On some aspects of the aerodynamic performance of ground-effect wings

Abstract

With the advent of the hovercraft and hydrofoil, high-speed, overwater travel has become a practical proposition. Nevertheless, there would appear to be an upper limit to the speed of these craft imposed by, on the one hand, the intake momentum drag of the hovercraft and, on the other, the drag of the submerged foils of the hydrofoil- One method proposed for reducing these drags employs aerodynamic lifting surfaces to off-load the cushion or hydrodynamic lifting systems. These surfaces, which are referred to as 'ground-effect wings', fall into two main categories, namely 'open' and 'closed'. The latter type is defined as that which mays in theory, be designed for zero induced drag; the former type is that which may not. By employing the linearized lifting-surface theory the minimum induced drag of an open configuration, consisting of a planar wing with end plates, is determined. The results of this theory are in agreement with experiment in predicting that the effect of end plates is to reduce the induced drag. However, the indications of the experiments are that the reduction in induced drag is somewhat greater than the theoretical prediction. There is evidence that this is due to the tendency of the end plates to suppress harmful non-linear effects such as edge separations at the tips of the wing and the sidewash at the wing. A theoretical and experimental study of the lift and induced drag of a closed configuration, comprised of a substantially planar wing with end plates and not designed ab initio for zero induced drag, is

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