Helicopter main-rotor/tail-rotor interaction

Preliminary results from a study to model the interaction aerodynamics and aeroacoustics of the main- and tail rotor of a helicopter in subsonic flow are presented. The configurations studied are: 1) two-bladed main- and tail rotors in hover, and 2) a four-bladed main rotor and two-bladed tail rotor in climbing flight. The unsteady pressure on the main- and tail rotor surf aces is computed with an unsteady 3-D panel method with full-span free wake simulation of the simultaneously rotating rotors. The computed pressures s erve as input to a Ffowcs Williams Hawkings-equation based acoustic code to evaluate the noise characteristics. For the hover configuration, the param eters varied were the distance between the rotor axes and the sense of rota tion of the tail rotor. Presence of the main rotor has a significant effect on the noise directivity and noise level of the tail rotor. Noise contribu tion of the tail rotor dominates during the climb.