Research On Airworthiness Certification Technology For Shimmy Of Aircraft Landing Gear Considering With Structural Factors

Based on the multiple accidents caused by landing gear,shimmy is an indispensable factor.Due to a lack of guidance methods about shimmy in aircraft airworthiness certification,the corresponding airworthiness certification points and methods are urgently needed.In this paper,the influence of various factors on the stability of shimmy is studied by means of the theoretical analysis(direct and indirect methods)and simulation analysis,and the main structural factors are considered as key points of shimmy airworthiness certification.According to the method of compliance verification,the key points are run through all aspects of airworthiness certification,and the shimmy airworthiness certification method is put forward.Firstly,a simplified rigid model and a model with lateral flexibility are presented.The method of algebraic stability criterion is used to judge the stability of shimmy,then the effects of mechanical trail,lateral stiffness,yaw stiffness,lateral damping and yaw damping factors on shimmy stability are analyzed,and the correctness of the analysis is verified through the method of solving eigenvalue.Secondly,the methods of control and energy to analyze shimmy stability are used.Based on the shimmy closed-loop feedback system,Nyquist criterion is used to determine the stability of shimmy,and analyze the influence of cornering stiffness,yaw stiffness and other factors on shimmy stability.Based on the energy formula of shimmy system,the influence of wavelength on shimmy stability by polar coordinate form is analyzed.Thirdly,based on the LMS Virtual.Lab Motion software,the shimmy simulation model is built,and the accuracy of constraints and buffer force in the model is verified by the simulation of drop test.Through the simulation settings of different conditions,the influences of damping coefficient,cornering stiffness,forward velocity and initial angle on the shimmy stability are analyzed.Finally,the structural factors of mechanical trail,lateral stiffness,yaw stiffness,lateral damping,yaw damping,cornering stiffness and damping coefficient are considered as airworthiness certification points.According to the method of compliance verification,shimmy airworthiness certification method of cordwood system is put forward,including analysis and calculation,laboratory test,test flight and qualified equipments.