Republic F-84 Thunderjet (2024)

* Late in World War II, the Republic Aviation company came up with a designfor a single-engine jet fighter, which would emerge as the "F-84 Thunderjet".It served with distinction in the Korean War. After the conflict, it wassupplanted by a swept-wing derivative, the "F-84F Thunderstreak", which wasalso built as a reconnaissance aircraft, the "RF-84F Thunderflash". Thisdocument provides a history and description of the F-84 family. A list ofillustration credits is included at the end.

[1] F-84 THUNDERJET

* In 1944, Republic Aviation began design work on the company's first jetfighter, a successor to the combat-proven Republic P-47 Thunderbolt. The"AP-23", as the company designated it, was designed by a development teamunder Republic's chief designer, Alexander Kartveli. The aircraft was to bepowered by one of the very first American axial-flow turbojet engines, theGeneral Electric (GE) TG-180. On 11 November 1945, the US Army Air Forces(USAAF) awarded Republic a contract for three prototypes, plus a static-testairframe, with the designation of "XP-84". The first XP-84 "Thunderjet", asthe type was known, performed its initial flight on 28 February 1946 fromMuroc Air Base -- now Edwards Air Force Base -- in California, the pilotbeing Major William A. Lein.

Although Kartveli had considered modifying the P-47 to turbojet propulsion,that idea proved unworkable, and so the XP-84 was a new design that owedlittle or nothing to the Thunderbolt. The Thunderjet's configuration wasbasically that of a "flying stovepipe", with an intake in the nose, and anairframe configuration that did reflect Republic's piston-fighter past:straight low-mounted wings, a conventional tail arrangement, a bubble canopythat slid back to open, and tricycle landing gear.

The XP-84 was powered by a J35-GE-7 turbojet, a production version of theTG-180, with 16.7 kN (1,700 kgp / 3,750 lbf) thrust. The wing was thick topermit fuel storage, there being no space for fuel tanks in the fuselage; thetailplane was at the base of the tailfin. Flight controls were conventional-- flaps, ailerons, elevators, rudder -- and manually actuated. All thelanding gear assemblies had single wheels, the nose gear retractingbackwards, the main gear pivoting in from the wings towards the fuselage.The main gear legs were long, being hydraulically compressed when retracting.The entire aft fuselage could be unbolted and pulled off for enginemaintenance. There was a hydraulically-actuated dive brake on the bellybetween the wings, and a bumper under the tail to protect againsttailstrikes.

The second prototype was flying in August 1946. On 7 September 1946, it seta US national speed record of 983 KPH (611 MPH) -- just short of thecontemporary international speed record set by the British Gloster Meteor F.4of 992 KPH (616 MPH). That record wouldn't stand for long, with aircraftspeed records falling in rapid succession for over a decade.

Deficiencies uncovered in initial prototype flight tests led to considerablerevision of the third prototype, which emerged as the "XP-84A". The changesled to a greater take-off weight, and so the YP-84A was fitted with anAllison-made J35-A-15 turbojet with 17.8 kN (1,815 kgp / 4,000 lbf) thrust.GE had been having trouble delivering an adequate supply of J35s, so Allisonwas brought in as an alternate source. Engine availability would prove atroublesome issue for the Thunderjet development program.

Even before the flight of the first prototype, on 4 January 1945, the USAAFhad awarded a contract to Republic for 25 service evaluation machines and 75production machines -- though the numbers were later changed to 15 and 85respectively. The 15 "YP-84A" service evaluation machines featured a morewere similar to the XP-84A, the major changes being armament of six12.7-millimeter (0.50-caliber) M2 Browning machine guns -- four in the noseabove the air intake, one in each wing root -- and provision for wingtipexternal tanks with a capacity of 872 liters (230 US gallons) each. One ofthem was later experimentally fitted with a solid nose and flush intakes, lowon the nose in front of the canopy.

* The initial production version was the "P-84B", with an Allison J35-A-15Cengine, providing the same thrust as the J35-A-15; faster-firing M3 Browningmachine guns; and an ejection seat, which would not be cleared for use andnot armed. Most or all of the YP-84As were brought up to P-84B standard.From the 86th example on, the P-84B featured retractable launch rails foreight 12.7-centimeter (5-inch) "High Velocity Air Rockets (HVARs)". TheThunderjet also had a retractable bomb rack near the wing root on each wing.The rack could carry a 225-kilogram (500-pound) bomb or comparable store.Although the prototypes were painted early on, the paints available at thetime tended to peel off readily at high speeds, and so Thunderjets wouldtypically fly in natural-metal finish.

