The Republic P-47 Thunderbolt, also known as the Jug, was the largest single-engined fighter of its day, and a vast improvement over the Curtiss P-40 Warhawk, its predecessor. It was one of the main United States Army Air Force (USAAF) fighters of World War II, and also served with other Allied air forces.
The P-47 was effective in air combat but proved especially adept at ground attack. It had eight .50-caliber machine guns, four per wing. When fully loaded the P-47 could weigh up to eight tons. A modern-day counterpart in that role, the A-10 Thunderbolt II, takes its name from the P-47.
Development
The P-47 Thunderbolt was the product of Russian immigrant Alexander de Seversky and Georgian immigrant Alexander Kartveli, who had left their homelands 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. While the resulting 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 a pair of .50-caliber (12.7 mm) 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 German fighters. Republic unsuccessfully attempted to improve the design, proposing the XP-47A. Alexander 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 all-metal construction (except for fabric-covered tail control surfaces) with elliptical wings. The cockpit was roomy and the pilot's seat was comfortable, "like a lounge chair" as one pilot would 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. gallons (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) and turning a four-bladed Curtiss Electric constant-speed propeller 146 inches (3.7 m) in diameter.
The XP-47B was a very large aircraft for its time with an empty weight of 9,900 pounds (4,490 kg), or 65 percent 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 0.50 caliber (12.7 mm) 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 in the form of the Hurricane and the Spitfire, these used the smaller 0.303 caliber (7.7 mm) 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 August 8, 1942, but before that mishap the prototype had achieved a level speed of 412 mph (663 kph) at 25,800 ft (7,864 m) altitude, and had demonstrated a climb from sea level to 15000 ft altitude in five minutes.
Operational history
Initial deliveries of the Thunderbolt to the USAAF were to the 56th Fighter Group, which was also on Long Island. The 56th served as an operational evaluation unit for the new fighter. Teething problems continued. A Republic test pilot was killed in an early production P-47B when it went out of control in a dive, and crashes occurred due to failure of the tail assembly. The introduction of revised rudder and elevator balance systems and other changes corrected these problems. In spite of the problems, the USAAF was interested enough to order an additional 602 examples of the refined P-47C, with the first of the variant delivered in September 1942.
Beginning in January 1943, Thunderbolt fighters were sent to the joint Army Air Forces-civilian Millville Airport in Millville, NJ in order to train civilian and military pilots.
Refinements of the Thunderbolt continued, leading to the definitive P-47D, of which 12,602 examples were built. The "D" model actually consisted of a series of evolving production blocks, the last of which were visibly different from the first.
The first P-47Ds were actually the same as P-47Cs. Republic could not produce Thunderbolts fast enough at its Farmingdale plant on Long Island, so a new plant was built at Evansville, Indiana. The Evansville plant built a total of 110 P-47Ds, which were completely identical to P-47C-2s. Farmingdale aircraft were identified by the "-RE" suffix after the block number, while Evansville aircraft were given the "-RA" suffix.
Bubbletop P-47s
All the P-47s to this point had a "razorback" canopy configuration with a tall fuselage spine behind the pilot which resulted in poor visibility to the rear. The British also had this problem with their fighter aircraft, and had devised the bulged "Malcolm hood" canopy for the Spitfire as an initial solution. This was fitted in the field to many North American P-51 Mustangs, and to a handful of P-47Ds (and far more on P-47Bs and P-47Cs). However, the British then came up with a much better solution, devising an all-round vision "bubble" canopy for the Hawker Typhoon. USAAF officials liked the bubble canopy, and quickly adapted it to American fighters, including the P-51 and the Thunderbolt.
The first P-47 with a bubble canopy was a modified P-47D-5 completed in the summer of 1943 and redesignated XP-47K. Another older P-47D was modified to provide an internal fuel capacity of 370 U.S. gallons (1,402 L) and given the designation XP-47L. The bubble canopy and increased fuel capacity were then rolled into production together, resulting in the block 25 P-47D (rather than a new variant designation). First deliveries to combat groups began in May 1944.
It was followed by similar bubble-top variants, including the P-47D-26, D-27, D-28 and D-30. Improvements added in this series included engine refinements, more internal fuel capacity, and the addition of dive recovery flaps. Cutting down the rear fuselage to accommodate the bubble canopy produced yaw instability, and the P-47D-40 introduced a dorsal fin extension in the form of a narrow triangle running from the vertical tailplane to the radio aerial. The fin fillet was retrofitted in the field to earlier P-47D bubble-top variants. The P-47D-40 also featured provisions for ten "zero length" stub launchers for 5 inch (127 mm) High Velocity Aerial Rockets (HVARs), as well as the new K-14 computing gunsight. This was a license-built copy of the British Ferranti GGS Mark IID computing gyroscopic sight which allowed the pilot to dial in target wingspan and range, and would then move the gunsight reticle to compensate for the required deflection.
The bubbletop P-47s were nicknamed "Superbolts" by combat pilots in the field.
