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Republic F-84 Thunderjet / Thunderstreak / Thunderflash Fighter-Bomber (1947)

Authored By Dan Alex | Last Updated: 8/12/2013

The F-84 series was the first post-war jet-powered fighter design for the United States.

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The Republic F-84 Thunderjet appeared as an American post-war design and played a pivotal role in the early years that was the Cold War. The nimble little system provided many an Allied nation with a nuclear-capable deterrent against Soviet incursion and played an important ground-attack role in the upcoming Korean War. The F-84 appeared in three major forms - the base original F-84 Thunderjet, the improved swept-wing derivative in the F-84 Thunderstreak, and the dedicated reconnaissance bird in the F-84 Thunderflash. Throughout her operational life, the Thunderjet family earned such unflattering nicknames as the "Hog", "World's Fastest Tricycle", "Iron Crowbar" and the "Lead Sled" due to her excessively long distance takeoff rolls.

Origins

Design of the Thunderjet can be traced back to the closing years of World War 2. In 1944, Republic chief designer Alexander Kartveli was already working on a replacement for the company's other produce - the fabled P-47 Thunderbolt. The Thunderbolt gained a tremendous reputation in the war for its versatility and prowess when facing off against air and ground targets alike. Nicknamed the "Jug", for its stoutly appearance (necessitated by additional ductwork running alongside the bottom of the fuselage), the Thunderbolt was a piston-driven, single-seat fighter aircraft that proved to be a God-send for the Allies. The Republic Aviation firm was firmly entrenched in the Pantheon of classic American warbirds as a result.

Taking the P-47's structure as a starting point, Kartveli attempted to configure the Thunderbolt to accept a centrifugal compressor-driven turbojet engine. Though a bolt attempt, the Thunderbolt's fuselage simply would not accommodate the centrifugal compressor engine's wide cross-section. As a result, an all-new fighter design attempt was broached, with the powerplant being of an axial compressor-driven turbojet engine. Though a more complex alternative, axial compressor-driven engines went on to be widely used to power various jet aircraft thanks to their high efficiency output and smaller cross-sections though still proving highly complex and expensive at the same time.

By September 1944, the USAAF (United States Army Air Force) was already developing a specification to upgrade its fighter groups. This specification called for a jet fighter powered by the General Electric TG-180 (Allison J35) axial flow turbojet engine with a top speed of 600 miles per hour and a range of 705 miles (combat radius). Armament was to be either 6 x .50 caliber heavy machine guns or 4 x 15.2mm heavy machine guns. The USAAF took note of the promising Republic jet-powered Model AP-23 design and, in November of 1944, Republic was given a no-competition contract calling for three prototypes to be designated as the XP-84 "Thunderjet". The selection of Thunderjet as the aircraft's official name deserves note here, for the aircraft would continue the "Thunder" product line from Republic begun by the P-47 all the while signifying the new aircraft's propulsion method of jet power.

Such was the potential of the Republic product that the USAAF made no attempt to hide their interest, resulting in an expanded contract for 25 YP-84A evaluation models and a further 75 P-84B production models. This was an interesting contract order for no XP-84 systems had even flown up to this point. Regardless, the USAAF saw the Republic design as a stronger and more potent alternative to the Lockheed P-80 Shooting Star jet-powered fighter ultimately introduced in 1945. Both the Republic and Lockheed designs went on to see service in the Korean War (the latter as the redesignated F-80 Shooting Star).

Early Drawbacks

While development of the XP-84 was under way, wind tunnel testing results forced some weight restrictions onto the Republic design, ultimately producing the XP-84A prototype. Early turbojet engines were in an inherent relatively under-powered state for the most part, forcing designers to pay close attention to the weight limits of their engineering feats. This proved critical to the success of the XP-84 and, as such, the XP-84A was now fitted with a more powerful General Electric J35-GE-15 series turbojet with a thrust output of up to 4,000lbf. First flight by an XP-84 was finally achieved on February 28th, 1946. The prototype XF-84 was quick to make a name for itself on a national level, achieving 607.2 miles per hour making it the fastest American-designed aircraft to date. This top speed was just 5 miles per hour slower than the world record set by a British Gloster Meteor (612.2mph). The prototypes were followed by a 15-strong batch of YP-84A models with a slightly improved engine of the same type and full armament complement and wingtip fuel tanks.

The USAAF Becomes the USAF

1947 brought about a major historical change to the defense structure of the United States. The USAAF was now branched into a dedicated air force known appropriately as the United States Air Force (USAF). As such, many facets of the pre-war modus operandi were also changed including the use of "P" for "Pursuit" aircraft. This instead fell out of favor and was replaced by the "F" designation system for "Fighter". This is why systems such as the Lockheed P-80 Shooting Star and the Northrop P-61 Black Widow would become the F-80 Shooting Star and the F-61 Black Widow by the time of the Korean War. Deliveries of the now F-84 Thunderjet began with the first F-84B's coming online in December 1947 with the 14th Fighter Group based at Bangor, Maine.


