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F-84F "Thunderstreak"

The F-84G, not the F-84E--from which that aircraft was progressively developed-was produced before the F-84F. Actually, the swept-wing, single-seat F-84F was largely a new aircraft.

Wings and tail with sweepback of 40 at 25 percent of the chord; use of many press forgings in wing structure instead of built-up components; wings fated with leading-edge auto slats; Wright J65W-3 turbojet engine, rated at 7,220 lb. s.t.; irreversible power-boost control system; upward-hinged canopy; perforated air-brakes hinged to the fuselage sides aft of the wing trailing edge; F-84G's in-flight refueling equipment, with inlet nozzle relocated in the upper surface of the port wing; F-84G's standard armament, but capable of carrying heavier loads of offensive stores, including atomic weapons; and two adaptable 450-gal (US) external tanks for long-range escort fighter missions.

The Air Force issued a revision of the GOR published by the AAF in September 1944. The revision called for significant increases of the operational performances required by the original document.

The F-84F aircraft was officially conceived in November 1949 in a letter proposal through which Republic offered to satisfy the USAF-revised GOR by changing its straight wing F-84 to a model incorporating a swept back wing and swept back tail. In a further proposal, the contractor offered to build an increased ordnance capability into the aircraft. Although its drawings were labeled F96, Republic also stated that the proposed low-cost aircraft would be a modification of the F-84E that was entering USAF inventory and that 55 percent of the F-84E tooling would be utilized for the new production. The Air Force tentatively endorsed Republic proposal in December 1949. During the same month, Republic was allocated one F-84E to build a prototype of its swept-wing aircraft. At the insistence of the Air Force, the paper F-96 was redesignated, officially becoming the F-84F on 8 September 1950. The aircraft's "Thunderstreak" nickname, result of a "new name" contest among Republic employees, was retained.

Republic delivered the YF-84F prototype at Edwards AFB, Calif., in May 1950. Phase I tests were started in June and completed in approximately 1 month by a Republic test pilot. Air Force pilots conducted Phase II tests, which ended 'in November, after 64 flights totaling 70 hours of flying time. The tests demonstrated conclusively that the 5,300 pounds of engine thrust generated by the YF-84F's Allison J-35-A-25 engine was not sufficient for the proper performance of the mission assigned the aircraft under the revised GOR of December 194$.

Almost as soon as the YF-84F flight tests had begun, both Republic and the Air Force realized the extent of the J-35-A-25 engine deficiencies and both agreed to rework an F--84E fuselage to fit the more powerful Sapphire jet engine, selected in mid-1950 as the best possible replacement. The Sapphire was a hand-tooled production of the British firm Armstrong Siddeley for which the Curtiss-Wright ~ Corporation at Wood-Ridge, New Jersey, had acquired a manufacturing license. However, production of the Wright YJ-65 (as the Sapphire engine was redesignated) was not expected to begin before September 1951. This forecast was the first indication that, if produced, the F-84F would be off Republic initial production schedule by at least 3 months. In any case, while the Air Force in December 1949 had practically bought the Republic-proposed F--84F, the engine deficiencies of the first F84F prototype created a new situation and procurement, which had been expected to be finalized in August 1950, was postponed. In November of the same year, the Air Materiel Command (AMC) recommended that two additional prototypes be built to evaluate the F-84F and Sapphire combination before to entertain further production consideration.

Before the additional prototypes could be obtained and prior to the testing of the Republic prototype with the Sapphire engine, Headquarters USAF ordered full production of the new combination. Because of the urgent need for improved fighter-bombers since the outbreak of the Korean war, the Air Force also directed the opening of second sources of production for both the airframe and engine. The Buick, Oldsmobile, Pontiac Assembly Division of the General Motors Corporation at Kansas City, Kans., was selected as the second producer of the F-84F airframe in January 1951, 1 month after the production decision. The Buick Division of the General Motors Corporation was also selected as the second source for the Sapphire engine.

The new F-84F prototype, powered by an "imported" Sapphire engine, was first flown from the Air Force Flight Center at Edwards AFB on 14 February 1951. While the performances were impressive, the airplane proved unsafe and flying was restricted to Edwards AFB.

This contract, AF 33(038-1438, covered production of 274 F-84Fs at a unit target cost of $215,035.27-about one-third of the aircraft's eventual unit price, all modification costs excluded. This first contract was amended in less than a year by nine supplementary agreements, which raised the F-84F procurement to the FY 51 approved total of 719 aircraft and endorsed substantial price increases. Two other definitive contracts, AF 33(600)--6704 and AF 33(60022316, were issued in FY 52 and FY 53, respectively, but the number of aircraft they covered was drastically reduced in later years. Believing the F-84F to be a production modification of the F-84E, no development contract preceded any of these contracts. However, notwithstanding nonavailability of the Wright YJ-65 engines until at least September 1961, Republic had optimistically signed on 22 March an Air Force fighter-bomber configuration contract, calling for delivery of the first F-84F productions in December 1951.