Initial deliveries of the P-84B, to the 14th Fighter Group, were in thesummer of 1947, roughly at the time when the USAAF became the US Air Force(USAF). A total of 226 P-84B machines was delivered from August 1947 toFebruary 1948, with the type redesignated the "F-84B" when the Air Forcemodified their aircraft designation scheme in 1948. The F-84B left a lot tobe desired in terms of serviceability and reliability, being often in thehangar; surprisingly for a Republic aircraft, it wasn't very sturdy. It hadbeen rushed into service with inadequate qualification, and would never bejudged acceptable for combat service. It was called a "Mechanic'sNightmare", problems being compounded by the difficulty of obtainingreplacement parts.

An update program was begun in 1949 to bring the F-84Bs up to better spec.Two were also modified to evaluate a scheme where they were towed behind aB-29 Superfortress to provide an escort for the bomber, with these machinesredesignated "EF-84B". The idea proved impractical.

The F-84B was followed by 191 "F-84C" machines from May 1948, which weresimilar to the F-84B but featured a revised electrical system and a morereliable J35-A-13C engine, with the same thrust as the J35-A-15. The F-84C,unfortunately, wasn't much more ready for service than the F-84B; theejection seat would still not be qualified for use. The F-84C wouldn't seecombat either, and both variants were quickly passed on to training and AirNational Guard (ANG) units, with the last of them out of service by 1954. 80F-84Bs were obtained by the US Navy as "F-84KX" unpiloted target drones,which was probably an appropriate use for them.

* The next version, the "F-84D", was a fast-track attempt to quickly correctthe worst deficiencies of the Thunderjet until a comprehensive redesign couldbe put into production; Republic was under a lot of pressure to get the F-84to work, with the Air Force considering cancellation of the program. TheUSAF put the F-84D through trials and determined it was more satisfactorythan its predecessors -- if not that much more. One problem was that many ofthe fixes were introduced in the course of production, with the result thatthe F-84 still remained a "Mechanic's Nightmare". In any case, the F-84Dfeatured:

• A J35-A-17D engine providing 22.25 kN (2,270 kgp / 5,000 lbf).
• Modified landing gear. The main-gear leg compression scheme in earlier models had been based on hydraulics, but in the F-84D it was purely mechanical, using a tie-rod scheme for actuation.
• Structural improvements such as thicker wing skins; the substantial increase in engine power allowed the F-84D to be substantially beefed up. The stronger wings of the F-84D would be retrofitted to surviving F-84Bs and F-84Cs.

Other changes included a winterized fuel system; a fin outboard on eachwingtip tank that prevented them from flexing the wings in flight; the pitottube relocated from the top of the tailfin to the engine intake; fixedinstead of retractable bomb racks; and a quick-release canopy. Incidentally,the ejection seat was finally cleared for use. 154 F-84D machines weredelivered from November 1948 to April 1949. The last of them had beenwithdrawn from service by 1954.

* The Air Force tolerated the F-84D on the basis that the comprehensiveredesign effort would finally yield a good aircraft. The result was the"F-84E", the definitive Thunderjet, which was optimized as a fighter-bomberand featured:

• A 30-centimeter (12-inch) fuselage stretch to provide a roomier co*ckpit.
• Stronger wings and improved wingtip tanks.
• The bomb racks updated to "wet" stores pylons, capable of carrying two 871-liter (230 US gallon) underwing tanks.
• A radar gunsight, initially the Sperry A-1B; it proved unreliable, stalling production until the A-1C was introduced.
• Provision for "jet (rocket) assisted take-off (JATO)" boosters to permit take-offs with higher loads.

The F-84E could carry an external load of 2,040 kilograms (4,500 pounds). Itretained the J35-A-17D engine of the F-84D. Initial flight of the firstF-84E was on 18 May 1949. A total of 843 F-84E machines was built up to July1951, with the type serving in the Korean conflict and about a hundred ofthem passed on to NATO forces, mostly the French Armee de l'Air, under the USMilitary Defense Assistance Program (MDAP).

The F-84E was used for trials of in-flight refueling using probe-&-droguerefueling, with two "EF-84E" test machines built to evaluate the concept.One EF-84E was the first jet aircraft to make a nonstop trans-Atlanticcrossing, on 22 September 1950. F-84Es in operational service were in somecases fitted with tip tanks featuring a refueling probe.

* The Thunderjet saw significant combat with US forces. Following theinvasion of South Korea by North Korea on 25 June 1950, US and South Koreanforces were pushed back into a perimeter around Pusan, in the southeastcorner of Korea. On 10 September, a US amphibious force landed at Inchon,the port of Seoul, effectively cutting off the supply lines to North Koreanforces to the south, and leading to their rapid pull-out north.

The decision was made to pursue the fleeing enemy north, with US and SouthKorean forces all but overrunning North Korea -- only to be sent fleeing backsouth in turn, when the Chinese intervened in October. Soviet dictator Josef Stalin supported the drive, most visibly by deploying the swept-wingMikoyan MiG-15 fighter, flown by Soviet pilots, to provide air cover. The USquickly introduced more advanced aircraft into the battle.

