The Republic P-47 Thunderbolt is one of the largest and heaviest fighter aircraft in history to be powered by a single 4-stroke internal combustion engine. It was built from 1941–1945. It was armed with eight .50-caliber machine guns, four per wing. When fully loaded, the P-47 weighed up to eight tons, and in the fighter-bomber ground-attack role could carry five-inch rockets or a bomb load of 2,500 pounds; it could carry more than half the payload of the B-17 bomber on long-range missions (although the B-17 had a far greater range). The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp engine—the same engine used by two very successful U.S. Navy fighters. The Thunderbolt was very effective as a short-to-medium range escort fighter in high-altitude air-to-air combat but was also adept at ground attack in both the World War II European and Pacific Theaters.
The P-47 was one of the main United States Army Air Forces (USAAF) fighters of World War II, and served with other Allied air forces, notably those of France, Britain, and Russia. Mexican and Brazilian squadrons fighting alongside the U.S. were equipped with the P-47.
The armored cockpit was roomy inside, comfortable for the pilot, and offered good visibility. A modern-day U.S. ground-attack aircraft, the Fairchild Republic A-10 Thunderbolt II, takes its name from the P-47.[Note 1]
The P-47 Thunderbolt, or the 'Jug' as it came to be known, was a design of Georgian immigrant Alexander Kartveli, and was to replace the Seversky P-35 that was developed earlier by Russian immigrant Alexander P. de Seversky (born in the same place as Kartveli: Tbilisi, Georgia).[Note 2] Both had fled from their homeland to escape the Bolsheviks.[Note 3]
P-43 Lancer / XP-47B
American pre-war fighter Republic P-43 Lancer
In 1939, Republic Aviation designed the AP-4 demonstrator powered by a Pratt & Whitney R-1830 radial engine with a belly-mounted turbocharger. While the resulting Republic P-43 Lancer was in limited production, Republic had been working on an improved P-44 Rocket with a more powerful engine, as well as on a fighter designated the AP-10. The latter was a lightweight aircraft powered by the Allison V-1710 liquid-cooled V-12 engine and armed with eight .50 in (12.7 mm) M2 Browning machine guns. The United States Army Air Corps (USAAC) backed the project and gave it the designation XP-47.
As the war in Europe escalated in spring 1940, Republic and the USAAC concluded that the XP-44 and the XP-47 were inferior to the Luftwaffe fighters. Republic unsuccessfully attempted to improve the design, proposing the XP-47A. Kartveli subsequently came up with an all-new and much larger fighter, which was offered to the USAAC in June 1940. The Air Corps ordered a prototype in September, to be designated the XP-47B. The XP-47A, which had almost nothing 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 cockpit was roomy and the pilot's seat was comfortable—"like a lounge chair", as one pilot later put it. The pilot was provided with every convenience, including cabin air conditioning. The canopy doors hinged upward. Main and auxiliary self-sealing fuel tanks were placed under the cockpit, giving a total fuel capacity of 305 U.S. gal (1,155 L).
A P-47 engine with the cowling removed. Uncompressed air enters through an intake under the engine, and is carried to the turbosupercharger behind the pilot via the silver duct at the bottom. The olive-green pipe returns the compressed air to the engine
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 would power the prototype Vought XF4U-1 fighter to just over 400 mph 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-fittingcowlings, 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 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 problematic 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 main landing gear struts and so that wing-mounted machine guns could be fitted, each main gear strut was fitted with a mechanism by which it telescoped out 9 in (23 cm) when extended.
The XP-47B was a very large aircraft for its time with an empty weight of 9,900 lb (4,490 kg), or 65% more than the YP-43. Kartveli is said to have remarked, "It will be a dinosaur, but it will be a dinosaur with good proportions." The armament consisted of 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 a 350-round capacity. Although the British already possessed eight-gun fighters, the Hurricane and the Spitfire, and even the 12-gun version of the Typhoon, they used smaller-caliber 0.303 in (7.7 mm) machine guns.
The XP-47B first flew on 6 May 1941 with Lowry P. Brabham at the controls. Although there were minor problems, such as some cockpit smoke that turned out to be due to an oil drip, the aircraft proved impressive in its first trials. It was eventually 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 (7,864 m) altitude, and had demonstrated a climb from sea level to 15,000 ft (4,600 m) altitude in five minutes.