Despite Republic's belief at the outset that 55 percent of the tooling used in the production of the F-84E would be adapted to the manufacture of the F-84F, experience proved that only 15 percent could be reusable. This problem was quickly compounded by a shortage of aluminum alloy and the fact that once available, the aluminum alloy could not be processed. Only three presses in the United States could produce the aluminum wing spar and rib forgings for the F-84F, and these presses were almost fully occupied with satisfying concurrent forging requirements for the B-47, which enjoyed the Brickbat Scheme's priority precedence (A high priority list of critical items designated for specific Air Force procurement programs).Unexpected difficulties also were encountered during the Americanization of the Sapphire engine. Again, contrary to the contractor's expectations, the scarcity of machine tools (diverted to higher priority programs) was a major problem until April 1952, when the Wright engine and the F-84F airframe finally were also assigned to the Brickbat Scheme. Other engine problems remained, however. Foremost in these problems was the engine's weight increase, which degraded its performance. By January 1952, the YJ65-W-1 engine was considered obsolescent and further modifications had to be made to keep it in operation.

On 3 December, the Air Force officially accepted the first two F84F productions that had been delivered in November 1952. The delivery date was an 11-month slippage from the contractor's schedule. Moreover, the Air Force approved a revised schedule authorizing further slippage at both the Republic and General Motors plants.

The YJ-65 engine was not interchangeable in successive models. Hence, an airplane built for the YJ-6b-W 1 was bound to use the engine. Yet, while Wright replaced the obsolescent YJ-65-W-1 with the improved YJ-64-W-1A and developed their successor, the more powerful J--65 engine. Republic had begun producing F--84F airframes at the rate of three per day and merely put them into storage pending delivery of a satisfactory engine. In mid-1953, while investigating the possibility of equipping the F-84F with a General Electric engine, the Air Force of necessity decided that the first 275 F-S4Fs would retain the YJ-65-W-1 engine. But for some 100 other F-84Fs that were fitted with the YJ-65-W-1A, all F-84Fs were eventually equipped with the J-65-W-3 engine.

Major difficulties were also encountered because of design deficiencies in the F-84F airframe and airframe components. Development of the F-84F's subsystems also proved more difficult than first anticipated. In mid-1953, after more than a year of corrective effort, the tail of the F-84F was still considered unacceptable for any kind of tactical operations; both the aircraft's longitudinal and lateral controls remained inadequate at high speeds; a redesign of the landing gear up-lock was necessary; the basic hydraulic system was still over-sensitive; the extremely sensitive electrical emergency system still caused concern; the aircraft's dive brakes were susceptible to damage from ejected spent cartridges; and none of the aircraft's weight problems had been solved.

By mid-1954, correction of most of the F-84F design deficiencies was assured, but unavoidable delays' occurred that created further difficulties. Incorporation of a stabilator in production F-84F aircraft, although approved in 1953, had to be postponed because of the long lead time required for the manufacture of the stabilator. In the meantime, in order to continue production, an interim measure was taken. A number of F-84Fs were equipped with the two-piece "poor man's flying tail," which consisted of an interconnected horizontal stabilizer and elevator. Although successfully flight tested by Republic, this expedient did not work. In December 1953 the Air Force directed that the installation be stopped and that the "poor man's flying tail" be removed from the aircraft already so equipped. By the end of 1954, numerous other expensive or time consuming modifications had been made or were scheduled for the near future. More than 785 F-84Fs had been modified through the installation of aileron spoilers at a cost of $4.7 million; 506 by receiving true air speed indicators for a $1.3 million outlay; and 258 F-84F airplanes were to be modified by installing the F-5 auto-pilot at an estimated cost of $3 million.

SAC's 506th Strategic Fighter Wing, at Dow AFB, Maine, re ceived the first F-34Fs. However, these aircraft, 14 of which were in the hands of SAC by mid-January, were of limited use because of their unsatisfactory engines and other deficiencies. They re quired special inspections and maintenance and were part of some 400 early F-84F productions, conditionally accepted by the Air Force. By May 1954, SAC had received 125 of the 400 F-84Fs having obsolescent YJ-65-W 1 engines, still deficient YJ-6S-W-1As or other shortcomings. Twelve similar aircraft were undergoing additional testing, 20 had been delivered to the Air Training Command (ATC) at Luke AFB, Ariz., and the remainder would be modified and also released to training.

Initial operational capability with J-65-equipped F-84Fs did not come until 12 May 1954, when a few of them finally reached TAC's 405th Fighter Bomber Wing at Langley AFB, Va. Although first on the priority list, the 405th had less than half its quota of new aircraft--36 against ?5--by the end of June. On 18 June, SACs first J-65-equipped F-,84Fs had joined the 27th Strategic Fighter Wing at Bergstrom AFB. This was another 6-month slippage of the latest delivery date which SAC had anticipated.

