In 1957, the Pratt & Whitney J57 jet engine powered many of the military’s top aircraft and was being integrated into the Boeing 707 and Douglas DC-8 airliners. But the noise of the engine posed a problem for communities near airports. NACA researchers installed the engine in the Altitude Wind Tunnel and experimented with noise-reducing nozzles. But they inhibited the engine’s performance. Eventually researchers developed an ejector located behind the nozzle that reduced the shock and resulting noise as the exhaust hit the atmosphere. This lowered the noise levels without effecting the thrust.
1 min read