A method for calculating the miss-distance of helicopter rotor was proposed. For the calculation of miss-distance

rotor inflow and tip-path-plane angle were required firstly. The rotor coupled N-S(Navier-Stokes )/free-wake model and rotor trim model of high accuracy and high efficiency were developed respectively. The method was validated using several numerical examples in both hover and forward flight. Applying the developed method

the effect mechanism of longitudinal forces and flight parameters on miss-distance was analyzed. Further

the ground noise radiated from the helicopter rotor was calculated. It demonstrated that the maximum ground noise was reduced by 4dB through the longitudinal forces and acceleration. At the same time

the relationship between miss-distance and flight parameters was studied and some instructive conclusions for low-noise flight were obtained.