Abstract
In this paper a method for the extraction of main and tail rotor noise from an acoustic pressure time history of a helicopter is described. The method is based on the classic Fourier series; however, modifications are made to account for nonperiodic and nonstationary data. Convergence of the method is demonstrated by the application of the method to artificial data. Thereafter the method is applied to wind tunnel data and flight test data for two different helicopters, one with a traditional tail rotor (Bo105) and one with a modern Fenestron (EC135). The results illustrate that a traditional tail rotor displays a rather tonal noise signature very similar to that of the main rotor, only smaller in amplitude and on a shorter time scale. The Fenestron displays a more chaotic noise signature with both a tonal and a broadband noise characteristic.
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