Comparative study of the influence of straigth and modified-tip rotor balance on loads and control response

Abstract

For performance improvement and noise reduction, swept and anhedral tips have been incorporated in advanced geometry rotor blades. While there are aerodynamic benefits to these advanced tip geometries, they come at the cost of complicated structural design and weight penalties. The effect of these tip shapes on loads, vibration and aeroelastic response are also unclear. In this study, a comprehensive helicopter aeroelastic analysis which includes rotor-fuselage coupling shall be, briefly, described and the analysis results for rotor blades with straight tip, tip-sweep and tip-anhedral shall be presented and compared. The helicopter modeled is a conventional one with a hingeless single main rotor and single tail rotor. The blade undergoes flap, lag, torsion and axial deformations. Aerodynamic model includes 3-state Peters-He dynamic wake theory for inflow and the modified ONERA dynamic stall theory for airloads calculations. The complete 6-dof nonlinear equilibrium equations are solved for analyzing any general flight condition. Response to pilot control inputs is determined by integrating the full set of nonlinear equations of motion with respect to time. The effects of tip-sweep and tip-anhedral on loads and vehicle response to pilot inputs shall be presented.