The objectives of this paper are to outline the use of Electrorheological (ER) fluid within an aerospace system. The advantages of ER fluid based systems are given followed by design considerations which include those related to the non-linearbehaviour of an ER fluid subjected to oscillatory shear. A control strategy is outlined for the use of a smart landing gear (LG) oleo incorporating ER fluid. The paper also considers the issues associated with airworthiness requirements and ER fluiddevices.For airworthiness approval a smart oleo based LG system above all has to be shown to be safe and as such has to be fault tolerant. A major failure for this application would be if the control strategy failed and the oleo damping coefficient wasconsistently too low, a backup system is therefore incorporated into the design and other potential modes of failure considered.A semi-active control strategy applied to a variable damping coefficient LG oleo has specific requirements, partly due to the fact that for the take-off and landing phases of flight they are different. A semi-active control strategy is outlined based onthe requirements for the alteration of damping coefficient according to the phase of an aircraft's flight. The strategy is the focus of current work to estimate the effectiveness of semi-active vibration control as applied to an undercarriage.
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