F-84 Thunderjet and F-84F Thunderstreak, Republic

F-84F Thunderstreak and F-84 Thunderjet Photo by R. de Wit.

The F-84F was a major redesign of the F-84, with sweptback wings and a new engine, and kept the same number only for political reasons. (It would have been the F-96 at first.) The F-84F was not easy to fly, but it potential was big enough to secure large orders and world-wide export. The RF-84F Thunderflash reconnaissance version had wing root intakes to make room for photographic equipment in the nose. The RF-84K's were parasatic reconaissance aircraft; they had anhedralled tailplanes to fit under the bomb bay of a B-36!.

Type: F-84F Thunderstreak
Country: USA
Function: fighter-bomber
Year: 1952
Crew: 1
Engines: 1 * Wright/Westinghouse J65-W-3 turbojet
Wing Span: 10.24 m
Length: 13.23 m
Height: 4.57 m
Wing Area: 30.19 m2
Wing loading: 292 kg/m²
Empty Weight: 6789 kg
Max.Weight: 12247 kg
Thrust/weight: 0.37
Max. Speed: 1060 km/h
Cruise speed: 865 km/h
Rate of climb: 41.7 m/s
Ceiling: 12000m (other sources claim 14000m)
Max. Range Ferry : 3440 km (with external tanks)
Armament: 6*12.7mm Browning M3 machine guns, 300 rounds/gun, 2720 kg on four external hardpoints

Type: RF-84F
Function: reconaissance
Year: 1954
Crew: 1
Engines: 1 * 3540 kg Wright J65-W-7
Max. Speed: 936 km/h
Ceiling: 12000 m
Armament: 4*mg 12.7 mm

F-84 Thunderjet

The Republic Aviation F-84 Thunderjet was an American-built turbojet fighter-bomber aircraft. Originating as a 1944 United States Air Force proposal for a daytime fighter, the F-84 flew in 1946. Although it entered service in 1947, the Thunderjet was plagued by so many structural and engine problems that a 1948 Air Force review declared it unable to execute any aspect of its intended mission and considered cancelling the program. The aircraft was not considered fully operational until the 1949 F-84D model and the design matured only with the definitive F-84G introduced in 1951. In 1954, the straight-wing Thunderjet was joined by the swept-wing F-84F Thunderstreak fighter and RF-84F Thunderflash photoreconnaissance aircraft. The USAF Strategic Air Command had F-84 Thunderjets (F-84s and RF-84s) in service from 1948 through 1957.

The Thunderjet became the Air Force's primary strike aircraft during the Korean War, flying 86,408 missions and destroying 60% of all ground targets in the war as well as 8 Soviet-built MiG fighters. Over half of the 7,524 F-84s produced served with NATO nations, and it was the first aircraft to fly with the U.S. Air Force Thunderbirds demonstration team.

The F-84 was the first production fighter aircraft to utilize in-flight refueling and the first fighter capable of carrying a nuclear bomb. Modified F-84s were used in several unusual projects, including the FICON and Tom-Tom dockings to the B-29 and B-36 bomber motherships, and the proposed XF-84H Thunderscreech supersonic turboprop.

F-84 Thunderjet Development

In 1944, Republic Aviation's chief designer, Alexander Kartveli, began working on a turbojet-powered replacement for the P-47 Thunderbolt piston-engined fighter. The initial attempts to redesign the P-47 to accommodate a jet engine proved futile due to the large cross-section of the early centrifugal compressor turbojets. Instead, Kartveli and his team designed a brand-new aircraft with a streamlined fuselage largely occupied by an axial compressor turbojet engine and fuel stored in rather thick unswept wings. On 1944-09-11, the United States Army Air Forces released General Operational Requirements for a day fighter with a top speed of 600 mph (521 knots, 966 km/h), combat radius of 705 miles (612 nm, 1,135 km), and armament of either six 0.50 inch (12.7 mm) or four 0.60 inch (15.2 mm) machine guns. In addition, the new aircraft had to use the General Electric TG-180 axial turbojet which entered production as Allison J35.

On 1944-11-11, Republic received an order for three prototypes of the new XP-84. Since the design promised superior performance to the P-80 Shooting Star and Republic had extensive experience in building single-seat fighters, no competition was held for the contract. The name Thunderjet was chosen to continue the Republic Aviation tradition started with the P-47 while emphasizing the new method of propulsion. On 1945-01-04, even before the aircraft took to the air, USAAF expanded its order to 25 service test YP-84A and 75 production P-84B (later modified to 15 YP-84A and 85 P-84B). Meanwhile, wind tunnel testing by the National Advisory Committee for Aeronautics revealed longitudinal instability and buckling of stabilizer skin at high speeds. The weight of the aircraft, a great concern given the low thrust of early turbojets, was growing so quickly that USAAF had to set a gross weight limit of 13,400 pounds (6,078 kg). The results of preliminary testing were incorporated into the third prototype, designated XP-84A, which was also fitted with a more powerful J35-GE-15 engine with 4,000 pound-force (17.80 kN) of thrust.

