Acoustical design features of boeing model 727

Abstract

Acoustic design features have contributed to the Boeing 727's acceptability to passengers and in operations at airports previously inaccessible to jet aircraft. The aircraft's JT8D-1 engine is inherently quiet, because of its low exhaust velocity and relatively large rotor-stator blade spacing. Further noise reduction is accomplished by wing shielding, inlet noise suppressors, and partial mixing of the turbine and fan exhausts. Low engine noise combined with high lift devices result in lower community noise levels than that from large-propeller aircraft during takeoff. Low interior noise levels have been maintained even though the 727 will operate in the noisy flight regime of high Mach numbers and low altitudes. To achieve this, the conventional double-wall treatment was supplemented with molded Fiberglas and perforated trim panels to improve absorption in critical areas and lead septum to reduce low-frequency noise in the aft section. Engine shock mounts were installed to minimize noise from engine vibration. The air-conditioning equipment, auxiliary power unit, hydraulic pumps, and light ballasts are examples of other equipment that was acoustically treated to make the 727 unusually quiet.