The XF-84H, a joint Air Force-Navy project based on the Republic F-84F, was originally designed to combine the speed of jet aircraft with the long range, low fuel consumption and low landing speed of propeller-driven aircraft. The XF-84H used an Allison XF-40-A-1 turboprop engine in a modified F-84 fuselage. Additional changes included a T-type tail and a triangular fin on the top of the fuselage to reduce the high torque produced by the propeller.
Between 22 July 1955 and 9 October 1956, two XF-84H prototypes (S/N 51-17059 and 51-17060) made twelve test flights. Eleven of the twelve flights ended in emergency landings. Sounds produced by the aircraft's turboprop engine caused nausea and headaches among ground crews, earning the XF-84H the unofficial nickname "Thunderscreech." Though the XF-84H was the fastest single-engine propeller driven aircraft ever built, it never approached supersonic speed. Due to poor performance and high maintenance requirements, the XF-84H never became operational. (text by the NMUSAF staff)
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