Stability Analysis Of Landing Gear Shimmy Considering The Structural Factors

Landing gear system failure accounts for most of the proportion of flight accidents,Accidents caused by landing gear shimmy is an important reason that can't be ignored,it brings the aircraft a major safety hazard.In this paper,the linear shimmy theory of algebraic stability criterion and stability criterion based on frequency response characteristics are used to study the influence of landing gear structure on the stability of the shimmy.Analysis the influence of freeplay on the Stability of Shimmy by Bifurcation Theory.In this paper,a simplified model of landing gear and a model of lateral flexibility of structure are established,then use algebraic stability criterion to determine the stability of the system,The effects of stability distance,lateral stiffness of strut,yaw stiffness,lateral damping,yaw damping and tire characteristics on the shimmy stability are mainly studied,the accuracy of algebraic stability criterion is verified by calculating the real part of matrix eigenvalue,then draw a graph of stable shimmy area when parameter changes.According to the model considering lateral flexibility of the structure,studied the problem of shimmy stability from the viewpoint of frequency stability criterion and energy.From the control theory point of view,consider landing gear and tires as a part of the closed-loop system and a closed-loop feedback system is formed.Then Nyquist criterion of stability is used to analysis the effects of tire lateral stiffness,yaw stiffness,lateral damping and yaw damping on the stability of shimmy,the conclusion is consistent with the stability criterion of algebra.From the conservation of energy,the energy expression of the shimmy system is writed down,the effect of wavelength on the stability of the shimmy is studied by using polar coordinates.Finally,respective advantages and disadvantages of algebraic stability criterion and frequency domain stability criterion are analyzed.Finally,the paper constructs a nonlinear dynamic model considering the structural clearance characteristics,the effect of structural clearance on the shimming equilibrium point is studied;the influence of the freeplay on the stable area of the shimmy;Impact of piston torsion damping and gap value on shimmy amplitude.The single-parameter bifurcation diagram of the system?twist angle amplitude—speed curve and the double-parameter bifurcation diagram are obtained.Some useful conclusions can be obtained,which can provide a theoretical basis for the occurrence mechanism and preventive measures of gap type shimmy.