F-84D/Es were sent to the theater, getting into the fight by early December,operating out of the airbase at Taegu initially providing escort for BoeingB-29 Superfortress bombers. The Thunderjet, a first-generation jet fighter,proved no match for the MiG-15, being slower and less agile, with 18Thunderjets lost for the destruction of 9 MiG-15s. The second-generationNorth American F-86 Sabre took over the air combat role, with the F-84finding its niche as a strike aircraft, replacing the Lockheed F-80 ShootingStar in that role. F-84s performed attacks with guns, rockets, bombs, andnapalm tanks; the type was seen as a stable gun platform, with pilotsbecoming skilled in accurately dropping munitions, and could soak up hitsthat would have brought down other types of aircraft.

The F-84E took up most of the load, the F-84D not being seen as particularlyacceptable for combat service -- it was slower, had shorter range, and thecramped co*ckpit was intolerable for larger pilots. Many F-84Ds sent into thetheater were simply parked and effectively forgotten.

By early 1951, the war had settled into a stalemate, the two sides jockeyingfor position in negotiations in bitter fighting along the front lines. TheUS attempted, with limited success, to influence the outcome using air power,the F-84 keeping busy with ground strikes -- not just on tactical targets, butalso on infrastructure targets such as dams and bridges, such strikes beingperformed with two 450-kilogram (1,000-pound) bombs, which the F-84E hadenough engine power to carry.

From 1952 into 1953, Japan-based Thunderjets, fitted with probe-equipped tiptanks, performed the first air combat operations using inflight refueling --though the HIGH TIDE missions, as they were codenamed, were limited innumber, operations from Japan being only required by congestion at the mainF-84 base in Taegu, and rendered unnecessary by building up Taegu.

Although the Thunderjet acquitted itself well in operational service it was,like the P-47 before it, regarded as an "Earth lover", disinclined to getinto the air, particularly in warm weather and with a heavy load, beingnicknamed the "Lead Sled", the "Hog", and "Super Hog". It was said that if arunway was built that went around the world, Republic would build an aircraftthat needed all of it. It was, however, easy enough to fly once in the air,though it was hazardous to exceed maximum speed in a dive.

After the conflict, F-84Ds were gradually handed over to Air National Guard(ANG) units, to be finally withdrawn in 1957. The F-84E was phased out offirst-line USAF service in the mid-1950s, finally being withdrawn from ANG /Air Force Reserve (AFR) service in 1959.

* The final version of the Thunderjet was the "F-84G" -- there was an"F-84F", but it was a more advanced aircraft than the Thunderjets and isdiscussed in the next section of this document; delays in the F-84F programled to production of the F-84G as a stop-gap, intended for the nuclear strikerole. Initial deliveries were in 1951.

The F-84G featured a J35-A-29 engine with 24.9 kN (2,540 kgp / 5,600lbf) thrust, the inflight refueling capability demonstrated on the EF-84E,and an autopilot to help fly the long missions enabled by inflight refueling.Originally, the F-84G used a boom refueling scheme, but this was replaced bya probe-and-drogue arrangement. The F-84G introduced a framed canopyreplacing the bubble canopy of earlier variants, which had proveninsufficiently robust; the framed canopy was generally refitted to earliermachines.

The F-84G could carry up to 1,815 kilograms (4,000 pounds) of conventionalordnance. The F-84G was the USAF's first operational nuclear strike fighter,adapted to carry the new 545-kilogram (1,200-pound) Mark 7 tactical nuclearweapon -- with yield programmable from 7 to 61 kilotons -- and using a "LowAltitude Bombing System (LABS)" to deliver the store. LABS permitted theF-84G to perform "toss bombing", with the aircraft releasing the bomb in aclimb, the bomb arcing back down over the target while the fighter made itsgetaway.

 ___________________________________________________________________ REPUBLIC F-84G THUNDERJET: ___________________________________________________________________ wingspan: 11.09 meters (37 feet 5 inches) wing area: 24.15 sq_meters (260 sq_feet) length: 11.60 meters (38 feet 1 inch) height: 3.91 meters (12 feet 10 inches) empty weight: 5,035 kilograms (11,095 pounds) MTO weight: 10,670 kilograms (23,525 pounds) max speed at altitude: 925 KPH (575 MPH / 500 KT) max speed, sea level: 1,000 KPH (620 MPH / 540 KT) service ceiling: 12,350 meters (40,500 feet) range, internal fuel: 1,075 kilometers (670 MI / 580 NMI) max range with tanks: 3,220 kilometers (2,000 MI / 1,740 NMI) ___________________________________________________________________

Initial deliveries of the F-84G to the USAF Tactical Air Command (TAC) werein 1951, with a total of 3,025 F-84G machines delivered by end of productionof the Thunderjet series in July 1953, making the F-84G the most heavilyproduced version of the F-84 series by far. 789 F-84Gs went to the USAF,which put them to good use in Korea, the variant going into combat in thetheater in 1952. An armistice put an end to the fighting on 27 July 1953; bythat time, the F-84 had flown over 86,000 sorties, dropping tens of thousandsof tonnes of bombs and expending tens of thousands of rockets. At least 335Thunderjets were lost -- over half to accidents, the bulk of the rest toground fire.

