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Republic Jet Fighter Aircraft (under construction)

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The Republic Aviation company, of Long Island, produced several designs for jet fighter aircraft. Some of these, such as the F-84 and F-105, made it into production and are fairly well known. Others, like the XF-91 or XF-103, are more obscure. This thread is intended to give a brief introduction to some of these designs.


Republic Aviation Jet Aircraft


F-84 Thunderjet

F-84F Thunderstreak

XF-84H Thunderscreech

XF-91 Thunderceptor


F-105 Thunderchief

AP-75 (XF-108 Competitor)

FR-150 (XFV-12 Competitor)


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F-84 Thunderjet


The development of the F-84 began in response to a 1944 USAAF requirement for a jet powered fighter aircraft. Under the internal company designation of AP-23, it was developed as a straight wing design powered by a single General Electric J35 turbojet engine. The J35 was chosen since it was an axial-flow engine, as this would allow the fuselage to have a lower cross section, reducing drag. The XP-84A first flew in early 1946, and became operational as the F-84B in 1947. However, there were numerous problems. The J35 engines were  unreliable, some reports indicate they had an average life of only 40 hours. Later models of the F-84 were fitted with improved versions of the J35, improving reliability somewhat. Additionally, the aircraft had structural issues, limiting the speed and maneuverability of early models. These problems were resolved soon, but the quick pace of jet aircraft development in the late 1940s meant that the F-84's conventional, straight wing design was outclassed. The F-84 did perform a vital role in the Korean conflict, but as a ground attack aircraft, not as an air superiority fighter.


The F-84 was involved in numerous experimental setups. These include the zero launch length point defense platforms; an F-84G was the first aircraft to test this in 1955. There was also the Project Tip Tow, which involved attaching F-84s to the wingtips of a B-29 (it was planned to use a B-36 operationally, but this was cancelled after the loss of an F-84 and B-29 during testing).




Performance characteristics of the F-84B can be found here; http://www.alternatewars.com/SAC/F-84B_Thunderjet_SAC_-_19_May_1950.pdf

Performance characteristics of the F-84E can be found here: http://www.alternatewars.com/SAC/F-84E_Thunderjet_Block_25_and_30_SAC_-_18_July_1951.pdf


The F-84 Thunderjet should not be confused with the F-84F, a swept wing derivative, or the XF-84H, an experimental turboprop powered variant. Confusingly, the F-84G is a designation for a straight wing variant of the F-84, produced following delays in the introduction of the F-84F. In addition to incorporating various improvements found on earlier F-84 models, the F-84G was capable of carrying a single Mark 7 nuclear weapon, one of the first tactical nuclear weapons developed.


The F-84 was exported to numerous US allied countries throughout Europe and Asia. Interestingly, about 230 aircraft were also sold to Yugoslavia in the 1950s; they served until the 1970s.







<will add more when I'm not horribly tired>

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F-84F Thunderstreak


By the late 1940s it was apparent that the F-84's base design was obsolete. The swept wing planform limited the F-84 to lower speeds than contemporary aircraft such as the F-86 or MiG-15. Wishing to extend the life of the design, Republic proposed modifying the design adding swept wings and tail surfaces. The engine was also upgraded to a J65 turbojet, providing superior performance.


The new aircraft was originally designated the YF-96, however, the designation was soon changed to F-84F, as it was planned that it could use most of the manufacturing equipment made for the F-84. The new aircraft first flew on 3 June 1950, and testing revealed that performance was improved, although it was still inferior to the F-86. However, the US Air Force ordered the new aircraft into production.


There were numerous issues with the introduction of the F-84F. It turned out that much less of the tooling could be reused than was originally hoped, delaying production and increasing costs. The J65 engines also suffered from problems, notably a tendency to flame out in poor weather. They were also underpowered, as the engines were installed at a slight angle with a bent exhaust pipe. These problems meant that the F-84F did not enter service until 1954, far later than planned. More F-84s (the G model) had to be purchased as an interim solution. By this point, the first prototype of the F-100 had flown, and reached supersonic speeds. The F-84F was clearly obsolete. However, it did serve for a few years, lasting until the early 1960s in US Air Force service, and until the 1970s in the Air National Guard. Like the F-84, the F-84F was used in the nuclear strike role, again carrying a Mark 7 weapon.



