Tests of N.A.C.A. airfoils in the variable-density wind tunnel Series 45 and 65
This is a 1931 NACA technical report of wind tunnel tests on airfoil families, issued by the National Advisory Committee for Aeronautics for aircraft designers and engineers. Its pictures are plain engineering line graphs in black ink on white: profile drag coefficient against lift coefficient, and lift coefficient against angle of attack, each with labelled curves for numbered airfoil sections. A designer could take from them the tradeoff between lift and drag across a family of wing shapes, shown as clean sweeping curves on gridded paper.
