Aeroelastic Stability Analysis of Stiff-in-plane Hingeless Rotors

Aeroelastic stability of stiff-in-plane hingeless rotors is investigated using the comprehensive analysis RCAS. Aeroelastic stability analysis of stiff-in-plane rotors in hover is compared to experimental measurements that shows an overall fair to good agreement for various rotor parameters. The analysis reveals that blade lead-lag damping decreases sharply and the blades become aeroelastically unstable when the blades stall. Stiff-in-plane rotor aeroelastic stability analysis in forward flight is compared to a previous numerical study. Then, using the rotor models as a baseline, a parametric study is performed for various rotor parameters including aerodynamic models, rotor speed, rotor thrust, lead-lag frequency, precone, contol system flexibility, and tip sweep. The parametric study covers lead-lag frequencies of stiff-in-plane rotors from 1.1 /rev to 1.4 /rev with a flap and a torsional frequencies of 1.15 /rev and 3.0 /rev. The parametric study shows that blade lead-lag mode of the stiff-in-plane hingeless rotors tends to become aeroelastically unstable at high advance ratios. Blade lead-lag damping of the stiff-in-plane rotors decrease as the lead-lag frequencies increase from 1.1 /rev to 1.4 /rev. Aeroelastic stability boundaries (advance ratio) increase as the rotor speed increases for a fixed rotor lift. Aeroelastic stability boundaries increase as the rotor lift decreases for a fixed rotor speed. Aerodynamic stall demonstrates significant effects on aeroelastic stability of stiff-in-plane hingeless rotors.