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Republic XF-84H
The Republic XF-84H "Thunderscreech" was an experimental turboprop aircraft derived from the F-84F Thunderstreak. Powered by a turbine engine that was mated to a supersonic propeller, the XF-84H had the potential of setting the unofficial air speed record for propeller-driven aircraft, but was unable to overcome teething aerodynamic deficiencies, resulting in the cancellation of the program.〔Knaack, Marcelle Size. ''Encyclopedia of U.S. Air Force Aircraft and Missile Systems: Volume 1 Post-World War II Fighters 1945–1973''. Washington, D.C.: Office of Air Force History, 1978. ISBN 0-912799-59-5.〕
==Design and development==
Although the USAF Wright Air Development Center was the key sponsor of the Republic Project 3347 turboprop fighter, the initial inception came from a U.S. Navy requirement for a carrier fighter not requiring catapult assistance.〔Keaveney 1987, p. 9.〕 Originally known as XF-106,〔Heyman, Jos and Andreas Parsch. ("Duplications in U.S. Military Aircraft Designation Series." ) ''designations-systems.net,'' 2004. Retrieved: 17 July 2010.〕 the project and its resultant prototype aircraft were redesignated XF-84H,〔Holder 2006, p. 18.〕 closely identifying the program as an F-84 variant, rather than an entirely new type.〔Keaveney 1987, p. 27.〕 With a projected contract for three prototypes, when the US Navy cancelled its order, ultimately, the remaining XF-84H prototypes became pure research aircraft built for the Air Force’s Propeller Laboratory at Wright-Patterson AFB to test supersonic propellers in exploring the combination of propeller responsiveness at jet speeds.〔Wilkinson 2003, pp. 2–3.〕
The XF-84H was created by modifying a F-84F airframe, installing a Allison XT40-A-1 turboprop engine〔("Fact Sheet: Allison T-40-A-10." ) ''Nationalmuseum.af.mil'', 2 April 2009. Retrieved: 17 July 2010.〕 in a centrally-located housing behind the cockpit with a long extension shaft to the nose-mounted propeller.〔 The turbine engine also provided thrust through its exhaust; an afterburner which could further increase power to , was installed but never used.〔Wilkinson 2003, p. 5.〕 Thrust was adjusted by changing the blade pitch of the -diameter Aeroproducts propeller, consisting of three steel, square-tipped blades turning at a constant speed, with the tips traveling at approximately . To counter the propeller's torque and "P-factor", the XF-84H was fitted with a fixed dorsal yaw vane.〔Keaveney 1987, p. 17.〕 The tail was changed to a T-tail to avoid turbulent airflow flow over the horizontal stabilizer/elevator surfaces from propeller wash.〔("Fact Sheet: XF-84H." ) ''Nationalmuseum.af.mil'', 26 August 2009. Retrieved: 17 July 2010.〕
The XF-84H was destabilized by the powerful torque from the propeller, as well as inherent problems with supersonic propeller blades.〔Wilkinson 2003, p. 2.〕 A number of exotic blade configurations were tested before settling on a final design.〔 Various design features were intended to counteract the massive torque, including mounting the left leading edge intake further forward than the right, and providing left and right flaps with differential operation.〔Winchester 2005, p. 233.〕 The two prototypes were equally plagued with engine-related problems affecting other aircraft fitted with T40 engines, such as the Douglas XA2D Skyshark and North American A2J Super Savage attack aircraft. A notable feature of the design was that the XF-84H was the first aircraft to carry a retractable/extendable ram air turbine. In the event of engine failure, it would automatically swing out into the airstream to provide hydraulic and electrical power. Due to frequent engine problems, as a precaution, the unit was often deployed in flight.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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