Aeroelastic stability testing and validation of a composite hingeless rotor in hover

Abstract

The aeroelastic stability of a composite hingeless rotor with elastic couplings is investigated in hover. A four-bladed, Froude-scaled, soft in-plane hingeless rotor model with various isotropic and graphite/epoxy composite flexures was designed and tested on a hover stand. By changing the flexure setting angle, the rotor with an isotropic flexure was tested to examine the effects of flap-lag coupling on stability. The effect of elastic flapwise bending-torsion and chordwise bending-torsion structural coupling on the aeroelastic stability were investigated using elastically coupled composite flexures. Lag mode stability test results are compared with the theoretical predictions obtained using the comprehensive aeroelastic rotor analysis, UMARC. The introduction of either negative chord-wise bending torsion coupling or negative flap-lag coupling has a stabilizing effect on the lag damping for positive collective pitch angles. Predictions agree with measured data. (Author)