Effects of yaw-roll coupling ratio on the lateral-directional departure prediction and restraint

The experimental data obtained from yaw-roll coupled wind tunnel tests are used for lateral-directional departure prediction, by linearizing the (beta) over dot model to extract nominal dynamic derivatives at each coupling ratio. The prediction results are compared with those of the existing engineering methods which are based on the conventional aerodynamic derivatives. The comparison shows that the yaw-roll coupling ratio has a great influence on the departure susceptibility. The departure resistance will loss in partial region of the coupling ratio when the angle of attack is higher than a critical value. According to the stable and unstable regions of coupling ratio, a two-segment stability augmentation system with two different feedback gain matrices is obtained by pole-placement method. The two-segment stability augmentation system is used in the simulations of straight and level flight, steady turn, spin recovery and Herbst maneuver. The simulation results are also compared with the applications of a fixed-gain stability augmentation system designed by the conventional aerodynamic derivatives. When the yaw-roll coupling effects are fully considered, the two-segment stability augmentation system is more effective for departure restraint and can provide a better flying quality with less control energy. (C) 2019 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.