While some Americans like to describe the loud noise from military jets as “The Sound of Freedom,” the Navy and Air Force of the 1950s created a jet-powered prop plane that was so loud it could give ground crews seizures.
Freedom is loud, folks.
But the fact that the XF-84H “Thunderscreech,” which the Navy wanted to fly from carriers, risked the hearing of sailors wasn’t even the stupidest thing about it. It was also extremely maintenance intensive, forced test pilots to sit just a few inches away from deadly machinery, and would try and roll itself over constantly.
So how did the 1950s military end up with such a terrible plane? It came from designers trying to reach just a little too far into the future.
By the end of World War II, it was clear to many top military minds that the future of aviation was in jets. The few jets that flew during the war were quickly made obsolete as designers leaned into the technology. America started producing the P-80 at the close of the war but quickly moved on to swept-wing fighters like the F-86. Fighting over Korea proved that the jet age was upon us. Prop planes were too slow to intercept enemy jets and were often sitting ducks against their faster peers.
But the military was running into issues with its jets. Most important, they needed a lot of fuel, limiting their combat range. The Navy also struggled with the high landing speeds required for jet fighters because carrier landings were preferably slow. Takeoffs weren’t great either, as many jets needed more than 1,000 feet of runway to take off. So the Navy and Air Force teamed up to create a plane that combined the best of the jet and propeller worlds. It was designed to be launched and recovered from a carrier — as fast as a jet but with the low landing speed and fuel consumption of a prop plane.
Unfortunately, the concessions needed to make that happen turned the resulting plane into a nightmare for pilots and ground crew.
The project started with an F-84F Thunderstreak. The F-84 family of jets was problematic. Still, despite some cost overruns and production and maintenance issues, the F-84 family was eventually manufactured in seven different variants and provided the first two Air Force Air Demonstration Squadron fleets.
The F variant of the F-84 was considered the best of the family and was selected in 1953 for a supersonic propeller experiment. The idea was to take a plane with a gas turbine engine and add a propeller to it. Ostensibly, the faster rotation of the propeller would allow it to generate nearly as much thrust as a jet engine at speed and much more at takeoff speeds. With proper gearing, it could take off on a shorter runway or deck than jet aircraft, and it would sip fuel.
The military added a 30-inch propeller that would spin at 3,000 revolutions per minute, pushing the outer half of the propeller to supersonic speeds. So someone standing in “the plane of the propeller” — precisely to its left or right — would experience over 100 sonic booms per second as each tip threw them out.
The plane was incredibly loud even if you weren’t in line with the propellers. Members of the program remember the control tower putting blankets over key equipment and themselves in case the plane, taking off on a runway a mile away, broke the tower’s glass. The sound was rumored to have caused miscarriages and definitely induced a seizure in a C-47 crew chief unlucky enough to get caught by surprise in the propeller’s plane.
The fast-spinning drive shafts created a terrifying situation for the pilots who were sitting above them. The driveshafts passed under the pilots before reaching the gearbox, so the two shafts weren’t rotating at 3,000 rpm — they were spinning at over 20,000 rpm. If a loose bolt were to fall onto a shaft and get thrown into the cockpit, it would have entered like a bullet.
Out of 12 test flights, 11 resulted in emergency landings.
But, for all of its flaws, the XF-84H — dubbed Thunderscreech by traumatized pilots and crew — did work. It delivered a massive amount of power as soon as pilots touched the gas. In fact, the two test pilots learned to be extremely careful accelerating because the plane was prone to spinning itself around the propeller if a pilot gave it too much gas.
The Navy backed out of the project first, and the Air Force followed soon after. One of the two prototype planes remains in the National Museum of the US Air Force in Dayton, Ohio.