The other 2,336 F-84Gs went to US allies under MDAP. Users included Belgium,Denmark, France, Iran, Italy, the Netherlands, Norway, Portugal, Taiwan,Thailand, Turkey, and even Yugoslavia. A number of European nations used theF-84E or F-84G in the reconnaissance role, with the wingtip tanks replaced bycamera pods.

The F-84G was the mount for the Air Force Thunderbirds flight demonstrationteam from 1953 into 1955, and was also flown by the USAF / Europe flightdemonstration team, the Skyblazers. A handful of F-84Gs were used to sample fallout from nuclear tests during 1955, these machines having theirwingtip fuel tanks replaced by sampling pods, containing filters to pickup atomic debris. These aircraft had to be decontaminated after landing.The F-84G didn't have the altitude performance to be very acceptable forthe job, being replaced in the sampling role by the Martin B-57 Canberra.

A total of 4,457 Thunderjets was built in all, including the threeprototypes. The last operator of the Thunderjet was Portugal, which phasedout its F-84Gs in 1976.

[2] F-84F THUNDERSTREAK / YF-84J

* Republic engineers felt they could take advantage of research obtained fromthe Germans on swept-wing aircraft to build a faster version of theThunderjet. In late 1949, using company funds the "AP-23M" effort modifiedthe 409th production F-84E with wings with a 40-degree sweepback plus asimilarly swept tail assembly, and fitted it with a J35-A-25 engine providing23.1 kN (2,360 kgp / 5,200 lbf) thrust; it also had a vee-shaped windshieldto improve streamlining. The modified aircraft performed its first flight on3 June 1950 and demonstrated some promise, being clocked on one test flightat a low-altitude speed of 1,115 KPH (693 MPH).

The Air Force was initially not very interested in Republic's work on the"YF-96A", as the type was initially designated -- but with the outbreak ofthe Korean War and subsequent encounters with the MiG-15, USAF interestincreased sharply. A production contract was awarded in July 1950, with thecontract stipulating fit of a more powerful Wright J65 turbojet, was alicense-built copy of the British Armstrong Siddeley Sapphire engine. InSeptember, the type was redesignated "F-84F", Air Force brass thinking iteasier to sell Congress a variant of an existing machine than an entirely newaircraft. It did get a new name, however: "Thunderstreak".

The initial prototype, redesignated the "YF-84F", was re-engined with animported Sapphire engine, flying for the first time in its new configurationon 14 February 1951. The fuselage had to be deepened to accommodate theSapphire engine, while the engine intake had to be enlarged, giving it anelliptical shape. Two more YF-84F prototypes were built in 1951 withimported Sapphire engines. One was a straightforward production prototype,while the other experimentally featured a solid nose and intakes in thewingroots. The intake configuration of the second prototype provedinefficient, but the idea wasn't thrown away.

Although deliveries of production aircraft were planned for the fall of 1951,delays cropped up due to engine manufacturing problems and other difficulties-- the wing design, for example, required heavy forgings that proved hard toobtain, so it had to be re-thought. The delays led to authorization ofproduction of the F-84G Thunderjet. Initial deliveries didn't take placeuntil the end of 1952, with first flight of a production machine on 22November 1952.

* While the Thunderstreak began life as a "minimum-change" derivative of theThunderjet, in the end the two designs were substantially different aircraft.Along with the swept flight surfaces, more powerful engine, deeper fuselage,and bigger engine intake, the Thunderstreak differed from the Thunderjet byfeaturing:

• Instead of an all-around bubble canopy, a one-piece clamshell canopy that lifted up and back above the fuselage on an arm, instead of the rear-sliding canopy of the Thunderjet. There were windows behind the clamshell canopy in a metal fairing. The vee-shaped windscreen was replaced by a sloped armor-glass windscreen.
• Twin perforated airbrakes on the sides of the rear fuselage, instead of one solid airbrake on the belly. Late production had a brake chute to reduce landing roll, with the brake chute retrofitted to older Thunderstreaks.
• Leading-edge slats; power-boosted flight controls; and a spine running down the back of the aircraft.

