Nonlinear Model Predictive Control of Urban Air Mobility Aircraft With Gust Disturbance

Abstract

The paper explores improving the ride quality of urban air mobility (UAM) aircraft by using a nonlinear model predictive controller (NMPC) for trajectory tracking in the presence of gusts. A hybrid UAM aircraft with traditional control surfaces and multiple rotors is studied. The aircraft's free-flight behavior is governed by a set of nonlinear rigid-body dynamic equations that consider the gyroscopic and inertial effects of the tiltrotors. The control inputs for the aircraft include the spin rate and acceleration of the rotors, their tilt angle and rate, and the deflections of traditional control surfaces, such as the elevator, aileron, and rudder. This research numerically studies the effects of NMPC in actively suppressing aircraft's dynamic responses to continuous stochastic gusts or discrete “1-cosine” gusts, which are applied symmetrically and asymmetrically on the lifting surfaces. The findings indicate that NMPC can effectively maintain the aircraft on its desired flight path, closely resembling the undisturbed level flight when it experiences moderate-intensity gusts. However, the controller's effectiveness decreases as the intensity of the gusts increases. The NMPC can no longer constrain the flight path deviation within a bounded range due to an increased pitch rate when the gust intensity surpasses a certain threshold. In addition, the discrete “1-cosine” gusts present more significant challenges, resulting in pitch angle deviations from the desired value, even at low gust magnitudes.