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The Sound of Rotorcraft

Published online by Cambridge University Press:  04 July 2016

J. W. Leverton
J. W. Leverton*
Affiliation:
Westland Helicopters Ltd, andInstitute of Sound and Vibration Research, University of Southampton
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Extract

The sound of a rotorcraft is very complex in nature since it is a combination of the sound produced by several individual sources, which in the main generate acoustic energy by more than one mechanism. Externally, the important sources are rotor noise and engine noise; while internally transmission system (gear) noise is an additional source. The frequency ranges associated with the various sources on a rotorcraft are summarised on the narrowband spectrum shown in Fig. 1. Main rotor noise is treated as two separate entities, rotational and broadband noise, while the tail rotor noise (if applicable) is dominated by its rotational components.

The following discussion is limited to gas-turbine-engined rotorcraft as, except for some of the small light-weight helicopters, the majority are powered by this type of engine. It is worth noting that on a piston-engined helicopter, the engine itself is the main noise generator, with the primary source being the exhaust noise emanating from the periodic expulsion of the hot gases of combustion. This produces harmonics at the engine firing frequency as indicated on Fig. 1, and in addition to being of high amplitude is very annoying since it occurs in the 200-1000 Hz range.

Type
Rotorcraft Section
Information
The Aeronautical Journal , Volume 75 , Issue 726 , June 1971 , pp. 385 - 397
Copyright
Copyright © Royal Aeronautical Society 1971 

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