NACA-RM-L51B13

Abstract

INTRODUCTION <br>The use of end plates as a means of increasing the effective aspect ratio of airfoils and thereby increasing lift-drag ratios has been investigated at various times. In general, these investigations have not led to the use of end plates on airplane wings. End plates have been used on tail surfaces where the necessity for having two surfaces at right angles to each other enables the end plates to serve two functions. Because hydrofoils normally will be supported by one or more struts extending through the water surface, it is possible to use the struts for a dual purpose by placing them at the ends of the hydrofoil where they also serve as end plates. This possibility, together with other considerations, such as structural and stability considerations might result in the desirability of using end plates on hydrofoils has led to the present investigation of the effect of end plates and end struts on the lift and drag characteristics of a hydrofoil. <br>Another problem considered in the present investigation is that of determining the effect of depth of submergence below the water surface on the characteristics of a hydrofoil. There is a great amount of aerodynamic data available for use in hydrofoil problems but, in general, these data are for a fluid without boundaries, whereas hydrofoils may operate close to the boundary formed by the water surface. In order to extend the usefulness of these existing data, an approximate theoretical solution for the effect of depth of submergence on the lift of a hydrofoil is developed. <br>Experimental data obtained with a hydrofoil of aspect ratio Ii- at various depths of submersion at speeds from 15 to 35 feet per second (Reynolds numbers from 0.873 x 10 ⁶ to 2.04 x 10⁶) and at angles of attack from -35&#176; to 4.0&#176;, with and without end plates and end struts, are presented. The investigation was conducted at speeds above the limiting speed of wave propagation (13.9 fps) for the 6-foot water depth of Langley tank no. 2. These experimental data are correlated with existing theory giving the effect of end plates on effective aspect ratio and with the developed theory giving the effect of depth of submergence on lift. <br>The method for obtaining a theoretical solution of the effect of depth on lift was suggested by Mr. Thomas A. Toll of the Langley Stability Research Division.