DYNAMIC-STALL AND STRUCTURAL-MODELING EFFECTS ON HELICOPTER BLADE STABILITY WITH EXPERIMENTAL CORRELATION

The effects of blade and root-flexure elasticity and dynamic stall on the stability of hingeless rotor blades are investigated. The dynamic stall description is based on the ONERA models of lift, drag, and pitc hing moment. The structural analysis is based on three blade models th at range from a rigid flap-lag model to two elastic nap-lag-torsion mo dels, which differ in representing root-flexure elasticity. The predic tions are correlated with the measured lag damping of an experimental isolated three-blade rotor; the correlation covers rotor operations fr om near-zero-thrust conditions in hover to highly stalled, high-thrust conditions in forward flight. That correlation shows sensitivity of l ag-damping predictions to structural refinements in blade and root-fle xure modeling. Moreover, this sensitivity increases with increasing co ntrol pitch angle and advance ratio. For high-advance-ratio and high-t hrust conditions, inclusion of dynamic stall generally improves the co rrelation.