Republic XF-84H Thunderscreech Experimental Fighter Aircraft
The Republic XF-84H attempted to mate a turbine engine with a supersonic propeller system but was limited to just two prototypes.
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The Republic XF-84H was an experimental airframe based on the jet-powered, single-seat Republic F-84F Thunderstreak fighter. The XF-84H development attempted to mate the existing Republic fighter airframe to a turbine engine arrangement utilizing a supersonic propeller system to produce a speedy fighting platform as an alternative to the fuel-hungry, underpowered turbojet breeds of the time. However, issues abounded in such an endeavor and the program resulted in just two troublesome prototypes being built and none were ever tested by USAF test pilots before the complicated program was cancelled. The noise generated from the powerful turboprop engine - reportedly heard as far away as 25 miles - earned the XF-84H its nickname of "Thunderscreech", staying consistent with the "Thunder" naming classification of the original Republic fighter series.
Republic had garnered a fine name for itself in World War 2 thanks to their development of the P-47 Thunderbolt. The aircraft proved her worth as both a competent dogfighter (making many aces of her pilots) and a stable gunnery platform when charged with attacking ground targets across Europe and the Pacific (trains proved a favorite in the European Theater). As great as she was, the aircraft was dropped from service immediately after the war during huge military purges in peacetime America. By the time of the Korean War, Republic had put forth their F-84 "Thunderstreak" - a single-seat fighter powered by a turbojet engine and sporting straight monoplane wings. The aircraft was quickly outclassed by the arrival of the Soviet Mikoyan-Gurevich MiG-15 "Fagot" single-seat, swept-wing jet fighter and attempts at improving the Republic F-84 resulted in a swept-wing version all their own - the F-84F. Approximately 7,500 F-84s were eventually built despite their limitations and these were fielded in great numbers as a fighter-bombers during the war over the Korean Peninsula.
Origins of the XF-84H itself emerged from a United States Navy requirement for a carrier-based fighter aircraft that could take off under its own power without the need for catapult-assisted launches. Republic attempted to produce such a product with their "Project 3347" demonstrator of which the United States Air Force's Wright Air Development Center became a supporter of. The aircraft took the existing F-84F Thunderstreak airframe and fitted the experimental Allison XT40-A-1 turboprop engine (powered by a pair of coupled jet turbines spinning a supersonic, three-bladed propeller) in an amidships fitting directly behind the cockpit. From the engine ran an extension shaft under the cockpit floor to the propeller fitted to the nose of the aircraft. The tail was revised by raising the elevators high along the vertical tail fin and away from the powerful prop wash to be developed by the blades. The development, as a whole, had the potential to supply the airframe with the speed and performance of a turbojet-powered aircraft but, at the same time, could offer the improved ranges and low-fuel consumption of a propeller-driven airframe.
Project 3347 evolved to become the "XF-106" but this was later redesignated under the more familiar "XF-84H" to keep her F-84 Thunderstreak roots in check. The United States Navy had three such prototypes on order but eventually cancelled them, leaving two completed prototypes to be used as research aircraft for the USAF Propeller Laboratory based out of Wright-Patterson AFB. The XF-84H was constructed at Republic's fabled Farmingdale facility before being delivered to Edwards AFB by train. First flight was recorded on July 22nd, 1955.
The XF-84H retained much of its appearance from the F-84F that it originated from. The obvious notable exception was the fitting of a nose cone containing the propeller system. She fielded a smooth, tubular fuselage that tapered off at the rear by the exhaust ring. Wings were swept back, mid-mounted monoplane assemblies and air intakes to aspirate the embedded turbines were fitted at the wing root leading edge. The cockpit sat aft of the nose cone and featured the same framing as found on the F-84F. A raised spine blocked most of the view to the rear. The empennage was dominated by a single vertical tail fin mounting a "T" style assembly that contained the horizontal planes - all tail surfaces were further swept back for maximum aerodynamic efficiency. The undercarriage was of the tricycle variety and dominated by the single-wheeled main landing gear legs retracting under each wing. The single-wheeled nose landing gear leg retracted rearwards forward of the cockpit floor.