Longitudinal Stability Assessment of Fixed-Wing UAV based on Fuzzy Closed-Loop Control

A fixed-wing UAV may lose its stability due to external disturbances from wind gusts, rainstorms, snow showers, and unpredicted weather conditions. The longitudinal control of the UAV plays an important role in dealing with longitudinal disturbances. This paper proposes adaptive closed-loop controllers based on fuzzy logic together with proportional-integral/derivative (PI/PD) control to attenuate the dynamic effects from disturbances, leading to the improvement of UAV longitudinal stability. The studied system uses a typical UAV model of the Cessna 182 to identify the UAV characteristics with respect to dynamic transfer functions for designing the relevant controllers. The fuzzy rule base is formulated to establish the suitable control gains of PI/PD, resulting in the improvement of dynamic responses in both transient and steady states. The case studies are performed in the MATLAB/Simulink® environment. The obtained results signify that the Fuzzy-PI and Fuzzy-PD controllers could significantly augment the longitudinal stability of the fixed-wing UAV, reducing system overshoots and settling time.