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The Republic P-47 Thunderbolt

In the entire history of military aviation, there has never been an airplane that could match the P-47 Thunderbolt for ruggedness and dependability. The pilots who flew it into combat called it "The Unbreakable" and "The plane that can do anything." They were not far from wrong.

P-47's often came back from combat shot full of holes, their wings and control surfaces in tatters. On one occasion a Thunderbolt pilot, Lieutenant Chetwood, hit a steel pole after strafing a train over Occupied France. The collision sliced four feet off one of his wings--yet he was able to fly back safely to his base in England.

The story of the P-47 began in the summer of 1940. At that time Republic was building the P-43 Lancer and had plans to produce a lightweight fighter, designated the P-44 Rocket. In view of combat experience in Europe, however, the Air Corps decided that if the United States became involved in the war something larger and better than the P-44 would be required.

Alexander Kartveli, Republic's chief engineer, quickly prepared a rough sketch of a new fighter. It was a daring concept. He planned to use the new Pratt & Whitney Double Wasp , 2,000 h.p. XR-2800-21 eighteen-cylinder two-row radial engine. It which was largest and most powerful aircraft engine ever developed in the United States. He also envisioned that his plane would have eight .50-caliber machine guns and enough armor plating to protect the pilot from every direction. These features added up to an airplane weighing about 4,000 pounds more than any existing single-engined fighter.

Without such power of the new 2,000 h.p. Pratt & Whitney Double Wasp , Kartveli could see no way of meeting the performance and load carrying demands being made by the U.S.A.A.F. From an engineering standpoint, the requirements presented some enormous problems, but far more problems were presented by the engine. The first of these was the need for an efficient super-charging duct system that would offer the least interrupted airflow. Kartveli therefore adopted the unorthodox method of designing this feature first and then building up the fuselage around it; the large turbo-supercharger was stowed internally in the rear fuselage, with the large intake for the air duct mounted under the engine, together with the oil coolers. Exhaust gases were piped back separately to the turbine and expelled through a waste gate in the bottom of the fuselage, and ducted air was fed to the centrifugal impeller and returned, via an intercooler, to the engine under pressure. Surprisingly, all this ducting of gases under temperature and pressure did not prove very vulnerable in combat, for the fighter was to become renowned for its ability to absorb battle damage and return home.

The new design was approved, and Republic began work on the first test model. The XP-47B was ready in just eight months and was taken up for its first test flight on May 6, 1941. It proved to be an outstanding success, and was able to do everything Kartveli had hoped, plus more. Its speed of 412 miles per hour was even higher than expected.

The conventional three-bladed propeller could not efficiently utilize the power of the new engine and a four-bladed propeller was adopted. Although this propeller was an admirable solution to the power gearing of the engine, there remained the problem of providing sufficient ground clearance for its 12-foot diameter. If a conventional undercarriage were to be employed its suspension would have been too far outboard to permit the wing installation of the guns and ammunition requested by the U.S.A.A.F., and therefore Republic had to design a telescopic landing gear which was nine inches shorter when retracted than when extended. Numerous other problems were to be faced in absorbing the loads and stresses which would be imposed when a battery of eight 0.5-in. guns (a phenomenal heavy armament for that time) was fired simultaneously, and in providing the necessary tankage for the quantities of fuel stipulated to make the machine the first true single-engined strategic fighter. Thus, it was only to be expected that when the first prototype, the XP-47B Thunderbolt, made its first flight, on May 6, 1941, it dwarfed not only its pilots but all previous fighters and, with a loaded weight of 12,086 lb., turned the scales at more than twice the weight of most of its contemporaries.

The prototype Thunderbolt first took to the air on May 6,1941. Production began with the P-47B, which entered United States Army Air Force service in November 1942, first becoming operational with the Eighth Air Force stationed in the UK on April 8,1943. The P-47B's range was not really good enough for escort duties, and its maneuverability was poor, but at least it offered a measure of real protection to the Allied bombers which had previously suffered very heavy losses.

To increase the tempo of flight development of the XP-47B such leading test pilots as Colonel Ira C. Eaker were employed, and at one time it was hoped that the design could benefit from combat testing with the R.A.F. in the Middle East. Production difficulties caused General "Hap" Arnold to notify the British Air Ministry, in September 1941, that it was considered inadvisable to do this until various teething troubles were eradicated, and an optimistic estimate of May 1942 was established as a target date for the Thunderbolt to be combat ready. This was eventually to prove almost a year out. Numerous problems soon presented themselves as the XP-47B test program advanced. At altitudes above 30,000 feet ailerons "snatched and froze", the cockpit canopy could not be opened and control loads became excessive.

773 production versions were ordered. But this was only the beginning. Before the war was over, a total of 15,579 Thunderbolts was built, about two-thirds of which reached operational squadrons overseas.

When, in January 1943, the U.S.A.A.F.'s 56th Fighter Group arrived in the United Kingdom with its massive Republic P-47 Thunderbolts, R.A.F. Spitfire fighter pilots banteringly suggested that their American colleagues would be able to take evasive action when attacked by undoing their harnesses and dodging about the fuselages of their huge mounts. The Thunderbolt was certainly big. In fact it was the largest and heaviest single engined single-seat fighter ever built! But sheer size was not to prove detrimental to the Thunderbolt's subsequent operational career.

The first tasks of the Thunderbolt, which began on April 8, 1943, were high-altitude escort duties and fighter sweeps in which the new aircraft acquitted itself well, despite the inexperience of its pilots. It was soon discovered that the heavy Thunderbolt could out dive any Luftwaffe, or, for that matter, Allied, fighter, providing a decisive method of breaking off combat when necessary, but at low and medium altitudes it could not match the rate of climb or maneuverability of German fighters. One shortcoming, which was even more marked in other Allied fighters, was that of insufficient range to permit deep penetration into Germany, but means were already being sought to add to the P-47B's 307 U.S. gallons of internal fuel. At the time of the Thunderbolt's European debut radial-engined single-seat fighters were a rarity, the only other such fighter operational in Europe being the Fw 190A. To prevent confusion between the two fighters of the opposing sides the engine cowlings of the Thunderbolts were painted white, and white bands were painted around the vertical and horizontal tail surfaces--an appropriate comment on recognition standards appertaining at that time, as it would seem impossible to mistake the sleek and beautifully-contoured German fighter for the portly Thunderbolt.

By mid-1943 improved P-47Cs were becoming available, with external fuel tanks to increase range and a longer fuselage to improve maneuverability. Next came the major production version, the P-47D, and then P-47Gs, and P-47Ms with more powerful engines, giving a maximum speed of 756 km/h (470 mph). They were used for anti V1 Flying Bomb duties.

The final version, the P-47N, was built primarily for use against the Japanese. The fastest model was the XP-47J, which did not go into production. On August 4, 1944, this plane reached a speed of 504 miles per hour. Production plans were shelved in favor of another P-47 development, the Republic XP-72.

P-47's flew more than 546,000 combat sorties between March 1943 and August 1945, destroying 11,874 enemy aircraft, some 9,000 locomotives, and about 6,000 armored vehicles and tanks. Only 0.7 per cent of the fighters of this type dispatched against the enemy were to be lost in combat.

Parker Information Resources
Houston, Texas
E-mail: bparker@parkerinfo.com

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