Tests of the NACA 65 sub 3 -018 Airfoil Section with Boundary-Layer control by Suction

Tests of the NACA 65 sub 3 -018 airfoil section with boundary-layer control by suction have been made in the Langley two-dimensional low-turbulence and Langley two-dimensional low-turbulence pressure tunnels. Slots were tested at 30 and 75 percent and at 45 and 75 percent of the airfoil chord at Reynolds numbers of 1.9 and 6.0 x 10 expn 6. An attempt was made to remove only a moderate amount of air through the slots and to locate the slots so that the low-drag properties of the airfoil could be realized. The results of these tests were compared with results for a plain NACA 65 sub 3 -018 airfoil section. A maximum section lift coefficient of 1.85 at a Reynolds number of 6.0 x 10 expn 6 was obtained on the NACA 65 sub 3 -018 airfoil section with boundary-layer control when the total amount of air removed corresponded to a flow having free-stream velocity through an area equal to approximately 1.2 percent of the wing area. This lift coefficient was found at approximately the same angle of maximum lift as for the plain airfoil and with suction slots at 45 and 75 percent of the airfoil chord. The surface discontinuity, which would be found with a flush-type sliding door placed at 45 percent of the airfoil chord, would not impair the low drag properties of this airfoil section.