A Robust Longitudinal Stability Augmentation System for Small Aircraft Under Parametric Uncertainty

Small unmanned aerial vehicles (UAVs) face flying quality problems different from those encountered by larger aircraft. The lower airspeeds and small dimensions make these vehicles more susceptible to gusts and stability and control issues, which may render the aircraft difficult to fly. Moreover, due to many factors, UAVs are often built with a considerable degree of uncertainty regarding their aerodynamic properties and flying quality. The resulting aircraft may present poor stability and handling characteristics. This work presents the conceptual design of a robust stability augmentation system (SAS), aimed at increasing stability characteristics and protecting aircraft prone to flying quality problems. In order to deal with parametric uncertainties, the controller was designed with the robust H-infinity technique. The design process is presented, and a parametric aircraft model is provided, together with longitudinal stability and control derivatives. Simulations are presented to show the effects of the controller on the aircraft behavior.