Noise Component Method for Airframe Noise

Abstract

A method was developed for predicting aerodynamic noise radiated by an airframe. Separate contributions are calculated for the clean wing, horizontal tail, vertical tail, landing gear, leading-edge slats and flaps, and trailing-edge flaps. Each noise component is predicted using scaling laws appropriate to that component, with amplitudes matched to available data. Spectra calculated by this method, the NASA Aircraft Noise Prediction Program (ANOPP) total aircraft method, and the drag element method are compared with flyover noise data for a twin-propeller lightplane, a business jet, and a jumbo jet. from high bypass ratio turbofans with extensive inlet and exhaust acoustic suppression, at approach power setting. Future certification levels must be based on what can be achieved with economically viable airframes and propulsion systems. Thus it is necessary to understand the fundamental processes of airframe noise radiation. Several methods for predicting airframe noise were examined by NASA as part of the Aircraft Noise Prediction Program (ANOPP). Two airframe noise prediction methods, the total aircraft method for aircraft in the clean con- figuration, and the drag element method for all con- figurations, were recommended2 and were subsequently programmed by NASA Aircraft Noise Prediction Office. Verification by comparisons with measured airframe noise spectra have not been published for the total aircraft method and were available for only a few cases for the drag element method. More recently, a noise component method was developed for the Federal Aviation Administration under Contract DOT-FA76WA-3821.3 The purposes of this paper are to describe that method, including recent revisions, and to evaluate the validity of these several airframe noise prediction methods by comparisons between calculated and measured flyover noise spectra. NASA ANOPP Methods Two NASA ANOPP methods for calculating airframe noise were obtained from NASA within one computer program. Option 1 of that computer program is the total aircraft noise method developed by Hardin 2 for clean air- frames. It was derived from a regression analysis of measured peak OASPL for selected aircraft flyovers. These OASPL's