Analysis And Recovery Of Aircraft's Spin Characteristics At High Angle Of Attack

Super maneuver performance has become an important evaluation of modern fighter, in which the military combat is required to fly at high angle of attack. However, when a military combat fly at high angle of attack, the control surfaces lose much of their effectiveness with the vortex flow, breakdown vortex flow and fully separated flow. All of these maybe lead to some unstable phenomena, such as stall and spin. Therefore, predicating accurately and recovering quickly from these unstable phenomena has become the key to the aerodynamic configuration and control system design. To solve this problem, this paper studies the most dangerous unstable phenomenon spin, including research on spin prediction, modal characteristics and dynamical characteristics of spin, influence and boundary of spin, spin recovery. The main works are as follows:Firstly, according to references, the twelve-state kinematic and six-degree-of-freedom equations of the military combat are established and the aerodynamic model is established based on wind tunnel test data. Then,n dynC? and LCDP criterion is designed, with which the stability of high angle of attack is analyzed. Thus the established model can be used as the foundation of spin prediction and recovery.Secondly, according to the established model, Equilibrium bifurcation diagrams versus different control surfaces are calculated based on continuation algorithm. With the calculated results, the spin state of military combat at high angle of attack can been predicted based on bifurcation theory. Time history analysis is used to verify the accuracy of the prediction.Then, the model characteristics of spin are studied deeply. Several spin models are studied under different rudder surfaces deflection firstly. Then, the influence of inertia of moment, velocity, height and position of centre of gravity is studied. In addition, For velocity vector roll maneuver, the spin boundary is calculated based on attainable sets.Thirdly, the traditional spin recovery law is ineffective when the fighter is under some special spin states. So the new spin recovery law with and without thrust vector based on slide mode control is designed. Besides, the influence of trim state and trim order for spin recovery is studied. In order to studying the effect of unsteady aerodynamic in spin recovery, the new aerodynamic model is established.Finally, for some spin models, the spin recovery law with thrust vector based on SLM can't change the situation. Therefor, a new spin recovery law is desigened with unidirectional auxiliary surfaces based on double power reaching law and the effectiveness is verified under those spin states. In addition, the influence analysis of double power reaching law and single power reaching law is studied.