Helicopter Noise Reduction by Individual Blade Control (IBC) - Selected Flight Test and Simulation Results -

A collaborative flight test programme was conducted to study among other objectives the potential of open-loop Individual Blade Pitch Control (IBC) to reduce the external noise of a helicopter in partial power decent, a flight regime known to generate the highly annoying Blade-Vortex Interaction (BVI) impulsive noise. The blade root control system employing actuators in the rotating frame, was installed on a BO 105 helicopter, which was flown over an extended linear microphone array. The acoustic measurements on the ground were synchronized to the flight track and rotor performance measurements supplemented by limited simultaneously acquired on-board acoustic and blade surface pressure data. Selected test results quantifying the noise reduction potential of the IBC technique, are presented and compared to numerical rotor simulation results calculated by the aeromechanic S4 code and the acoustic AKUROT code of the DLR. A significant noise reduction benefit (exceeding 5 dB) of the maximum A-weighted (BVI) noise level was obtained for the 2/rev IBC mode; further, over a wide range of IBC phase angles simultaneous noise and vibration reductions were observed. The complete data base acquired will contribute to the development and validation of a fast control algorithm for closed-loop IBC applications.