Aircraft pitch attitude control in presence of uncertain aerodynamics

The problem of aircraft pitch attitude control with guaranteed transient performances in the presence of uncertain aerodynamics is discussed. The fast dynamical controller with the relative highest derivative of aircraft pitch attitude in feedback loop is used. Consequently, two-time-scale motions are induced in the closed-loop system and the method of singular perturbation is used to analyze the closed-loop system properties. Stability conditions imposed on the fast and slow modes and sufficiently large mode separation rate can ensure that the full-order closed-loop system achieves the desired properties in such a way that the aircraft pitch attitude transient performances are desired and insensitive to external disturbances and variations of aerodynamics properties. The circle criterion is used to ensure the absolute stability of the fast motions in the presence of uncertain aerodynamics.