Dynamics And Reliability Analysis Of Retraction Of Landing Gear

With the increasing demand of the civil aircraft,the shortening of the clearing cycle renders the increase in aircraft take-off and landing year by year,as a result,the performance of the landing gear is put to great tests.The frequent malfunction of the landing gear retraction system has severely influenced the safety of the aircraft;consequently,carrying out detailed reliability research on the landing gear retraction system is of great significance to guide the design and to improve the reliability performance of the landing gear retraction system.In this paper,a 3D main landing gear of a certain airliner is treated as the object of study,and research is conducted on the landing gear retraction system,as well as its reliability,locking mechanism performance and tolerance design.The main contents are shown as follows:Firstly,the dynamic model of the landing gear retraction system is constructed on the basis of the Lagrange equation,meanwhile,the kinetic equations of the hydraulic system is derived based on the power bond graph method,and the two models are used in combination to solve and analyze the dynamism of the landing gear retraction system,the experimental results of which are used to verify the theoretical solution.The effects of the critical parameters,such as crosswind,frictional resistance,damping hole,liquid slug and oil leakage on the landing gear retraction performance are analyzed on account of the model,the analysis results of which could be used to guide the parameter design of the landing gear retraction system,retraction failure analysis and reliability research.The difference of the retraction time and stipulated time is selected as the reliability performance function based on the failure mechanism of the landing gear retraction system.The advantages and disadvantages of the reliability analytical methods of various surrogate models are compared and analyzed on the basis of the characteristic of the retraction time being the implicit function,and the quadratic polynomial response surface method is selected when taking the factors such as the calculation accuracy,efficiency and stability into comprehensive consideration,the calculation accuracy of which is verified with the Monte-Carlo experimental results.Afterwards,thorough analysis is carried out on the reliability of the landing gear retraction system after taking the means and standard deviation of the critical parameters such as crosswind,frictional resistance,damping hole,liquid slug and oil leakage into consideration.In order to build the landing gear retraction kinetic model with structural gap and assembly error,the multi-disciplinary collaborative simulation technique is introduced.First of all,the combined simulation models of the landing gear retraction mechanism dynamics and hydraulic system kinetics are constructed based on the LMS Virtual.Lab Motion(a multi-body dynamics simulation platform)and the LMS Imagine.Lab AMESim(a system simulation platform),respectively.To consider the structural gap and the assembly error,HyperMesh/ NASTRAN are adopted to generate the flexible models of all structural parts,construct the rigid-flexible coupling model of the landing gear retraction mechanism,and verify the collaborative simulation model with the experimental data of damping characteristics,assembly error performance and structural gap performance.Subsequently,the effects of the assembly error and structural gap on the landing gear retraction performance are analyzed based on the model,and the reliability of the landing gear retraction structure is analyzed with the structural strength interference model.It is proposed in this paper to adopt the bifurcation theory to study the locking mechanism performance,and the jump phenomenon(the problem of the steady state transition)at the moment close to lock the locking mechanism is explained in combination with the central mechanism problem.The effects of various unlock forces on the landing gear retraction track is analyzed at first with regard to the landing gear retraction mechanism performance problems,5 different retraction regions are found,and the two state variables,critical unlock force and critical unlock positions are defined;secondly,the effects of three factors,namely,spring stiffness,original length and installation site on the two state variables are analyzed in detail;finally,optimization analysis is conducted on the critical unlock force under the premise of guaranteeing the locking ability of the locking mechanism.It is demonstrated in research that the bifurcation theory could rapidly and accurately analyze the variation relation of the characteristic position of the locking mechanism with the structural parameters,which could sufficiently guide the preliminary design of the aircraft landing retraction mechanism parameters.The R-F reliability method is introduced into the tolerance design of the spatial landing gear retraction mechanism.Optimization design of the tolerance of all structural parts of the landing gear is conducted after taking the closed loop tolerance index,successful assembly rate and processing cost into comprehensive consideration,and overly tight tolerance requirements produced by conventional methods(extremum method and probability method)are solved.Meanwhile,R-F method could also solve the problems of non-linear dimension chain equation and non-normal dimension variable existing in the tolerance design of the spatial mechanism.In addition,the surrogate model method is proposed to replace the original non-linear dimension chain equation regarding the problem of difficulty in simplifying the spatial mechanism dimension chain equation,which has remarkably improved the design efficiency of tolerance.Later,the calculation results of different surrogate model methods are compared,the advantages and disadvantages are analyzed,and the scope of application of different surrogate model methods is given.The tests for the influence of damping hole,assembly error and structural gap on the performance of the main landing gear retraction system are designed,and research is conducted on the test results,the results of which indicated that the orifice variation has great influence on the dynamic response of the retraction hydraulic system,while the upper assembly error has great influence on the structural loading but little influence on the hydraulic system response,and the structural gap has relatively little influence on the retraction system.