The first 275 Thunderstreaks had the J65-W-1 engine, built by Curtiss-Wright;the next hundred had the improved J65-W-1A; and then production stabilized onthe much more satisfactory J65-W-3 or Buick-built J65-B-3 engine. All had32.1 kN (3,275 kgp / 7,220 lbf) thrust, the differences being changes toprovide more reliability. Final production aircraft had the J65-W-7 orJ65-B-7 with 34.7 kN (3,540 kgp / 7,800 lbf) thrust. Early production withthe -1 or -1A engines could not be re-engined with later J65 variants; theseaircraft had short service lives.

Armament was the same as for the F-84E, with six M3 Browning machine guns --four in the nose, one in each wingroot -- and the F-84F featured four storespylons, with a maximum load capacity of 2,720 kilograms (6,000 pounds). TheThunderstreak could not be fitted with wingtip tanks, but the inboard pylonswere "wet" and could each carry a 1,705-liter (450 US gallon) external tank.As with the F-84G, the F-84F could carry a tactical nuclear weapon, with aLABS system for toss bombing. Incidentally, although Thunderstreaks oftenflew in natural metal colors, later in their lives disruptive camouflagepaint schemes were often applied.

 ___________________________________________________________________ REPUBLIC F-84F THUNDERSTREAK: ___________________________________________________________________ wingspan: 10.24 meters (33 feet 7 inches) wing area: 30.19 sq_meters (325 sq_feet) length: 13.23 meters (43 feet 5 inches) height: 4.39 meters (14 feet 5 inches) empty weight: 6,275 kilograms (13,830 pounds) MTO weight: 12,700 kilograms (28,000 pounds) max speed, sea level: 1,120 KPH (695 MPH / 605 KT) service ceiling: 14,000 meters (48,000 feet) combat radius (with drop tanks): 1,305 kilometers (810 MI / 705 NMI) ___________________________________________________________________

The Air Force was not very happy with the F-84F at first. The engine, asmentioned, had reliability problems, while the aircraft landed unpleasantly"hot", and handled badly at high speeds. Production was suspended in 1954,with a Project RUN IN initiated to work out the problems. Production resumedin 1955.

Late production Thunderstreaks featured an "all-moving" tailplane, instead ofthe fixed tailplane with elevators of early production aircraft, which helpedreduce the tendency of the aircraft to "pitch up" in high-speed stalls.However, there would always be limitations on maneuvers that might beattempted with the F-84F -- though in maturity, it was seen as a tough andreliable aircraft.

A total of 2,711 Thunderstreaks, not including the two protos, was built toend of production in August 1957. 2,112 of these were built by Republic atthe company plant at Farmingdale, New York, while the remaining 599 werebuilt by General Motors at a plant in Kansas City. There was some perceptionthat GM-built Thunderstreaks were inferior to Republic-built ones. Of thetotal production, 1,410 went to the USAF.

The F-84F was introduced into USAF service in early 1954, initially beingused as a long-range escort fighter by the Strategic Air Command (SAC), toprotect the vulnerable Convair B-36 on long-range missions. Assignments ofproduction were split evenly between SAC and TAC. There were 12 wings ofThunderstreaks by 1955, with six for SAC and six for TAC.

With the phase-out of the B-36 and its replacement by the Boeing B-52, theThunderstreak became the mainstay of TAC, all F-84Fs being out of SAC serviceby 1957. They didn't remain in TAC service much longer, being replaced bythe North American F-100 Super Sabre by the end of the decade. The Air ForceThunderbirds flew the Thunderstreak from 1955 into 1956, when it was alsoreplaced by the F-100.

TAC Thunderstreaks were handed over to the ANG from early 1958. In 1961,Soviet agitation over Berlin led to the activation of four ANG wings flyingthe F-84F, with these aircraft then constituting three active USAF wingsuntil 1964, when they were returned to the ANG again, being replaced by theMcDonnell-Douglas F-4 Phantom. ANG use of the F-84F declined through thedecade, with the last of them removed from service in 1971.

* 1,301 Thunderstreaks were provided under MAP to US allies, includingBelgium, France, Germany, Greece, Italy, the Netherlands, and Turkey. FrenchF-84Fs were the only Thunderstreaks to go to war, flying strikes againstEgyptian targets from bases in Cyprus and Israel during theAnglo-French-Israeli invasion of Egypt in 1956. A Turkish F-84F was the onlyThunderstreak known to have scored an air-to-air kill, shooting down an IraqiIlyushin Il-28 Beagle bomber that strayed into Turkish airspace on 16 August1962.

* Two "YF-84J" Thunderstreaks were built as modifications of F-84F airframesobtained from the production line, one with a GE XJ73-GE-5 and the other withan XJ73-GE-7 engine, providing 38.9 kN (3,970 kgp / 8,750 lbf) and 39.7 kN(4,045 kgp / 8,920 lbf) thrust respectively. They were built as insurancedue to the problems with the J65 engine. These machines had deeper fuselagesand bigger intakes to accommodate the more powerful engines. They also had adistinctive "upper lip" like the F-86, presumably for a radar gunsight.

