Stability of Hingeless Rotor Blades in Hover with Pitch-Link Flexibility

Abstract

A stability analysis of a single cantilevered helicopter rotor blade in hover is presented. The blade is represented by an elastic uniform beam, cantilevered in bending and having a torsional root spring to simulate pitch-link flexibility. Nonlinear equations are adapted for a linearized stability analysis about the blade equilibrium operating condition. Numerical results are obtained for hingeless rotor configurations having pitchlink flexibility, precone, droop, twist, and flap-lag structural coupling. The results indicate that hingeless rotor stability characteristics are sensitive to changes in most configuration parameters. For a given torsion frequency, the effect of pitch-link flexibility is generally found to be similar to the effect of blade torisional flexibility. Droop and precone, although physically similar, exhibit different effects on stability when pitch-link flexibility is present. Twist is shown to influence the stability by altering the flap-lag structural coupling.