The first new fighter of the postwar period was Republicís XP-84, a response to a September 11, 1944, Air Force requirement for the best speed and range obtainable from jet propulsion. Alexander Kartveli offered his AP-23 design on November 2 and a November 11 letter contract ordered three prototypes.
General Electricís TG-180 (called J35 since 1945) axial-flow engine permitted a long narrow fuselage whose streamlining contributed to the expected 600-mph speed and 1,300-mile range. The first nose air intake on an American jet permitted straight-through air flow. Fuel was carried within the fuselage and in wings thick enough to contain the retracted main wheels of the tricycle landing gear.
The mid-wing single-seater was built in Farmingdale, New York, and flown aboard an XC-97 to Muroc. When Major Wallace Lien made the first XP-84 flight on February 28, 1946, it had already earned a 100-plane contract on January 5. The second XP-84 prototype was stripped to set a United States speed record of 611 mph on September 7, but this could not be matched under service conditions.
Production began with 15 YP-84As delivered in February 1947; similar to the prototypes, but with J35-A-15 engines now made by Allison, and 165-gallon wing-tip drop tanks were added. Four .50-caliber M-2 guns were mounted above the nose air intake and two more were in the wing roots. Successful tests added another 486 planes to the contracts by October 1947, and the 14th Fighter Group was chosen to be the first P-84 unit.
P-84B Thunderjets appearing in June 1947 also had J35A-15s, but standardized the faster-firing M-3 guns, with 300 rpg, and ejector seats. The first 85 did not have the eight retractable under wing rocket racks of the last 141. Just as deliveries were being completed, these fighters were grounded on May 24, 1948, due to a host of maintenance and safety problems. The waiting planes were redesignated F-84B on June 11.
Production resumed with J35-A-13 engines found more dependable than the A-15. From May to November 1948, 191 F-84Cs were delivered, and 154 F-84Ds followed by April 1949. Only internal mechanical changes distinguished the D from the C, and the Air Force came close to canceling the troubled Thunderjet program until a major modification program was approved in May 1949. Thunderjets served the 20th, 31st, 33rd, 34th, and 78th Fighter Groups, but mechanical problems persisted.
The improved performance of the F-84E, with a 4,900-pound thrust J35-A-17 and increased JP-1 fuel capacity in a longer fuselage, restored confidence in Republic fighters. Ordered December 29, 1948, and first flown May 18, 1949, the F-84E-1 added inboard pylons under the wings for two 1,000-pound bombs or 11.75-inch rockets for ground-attack missions. These pylons could add two 230-gallon drop tanks to the two 230-gallon wingtip tanks. Sperry APG-30 radar-ranging for an A-1B gun sight became standard.
The 27th, 12th, and 31st Fighter-Escort Wings were the first to use the E model. Republic delivered 843 F-84Es by June 1951, the last 270 (F-84E-25/-30) with a J35-A-17B and new tail pipe ejector.
The F-84Eís increased power brought the Thunderjet close to the straight wingís speed limit (Mach .82), and Republic offered a swept-wing version on November 10, 1949. A February 24, 1950, contract change ordered the last (409th) F-84E-15 built as the YF-96A, with a 5,200-pound thrust XJ35-A-25, and 40į sweep on wings and tail. First flown on June 3, 1950, at Edwards AFB, that prototype became the YF-84F on September 8, since tooling was then expected to be 55% the same as that of the F-84E. Actually, barely 15 per cent of the straight-wing F-84E components could be used in the final F-84F model.
Alarm over the Korean War led in July to an order for production models to be powered by 7,200-pound thrust Wright J65s, an American-built version of the British Armstrong-Siddeley Sapphire engine. General Motors was chosen to manage a second production line in a Kansas City factory once used to make B-25s.
F-84F production was delayed by complexities of the new wing structure and the engine, so delivery began in July 1951 of an interim type designated F-84G with the straight wing, a 5,600-pound thrust J35-A-29, and reinforced canopy. Essentially an F-84E fitted for long-range flying, the F-84G had an automatic pilot and a receptacle on the left wing for air refueling by a flying boom of a Boeing KB-29P or KC-97E tanker, instead of the probe and drogue technique tested with tip tanks on modified F-84Es, and used on F-84G missions when only older tankers were available.
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