This made the aircraft a pig to fly for the test pilots who had to constantly compensate for this. The powerful torque caused the aircraft to want to spin around the propeller, like a helicopter without a tail rotor. The rotating propeller was so powerful that the aircraft’s handling was severely affected. These shafts suffered extreme vibrations at certain speeds, and the mechanism that controlled the stubby propeller’s pitch was prone to failure. Each engine had an 18 ft shaft to the gear box. The T40 engine proved to be a mechanical nightmare. Its problems, like the noise, originated from the engine and propeller system. The XF-84H did have incredible acceleration, but that was about it. The only potential rivals being rocket powered aircraft like X-15. Looking at the affects it had on the personnel in the vicinity of the XF-84H, it is most likely the loudest aircraft in history. The actual decibels reached by the aircraft were never recorded (probably because everyone wanted this thing gone as quick as possible). FS-059, the only XF-84H to survive today. Eventually, the air base became so tired of the XF-84H, they made Republic tow it out to Rogers Dry Lake for future tests. The control tower’s sensitive instruments were also at risk. Personnel at Edwards AFB had to communicate with visual signals during tests. It was discovered after the 30 minute test he had been severely incapacitated by the noise.Īnother report states that a Republic engineer experienced a seizure after exposure to the XF-84H, and ground crews would become nauseous from being near it. In once instance, a test run of the XF-84H’s engine took place while a serviceman, unbeknown to the test crew, was inside a nearby C-47. It was so loud, it could physically knock a man down if he walked through the shock waves. Reportedly, this deafening noise could be heard over 25 miles away. As the propeller speed doesn’t change, this meant a sonic shock wave continuously emanated out laterally from the propeller for hundreds of metres. The blades span so quick, that the outer 60 cm of the blades were travelling faster than sound, at about Mach 1.18 or 900 mph. Unfortunately, the constant speed the propeller turned at – was supersonic. During the tests, many issues were observed.Īircraft speed was controlled by rotating the propeller blades themselves, as the XF-84H’s propeller rotated at a constant speed. The XF-84H’s Noiseīoth aircraft were sent to Edwards Air Force Base (Edwards AFB) for testing. This is where the problems of the XF-84H start. In total, the output of the T40 was 5,850 hp, making it one of the most powerful engines in the world at the time. The two engines met at a common gearbox that rotated the propeller. The engine chosen was the Allison T40 turboprop engine, which comprised of two T38 turboprop engines mounted side by side. The XF-84H was created to combine the best of both worlds high speed, and fast acceleration. A conventional piston aircraft from WW2, a P-51D.Ī propeller however, provides immediate power. Take-offs were harder too, as longer acceleration needs a longer runway. If a pilot needed to suddenly increase speed while coming into land, you could make a cup of tea before the engine would respond. This could cause pilots trouble on landing, which is essentially a tightrope balance of slowing down enough, while not falling out the sky. Jets may have been the engineers’ newest toy, but the old propeller still had a major advantage over jet engines.Įarly turbojet fighters suffered with poor acceleration. Without a physical propeller to turn, the sky was quite literally the limit in terms of speed. Jet engines considerably improved the top speed an aircraft can reach. The ‘jet age’ was here, and the newfangled jet engine had almost completely replaced the propeller engine in fighter aircraft. Like many other strange airborne concepts, this aircraft began in the 1950s. The F-84F from which the XF-84H was based. It was based on the F-84F, and has the unenviable record as the loudest aircraft in history, earning it the nickname ‘Thunderscreech’. This aircraft however, was too much for even the most daring test pilots. It was born in the 1950s, an era where if it had an wings and was dangerous, the US would test it. The Republic XF-84H is probably one of the most disliked aircraft the United States has ever put in the air.
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