Helicopter control to trim in forward flight

Abstract

A theoretical estimation of the flapping and feathering (cyclic pitch) to trim the helicopter rotor in forward flight is given and the equivalence of the two systems is shown. The feathering amplitudes to trim the complete helicopter are then estimated and compared with experimental flight values obtained on the Sikorsky R-4B and S-51 helicopters. The effects of centre of gravity position, fuselage pitching moment, etc., are considered and the delta-3 hinge effect is dealt with in an appendix. The effect of slipstream curvature on lateral control is included. Satisfactory agreement of the theoretical and experimental results is obtained. In the iongitudinal trim, the fuselage pitching moment in the presence of the rotor slipstream is a most important contribution. In the lateral trim, the induced velocity distribution and the tail rotor behaviour have a large influence and must be taken into account.