.
Specification of Republic F-72C:
Powerplant: One 3800 hp Pratt & Whitney R-4360-19 Wasp Major air-cooled radial engine. Performance: Maximum speed was 525 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 5480 feet per minute, and climb rate at 25,000 feet was 3650 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 44,000 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. Armament was six 0.5 inch machine guns and up to 4,000 pounds of bombs or rockets
Republic F-72D Thunderstorm
A postwar development of the F-72C, the F-72D had the 4,150 hp R-4360-54 engine. The aircraft was armed with 4 20mm cannon in the wings, these being regarded as a good compromise between the air-to-air capability of the .50 caliber machine gun and the ground attack virtues of the 37mm M-9. Production was eased by the reduction in demand for the R-4360 engine following the end of the war and the consequent slowdown in B-36 production. Consequently, F-72Ds re-equipped most Fighter groups that were scheduled to remain equipped with piston-engined fighters. Consequently the F-47 and F-63 were quickly replaced by the F-72D. With the major reductions in tactical air forces in the early 1950s, most of those squadrons became part of the Air National Guard and flew their F-72s until F-94 Starfires became available. Oddly, the increased engine power of the F-72D did not confer any apparent performance benefits, a strong indicator that piston-engined fighters had reached their peak.
Republic XF-72E Thunderstorm
A high-altitude fighter version of the F-72 intended to defend against B-36 class bombers. It had extended wings, a pressurized cockpit and a turbocharger optimized for high altitude. All armor was stripped out and armament was reduced to two 0.5 inch M-3 machine guns. This version proved to have a service ceiling of approximately 51,000 feet and was thus able to threaten a B-36. However, it proved unable to intercept the big bombers and the concept was not further developed.