Push-forward/pull-backward trim for helicopter based on hybrid genetic algorithm

To solve the problems that helicopter trim model has multivariate nonlinear equations, it is difficult to determine its initial value and the global optimal solution is non-unique, an efficient hybrid iteration algorithm is presented in this paper, which combines the genetic algorithm and the quasi-Newton method. The dynamic equations of the different modules of the helicopter are introduced. In modeling the rotor, considering characteristics of the motion and control of the rotor in the actual flight environment, an aerodynamic model of rotor based on dynamic inflow and the blade element theory with the rotor trim is established. The trim control vector and the constraint equations for push-forward/pull-backward are deduced in detail based on helicopter flight dynamic model. Since the objective function is constructed, trim problems are transformed into optimal computation. UH-60A helicopter in the push-forward/pull-backward flight is trimmed, and the trim results are compared with flight test data. It is shown that the pull-backward results agree well with flight data, and there is the discrepancy between the push-forward results and flight data. The primary contribution to the discrepancy of the trim of collective and pedal comes from inaccurate prediction of the unsteady aerodynamic characteristics of the rotor. It is a universal method that can be applied to helicopter trim simulation of different stable flight conditions.