The first YF-84J prototype performed its initial flight on 7 May 1954.Performance was excellent, with the prototype breaking Mach 1 in levelflight. However, the problems with the F-84F were resolved, and the secondYF-84J prototype never flew. It is believed both machines reverted to F-85F standard, and went into operational service.

[3] RF-84F THUNDERFLASH

* As long as the USAF was obtaining the much improved F-84F Thunderstreakfighter, the Air Force decided to use the same machine as a reconnaissanceaircraft to replace the Lockheed RF-80 Shooting Star. Since thereconnaissance mission implied a solid nose, the second YF-84F test machine,with the wing-root intakes, was used as a basis for the reconnaissancemachine. The sole "YRF-84F" prototype of the "Thunderflash" performed itsinitial flight on 3 February 1952, with Carl Bellinger at the controls. Production was delayed by the same problems that afflicted the F-84F; althoughthe first production "RF-84F" was delivered in 1953, the Thunderstreak wasn'tin proper USAF service until 1955.

The intakes and wings were enlarged; each wing had twin fences, adopted toimprove flight stability in response to YRF-84F tests. There were sixcameras in the nose -- one forward-facing, one vertical, two to each side --plus twin M3 Brownings on the outer walls of each air intake, for a total offour guns. The underwing stores pylons were retained for photoflash flaresor external tanks; a spoiler was fitted to the top of each wing in laterproduction to increase the roll rate, to make it easier to drop externaltanks. Production machines featured a Wright J65-W-7 engine with 34.7 kN(3,535 kgp / 7,800 lbf) thrust.

A total of 715 RF-84Fs was built up to end of production in January 1958.The majority served with the USAF Tactical Air Command and Strategic AirCommand. However, 386 of the total number were provided to US allies underMAP, with users including Belgium, Denmark, France, Greece, Italy, theNetherlands, Norway, Taiwan, Turkey, and West Germany.

The Thunderflash's service with the USAF was short-lived, the type beingreplaced by the McDonnell RF-101 Voodoo from the late 1950s, with the RF-84Fspassed on to the ANG. They remained in ANG service into the late 1960s. The RF-84F lingered on in foreign service through the next decade.

In the course of tensions between Turkey and Greece over Cyprus in the early1960s, Thunderflashes of both sides reconnaissance sorties, with TurkishThunderjets also participating in ground-attack missions in the theater in1964. During further tensions in 1974, Turkish Thunderflashes flew morereconnaissance sorties, with one shot down. This appears to have been theonly combat loss of an RF-84F.

[4] EXOTIC CONCEPTS / XF-84H / XF-91 THUNDERCEPTOR

* In the postwar period, the USAF investigated the "parasite fighter"concept, working on the "Fighter Conveyor (FICON)" project, in which a B-36was to carry a Thunderjet nestled under the bomb bay -- the principle notbeing that the F-84 would provide an escort, but that it would perform anuclear strike, the B-36 simply hauling the F-84 to within range of thetarget.

Tests were performed with a B-36 converted to carry an F-84E, trialsbeginning in 1952. They proved satisfactory enough to move on to theadaptation of a Thunderstreak to the FICON role, an F-84F being given a nosetrapeze, plus a drooping tailplane to ease fit in the B-36, and assigned thedesignation of "YRF-84F".

Tests also showing that satisfactory, the Air Force committed to the concept-- though the role was changed to reconnaissance instead of nuclear strike,using the Thunderflash instead. Ten B-36 bombers were converted to carrieraircraft; 25 RF-84Fs were modified with a retractable skyhook and droopingtailplanes, to be redesignated "RF-84K". FICON actually went into formalservice in the mid-1950s for about a year. Records suggest that it wasn'tvery practical, particularly with respect to recoveries in bad weather, andit never reached full operational status. In any case, the introduction ofthe long-range Lockheed U-2 "Angel" reconnaissance aircraft in 1956 --and the phase-out of the B-36 -- meant the end of FICON.

* Another scheme, known as "Tip-Tow" or "MX-108A", involved a B-29 modifiedto allow F-84s to hook up wingtip-to-wingtip using a clamping module on eachof the B-29's wingtips. Tip-Tow tests were conducted from 1950, which cameto an abrupt end on 24 April 1953, when an F-84 flipped over and tore off thewing of the B-29, with all crew killed in the disaster. The problem was thepresence of vortices around the B-29's wingtips that made the hookups verytroublesome.

