The Acoustic Environment of a Deflected-Jet Vtol Aircraft

摘要

A noise survey conducted on a deflected-jet VTOL aircraft is described. The test aircraft was mounted on a vertical thrust stand with the nozzles oriented in the 'hover-stop' position while engine runs were made at different power settings. Forty-one (41) microphones were located in the field on the port side of the aircraft and six (6) microphones were located at positions near the aircraft skin. The height of the field microphones was varied (5 ft, 10 ft, and 15 ft). One-third octave band spectra obtained from all microphones and for all engine power settings were flat and did not exhibit the 'haystack' shape which is characteristic of a free jet. Typical one-third octave band sound pressure level spectra and contours of overall sound pressure level are presented. Estimates of jet total acoustic power are developed from the measurements and related to engine operating parameters. Expressions are derived to predict the one-third octave band spectra at positions in the field and on the vehicle from similarly configured aircraft for various engine operating conditions. (Author)