Loudest aircraft
XF-84H Thunderscreech, Republic Aviation Corporation
Loudest ranked #1
United States (Edwards Air Force Base)

The loudest aircraft ever flown was likely the Republic XF-84H "Thunderscreech", a turboprop-driven variant of the US Air Force's F-84 Thunderjet fighter. No scientific measurements of the aircraft's noise levels were ever made, but during engine run-up tests at Edwards Air Force Base, California, in July 1955, the base received noise complaints from homes as much as 40 km (25 miles) away. The screeching whine of the aircraft's propeller required all ground crew communication to be conducted using signal flags and lights. It caused men caught in the prop-wash to vomit or faint, and even triggered a seizure in one nearby engineer. It was so loud that the base commander, worried it was damaging the control tower near the runway, eventually demanded that the Thunderscreech be towed out to a dry lakebed on the other side of a ridge for engine tests.

The Thunderscreech was developed in response to problems with early jet fighters. These aircraft could fly at high speeds, but their engines were very slow to accelerate and to respond to changes in throttle settings. This caused problems for pilots, particularly when operating from aircraft carriers. If a pilot found themselves descending too fast they often couldn't power out of the dive in time to avoid catastrophe.

The Thunderscreech used a kind of engine called a turboprop, which uses a jet-engine-like gas turbine to drive a propeller. The engine was set to run at a constant RPM, with the speed being controlled by changing the pitch of the propeller blades.

The engine itself was not particularly loud; the intense noise came from the three-bladed propeller. Because it was running at a constant 2,100 RPM, the tips of the propeller blades were always moving at around Mach 1.18 (1,457 km/h; 905 mph) giving each its own sonic boom. Standing alongside the aircraft, these booms would come at a rate of more than a hundred a second, blurring together into a screeching roar.

The only aircraft that might be able to compare to the Thunderscreech is the Soviet/Russian Tu-95 "Bear", a massive strategic bomber and reconnaissance aircraft powered by four huge turboprops. Although these props don't run as fast as the ones on the Thunderscreech, they are contra-rotating (arranged so that each engine drives two propellers mounted on the same shaft that spin in opposite directions). The complex turbulent airflow between the two propellers creates a deep buzzing noise that can be heard from many miles away. Tu-95s, which entered service in 1952 and are still flying today, are so loud that submarine crews can hear them on patrol, even when submerged. That said, the fact that they are able to be operated on routine missions (it was even converted into an airliner, the Tu-114) implies that the noise levels are more manageable than those described during the testing of the Thunderscreech.

The XF-84H program was cancelled after only 12 short test flights. In addition to the impractical noise levels, the aircraft also exhibited poor handling characteristics, mechanical unreliability and failed to achieved expected speeds.