S. Lefebvre
G. Billoud
H. Ribet
J. Paillard
MATRA MS2i, Division ATIS, 3 avenue du centre, Guyancourt, BP 235, 78052 Saint Quentin en Yvelines Cedex, France
This paper describes an active noise control experimental implementation in propeller aircraft. It relies on synchronous excitation of acoustic sources in order to minimize the sound field measured at passenger head height by a set of microphones. System performance predictions coupled with optimization algorithms showed that 32 loudspeakers and 48 monitoring microphones were needed for achieving satisfactory noise reduction. Therefore, a multivariable (48 inputs--32 outputs) digital adaptive controller, based on the time domain filtered-X LMS algorithm, has been developed. It comprises 20 boards plugged in a VMEBus adding up to more than 200 Mflops. The controller has been tested in a Dornier 228, two 4-blade propeller aircraft, under cruise conditions. An averaged reduction of 11 dB for the 1xBPF, 10 dB for the 2xBPF, and 6 dB for the 3xBPF was achieved, which was in accordance with predictions (12 dB at 1xBPF). The reduction was the most significant in the front of the cabin, where the initial noise level was the highest. The optimum noise reduction was reached within 30 s. [European Brite-Euram Aero project n(degrees)0028 ``ASANCA,'' supported by the Commission of European Community, DG-XII.]