Measurements of Life Coefficients for a Family of Conical Ring Tails Planing on Water

Abstract

When it is expected that the afterbody of a projectile will plane on the free surface of an open cavity, the lift coefficient of the planing shape is of primary concern to the projectile design engineer. To provide basic data applicable to the design of an afterbody subject to such planing conditions, lift coefficients have been determined for a family of rings planing on a flat water surface. Changes in chord-diameter ratio and in flare angle were the model variables while angle of attack and submergence were varied during the course of the measurements of lift force. In order to eliminate strut and afterbody configuration as a further necessary variable in the present tests, the models were supported from the top so as to minimize interference with the basic flow pattern produced by a simple ring. All ring edges were cut perpendicular to the ring axis and lap finished to a blunt and sharp cornered configuration that could be easily reproduced. Photographs of typical test conditions are included in this report so that the proper flow configuration can be associated with various points on the plots of lift coefficient. With judicious selection from the graphs, and careful consideration of the flow pattern, it should be possible to gain insight into the lift forces that would act on a prototype ring tail whose shape is different from those tested during this investigation.

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