Static roll stiffness characteristics of two multicell type air cushion systems

Abstract Although there is growing interest in the use of flexible skirted air cushions for various off-road and other over-land transportation tasks, relatively little data on their suspension properties are available in the open literature. This paper presents the results of some experimental studies of the static roll stiffness of two resistance orifice-fed multicellular cushion designs. The conditions for scaling the tests to full-size behaviour are discussed. A simple theory, based on the assumptions that the skirt material is an inelastic membrane and that the cushion air flow can be described by one-dimensional orifice flow laws, is developed for one of the cushion systems. Good agreement between theory and experiment is obtained under certain restricted conditions, but in general the experimental results show that the skirt material properties can play an important role. This manifests itself in two ways: as a potential scaling problem, and the appearance of hysteresis in the rolling moment produced by the cushion. The latter can, under certain circumstances, be so large as to completely destroy its stiffness when rolled. At least two hysteresis mechanisms are indicated, and one has been observed. This is a buckling failure of the cells leading to large-scale venting and consequent loss of pressure. A detailed explanation of the other mechanism has not been obtained, but it is noted that skirt-ground friction does not appear to be important. It is concluded that a careful study of the structural properties of air-inflated cones is required. In particular, buckling phenomena need clarification.