Abstract:

ESDU 82027 gives a graphical method, and a computer program (ESDUpac A8727), for estimating the free-field values of one-third octave band lateral attenuation. Lateral attenuation is defined as the difference between the under-the-flightpath and sideline free-field levels where the propagation distance of the two sound levels is the same. The range of applicability includes sideline noise-levels for turbo-fan and turbo-jet powered aircraft with either rear fuselage or underwing mounted engines when the elevation angle of the aircraft, relative to an observer at the sideline location, is greater than five degrees, the wind speed is less than 6 m/s (20 ft/s) and there are no temperature inversions. The use of the graphs and program is explained by means of a worked example that also illustrates the format of the input and output.

An addendum discusses the estimation of sideline noise in subjective noise metrics.