Aeromechanical stability of a bearingless composite rotor in forward flight

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Aeromechanical stability of a bearingless composite rotor in forward flight

Tracy, A.L. / Chopra, I.

The aeromechanical stability of a helicopter with an elastically coupled bearingless rotor in forward flight is investigated. A new finite element based structural analysis including the effects of transverse shear and warping restraint is incorporated into the University of Maryland Advanced Rotorcraft Code (UMARC). The effects of transverse shear are implicitly included through static condensation of the shear degrees of motion. The effects of restrained warping are incorporated approximately by modifying the torsional stiffness distributions along the blade. Three soft in-plane bearingless rotor configurations, including bending-torsion structural couplings are analyzed. The analysis covers free flight propulsive trim, blade steady periodic response, and stability of the perturbed rotor-body system. Elastic pitch-lag couplings caused by the ply layup of the flexbeam have a significant effect on the vibratory response, hub loads, and aeroelastic stability of a bearingless rotor. Negative pitch-lag coupling has a stabilizing effect on the lag mode stability in both hover and forward flight.