farid Shahmiri - malek ashtar

The main purpose of this paper is concerned with the sensitivity analysis of main rotor dynamic response pertaining to variation of some relevant system parameters effectively supports the preliminary design of both articulated and hingeless helicopter rotor configurations. The methodology is laid out based on Galerkin solution of partial differential equation (PDE) of main rotor with flexible blades in modal space, and developing of some significant expressions useful for direct and cross-coupled damping and control response prediction. The methods followed in this particular discipline supports the derivation of main rotor PDE for flexible flapping in non-linear closed form accompanied with procurement of response derivatives, Galerkin method of solution, linearization, modal analysis and harmonic balance application. The main advantage of this approach is to render main rotor direct, cross damping and control derivatives for each harmonic of the blade deformations associated with the calculated pitching and rolling moments. The sensitivity expressions enables the prediction of direct, cross damping and control derivatives of main rotor response in terms of the most expressive system parameters, including flap frequency ratio, stiffness number, blade response Lock number, and physical hinge offset, necessary for design of modern helicopters. Finally, the results are depicted in graphical forms for a range of system parameters and operating conditions. Comparison of damping and control derivatives in hover, shows a small effect of offset hinge on the main rotor direct response, whereas, the cross derivatives have a strong dependence on combination of stiffness and offset. Furthermore, Comparison with the full aeroelastic analysis shows that the obtained predictions approximate the true elastic of the main rotor behavior.