Simulation Analysis of a Flight Control Law with In-Flight Performance Optimization

A flight control system is designed to perform in-flight optimization of redundant control effectors on a rotorcraft in order to minimize power required at a given flight condition. This "Fly to Optimal" (FTO) control law is tested in simulation using the GENHEL model of the UH-60A and a compound version of the UH-60 with lifting wing and vectored thrust ducted propeller (VTDP). A model following controller is implemented for the pitch, roll, yaw, heave and rotor RPM axes. An outer loop is designed to control forward and sideward translational rate and hold airspeed and altitude during optimization. Two approaches were used to perform in-flight optimizations. A Golden Section search method was used to find optimal rotor RPM on a conventional helicopter, where the single redundant control effector is rotor RPM. A method based on the Adaptive Performance Optimization (APO) methods was used to optimize trim on a compound rotorcraft with several redundant control effectors. The controller can be used to optimize rotor RPM and compound control effectors through flight test or simulations in order to establish a schedule. Alternatively, in-flight optimizations can be performed in level flight cruise conditions without altering flight conditions significantly. Simulation results show the FTO method to be effective in reaching optimal, although in some cases requiring relatively long period of simulated flight time.