A simplified method for the calculation of airfoil pressure distribution
This is a 1939 NACA technical report on a simplified method for calculating airfoil pressure distribution, issued by the National Advisory Committee for Aeronautics for aeronautical engineers and researchers. Its pictures are plain engineering line charts with grid backgrounds, plotting pressure coefficient against chord position for several NACA airfoil sections, with measured and calculated curves drawn as dashed and solid lines and labelled with legends and captions. A designer could take from them a restrained scientific graph style: sparse grids, clear legends, and dual curves for comparison.
