This Experimental Fighter Plane Was So Loud It Triggered Seizures On The Ground

Sonic booms might be loud. Really loud. Commercial aviation was restricted from breaking the sound barrier after a handful of assessments in the Nineteen Sixties confirmed just how dangerous going supersonic may very well be to those still on the ground. That hasn’t stopped us from getting reminders, as a few weeks back in Chicago the Thunderbirds made some window-shattering harm.

Even just one or two sonic booms might be extremely loud, but what if there was a airplane that made one that was fixed? What form of carnage might that create? Against the grace of God and man, the U.S. Air Force and Navy unintentionally discovered the reply in 1955.

Meet the Republic XF-84H “Thunderscreech,” a airplane that, despite setting the file for propeller-driven pace, would go away a legacy baked in infamy. Its huge turboprop motor made the airplane need to consistently barrel-roll and vibrated the airplane into an emergency touchdown almost every time it flew.  But it was ready to push its propellers to speeds past the sound barrier, and turn out to be a sonic increase machine, giving it the unofficial file for the loudest airplane ever constructed.

This factor sucked. Let’s discuss about it.

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Meet the Screech

In the mid-Fifties, jet engines had been the recent commodity, with early jet fighters just like the p-80 and F-84 simply ready to outrun prop-driven fighters. But these new jets sucked through fuel, and not like the snappy and responsive props, needed time and space to absolutely spool up and get to pace.

For the Navy, that was a drawback. Aircraft carriers lacked the real estate for a jet to take off without some help from a catapult. But the tech was still in its infancy, and early launch systems struggled to get the heavy fighters up to full tune. What the Navy needed was an interceptor that might fly off the deck unassisted, but still have the efficiency of a jet fighter. The Air Force appreciated the idea as effectively, trying for an escort for long-range bombers that may very well be far simpler on fuel than its jet counterparts.

What Republic got here up with was a modified F-84F Thunderstreak, ripping out its jet engine and changing it with an Allison XT40 turboprop engine, cranking out an unreal 5,850 horsepower. Unlike World War II-era fighters, that engine had a fixed pace, shifting the propeller at 2,100 rpm from startup to shutdown, with pilots adjusting the propellers’ pitch to control thrust. That helped the airplane with its giddy-up, but the engine’s unreal torque was enough for the complete airframe to attempt rotating around the propshaft, basically wanting to do a nonstop barrel roll. And there have been other, far more noticeable points.

Sickening sounds

That Allison motor was rotating fast enough to push the ideas of the airplane’s three propellers to supersonic speeds, basically creating a fixed sonic increase. On the ground, it may very well be heard over 20 miles away. In the air, it sounded one thing like this:

That still cannot do the airplane’s quantity justice, as industrial laws keep audio system and headphones from being loud enough to make you sick. That retains you from having a seizure, not like a crew chief working on a C-47 who collapsed listening to the engine during a warm-up. Other ground crews reported nausea and complications as a consequence of working close to the airplane. And it wasn’t a lot better in the cockpit. After the XF-84H had its maiden flight, says Smithsonian Magazine, take a look at pilot Lin Hendrix hopped out and walked over to Republic’s chief engineer Jim Rust, saying, “You aren’t big enough and there aren’t enough of you to get me in that thing again.”

Henry Beaird flew the rest of the assessments, but the drama was far from over. Ten of his 11 flights had such unhealthy vibration from the driveshaft that they had to be cut short.

surprisingly, not a ton of people had been amped for a deafening airplane that shook itself aside and consistently rolled, and the project closed after the ultimate take a look at flight in October of 1956. The program ended with the XF-84H prototypes reaching a top pace of 520 mph — nowhere close to the projected restrict of 670 mph. It was finally outpaced by the current quickest prop-driven airplane, the Tupolev TU-95. One of the planes Russia misplaced in Ukraine’s June 2025 drone strike, that bomber has 4 engines that propel it to 575 mph — while not making its crew sick.

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