Optimization of a Tapered Metering Pin in a Landing Gear Shock Absorber (SAE Paper 2021-01-0020)

Landing gear is one of the fundamental parts of an airplane. Most modern aircraft uses oleo-pneumatic shock struts in the landing gears. In this study, a landing gear was modelled as a mass-spring-damper system. Components of landing gear including oleo-pneumatic shock strut, wheel and tire were included in the model. Additionally, shock strut was modelled with a tapered metering pin to vary the area of the orifice through which hydraulic oil passes as the landing impact force start acting. Tip and hub outer diameters of the metering pin were considered two variables. Vertical acceleration (indicating landing impact force or g-force) and shock absorber displacement were calculated as resultant parameters. Both of these output parameters are inversely proportional to each other and are needed to be minimized individually. Therefore a composite objective function was established to include and optimize those two output parameters with equal weight and simultaneously. Equations of motion were solved in a Matlab/Simulink environment. Genetic algorithm (GA) optimization technique was employed for optimization part. GA is a mathematical algorithm in solving complex problems and optimization tasks. GA is based on concept of evolution which was adapted to a computational algorithm to find a solution to a problem called objective function. Results obtained showed satisfactory and well balanced values of objective function which are vertical acceleration (g-force) and shock absorber displacement. Similarly, hub and tip diameters of the metering pin were optimized in the given range. Genetic algorithm was successful in finding the optimum values and showed that it is a useful algorithm for optimization of this kind of problems in addition to many application areas.