TESTS IN THE NACA TWO-DIMENSIONAL LOW-TURBULENCE TUNNEL OF AIRFOIL SECTIONS DESIGNED TO HAVE SMALL PITCHING MOMENTS AND HIGH LIFT-DRAG RATIOS

摘要

Airfoil sections that have sma11 or zero pitching moment coefficients and high lift-dreg ratios have been developed and tested. With sections having pitching-moment coefficients close to zero, maximum section lift drag ratios that were almost twice as great as these which have been attained on sections of the NACA 230-series air foils were attained in the Reynolds number range from 1.7 X 106 to 3.2.X 108. Such characteristics are desirable for rotor-blade sections, but the new sect ions have the disadvantage that they are unduly sensitive to roughness. The action of forces caused by the rotation of the blades on the partly stalled regions over the rear portion of the airfoils in the rough condition is not well understood, but it is believed that the action may be beneficial. It is felt desirable that some of the new sections be tested in a full-scale rotor.