The problem of prediction of airplane drag divergence Mach number was investigated and an empirically determined expression was obtained that is applicable to clean airplane configurations whose wing shapes lie Within the general limits of 0° to 47° sweepback, aspect ratios of 2 to 10, and thickness ratios of 4 per cent to 12 per cent. Subsonic-type airfoil sections are implied, and the fuselages are of the conventional convex shape. Comparison of the predicted values with experimental and aircraft manufacturers' performance estimate values indicates that the accuracy of the method is within ± 2 per cent. Such special problems as the prediction of the effect on drag divergence Mach number of thickened wing root air intake configurations and large interference effects of certain nacelle locations a.re beyond the scope of this paper.
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