An Initial Analysis of Transient Noise in Rotorcraft Maneuvering Flight

Abstract

This paper examines the additional noise produced by a helicopter rotor during a short-time maneuver, which we call “transient maneuver noise.” A coupled flight simulation/noise prediction system was developed to predict the low-frequency noise generated during transient maneuvers. The system is partially validated for steady noise predictions in this paper. A simulation of a complex 80-second maneuver flight is performed and transient maneuver noise is identified both in the entry and exit of a coordinated turn. The characteristics of the transient maneuver noise were examined in detail by studying the turn entry. The noise generated during short-duration maneuvers is due to multiple sources: aperiodic blade motions, aircraft attitude changes, and transient aerodynamic loading. More aggressive maneuvers produce higher noise levels. The primary effect of a transient maneuver on thickness noise is to change the acoustic directivity, while both loading noise directivity and levels change significantly during aggressive maneuvers.