Aeroelastic stability investigation of a composite hingeless rotor in hover

The aeroelastic stability of a composite hingeless rotor with elastic couplings is investigated in hover. A two-bladed, Froude-scaled, soft in-plane hingeless rotor model with various isotropic and graphite/epoxy composite flexures was designed and then tested on a hover stand. The rotor with an isotropic flexure was tested first to examine the experimental procedures. The effects of elastic flapwise bending-torsion and chordwise bending-torsion structural coupling on the aeroelastic stability were then 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 (University of Maryland Advanced Rotorcraft Code). The introduction of,negative chordwise bending-torsion coupling has a stabilizing effect on the lag damping for positive collective pitch angles. Predictions agree with measured data.