Research On Unsteady Aerodynamic Models And Flight Simulation For The Aircraft Oscillation At High Angle Of Attack

The wind tunnel test for the large amplitude motion of a fighter model at high angle of attack was carried out in NH-2 low speed wind tunnel in this subject. The unsteady aerodynamics of the fighter model was measured during in oscillating in pitching motion, yawing motion, rolling motion or yawing-rolling coupled-motion. First of all, some of the unsteady aerodynamic characteristics were acquired by analyzing the wind tunnel test results in this paper. The results show that the aerodynamic characteristics of multi-degree of freedom motion are more complicated than that of single degree and there are some differences on the aerodynamic characteristics between the test results of coupled motion and the linear superposition results of two single degree of freedom motions. In addition, compared with the results of wind tunnel test about dynamic derivative and rotary balance, the results of the test in the subject show a greater difference.Secondly, the modeling method of fuzzy logic was investigated. It is indicated that the value of the convergence coefficient is a basic factor determining the speed and precision of modeling. And then, the effects of variables on mathematic modeling were studied. The results show that the angles and angular velocities reflecting the essence of motion should be selected as modeling variables, when the fuzzy logic modeling will be established. And considering yawing-rolling coupled-motion, the coupling ratio reflecting coupling degree should be still added.Thirdly, the applicability of 4 kinds of unsteady aerodynamic models was analyzed in this paper. It is indicated that the linear superposition model, dynamic derivative superposition model and mixed model are suitable to the test results at the small angle of attack, but not at the large angle by means of comparison among these aerodynamic models. But in spite of any angle of attack, the aerodynamic characteristics of coupled-motion are reflected well to the test results by the unsteady aerodynamic model of fuzzy logic.At last, using these unsteady aerodynamic models of different forms, the longitudinal dynamic responses were calculated with the oscillating control inputs. The simulation results show that, it is necessary for simulating the trajectory of actual flight factually to consider coupling effects in the unsteady aerodynamic model.