During 1955, the same concept was tested with a B-36 -- one earlier used forFICON tests -- and two RF-84Fs under the obscure program name of "Tom-Tom".Tom-Tom ran into the same problems as Tip-Tow, with an RF-84F actually tornaway from the wingtip of the RB-36F on 23 September 1956. Nobody was hurt,but the scheme was immediately abandoned.

* FICON was not by any means the only unusual experiment in the Thunderjetline. In 1953, tests were performed using an F-84G "Zero Length Launch / MatLanding (ZELMAL)" scheme. The idea was that the Thunderjet would be blastedinto the air with an oversized JATO booster from a trailer-transporter -- andthen land, gear up, on a huge inflatable mat, 25 x 245 x 1 meters (80 x 800 x3 feet) in size, and snag an arresting cable to stop.

Tests were begun in December 1953 at Edwards AFB. The launches wereperformed off a trailer normally used to launch a Matador cruise missile, andit is plausible that the Matador JATO booster was used as well. Take-offswere surprisingly easy, but the mat landings were another matter. Theinflatable mat, which was transported on a couple of trailer trucks, leakedthe first time it was set up, and portions had to be sent back to Goodyear,the manufacturer, for repairs.

The first mat landing didn't take place until 2 June 1954. It was a fiasco.The F-84G's arresting hook tore up the mat, and the aircraft was so badlydamaged that it had to be written off. The test pilot, Robert Turner, waslaid up with back injuries for months. Two more mat landings were performed,and though the results were nowhere near as bad as the first landing, theidea was still clearly unworkable. George Rodney, one of the test pilots,described the mat landings: "We tied ourselves into the seat real well, sowe wouldn't pitch forward into the control column and the instrument panel,but unfortunately your head, it goes into a big arc and comes down on yourchest."

ZELMAL was terminated after 28 launches. Rodney commented: "It needed somework, that was for damn sure." The Air Force abandoned the concept for atime, though further work was performed later on zero-length launch of theNorth American F-100 Super Sabre and the Lockheed F-104 Starfighter, matlanding being wisely abandoned in favor of conventional landing on anairstrip. ZEL was never actually fielded, however; although it worked asspecified in maturity, the scheme being seen as more trouble than it wasworth.

* One of the most exotic of the offshoots of the Thunderjet was the"Thunderceptor", designed as the "AP-31" in response to a USAAF requirementissued in late 1945 for a high-speed, high-altitude interceptor capable ofsupersonic flight. Two "XP-91" prototypes were ordered in 1946, the firstflying as the "XF-91" on 9 May 1949, with Carl Bellinger at the controls.

The XF-91 had some resemblance to the F-84, but it was largely a newaircraft. The Thunderceptor was a "hybrid" fighter, initially fitted with asingle J47-GE-3 turbojet providing 23.1 kN (2,360 kgp / 5,200 lbf) thrust.This was then replaced with an afterburning variant that kicked up thrust by30%. Finally, four Reaction Motors XLRII-RM-9 liquid fuel rocket motors --also used on the Bell X-1 rocket plane -- providing 6.67 kN (680 kgp / 1,500lbf) thrust each were added, with two fitted above the engine exhaust and twobelow.

The wing design was very unusual. It had a sweep of 35 degrees and was widerand thicker at the wingtips than at the root, the idea being that thisconfiguration provided good low-speed handling. The wing could be pivotedfor a higher angle of attack on take-offs and landings, and had leading-edgeslats to reduce landing speed. The main landing gear assemblies wouldn't fitinto the inner wing, so they retracted outward into the wing. Each of themain gear assemblies had twin wheels arranged in tandem to allow them to fitinto the wing. Armament was to be four 20-millimeter cannon, though armamentwas never actually fitted.

 ___________________________________________________________________ REPUBLIC XF-91 THUNDERCEPTOR: ___________________________________________________________________ wingspan: 9.52 meters (31 feet 3 inches) wing area: 29.73 sq_meters (320 sq_feet) length: 13.18 meters (43 feet 3 inches) height: 5.51 meters (18 feet 1 inch) empty weight: 7,190 kilograms (15,855 pounds) MTO weight: 12,935 kilograms (28,515 pounds) max speed at altitude: 1,585 KPH (985 MPH / 855 KT) service ceiling: 15,250 meters (50,000 feet) range with tanks: 1,885 kilometers (1,170 MI / 1,120 NMI) ___________________________________________________________________

Two XF-91s were built, the first flying on 9 May 1949. Once all the bugswere worked out, the Thunderceptor turned out to be blazingly fast, with alevel speed of 1,810 KPH (1,125 MPH) in level flight with all five enginesburning. Despite its somewhat eccentric design -- the thing looked like ithad been dreamed up by a 1950s science-fiction writer -- the test pilots werevery impressed with the machine and were disappointed that it did not go onto a production derivative, the program being abandoned to focus ondevelopment of what would become the Convair F-102 Delta Dagger, whichled to the superlative F-106 Delta Dart.

