Acoustical Study of the Ch-47b (Chinook) Helicopter

Abstract

Sound measuz:ements were conducted In the CH-47B (Chinook) Helicopter under conditions of normal cruise, maximum continuous power, level M t at various air speeds, hover, level acceleration and deceleration, and partial-" ower descent. Results are presented and compared with applicable parts of Miitary Specification MIL-A-8806A and U. S. Army Human Engineering Laboratories Standard S-1-638. Variations of the noise from that specified in these documents are discussed, and it is recommended that the noise be reduced to conform to the specified levels.

A Technique for Measuring the External Noise of a Moving Helicopter

“…However, there is general agreement that terrain effects are small at angles of greater than 70 (2) to 100 (15). The primary problem in defining terrain effects lies mainly in the nearly infinite variation in terrain features from place to-place.…”

“…The primary problem in defining terrain effects lies mainly in the nearly infinite variation in terrain features from place to-place. Data is available that may be used for particular terrain, such as grassland and jungle (2). Since our test site did not fit the available data we did not calculate SPLs at angles less than 100 or greater than 1700.…”