Validation through Flyover Noise Tests of the Overall Amplification or Diminution Effect of Superposing "Artificial" Propeller and Piston-Engine Exhaust Sound Waves

Abstract

The main sources dominating the far-field noise of a G.A. piston engine propeller aircraft have been identified to be the propeller and the engine exhaust. Therefore, the noise received on the ground during the flyover of such airplanes results from the superposition of the individual propeller and engine exhaust sound waves. Although the individual waveforms of both the propeller and the engine exhaust signals received change very little when the aircraft is passing overhead, the combined waveform (superposition) of these two signals - as observed on the ground - changes quite dramatically. A computational study has been condicted where simulated engine exhaust and propeller sound signals were combined at different phase shifts. The phase angle differences actually correspond to different locations of the aircraft moving along a horizontal flight path relative to an observer on the ground.