Comparison of predicted engine core noise with current and proposed aircraft noise certification requirements

Abstract

Predicted engine core noise levels for subsonic CTOL aircraft engines are compared with measured total aircraft noise levels and to current and proposed federal noise certification requirements. Comparisons are made at FAR-36 measuring stations and take into consideration both full and cutback power operations at takeoff. The spectral shape used for the prediction of core noise is identified as the spectral envelope, with a peak at 400 Hz which is assumed to be shifted in flight by a Doppler shift in frequency. Preceived noise levels are computed for appropriate engine power settings at desired flight conditions, and reductions in sideline noise levels are made to account for jet and airframe shielding effects. Results indicate that core noise can provide a barrier to the proposed EPA stage 4 and 5 federal noise rules for wide-body aircraft, with the most severe core noise problem occurring at takeoff and sideline measuring stations.