NOISE CHARACTERISTICS OF JET AIRCRAFT AT HIGH-SPEED LOW-ALTITUDE FLIGHT

Flyover noise measurements are evaluated for four different military j et aircraft types flying at low altitudes. Flight Mach numbers ranged from 0.5 to 0.9. The analysis shows that noise immission is likely cau sed by jet mixing and broadband shock associated noise. Based on the e xperimental results existing noise prediction schemes are extended tow ards higher subsonic flight Mach numbers. The novel prediction schemes describe the observed acoustic signatures quite accurately. This hold s for the overall sound pressure level in dependence of the emission a ngle and for 1/3-octave spectra. The prediction schemes are used to de monstrate and quantify the noise reduction potential achievable by var ying flight Mach number and flight altitude.