The frequency response of the ordinary rotor blade, the Hiller servo-blade, and the Young-Bell stabiliser

Abstract

The present report deals with the frequency response of pivoted gyratory systems, and in particular, with the response of the ordinary rotor blade, the Hiller servo-blade, and the Young-Bell stabiliser to sinusoidal disturbances caused by pitching oscillations with constant amplitude. Physically, the problem corresponds to a single degree of freedom system excited by beats. The resulting forced oscillations are characterised by the two following phase angles :- (a) a phase angle in the plane of rotation (b) a phase angle of the oscillation of the tip-path plane, where the tip-path plane may be considered as a solid body. The latter, which is the controlling consideration, depends on the specific damping of the system and the frequency ratio. In general, the tip-path plane of the systems mentioned above oscillates in two directions, longitudinal, and lateral, where both modes of oscillation can be split up into components in phase with the attitude and in phase with the rate of change of attitude. For each individual system explicit formulae are given and the effect of the frequency ratio on the control characteristics of the Bell stabiliser and Hiller servo-blade is shown by vector loci.