The Development of a Two-Dimensional, High-Endurance Airfoil with Given Thickness Distribution and Reynolds Number.
NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER BETHESDA MD AVIATION AND SURFACE EFFECTS DEPT
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A design procedure has been developed that permits a high-endurance airfoil shape to be determined for a given initial thickness distribution and chord length Reynolds number. The Strand method, which is based on the Stratford theory of incipient separation and the optimization principle of the calculus of variations, was utilized to yield an optimized velocity distribution. Upper surface lift was maximized by the resultant distribution however, the total lift was not maximized because of restrictions on the thickness distribution. A generalized parametric study of the upper surface velocity, lift, and drag characteristics for various flow conditions resulted in a series of preliminary design curves. These were used to select appropriate design lift coefficients and LD ratios for further study. After the basic performance characteristics had been selected, a linear theory was used to determine the camber distribution of the airfoil. The velocity distribution that corresponded to the initial thickness and camber distribution obtained from the linear theory was then utilized as the initial input to a fully nonlinear theory the James airfoil design method to determine the final airfoil shape. Several iterations of the input were design method to determine the final airfoil shape. Several iterations of the input were necessary to obtain an output velocity distribution that was close to the desired one. The Von Doenhoff separation criterion was applied to the lower surface to determine whether separation would occur at the design condition. Computations showed that the flow was fully attached.