The Effect of Surface Irregularities on Wing Drag. IV - Manufacturing Irregularities. 5; Manufacturing Irregularities
This is a 1938 NASA technical report, part of a series on how surface irregularities affect wing drag, prepared for aeronautical engineers and researchers. The first picture is a scaled profile drawing comparing a wind-tunnel model of an airfoil with the true NACA 23012 section and a service wing, while the second shows a wing section with a fine wavy surface distortion mounted on a frame against a window grid. A designer could take from them the idea of tracing small surface deviations against an ideal curve, shown as thin overlaid lines on a clean technical drawing.
