Influence of System Parameters on Main Rotor Responses

The main purpose of this paper is the sensitivity analysis of main rotor direct and cross- coupled responses, pertaining to variation of some relevant system parameters. the system parameters are considered as flap frequency ratio, stiffness number,lock number,and flapping hinge offset, necessary for the preliminary design of articulated and hingeless helicopter rotor configurations. the methodology is laid out on the basis of galerkin solution presentation of the main rotor partial differential equation (pde), required for the modeling of flexible blades. in this particular discipline, the main rotor pde for a blade elastic motion is obtained in a non-linear closed form. the galerkin solution, linearization, modal analysis and harmonic balance method result in some expressions, which are significant for the prediction of main rotor responses. the main advantage of the methodology is to find explicitly main rotor control and damping derivatives, including cross and direct damping, for each harmonic of blade deformations.accordingly, the main rotor pitching and rolling moment functions are also calculated on the basis of derivatives, presented in terms of system parameters. finally, the results are depicted in graphical forms in the range of system parameters and operating conditions. comparisons of the control and damping derivatives in hover show a small effect of hinge offset on the main rotor direct response, whereas the cross derivatives have a strong dependence on the combination of stiffness number and hinge offset. furthermore, comparison with the full aeroelastic analysis shows that the obtained results approximate the true elastic responses