The RF-84F Thunderflash was a dedicated reconnaissance variant of the F-84F. It was easily distinguished from regular F-84Fs by the wing root intakes and cameras in the nose of the aircraft. A few of these aircraft were converted to the RF-84K, for use in the FICON project.




The YF-84J was an attempt to improve the performance of the F-84F by fitting the J73 engine used in the F-86H. This required a substantial redesign of the aircraft. Though one of the prototypes did break the sound barrier, it was judged not to be worth the effort.





Like the F-84, the F-84F was exported to numerous NATO countries, such as West Germany. However, it did not see widespread service in non-NATO nations like the F-84 did. This website lists the ultimate disposition of various F-84F airframes; http://www.millionmonkeytheater.com/F-84F.html

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XF-84H Thunderscreech




Yes, that is a Confederate Flag in the window.


Early jet engines suffered from very poor acceleration; it would take several seconds for the engine to spin up from idle to full thrust. While this was problematic enough for a land based aircraft, it was even worse for naval operations. The US Navy, knowing that piston-engined aircraft were becoming obsolete, sought an airplane that combined the performance of a jet with the benefits of a piston engine.


It was decided to modify the F-84F Thunderstreak to create the new aircraft. Originally, the program received the designation of XF-106, thought it was soon changed to XF-84H. Modifying the F-84F to be powered by a propeller would be a challenge. Conventional propellers lose efficiency as the blades approach transonic speeds. With the Thunderscreech designed to operate at speeds around Mach .9, the blades would be supersonic at all times. A specially designed supersonic propeller would have to be used; this would reduce efficiency at low speeds, but provide massive benefits in the transonic range.





The blades are clearly shaped for transonic performance.


The chosen powerplant for the XF-84H was the Allison T40 turboprop. This engine would power many other experimental or limited production aircraft of the time, such as the A2D and R3Y. It was a complex engine, essentially consisting of two side by side turboprop engines, with two driveshafts attached to a common gearbox. The engine was to be mounted behind the pilot, with a shaft passing through the cockpit area attaching to the propeller gearbox. Several other modifications were also present; the horizontal tailplanes were moved to the top of the vertical fin, to keep them out of disturbed air behind the propeller. A small dorsal fin as added to counteract the yaw induced by the propeller.





The XF-84H first flew on 22 July 1955, and flight testing revealed numerous issues with the Thunderscreech. Most of these were associated with the engines. The Allison T40 was unreliable, and especially suffered issues with the gearbox (these problems actually led to the loss of one of the A2D prototypes). The high speed, turbulent airflow coming off the propeller made the aircraft difficult to control. One of the most unique problems caused the XF-84H was the sound. With the propellers rotating at supersonic speeds for the entire run of the engine, a continuous rotating shockwave was formed. Not only did it make the aircraft unbearably loud (it was said that it could be heard from 25 miles away), but it was also rumored to create low frequency vibrations that caused physiological effects. Headaches, nausea, loss of bowel control, and even seizures had been reported.


What really killed the XF-84H was its unreliability and poor performance. Only 12 test flights were flown by the two prototypes, accumulating less than 20 hours of flight time. Almost all flights ended in forced landings. The top speed achieved was Mach 0.7, a respectable value for a propeller aircraft, but far from the design speed of Mach 0.9. (The Tu-114 would later reach a speed of Mach 0.73, beating the XF-84H). Additionally, as the Navy gained experience with jet operations, it was realized that a turboprop powered aircraft was not necessary. By 1956, the program was wrapped up. Several improvements were planned in the XF-84H program, such as the fitting of a more powerful T54 engine, and addition of an afterburner. Neither of these happened. One of the aircraft was scrapped, while the other is on museum display.







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The F-84 was involved in numerous experimental setups. These include the zero launch length point defense platforms; an F-84G was the first aircraft to test this in 1955. There was also the Project Tip Tow, which involved attaching F-84s to the wingtips of a B-36 to extend the fighter's range.








You must be zonked, that's a B29.


Great thread nonetheless.

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