An investigation of lateral-directional departure behavior based on yawing-rolling coupled wind tunnel tests

The traditional aerodynamic model based on the dynamic derivative tests and the beta center dot model based on the yawing-rolling coupled motion tests are compared with respect to aerodynamic data, prediction of lateral-directional departure, and flight simulation. The study shows that the traditional model cannot fully reveal the unsteady aerodynamic characteristics and predict completely the departure behavior due to yaw-roll coupling. On the other hand, the beta center dot model can reveal the departure behavior of an aircraft at some specific coupling ratios when the angle of attack reaches a critical value or more, using the aerodynamic data obtained from the yawing-rolling coupled wind tunnel tests. The comparison of flight simulation results shows that the lateral-directional departure is closely related to the coupling ratios, and for the investigated aircraft, the departure is mainly caused by the unsteady yawing and rolling moments at the coupling ratios showing unstable features.