Metering Pin Diameter Optimization of an Aircraft Landing Gear Shock Absorber

Abstract

One of the most important components of an aircraft is the landing gear. In today`s modern landing gears, mostly oleopneumatic shock struts are used. Analytically, landing gear can be modeled as a mass-spring-damper system. The model used in the study included landing gear components such as the oleo-pneumatic shock strut, tire and wheel. Furthermore, a tapered metering pin was added to model in order to control the area of the orifice by which hydraulic oil flows during the act of landing impact force. Landing gear design usually aims to minimize two elements which are vertical acceleration and displacement of aircraft mass. The impact force during landing is indicated by vertical acceleration. Displacement of shock absorber should be minimum to decrease the size, weight and space needed for the landing gear system. An optimization problem was defined to minimize those two parameters within the range of given inputs. For this purpose, a composite objective function was created to include and optimize the two output parameters simultaneously with equal weight. Among many inputs, metering pin hub and tip external diameters were selected as variables for the optimization and other inputs were kept constant. For the optimization study, genetic algorithm method was coupled with the Matlab/Simulink model of the landing gear model. After some iterations, solution was converged to determine the two diameters of the metering pin where the vertical acceleration and displacement of aircraft mass are minimized as an objective. At the end of optimization process, vertical acceleration of aircraft mass was reduced from 2.433 g to 1.7828 g (-36.47%) within the given constraint of 2 g maximum. Displacement of aircraft mass X1 was increased from 0.2982 m to 0.3682 m (+23.47%) which is in an acceptable limit of 0.4 m.