Report on Noise Reduction Benefits based on HELINOVI Aeroacoustic Main/Tail Rotor Test and Post-Test Prediction Results

The EU HeliNOVI project is designed to resolve the deficiency in TR noise research and is part of the continuing EU effort towards improving the understanding of TR noise reduction and vibration reduction technology by means of a comprehensive investigation of MR/TR interaction noise and rotor induced vibrations through both theory and experiment. As regards the experimental part of the HeliNOVI project, a comprehensive wind tunnel test campaign was launched. The test model is a 40% scaled BO105 helicopter model with instrumented main/tail rotor and fuselage. The importance of tail rotor and of main / tail rotor interference noise as well as of tail rotor noise reduction potentials is investigated in detail. The tested configurations involved in the test are BO105 main rotor (MR) and tail rotor (TR) in combined and isolated conditions. In addition, a number of noise reduction techniques are tested; (1) TR sense of rotation (NACA 0012 TR used), (2) Variation of position between MR and TR (S102 TR used), (3) Variation of rotor rotational speed. As regards the theoretical part of the HeliNOVI project, five codes of varying complexity from 6 organizations have been used in producing the pre/post-test data base of numerical results plus flight mechanics codes for determining the control angles. The adaptation and validation of reliable prediction tools, with reference to the new experiment data set as well as numerical simulations on noise reduction techniques are conducted. The flight conditions covered include level, climb, and descent flight at various flight speeds. The objectives of this report are to analyse the effect of several TR noise reduction techniques on helicopter noise reduction. The analysis will be conducted by using both the test and prediction results and will focus on some common results produced by both test and numerical simulations. The investigation will include tip speed reduction, the sense of TR rotational direction and different TR rotor position. The experiment results used in analysis contain (1) inflow microphone measurements, (2) unsteady blade pressure. The noise reduction benefit will be discussed