Aeroelastic analysis of helicopter rotor blades with advanced tip shapes

A systematic investigation of the effects of tip sweep, anhedral and planform taper on helicopter rotor blade response and loads is conducted using comprehensive structural and aerodynamic models. A finite element method is used for the structural analysis, and a three-dimensional (3D) finite difference aerodynamic analysis based on unsteady transonic small disturbance theory is used to calculate the aerodynamic forces. The blade and its tip are treated as elastic beams undergoing flap bending, lag bending, elastic twist and axial deflections. Nonlinear transformation relations based on moderate rotations are used to assemble the blade and tip elements. The blade response is calculated from nonlinear periodic normal mode equations using a finite element in time scheme. Vehicle trim and rotor elastic response are calculated as one coupled solution using the Newton method. Tip sweep introduces a kinematic axial-lag coupling and a straightening effect of the centrifugal forces, which significantly influence the lag dynamics. Three dimensional aerodynamic effects on torsional response are quite considerable for swept-tip and anhedral-tip blades.