The Tire Factors Research On Airworthiness Certification On Nose Landing Gear Shimmy

The self-excited shimmy phenomenon of the nose landing gear is a kind of harmful vibration,which can affect the quality of aircraft ground motion,and even threat the safety of the passengers and the flight crew.However,there are no shimmy related regulations and specifications can be found in the applicable requirements of airworthiness in CCAR,as well as no airworthiness orders and advisory circulars can be taken into implement for shimmy review.This thesis focuses on the approaches available to shimmy airworthiness review: digital simulation based on a mathematical model and dynamic simulation of multi-body on virtual prototype.First,it introduces the stretched string theory and point contact theory and their derivations.And then it also interprets the models developed by Von Schlippe、Smiley、Pacejka、Keldysh、Moreland in detail.It also clearly describes the mathematical modeling process for nose landing gear shimmy analysis as well as lots of equations of motion.Applying those different models into the mathematical model,results corresponding to different tire models can be obtained from shimmy analysis on those equations,and distinguishing the differences among the results,analyzing the causes.A complete description of the approach of simulating nose landing gear virtual prototype was made on LMS,which is for shimmy airworthiness review.The method for shimmy verification is using road barrier to excite the vibration of the nose landing gear model with complex tires.Compared the results with this from mathematical models,and analyzed the possible cause of difference among those results,as well as the applicability and precautions of two different methods in the airworthiness review.To study the variation of the tire parameters in the shimmy bench test,a radial stiffness tests was completed on the curved surface simulated the flywheel test.The radial stiffness of the tire surface is simulated.The results show that the radial stiffness of the tire decreases gradually with the decrease of the radius of the surface,and it is reasonable to deduce the other stiffness parameters also conform to the same change.Therefore,the large flywheel test should try to choose a larger diameter flywheel to reduce its impact on the oscillation test results.The conclusion is the radial stiffness of the tire is reduced with the decrease of the radius,and it is reasonable to assume that the other stiffness parameters of the tire also follow the same change.Therefore,the large flywheel test should try to choose a flywheel with larger diameter to reduce its impact on the shimmy test results.