Reliability Analysis Of Retraction System And Energy Absorption Characteristics Of Aircraft Landing Gear

With the rapid development of aviation industry,the reliability of aircraft has been greatly improved.However,the flight accidents caused by the failure of landing gear retraction mechanism still occur from time to time.Furthermore,in the existing analysis models of landing gear energy absorption characteristics,the evaluation and trend analysis of the influence of the piston rod stiffness,the temperature in the chamber and the initial inflation pressure on the energy absorption characteristics is seldom carried out,while in the reliability analysis of energy absorption characteristics,it is even less to consider the uncertainty of the above factors.Taking the strut landing gear as the research object,and the reliability analysis of landing gear retraction mechanism is carried out in the paper.At the same time,on the basis of the conventional factors affecting the reliability of the energy absorption characteristics,the above factors are introduced to carry out the reliability analysis of the energy absorption characteristics.The main work and innovation of this paper are as follows:(1)In view of diversity of reliability analysis methods of landing gear retraction mechanism,the reliability analysis flow applicable to landing gear retraction mechanism is developed in detail,and the reliability analysis method of landing gear retraction mechanism is systematically clarified.This method reasonably integrates functional hazard analysis(FHA),failure mode and effect analysis(FMEA),fault tree analysis(FTA)and common cause analysis(CCA),which can identify the main factors affecting the failure of landing gear retraction mechanism and provide effective guidance for the reliability design of landing gear retractable mechanism.(2)Aiming at the failure of landing gear emergency extension function in the test of a newly developed civil aircraft in China,the failure analysis of landing gear emergency extension function based on mixture of reliability model is carried out.The bottom event of "excessive passive torque of landing gear emergency extension strut rotating axis" is considered as the mixed failure caused by mechanism start-up failure and mechanism continuous movement failure,which re-fines the bottem event modeling technique and establishes reliability model conformed to engineering practice.Through the sensitivity analysis,the main moments affecting the fault of the landing gear emergency extension system are defined.Under the guidance of the sensitivity analysis results,a new driving scheme of the landing gear front door drive mechanism is proposed,and the effectiveness of the proposed scheme is verified by the iron-bird test,which solved the engineering problem of the failure of the landing gear emergency extension function.(3)In order to investigate the impact of the landing gear piston rod stiffness on the energy absorption characteristics of shock absorber,HyperWorks is used for the flexible treatment of the piston rod,and the simulation model of rigid-flexible coupling drop tests for landing gear is established by co-simulation of Adams/Aircraft.The validity of the model is verified by comparing the simulation results with the experimental values,and the impact of the piston rod stiffness on the air spring force,the oil damping force,the vertical force of the tire and the energy absorption efficiency are discussed.In order to better guide the design of landing gear structure,the stiffness design interval of landing gear piston rod is further explored.The analysis results show that: when the piston rod stiffness is lower than the lower limit of the design interval,the energy absorption efficiency of shock absorber decreases significantly;when the piston rod stiffness is higher than the upper limit of the design interval,the energy absorption efficiency is basically unchanged.So the impact of the landing gear piston rod stiffness on its energy absorption characteristics can be ignored.(4)Considering the influence of the temperature change in the landing gear chamber on shock absorber energy absorption characteristics,the landing gear is reasonably divided into mechanical sub-module,friction sub-module,heat sub-module and an input interface module,which effectively improves the complexity of the landing gear thermal response analysis model.With the help of Matlab/simulink and HyperWorks co-simulation platform,the structure thermal response analysis model of landing gear shock absorber is established.The variation trend of the temperature in the upper and lower chamber of the shock absorber and the temperature in the upper and lower bearing support with time is made clear by the simulation analysis of drop test.The oil damping and the amount of work of the shock absorber in the traditional equivalent model and the improved model are compared and analyzed.(5)Aiming at the difficulty of obtaining functional functions of landing gear energy absorption reliability analysis,an improved response surface method(IRSM)and an improved support vector machine(ISVM)are proposed.Based on the research in chapter 4and chapter 5,the uncertain input variables for reliability analysis of landing gear energy absorption characteristics are supplemented and improved.Taking the landing gear overload coefficient,stroke and energy absorption efficiency as the output response,the mathematical model between the input variable and the output response is fitted with,and the reliability analysis of the landing gear energy absorption characteristics is carried out.The results show that the three supplementary factors have a great influence on the reliability of the landing gear energy absorption characteristics,especially the initial inflation pressure.In addition,compared with the results of monte-carlo-method(MCM),the proposed method has high computational efficiency,and can meet the accuracy requirements.