In 1952, the first prototype Thunderceptor was refitted with a nose radomefor AN/APS-6 radar at the top of the intake, while the second was refittedwith a vee / butterfly-style tail. The vee tail had been envisioned at theoutset, but had seemed too radical even for the XF-91; it reduced drag andprovided incrementally higher speed. The first prototype, with the AN/APS-6radar, is now on display at the USAF Museum in Dayton, Ohio.

* In another eccentric experiment, in the early 1950s, both the US Air Forceand Navy were interested in turboprop-powered fighters, which had thepotential for longer range and shorter take-offs with heavy loads thanexisting jet fighters. A team at Republic under Joseph Freeman came up witha design based on the Thunderstreak with the company designation of "AP-46".The program was given the go-ahead, and was given the military designation of"XF-106". The Navy dropped out, but the Air Force stayed with the effort.The name was changed to "XF-84H" and two prototypes were built, the firstperforming its initial flight on 22 July 1955.

The XF-84H was powered by an Allison XT40-A-1 turboprop providing 4,360 ekW(5,850 EHP), the XT40 consisting of two T38 turboprop cores driving a singlegearbox, and turning a three-bladed Aeroproducts propeller with a diameter of3.66 meters (12 feet). It also featured a tee-tail arrangement, with anall-moving tailplane mounted on top of the tailfin -- the tee tail was tokeep the tailplane out of the prop wash -- and a small triangular ventral finbehind the co*ckpit to help cancel torque.

 ___________________________________________________________________ REPUBLIC XF-84H: ___________________________________________________________________ wingspan: 10.21 meters (33 feet 6 inches) wing area: 30.75 sq_meters (331 sq_feet) length: 15.69 meters (51 feet 6 inches) height: 4.69 meters (15 feet 5 inches) empty weight: 7,890 kilograms (17,390 pounds) normal weight: 10,435 kilograms (23,000 pounds) max speed at altitude: 1,080 KPH (670 MPH / 580 KT) range with tanks: 3,790 kilometers (2,355 MI / 2,050 NMI) performance specifications are estimates ___________________________________________________________________

Potentially, the XF-84H was the fastest prop aircraft ever built, with anestimated speed of 1,080 KPH (670 MPH). It didn't get close to that, and infact it was a nightmare in all respects. Early turboprops tended to betemperamental, and the XT40 appears to have been a particularly hard case.Flight tests suffered from continuous malfunctions, particularly of thegearbox; its handling was poor, particularly because of the vicious torqueproduced by the prop; and the noise levels produced were staggering, said tobe able to make people nauseous blocks away. It had to be towed well awayfrom human habitation before the engine was turned over; the machine wasnicknamed the "Thunderscreech".

The second prototype was completed and did make it into the air in 1956, butby that time the Air Force had suffered enough of the project, and it wascancelled. The two prototypes had performed only twelve flights, and all butone had resulted in an emergency landing -- in some cases precautionary, thetest pilots having learned fear of the thing. One XF-84H survives at theUSAF Museum at Wright-Patterson AFB in Dayton, Ohio.

[5] COMMENTS, SOURCES, & REVISION HISTORY

* Sources include:

• F-84 THUNDERJET IN ACTION by Larry Davis & David Menard, SQUADRON-SIGNAL PUBLICATIONS, 1983
• "Republic F-84" by David Willis, INTERNATIONAL AIR POWER REVIEW, Volume 24 2008, pages 132:165.

* Illustration credits:

• BANNER: F-105D with Shrike anti-radar missiles in Southeast Asia / 1966 / USAF
• Republic XF-84 Thunderjet prototype / Republic?
• Republic F-84C Thunderjet / USAF
• Republic F-84E firing HVAR rockets / USAF
• Republic F-84E in Korea / USAF
• Italian F-84G / 2011 / Alan Wilson / Creative Commons Share Alike License
• Thunderbirds F-84Gs / USAF
• Republic F-84F Thunderstreak / USAF
• Republic F-84F Thunderstreak / Chaumont, France / 1961 / USAF
• Republic F-84J Thunderstreak prototype / Republic?
• Republic RF-84F Thunderflash / Sioux City IO USA / 2013 / USAF photo by MSGT Vincent De Groot
• FICON air recovery
• F-84 zero-length launch / USAF?
• Republic XF-91 Thunderceptor / Republic?
• Republic XF-84H "Thunderscreech" / Republic?

* Revision history:

 v1.0.0 / 01 mar 17 v1.0.1 / 01 feb 19 / Review & polish. v1.1.0 / 01 mar 21 / Illustrations update. v1.1.1 / 01 may 21 / Minor fixes. v1.1.2 / 01 mar 23 / Review & polish.