An investigation was made in Langley tank no. 2 of the effect of end plates and end-mounted struts on the lift-drag ratios of a hydrofoil. The hydrofoil had an aspect ratio of 4. The tests were made at various depths below the water surface at speeds from 15 to 35 feet per second corresponding to Reynolds numbers from 0.873 X 106 to, 2.04 x 106. These speeds were all above the limiting speed of wave propagation (13.9 fps) for the 6-foot water depth used and below the range at which cavitation occurs.nOnly small improvements were found in the maximum lift-drag ratios by the addition of end plates and these improvements occurred only at low lift coefficients with small end plates. As the lift coefficient was increased above the value for maximum lift-drag ratio the optimum end-plate size increased; however, the absolute value of lift-drag ratio decreased. The detrimental effect of the drag of the additional strut for a hydrofoil using end struts in contrast to a single central strut was greater than any beneficial effects due to the end-plate effect of the end struts. The ratio of the effective aspect ratio to the geometric aspect ratio varied with end-plate size approximately as predicted by aerodynamic theory (Von Karman and Burgers). Although the hydrodynamic data obtained with the end plates were slightly higher than the theoreti¬cal curve, the agreement was good when the accuracy to which such data could be obtained is considered. An approximate theoretical solution of the effect of depth on the lift of a hydrofoil was developed. The agreement of the experimental results with the results given by this solution was good.
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