Optimal inerter-based shock-strut configurations for landing gear touch-down performance

This paper investigates the possibility of improving aircraft landing gear touch-down performance by adding an inerter alongside a linear passive shock strut. The inerter is a novel mechanical element with the property that the applied force is proportional to the relative acceleration between its terminals. A simplified landing gear model is presented and the baseline performance of a conventional oleo-pneumatic shock absorber is established. Candidate layouts with linear mechanical components including inerters are considered using three objective functions: the strut efficiency, the maximum strut load and the maximum stroke. It is demonstrated that improved touch-down performance can be achieved with a linear inerter-based configuration. However it is also observed that the potential energy stored in the gear at the end of the first compression stroke exceeds that of the baseline nonlinear system. This suggests a poorer elongation stage might be observed. To address this, an additional constraint on energy dissipation is then considered. To achieve a reduced potential energy, a double-stage compression spring is introduced. With this, inerter-based configurations that provide improvements for the performance indices of interest are identified and presented.