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FLIGHT EVALUATION OF ADAPTIVE HIGH-BANDWIDTH CONTROL METHODS FOR UNMANNED HELICOPTERS

This paper summarizes design of a highbandwidth nonlinear adaptive attitude command system for an unmanned helicopter test bed, and presents an evaluation of the controller in both nonlinear simulation and flight test. The attitude command system features a dynamic inversion control law augmented by an on-line neural network. The design is cast in an output feedback setting. The inverting control law is based on a simple linear model of the helicopter and its actuators at the hover condition. An error observer-based method for output feedback design uses either a proportional plus derivative, or a proportional, integral and derivative form for the linear compensator. Pseudo control hedging is employed to prevent adaptation to input characteristics such as actuator position and rate saturation. A brief description is given of the unmanned helicopter testbed, real-time control system implementation, simulation, and flight test facilities. Stable adaptation for a design natural frequency up to 9 radians per second is flight demonstrated in the presence of actuator and unmodeled control rotor dynamics, system time delays, sensor noise, sensor latency, gusts and input saturation.