Deficiencies found in the J-65-equipped F-84Fs, accepted since May 1954, compelled the Air Force to ground several of the aircraft and to suspend Republic deliveries. Other stringent measures ensued. In August the contractor was directed to reduce its daily output from five to three aircraft-two F-84Fs and one RF84F--and in September a hold order was placed on 400 of the last 500 articles scheduled for production. The Air Force concurrently initiated a series of new operational suitability tests. Referred to as Project Run In, these tests upon completion in November 1954 "proved the F-84F a satisfactory fighter-bomber, capable of the mission role for which it had been planned" as well as a "considerably better aircraft than the [F-84]G." The results of Project Run In, together with Republic reorganization of its quality control group and increases in plant personnel, induced the Air Force to approve an accelerated delivery schedule that would make up for some of the time lost. This year-end schedule called for all Republic-stored aircraft to be readied for delivery late in March 1955.

Early in 1955 TAC F-84F units experienced difficulties in the aircraft's braking system. Meanwhile, the new J-65-equipped F84Fs continued to present problems.

Engine failures in late 1954 led to the grounding of all F-84Fs in early 1955. Because of the latest grounding, the Air Force once again stopped accepting F-84F deliveries. Although a number of engines had to be overhauled, most grounded aircraft returned to flying status after inspection. The production hold-order of September 1954 was rescinded in February 1955, after which F-84F deliveries were resumed. The idea of making F-84Js out of some F/RF-84Fs--by exchanging the J-65 engine for the General Electric J-73--was reconsidered but rejected for the last time in March. Soon afterward, however, SAC and TAC F-84Fs again experienced a number of engine flame outs when flying in heavy precipitation. Several accidents occurred in severe weather because of engine failures that were attributed to faulty compressor shrouds. Pending correction, flying restrictions were imposed.

F-84F production slipped another 6 months in 1956. This time the slippage stemmed from a 4-month labor strike at Republic early in the year.

With Republic delivery of the last MAP F-84F. Republic production of USAF F-84Fs ended in February 1957, that of General Motors in February 1955. Total F-84Fs Accepted: 2,348-852 for MAP and 1,496 for the Air Force. Air Force's total represented a reduction of 756 articles from the contingent originally funded. The Air Force also accepted three YF--84Fs from Republic. The acceptance rate was; Forty-eight F-84Fs were accepted in FY 53 from the Republic plant in Farmingdale, N.Y., 510 in FY 54, 597 in FY 55, 103 in FY 56, and one in FY 57. One F-84F, built in Kansas City by the General Motors Corporation, was accepted in FY 53, 56 in FY 54, and 180 in FY 55. The F-84Fs earmarked for MAP were accepted by the Air Force between FY 55 and FY 58-77 in FY 55, 326 in FY 56, 400 in FY 57, and 49 in FY 58. All MAP F-84Fs were manufactured at the Republic plant.

Cost per aircraft: $769,330.00-airframe, $562,715; engine (installed), $146,027; electronics, $9,623; ordnance, $9,252; armament, $41,713.

Soon after the F-84Fs arrived in SAC and TAC, they were turned over to the ANG. SAC transferred its first lot in August 1954. The remainder were cleared from the regular combat inventory by IO January 1958, when TAC released its last aircraft. TAC received some F-84Fs in July 1958, when it assumed former ATC responsibilities at Luke and at Nellis AFB, Nev., but these aircraft were used only for training.

The Berlin crisis of 1961-1962 brought four ANG wings of F-84Fs to active duty. A number of these units were deployed to Europe, the other trained under TAC for possible contingency deployment. In late 1961 the Air Force decided to retain the ANG F-84Fs after the wings returned to state control. These F--84Fs would equip USAF tactical fighter units to be activated. Then, as the new units received later-model aircraft, the F-84Fs would be returned to the Guard. The Air Force would loan the F,84Fs to the ANG until required by the newly activated units. This would avoid downgrading ANG capability until absolutely necessary.

Despite all efforts, operationally ready F-84Fs decreased early in the year. Recall of the ANG units made spare parts more critical. Age of the F-84F imposed heavier maintenance requirements. In March, all F-84Fs were grounded for replacement of corroded control rods. Modifications were also necessary to increase the aircraft's conventional ordnance capability. In effect, some 1,800 manhours were expended on each of the 222 F-84Fs that tempo rarity equipped TAC's new 12th and 15th Tactical Fighter Wings and the new 366th TFW of the United States Air Forces in Europe (USAFE).

USAF. As more modern fighters became available, F-84Fs were returned to the ANG. In June 1964, 13 years of MAP F-84B/C/F training at Luke AFB, ended in favor of the F-104G program. In July 1964 TAC returned the last USAF F-84Fs to the ANG.

The Guard still had 56 F--84Fs in November 1971 when a serious accident occurred due to structural corrosion. The 183rd Tactical Fighter Group, Springfield, Ill., the only ANG unit still equipped with F-84Fs, was programmed for F-4C aircraft, and over 90 percent of the grounded F-84Fs showed signs of stress corrosion. Hence no repairs were made. In February 1972, however, the Air Force used two ANG F-84Fs in developing repair procedures that would be offered to the many allied nations using the elderly aircraft.

The F-84F aircraft saw long service with some of the United States's most sophisticated allies. Beginning in 1955, the French Air Force flew F-84Fs for over 10 years. In 1972 the aircraft was still flown by air forces in such countries as Denmark, Italy, Belgium, the Netherlands, Greece, and Turkey.

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Page last modified: 07-07-2011 02:31:35 ZULU