History
Introduction and Background
The development of the P-47 Thunderbolt was pioneered by Alexander Kartveli, the Georgian designer who immigrated to the United States in the late 1920s. He was hired by Seversky as the chief engineer at Seversky Aircraft Company and worked together on a series of aircraft projects, such as the Seversky P-35, in the late 1930s.
In 1939, Seversky was removed as head of his company, and the company was reorganized as the Republic Aviation Company. Kartveli was appointed to lead a new project to develop a new lightweight high-altitude interceptor to replace the Seversky P-35, as requested by the US Army Air Corps. Two concept works emerged, the XP-44 and XP-47. The XP-44 was a progressive development of the P-43 Lancer; on August 1, 1939, Kartveli designed and proposed an AP-10 demonstrator that would eventually be known as the XP-47. The AP-10/XP-47 was to be powered by a 1,150 hp Allison V-1710-39 12-cylinder inline engine and included two nose-mounted .50-cal M2 Browning machine guns. The estimated gross weight was around 4900 pounds, and the maximum speed was around 415 mph.
The USAAC was impressed with the AP-10 proposal but stated insufficient armament as its key concern. Kartveli revised the AP-10 by including two more .30-cal in each wing, raising the gross weight to 6,570 lb. The USAAC was satisfied with the revised proposal and ordered a single prototype to be developed under the designation XP-47 in November 1939. In addition to the XP-47, the USAAC also ordered another prototype, the XP-47A, on January 17, 1940. The unarmed XP-47A was constructed first without military equipment, and it would be studied in the test flight before the XP-47.
Development and Design
At this point, the P-47B development had originated in the spring of 1940 when the Republic Aviation Company and the USAAC learned that their XP-44 and XP-47 were inferior to Luftwaffe fighters based on the combat intel reports. The USAAC abandoned the idea of a short-range lightweight interceptor and analyzed that the fighter needs to fly faster, at greater altitudes, over longer distances, and armed with heavy armament. While the USAAC authorized new fighter contracts, it issued new requirements that the fighter had to meet to get accepted into the service. The following requirements were:
- The aircraft must attain at least 400 mph at 25,000 feet.
- It must be equipped with at least six .50 caliber machine guns, with eight preferred.
- The armor plate must be fitted to protect the pilot.
- Self-sealing fuel tanks must be fitted.
- Fuel capacity was to be a minimum of 315 gallons.
Republic desperately tried to improve the existing designs, but the XP-44 and XP-47 & XP-47A projects were immediately canceled as they failed to meet the requirements. Kartveli was called in from the Experimental Aircraft Division of the USAAC and informed about the prototypes being canceled. During his return to New York on a train, he took a sheet of paper and drew a completely new design; he kept the basic cockpit design, stretched the fuselage, reshaped the tail surfaces, and increased the wing span, all changes to accommodate the heavy firepower, protection, and more powerful engine.
On June 12, 1940, Kartveli proposed his new design to the USAAC. It was to be powered by a turbo-supercharged Pratt & Whitney R-2800 Double Wasp 18-cylinder radial engine. Its armament was increased to eight .50-cal machine guns. He ultimately formulated and brought a heavy fighter that would put itself as the bane of the Luftwaffe’s existence in 1944. The USAAC approved his design since it met the requirements despite the fuel load being smaller than outlined. The USAAC ordered a single prototype on September 6, 1940, under the designation XP-47B. The XP-47A and XP-47B almost had no commonalities at all. The XP-47B was built as an all-metal fighter with a hinged canopy and elliptical wings. Self-sealing fuel tanks were incorporated and placed under the cockpit, giving a total fuel capacity of 305 US gal. It was powered by a 1,960 hp XR-2800-21 engine.
