PROPELLER LIFTING-SURFACE CORRECTIONS

Abstract : Correction factors for camber, ideal angle due to loading, and ideal angle due to thickness, which are based on propeller lifting surface theory, are presented for a series of propellers. This series consists of optimum free- running propellers with chordwise loadings the same as an NACA a = 0.8 mean line and with NACA-66 chordwise thickness distributions. The results of the calculations show that the three-dimensional camber and ideal angle are generally greater than the two-dimensional camber and ideal angle at the same lift coefficient. The correction factors increase with increasing expanded area ratio, and those for camber and ideal angle due to loading decrease with increasing number of blades. Thickness, in general, induces a positive angle to the flow, which necessitates a correction to the blade pitch. This ideal angle is largest near the blade root and decreases to negligible values toward the blade tip and increases with increasing number of blades. Skew induces an inflow angle, necessitating a pitch change which is positive toward the blade root and negative toward the blade tip.