Republic P-47 Thunderbolt

The Republic P-47 Thunderbolt is a World War II-era fighter aircraft produced by the American company Republic Aviation from 1941 through 1945. It was a successful high-altitude fighter, and it also served as the foremost American fighter bomber in the ground attack role. Its primary armament was eight .50-caliber machine guns, and it could carry 5-inch rockets or a bomb load of 2,500 lb (1,100 kg). When fully loaded, the P-47 weighed up to 8 tons, making it one of the heaviest fighters of the war.

The Thunderbolt was effective as a short- to medium-range escort fighter in high-altitude air-to-air combat and ground attack in both the European and Pacific theatres. The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp 18-cylinder radial engine, which also powered two U.S. Navy/U.S. Marine Corps fighters, the Grumman F6F Hellcat and the Vought F4U Corsair. An advanced turbosupercharger system ensured the aircraft's eventual dominance at high altitudes, while also influencing its size and design.

The P-47 was one of the main United States Army Air Forces (USAAF) fighters of World War II. It also served with other Allied air forces, including those of France, the United Kingdom, and the Soviet Union. Mexican and Brazilian squadrons fighting alongside the USAAF also flew the P-47.

The armored cockpit was relatively roomy and comfortable and the bubble canopy introduced on the P-47D offered good visibility. Nicknamed the "Jug" owing to its appearance if stood on its nose, the P-47 was noted for its firepower and its ability to resist battle damage and remain airworthy. A present-day U.S. ground-attack aircraft, the Fairchild Republic A-10 Thunderbolt II, takes its name from the P-47.

The P-47 Thunderbolt was designed by Alexander Kartveli, a man of Georgian descent. It was to replace the Seversky P-35 developed earlier by a Russian immigrant named Alexander P. de Seversky. Both had fled from their homeland, Tbilisi, Georgia, to escape the Bolsheviks. In 1939, Republic Aviation designed the AP-4 demonstrator powered by a Pratt & Whitney R-1830 radial engine with a belly-mounted turbocharger. A small number of Republic P-43 Lancers were built, but the Republic had been working on an improved P-44 Rocket with a more powerful engine, as well as on the AP-10 fighter design. The latter was a lightweight aircraft powered by the Allison V-1710 liquid-cooled V-12 engine and armed with two .50 in (12.7 mm) M2 Browning machine guns mounted in the nose and four .30 in (7.62 mm) M1919 Browning machine guns mounted in the wings. The United States Army Air Corps (USAAC) backed the project and gave it the designation XP-47.

In the spring of 1940, Republic and the USAAC concluded that the XP-44 and the XP-47 were inferior to Luftwaffe fighters. Republic tried to improve the design, proposing the XP-47A, but this failed. Kartveli then designed a much larger fighter, which was offered to the USAAC in June 1940, which ordered a prototype in September as the XP-47B. The XP-47A, which had little in common with the new design, was abandoned. The XP-47B was of all-metal construction (except for the fabric-covered tail control surfaces) with elliptical wings, with a straight leading edge that was slightly swept back. The air-conditioned cockpit was roomy, and the pilot's seat was comfortable—"like a lounge chair", as one pilot later put it. The canopy doors hinged upward. Main and auxiliary self-sealing fuel tanks were placed under the cockpit, giving a total fuel capacity of 305 US gal (254 imp gal; 1,155 L).

Power came from a Pratt & Whitney R-2800 Double Wasp two-row, 18-cylinder radial engine producing 2,000 hp (1,500 kW) — the same engine that powered the prototype Vought XF4U-1 fighter to just over 400 mph (640 km/h) in October 1940—with the Double Wasp on the XP-47B turning a four-bladed Curtiss Electric constant-speed propeller of 146 in (3.7 m) in diameter. The loss of the AP-4 prototype to an engine fire ended Kartveli's experiments with tight-fitting cowlings, so the engine was placed in a broad cowling that opened at the front in a "horse collar"-shaped ellipse. The cowling admitted cooling air for the engine, left and right oil coolers, and the turbosupercharger intercooler system. The engine exhaust gases were routed into a pair of wastegate-equipped pipes that ran along each side of the cockpit to drive the turbosupercharger turbine at the bottom of the fuselage, about halfway between the cockpit and tail. At full power, the pipes glowed red at their forward ends and the turbine spun at 21,300 rpm. The complicated turbosupercharger system with its ductwork gave the XP-47B a deep fuselage, and the wings had to be mounted in a relatively high position. This was difficult since long-legged main landing gear struts were needed to provide ground clearance for the enormous propeller. To reduce the size and weight of the undercarriage struts, and so wing-mounted machine guns could be fitted, each strut was fitted with a mechanism by which it telescoped out 9 in (23 cm) while it extended.

The XP-47B was very heavy compared with contemporary single-engined fighters, with an empty weight of 9,900 lb (4,500 kg), or 65% more than the YP-43. Kartveli said, "It will be a dinosaur, but it will be a dinosaur with good proportions". The armament was eight .50-caliber (12.7 mm) "light-barrel" Browning AN/M2 machine guns, four in each wing. The guns were staggered to allow feeding from side-by-side ammunition boxes, each with 350 rounds. All eight guns gave the fighter a combined rate of fire of around 100 rounds per second.

The XP-47B first flew on 6 May 1941 with Lowry P. Brabham at the controls. Although minor problems arose, such as some cockpit smoke that turned out to be due to an oil drip, the aircraft proved impressive in its early trials. It was lost in an accident on 8 August 1942, but before that mishap, the prototype had achieved a level speed of 412 mph (663 km/h) at 25,800 ft (7,900 m) altitude and had demonstrated a climb from sea level to 15,000 ft (4,600 m) in five minutes.

Though the XP-47B had its share of shakedown troubles, the newly reorganized United States Army Air Forces placed an order for 171 production aircraft, the first being delivered in December 1941.