Patent ID: 8061962

Claim:
A method of optimizing an anti-torque device ( 2 ) for a rotorcraft that is noise certified at a forward velocity V, the rotorcraft comprising a multi-bladed ducted tail rotor ( 7 ) of diameter D with a given number b of variable pitch blades ( 10 ), mounted to rotate at a speed of rotation Ω substantially coaxially in an airflow duct ( 6 ) of axis extending substantially transversely relative to the rotorcraft and passing through a fairing ( 5 ) incorporated in the tail portion of the rotorcraft, wherein the following steps are performed: a bottom limit frequency FL is selected for a predetermined one-third octave centered on a center frequency FC; the perceived frequency FP of the tone produced by said ducted tail rotor anti-torque device is determined by multiplying the emission frequency FE of that tone by a multiplicative coefficient C to take account of the Doppler effect, i.e.: FP=C×FE the parameters relating to the diameter D of the rotor, the given number b of blades, and to the tangential speed U at the ends of the blades are selected so that the perceived frequency FP of the tone as given by: C×[U× ( n×b ) ±m ]/( π×D) is less than the bottom limit frequency FL of a predetermined one-third octave centered on a frequency FC, n and m being positive integers.