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Specifications for the
Republic F-84 Thunderjet / Thunderstreak / Thunderflash
Fighter-Bomber


Focus Model: Republic F-84F Thunderjet
Country of Origin: United States
Manufacturer: Republic / General Motors - USA
Initial Year of Service: 1947
Production: 7,524


Crew: 1


Length: 37.43 ft (11.41 m)
Width: 36.42 ft (11.10 m)
Height: 14.99ft (4.57 m)
Weight (Empty): 13,830 lb (6,273 kg)
Weight (MTOW): 28,001 lb (12,701 kg)


Powerplant: 1 x Wright J65-W-3 turbojet engine generating 7,220lbs of thrust.


Maximum Speed: 695 mph (1,118kmh; 604 kts)
Maximum Range: 860 miles (1,384km)
Service Ceiling: 45,997 ft (14,020 m; 8.7 miles)
Rate-of-Climb: 7,400 feet per minute (2,256 m/min)


Hardpoints: 2
Armament Suite:
STANDARD:
6 x 12.7mm machine guns (4 in forward upper fuselage and 2 in wing roots).

OPTIONAL:
24 x 5in rockets
2 x Conventional Drop Bombs OR Napalm

Up to 6,000lbs of externally-held ordnance.


Variants:
XP-84 "Thunderjet" - Straight wings; 1st prototype model (1946); General Electric J35-GE-7 turbojet engine; two prototypes produced.


XP-8A "Thunderjet" - Straight wings; 3rd Prototype model; General Electric / Allison J35-GE-15 engine.

YP-84A - Straight wings; service Test Platforms; 15 examples produced

P-84B (F-84B) "Thunderjet" - Straight wings; XP-84A production model; initial production version; redesignated to F-84B in 1947 under USAF; 226 examples produced.

F-84B - Redesignated from P-84B following 1947.

EF-84B - Straight wings; 2 x F-84B conversions for parasite fighter project involving a modified Boeing EB-29A Superfortress.

F-84C "Thunderjet" - Straight wings; revised electrical and hydraulic system; improved J35-A-13C engine; 191 examples produced.

F-84D "Thunderjet" - Straight wings; fitted with J35-A-17D series engine; structural revisions including landing gear; thicker wings; relocated pitot tube to inside of air intake; finned wingtip fuel tanks; 154 examples produced.

F-84E - Post-Korean War; straight-wings; lengthened fuselage and larger cockpit; fitted with J35-A-17D series engine; Sperry AN/APG-30 radar-ranging gunsight; RATO capable; "wet" wings for additional fuel stowage; 843 examples produced.

EF-84E - 2 x F-84E conversions as test subjects for air-refueling exercises.

F-84G - Nuclear capable (Mark 7 bomb); LABS implementation; fitted with J35-A-29 series engine; autopilot; in-flight refueling as standard via wingtip tanks or fuel probe; revised canopy; 3,025 examples produced.

EF-84G - Proposed "Zero Length Launch" capable interceptor; fitted with MGM-1 Matador cruise missile rocket booster; never produced.

F-84KX - USN target drone conversions of at least 80 F-84B models.

YF-96A "Thunderstreak" - Initial Swept-Wing Prototype Designation

XF-84F "Thunderstreak" - 2 x swept-wing variant prototypes; fitted with Wright J65 engine.

F-84F Thunderstreak - Swept wings; fitted with Wright J65-W-1 turbojet engine (later models with Wright J65-W-3 engines); 2,711 production examples built by Republic and General Motors.

RF-84F "Thunderflash" - Swept-Wings; final development model of F-84 series; dedicated reconnaissance variant; fitted with J65-W-7 engine; air intakes relocated to fuselage sides; nose covered over and fitted with camera equipment; 715 examples produced.

RF-84K -Reconnaissance Variant proposed with parasite fighter program involving Convair GRB-36 Peacemaker.

XF-84H "Thunderscreech" - Swept-Wings; proposed supersonic turbo-prop powered variant; never produced.

GRF-84F - Proposed aerial launch and recovery fighter launched from Convair GRB-36 Peacemaker.

YF-84J - Two examples used to develop the General Electric J73 series engine.


Operators:
Belgium; France; Denmark; Germany; Greece; Iran; Italy; Netherlands; Norway; Portugal; Taiwan; Thailand; Turkey; Yugoslavia; United States