A theoretical and experimental investigation was made of the effect of the free-water surface and rigid boundaries on the lift and drag of an aspect-ratio-10 hydrofoil at both subcritical and supercritical speeds. The experimental investigation was made in Langley tank no. 1 and Langley tank no. 2 at 0.84 and 3.84 chords submergence at subcavitation speeds from 5 to 45 feet per second corresponding to Reynolds numbers from 0.18 X 106 to 1.64 X 106.nApproximate theoretical solutions for the effects of the free-water surface and rigid boundaries on lift and drag at supercritical speeds are developed. An approximate theoretical solution for the effects of these boundaries on drag at subcritical speeds is also presented. The agreement between theory and experiment at both super¬critical and subcritical speeds is satisfactory for engineering calculations of hydrofoil characteristics from aerodynamic data.nThe experimental investigation indicated no appreciable effect of the limiting speed of wave propagation on lift-curve slope or angle of zero lift. It also showed that the increase in drag as the critical speed is approached from the supercritical range is gradual. This result is contrary to the abrupt increase at the critical speed pre¬dicted by theory.
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