Analysis of the unsteady-loading noise generated by helicopter in-fin tail rotors

An experimental apparatus for evaluating the noise generated in helicopter in-fin tail rotors is described, and a model of unsteady loading noise has been developed in order to account for the observations. When the in-fin tail rotor is functioning at zero incidence, the two principal noise sources, the preturbulence of the rotor itself and the rotor-stator interaction noise, are found to be distinct, with the rotor-stator interaction manifesting itself by residual lines of the first two harmonics of the blade passage frequency. At large incidence, the rotor-stator interaction appears to dominate the spectral structure.