The XF-84H aircraft became a nightmare for both pilots and air traffic controllers due to its noise, which could be heard from a distance of up to 40 kilometers, earning it the nickname “Thunderscreech.”
In 1955, the United States Air Force developed a prototype aircraft named the XF-84H, manufactured by Republic Aviation. The purpose of the XF-84H was to determine whether a fighter jet could launch directly from an aircraft carrier without a catapult. A propeller turbine engine was chosen to power the aircraft because such engines use large propellers to move significant volumes of air, allowing the plane to generate greater thrust at lower speeds. Greater thrust equates to faster acceleration, which helps shorten takeoff times.
XF-84H aircraft in flight. (Photo: U.S. Air Force)
The XF-84H was based on the well-known F-84 Thunderstreak delta-wing design but was equipped with an Allison XT40-A-1 propeller turbine engine generating 5,850 horsepower, featuring three steel blades. With a diameter of nearly 3.7 meters, the propeller was so large that even at idle thrust, the tips of the blades moved at supersonic speeds, creating a continuous sonic boom audible from 40 kilometers away. The shockwaves were powerful enough to knock over an adult male.
The horrific noise of the XF-84H led to its nickname “Thunderscreech.” The engine of the Thunderscreech operated at full throttle at all times, with the aircraft’s propeller spinning at 2,100 RPM. Thrust was generated while adjusting the angle of the blades. The response from the propeller was immediate, but the noise was unbearable.
Edward von Wolffersdorff, who led the test pilot team including Henry Beaird, feared that shockwaves from the propeller would shatter windows in the control tower located about 1.6 kilometers from the runway. To prevent injuries from broken glass, whenever the XF-84H flew, air traffic controllers would duck under their desks with the radio and cover themselves with blankets. “No one ever really measured the volume. I think they were afraid the measuring equipment would break,” Beaird recalled.
The XF-84H was not well-received at Edwards Air Force Base, not only due to its noise. XF-84H was an impractical machine, taking half an hour to start up and prepare for takeoff, making it unsuitable for combat. Besides the noise and delays, mechanical issues contributed to its poor reputation.
The T40 propeller turbine was a “nightmare machine.” The XF-84H experienced vibrations stemming from the supersonic propeller and the strong torque generated by the engine. Lin Hendrix, one of Republic Aviation’s test pilots, flew the aircraft once and refused to fly it again.
Hank Beaird flew the aircraft 11 times, with 10 of those flights ending in emergency landings. Ultimately, no one wanted to be associated with the XF-84H. The U.S. Air Force canceled the project after only two XF-84Hs were built, with a total flight time of less than 10 hours. The XF-84H is considered the fastest propeller-driven aircraft ever built, with a maximum speed of 1,078 km/h, although neither of the two produced aircraft flew faster than 724 km/h.
