M. Kallergis

The main sources dominating the far-field noise of a G. A. piston engine driven 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 conducted 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. Through validation flight tests with real airplanes it was subsequently established that the shapes of the computed superpositions of signals are quite similar to measured signals. Specifically such validation flights were conducted with a Cessna 207 A (with a Continental 6-cylinder 4-stroke piston engine and a McCauley 3-blade variable pitch propeller) and an LFU 205 (with a Lycoming 4-cylinder 4-stroke piston engine with a Hartzell 2-blade variable pitch propeller). In obtaining such a beneficial (viz. noise reducing) effect through dedicated superposition of engine exhaust and propeller sound waves it is of the utmost importance to employ exhaust systems where the exhaust pipes from the individual cylinders to the common exhaust orifice are of equal length. Only then can one expect the desired phasecorrect superposition effect.

First Joint CEAS/AIAA Aeroacoustics Conference, München, 1995

Conference Paper

englisch

21,0 x 29,7 cm, 10 Seiten

DGLR-Bericht, 1995, 1995-01, First Joint CEAS/AIAA Aeroacoustics Conference - Proceedings; S.213-222; 1995; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1995