A Method for Reducing Flyover Noise of Propeller-Driven Aeroplanes on the Basis of Dedicated-Phase Superposition of Propeller- and Exhaust-Noise.

Abstract

It has been demonstrated that arranging the sound fields of a propeller and the piston engine exhaust in anti-phase seems indeed a viable technique to reduce the flyover noise of propeller aeroplanes equipped with piston engines. As the experimental results obtained in the near- and far-field of an aeroplane in flight are very encourageing, the application of this noise reducing technique to a more suitable test aeroplane is presently prepared. Higher noise level reductions seem possible with optimizing the relative positions of the sound sources of the aeroplane. The requirement for an improvement can be readily accomplished.