The first prototype XP-84 was transferred to Muroc Army Air Field (present-day Edwards Air Force Base) where it flew for the first time on 28 February 1946 with Major William A. Lien at the controls. It was joined by the second prototype in August, both aircraft flying with J35-GE-7 engines producing 3,745 pound-force (16.66 kN) of thrust. The fifteen YP-84As delivered to Patterson Field (present-day Wright-Patterson Air Force Base) for service tests differed from XP-84s in having an upgraded J35-A-15 engine, carrying six 0.50 inch (12.7 mm) Browning M2 machine guns (four in the nose and one in each wing root), and having the provision for wingtip fuel tanks holding 226 US gallon (870 L) each. Due to delays with delivery of jet engines and production of the XP-84A, the Thunderjet had undergone only limited flight testing by the time production P-84Bs began to roll out of the factory in 1947. In particular, the impact of wingtip tanks on aircraft handling was not thoroughly studied which proved problematic later.

After creation of United States Air Force by the National Security Act of 1947, the Pursuit designation was replaced with Fighter, and P-84 became the F-84.

F-84s were assigned to the 27th Fighter Wing, 27th Fighter Escort Wing, 27th Strategic Fighter Wing, 31st Fighter Escort Wing, 127th Fighter Day Wing, 127th Fighter Escort Wing, 127th Strategic Fighter Wing, 407th Strategic Fighter Wing and the 506th Strategic Fighter Wing of the Strategic Air Command from 1947

F-84F Thunderstreak/Thunderflash

In 1949, Republic created a swept wing version of the F-84 hoping to bring performance to the F-86 level. The last production F-84E was fitted with a swept tail, a new wing with 38.5 degrees of leading edge sweep and 3.5 degrees of anhedral, and a J35-A-25 engine producing 5,300 pound-force (23.58 kN) of thrust. The aircraft, designated XF-96A flew on 3 June 1950. Although the airplane was capable of 602 knots (1115 km/h), the performance gain over F-84E was considered minor. Nonetheless, it was ordered into production in July 1950 as the F-84F Thunderstreak. The F-84 designation was retained because the fighter was expected to be a low-cost improvement of the straight-wing Thunderjet with over 55 percent commonality in tooling. In the meantime, USAF arranged for the British Armstrong-Siddeley Sapphire turbojet to be built in the United States as the Wright J65 in the hopes that the more powerful engine would improve high-altitude performance. To accommodate the larger engine, YF-84F with a British-built Sapphire as well as production F-84Fs with J65 had a vertically stretched fuselage with the air intake attaining an oval cross-section. Production delays with the F-84F forced USAF to order a number of straight-wing F-84Gs as an interim measure.

Production quickly ran into problems. Although tooling commonality with the Thunderjet was supposed to be 55 percent, in reality only 15 percent of tools could be reused. To make matters worse, the F-84F utilized press-forged wing spars and ribs. At the time, only three presses in United States could manufacture these and the priority was given to the B-47 Stratojet bomber. The YJ65-W-1 engine was considered obsolete and the improved J65-W-3 did not become available until 1954. When the first production F-84F finally flew on 1952-11-22, it differed from the service test aircraft in having a different canopy which opened up and back instead of the sliding to the rear as well as airbrakes on the sides of the fuselage instead of the bottom of the aircraft.

The aircraft was considered not ready for operational deployment due to control and stability problems. Since early aircraft suffered from accelerated stall pitch-up, F-84F-25-RE introduced an all-moving tailplane. A number of aircraft were also retrofitted with spoilers for improved high-speed control. As the result, the F-84F was not declared operational until May 1954. Project Run In operational tests completed in November 1954 finally found the aircraft to be to USAF satisfaction and considerably better than the F-84G. However, ongoing engine failures resulted in the entire fleet being grounded in early 1955. Furthermore, the J65 continued to suffer from flameouts when flying through heavy rain or snow. As the result of the delays, the active duty phaseout began almost as soon as the F-84F entered service in 1954, and was completed by 1958. Increased tensions in Germany assocated with construction of the Berlin Wall in 1961 resulted in reactivation of the F-84F fleet. In 1962, the fleet was grounded due to corrosion of control rods and a total of 1,800 man hours was expended to bring each aircraft to full operational capacity. The aircraft were finally retired in 1964. Stress corrosion forced retirement of ANG F-84Fs in 1971.

The second YF-84F prototype was completed with wing-root air intakes which were not adopted for the fighter due to loss of thrust. However, this arrangement permitted placement of cameras in the nose and the design was adopted for the RF-84F Thunderflash reconnaissance version. The first YRF-84F was completed in February 1952. The aircraft retained an armament of four machine guns and could carry up to fifteen cameras. Innovations included computerized controls which adjusted camera settings for light, speed, and altitude, a periscope to give the pilot better visualization of the target, and a voice recorder to let the pilot narrate his observations. Being largely identical to the F-84F, the Thunderflash suffered from the same production delays and engine problems, delaying operational service until March 1954. The aircraft was retired from active duty in 1957, only to be reactivated in 1961, and finally retired from ANG in 1972.


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