Modeling Dynamic Pressure Loss by Absorption in Oleo-Pneumatic Shock Absorbers without Separator

Abstract

A model for the dynamic pressure loss in standard oleo-pneumatic shock absorbers without gas-oil separator for avionics applications is introduced. The dynamics of such a device under load variations is primarily determined by the throttle between the oil chamber and the gas chamber. During operation, gas is absorbed by the oil upon compression and desorbed upon expansion, which are processes that extend over time and entail hysteresis. It is found that the assumption of isothermal conditions is sufficient. An excellent alignment is achieved by the model and the measured hysteresis across diverse drop test scenarios, adjusting a single parameter to a value that is physically reasonable. The standard deviation of the error in pressure is σp = 0.49 bar. Moreover, the model rests on thermodynamic considerations and experimental gas solubility data, while it is consistent with other laboratory data from the literature.