Effects of three-dimensional aerodynamics on blade response and loads

A comprehensive rotor aeroelastic analysis based on finite element theory in space and time is coupled with a three-dimensional transonic small disturbance finite difference analysis to investigate three-dimensional aerodynamic effects on blade response and loads in forward flight. Each blade is assumed to be an elastic beam undergoing flap bending, lag bending, elastic twist, and axial deflections. The blade steady response is calculated from nonlinear periodic normal mode equations using a finite element in time scheme. For induced inflow distributions on the rotor disk, a free wake model is used. Dynamic stall and reverse flow effects are also included. Vehicle trim and rotor elastic response are calculated as one coupled solution using a modified Newton method. The blade loads and structural bending are calculated for two blade configurations: a straight-tip blade and a 30-deg swept-back tip blade. Calculated results are correlated with flight-test data obtained from the Gazelle helicopter (with a straight-tip blade) for two level flight speeds. Results then are calculated for this rotor with a swept-tip configuration and the effects of three-dimensi onal aerodynamics are assessed. Considerable three-dimensional aerodynamic effects are observed in the swept-tip blade.