Research On Unsteady Aerodynamic Models At High Angle Of Attack And Spin Simulation Of Aircraft

A wind tunnel test for the large amplitude and unsteady coupling motion at high angle of attackof a fighter model was carried out in the NH-2low speed wind tunnel in NUAA. Yaw-roll couplingmotion in different coupling ratio was measured, while dynamic tests were carried out with the aileronand rudder biased. Based on analysis of a large number of sample data, the efficiency of aileron andrudder was found severely reducing at high angle of attack of coupling motion. At the same time, theefficiency of control surface was affected by the coupling ratio.Based on the classic six-degree-freedom nonlinear equations, a novel equation with totalaerodynamic forces named unsteady model was proposed. With the comparison between mixed modeland unsteady model, the unsteady model was proven that it was more suitable for spin simulation.The unsteady model was used to simulate the spin motion at different deflection of controlsurfaces. Then the hysteresis characteristics of the various stages during the spin simulation wasanalyzed. In most cases, the divergence characteristic of hysteresis loop for yawing moment is themain reason for the fighter getting into the spin. In addition, the convergence characteristics ofhysteresis loop is the root cause for the fighter getting out of spin motion.Finally, the influence of characteristics in spin motion with different moments of inertia, differentstatic characteristics, different rudder efficiencies and different angles of attack when entering wasstudied. The result shows that the inertia affects the vertical and horizontal characteristics of spin,static characteristic decides the anti-spin performance and rudder efficiency affects the performancefor a fighter to get out of spin motion. At the same time, the fighter can’t get into the spin with a highangle of attack when entering, because it is difficult to enter the vertical oscillation state.