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

The wind tunnel test for the large amplitude motion of a fighter model was carried out inNH-2low speed wind tunnel in this subject. The test concerned about the efficiency of theailerons or rudder during the maneuvering motion of the model at high angle of attack. Themovement of the model included rolling motion, yawing motion and yawing-rollingcoupled-motion.In this thesis, the efficiency of the ailerons and rudder of fighter model was analyzed basedon numerous test data, the result shows that the efficiency of ailerons and rudder during themodel’s coupled-motion at high angle of attack is less than static efficiency. Moreover, the rate ofcoupled-motion influenced the efficiency greatly.Secondly, there is a method of linear “extrapolation” used to estimate the unsteadyaerodynamic forces of the model in high frequency motion by the aerodynamic modeling. Theresult shows that the unsteady aerodynamic forces predicted by this method were consistent withthe test data very well. On the basis of above, the unsteady aerodynamic model caused by the rateof sideslip was established by the combination of the test sample data at lower frequency and theextrapolated data at higher frequency.Thirdly, in this thesis, the applicability of mixed model and unsteady model based on thesimulation of spin motion was investigated. It indicated that the steady result of characteristics ofspin simulation cannot be obtained by the mixed model but can be obtained by the unsteadymodel with different ailerons deflection. In addition, the unsteady model was used to simulatespin motion at different deflection of ailerons and rudders. The result shows that, the fighter canboth get into and get out of spin motion with three different deflections. The investigation ofhysteresis loop of unsteady aerodynamic during the three states of spin motion simulation showsthat the divergence characteristics of hysteresis loop is the very reason which lead the fighter toget into spin motion and the convergence characteristics lead to get out of spin motion.At last, the influence of the inertia of fighter to spin simulation was investigated. The resultindicated that moments of inertia of three axes performance great influence to the characteristicsof spin motion, compared with the little influence by the product of inertia of x and y axes.