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Republic XP-72 Super Thunderbolt High-Altitude Fighter (1944)

Authored By Staff Writer | Last Updated: 6/30/2014

The XP-72 Wasp Major-powered Super Thunderbolt would have been an exceptional fighter but favorable events in WW2 all but killed its promising development.

The XP-72 Wasp Major Thunderbolt was intended to be an "ultimate" design of the highly successful P-47 Thunderbolt fighter-bomber as produced by Republic. The XP-72 was to incorporate the successful P-47 airframe and mate it to the experimental and massive Pratt & Whitney R-4360 Wasp Major engine which was rated at 3,500 horsepower. The end result, however, was the changing times of war that found no place for such a machine. Unfortunately, the Wasp Major Thunderbolt, as exceptional a craft as it was in development, would see no more than two prototypes produced.

The XP-72 made use of the airframe fuselage and wings of the P-47 system. Some alterations to accommodate the large Pratt & Whitney were made to the airframe and included an under-fuselage cowling to allow for proper air intake to the powerplant. In all, it was pretty much as the name suggested - a "Super Thunderbolt".

Developed as soon as the P-47 was entering service, the Republic team focused on two preliminary designs that were to take the benefits of the existing P-47 and improve upon it wherever possible. The US Army Air Force accepted both initial designs, the former being an XP-69 mated with a Wright R-2160 radial engine and the XP-72 fitted with the powerful Pratt & Whitney engine. As the designs progressed, the XP-69 design - complete with high-altitude features including a pressurized cockpit and an armament of 2 x 37mm cannons and 4 x 12.7mm machine guns - was dropped on May 11th, 1943, in favor of the more promising XP-72. Two XP-72 prototypes were ordered on June 18th, 1943.

The first XP-72 flew on February 2nd, 1944, and sported a four-blade propeller. Interestingly enough, the development process of the aircraft was very much unlike other aircraft in that its development yielded very few delays. The first prototype flew through the air with ease - even with the turbocharger off - at a very exceptional speed of 480 miles per hour (though neither XP-72 prototype would ever exceeded 500 miles per hour in these flight tests). The aircraft was reportedly quite responsive and - as most pilots would state - "a joy to fly". With the XP-72 achieving great leaps in its development, the system was envisioned to rival the high-speed, high-altitude performance found in the latter series of British Supermarine Spitfires but at the same time offering extended range. The system might have also been a good fit for interception of German V-1 rockets plaguing Southern England than the Spitfires already charged with the task.

The second prototype model featured an Aero-Products contra-rotating propeller arrangement (three blades to a propeller component equaling six total blades), the XP-72 was estimated with top speed of 550 miles per hour. Armament for the system would have been an array of 6 x 12.7mm (.50 caliber) machine guns mounted in the wings (down from the 8 x 12.7mm arrangement found in the base production P-47 Thunderbolt series. An alternative weapons loadout in the contract would have allowed for an alternative armament of 4 x 37mm cannons in place of all machine gun armament. Additionally, hardpoints under the wings would allow for the use of high-explosive rockets, 2 x 1,000lbs bombs or 2 x fuel droptanks as needed.

Despite these performance gains and relatively easy development process, the conditions in the later years of the war were changing on a weekly basis. This resulted in the fact that there was no longer a need for a high-altitude, high-speed interceptor - especially with the gains being made in the field of turbojet technology. As such, the two XP-72 prototypes were dropped from further development and scrapped by war's end, though a contract for 100 examples was awarded (this too cancelled). The XP-72 "Super Thunderbolt" would go down as just another the Second World War's "what-might-have-been" projects. The imagination is left to wonder what impact, if any, this powerful machine would have had if produced.

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Specifications for the
Republic XP-72 Super Thunderbolt
High-Altitude Fighter

Focus Model: Republic XP-72 Super Thunderbolt
Country of Origin: United States
Manufacturer: Republic Aviation - USA
Initial Year of Service: 1944
Production: 2

Crew: 1

Length: 36.61 ft (11.16 m)
Width: 40.91 ft (12.47 m)
Height: 16.01ft (4.88 m)
Weight (Empty): 11,473 lb (5,204 kg)
Weight (MTOW): 17,491 lb (7,934 kg)

Powerplant: 1 x Pratt & Whitney R-4360-13 28-cylinder air-cooled radial piston engine generating 3,450hp.

Maximum Speed: 490 mph (788kmh; 425 kts)
Maximum Range: 1,200 miles (1,931km)
Service Ceiling: 41,998 ft (12,801 m; 8.0 miles)
Rate-of-Climb: 5,000 feet per minute (1,524 m/min)

Hardpoints: 2
Armament Suite:
6 x 12.7mm machine guns in wings

4 x 37mm cannons in wings

2 x 1,000lb bombs
2 x Droptanks

P-47 "Thunderbolt" - Production Series Designation of base P-47 design on which the XP-72 was built upon; 8 x 12.7mm machine guns.

XP-72 "Super Thunderbolt" - Prototype Series Designation; two examples constructed; 6 x 12.7mm machine guns; 1 x Pratt & Whitney R-4360-13 Wasp Major engine of 3,450 horsepower.

United States