POA * ONLINE SUBSCRIPTION ONLY

ESDU 76020 gives a method based on the Gutin theory for the first harmonic sound pressure level, together with corrections that enable estimates of higher harmonic levels to be derived. The method predicts the first harmonic to 3 dB for 75 per cent of experimental data compared with it, and higher harmonics to 10 dB for 93 per cent of the data; it is applicable to static rotors and propellers or to forward speeds up 40 knots (20 m/s). The input parameters for the method are thrust and thrust coefficient, engine power, number of blades and diameter, tip Mach number and distance to observer.

Both a graphical method and a computer program are included in this Item.