The XP-47B was first flown on May 6, 1941, only eight months after the order had been placed. The load weight was 12,086 lb, making the XP-47B the heaviest and largest fighter, almost twice as heavy as its performance, but the performance was higher than expected, with a maximum speed of 412 mph. Although the XP-47B had to make an emergency landing after encountering the issues that arose, such as the cockpit smoke, the XP-47B had further impressed the USAAC officials in its early trials. The XP-47B crashed in an accident on August 8, 1942. Despite that, the newly reorganized United States Army Air Forces placed an order for the first batch of 773 production P-47 aircraft.
Production and Testing
The first P-47B was produced and introduced as the hybrid prototype-production fighter for further service testing in the US Army. The first P-47B with serial 41-5895 was delivered to the Army on December 21, 1941, at Wright Field, and it was scheduled to undergo flight evaluations to analyze the metrics. The next four P-47Bs were produced and delivered in mid-March 1942, only eight months after the XP-47B prototype had first flown. These planes were also used for extensive evaluations. They were powered by a 2,000 hp production R-2800-21 engine with a turbo-supercharger. The engine drove a 12’ 2" diameter Curtiss Electric C542S-A6 propeller.
Numerous issues surfaced as the evaluations advanced, as a P-47B crashed on Long Island on March 26, 1942. The issues found by the investigations included structural failure, frozen ailerons at high altitudes, a jammed canopy, and uncontrollable forces. The fabric covering for the elevators was ruptured after high-speed flights, as the aerodynamic pressures caused it to balloon out and burst. All issues were identified; these prompted the USAAF officials to place flight restrictions on P-47Bs and delay additional aircraft’s entry into the service until May 1942.
The issues were addressed by the following changes: the original sideway-hinged canopy was replaced by a rearward-sliding canopy, eliminating the jamming, with the dorsal radio antenna moved further aft. The fabric-covered control surfaces were redesigned and replaced by stronger metal ailerons and elevators. The ailerons were revised in shape and fitted with blunt noses to alleviate the excessive control forces, and the balanced trim tabs were incorporated to reduce rudder pedal loads.
All of these changes were applied to the production of additional P-47Bs.
In short, the P-47B differed from the XP-47B in having a 2,000 hp production R-2800-21 engine, a sliding canopy, redesigned metal ailerons and elevators, rudder trim tabs, and some other minor modifications, such as internal equipment. The new changes raised the empty, normally loaded, and maximum loaded weights to 9346, 12,245, and 13,360 pounds, respectively. Consequently, the climb to 15,000 feet now took 6.7 minutes rather than the five minutes originally. Thanks to the new production engine with increased power, the P-47B could fly at a maximum speed of 429 mph at 27,000 feet.
USAAF Service
The P-47Bs were first issued to the 56th Fighter Group in the middle of 1942. The group was based near New York City, near the Farmingdale plant, where Republic engineers could observe and assist in solving additional issues as they arose.
Onwards, the 56th Fighter Group used and flew the P-47Bs mainly for testing and operational training. The 56th Fighter Group encountered difficult challenges when operating P-47Bs as a new type of heavy fighter. It had lost 13 pilots and 41 aircraft in accidents. By the end of June, the 56th FG had damaged or destroyed half of its aircraft.
Many crashes were the fault of pilot inexperience, and most were related to loss of control during high-speed dives. For example, the P-47B’s rudder was ripped off in high-speed flight. These incidents prompted the USAAF officials to order on August 1, 1942, to restrict P-47B’s speed to 300 mph or less and prohibit aerobatic maneuvers.
In addition, the 80th Fighter Group was moved to Farmingdale and assigned to begin the training on new P-47Bs. The last P-47B was delivered in September 1942; only 171 of 773 were completed as P-47Bs before production switched to the P-47C with several improvements.
For the remainder of the war, the P-47B was restricted to use for testing and training. No P-47B was sent into combat, and the P-47B’s designation was changed to RP-47B in 1944, where the R stood for Restricted as not to be used for combat.
The P-47’s nickname, Thunderbolt, was thought up by the Republic’s Director of Military Contracts, C. Hart Miller. The company approved the nickname, and the name was forever stuck to the P-47 models.
