Effect of in-plane induced velocities on the steady state modelling of a helicopter using a time marching wake

Abstract

The effect of an accurate prediction of the induced velocities on the steady state flight solution of a helicopter was investigated with a flight dynamics model coupled with a time-marching free wake. In particular, the radial and tangential induced velocities, often neglected, were added to the model. The results were obtained for arange of speeds and turn rates and validated against flight test data. The radial induced velocity was found to be very small, except for the regions where the vortex filaments were very close to the rotor. The tangential induced velocity, on the other hand, was more significant in magnitude and its effect on the angle of attack and aerodynamic loads was described. In general, the tangential induced velocity was found to lower the angle of attack over much of the rotor, except for on the rear retreating side where it had the opposite effect. The trim results showed that a similar trend is obtained with both models, however including all induced velocities produces slightly higher power and collective requirements, but similar or moderately lower values for the helicopter orientation and cyclic controls. It was also found that the effects of the in-plane induced velocities on turning flight were not symmetrical, with slightly different predictions on left and right turns.