Gas-Liquid Ratio Imbalance Indicators of a Fighter Aircraft Shock Absorber

An oleo-pneumatic shock absorber of a fighter aircraft loses some of its nitrogen charge and oil fill over time, due to leakage through seals. Usually, only gas can be added to shock absorber in line maintenance. This creates an imbalance to the ratio between gas and oil, and affects both the damping and the stiffness of the shock absorber. Measuring the gas and liquid content inside a shock absorber is infeasible. Thus, other variables that can act as indicators of an imbalance, must be identified. A coupled model of a fighter aircraft landing gear and its shock absorber is created. Using the model, landings with different sink speeds and aircraft masses has been simulated. Simulations with a standard, and later imbalanced, gas-liquid ratio are conducted. Results from these simulations are discussed and presented here, and variables that can be used as indicators of this imbalance are identified. This information can be used to potentially improve maintenance planning.