Time delay compensation in lateral-directional flight control systems at high angles of attack

The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack. In this investigation, the effects of time delay on the lateral-directional stability augmentation system in high-α regime are discussed based on the $\stackrel{?}{\beta }$ model, which is proposed in our previous work and proved as a more accurate aerodynamic model to reveal the lateral-directional unsteady aerodynamic characteristics at high angles of attack. Both the $\stackrel{?}{\beta }$ model and the quasi-steady model are used for simulating the effects of time delay on the flying qualities in high-α maneuvers. The comparison between the simulation results shows that the flying qualities are much more sensitive to the mismatch of feedback gains than the state errors caused by time delay. Then a typical adaptive controller based on the conventional dynamic derivative model and a gain-prediction compensator based on $\stackrel{?}{\beta }$ model are designed to address the time delay in different maneuvers. The simulation results show that the gain-prediction compensator is much simpler and more efficient at high angles of attack. Finally, the gain-prediction compensator is combined with a linearized $\stackrel{?}{\beta }$ model reference adaptive controller to compensate the adverse effects of very large time delay, which exhibits excellent performance when addressing the extreme conditions at high angles of attack.