An extended theory of thin airfoils and its application to the biplane problem
This is a 1931 NACA-era aeronautical technical report, published by NASA Technical Reports Server, extending thin airfoil theory and applying it to biplane wing problems for aerodynamic engineers and researchers. The four pictures are graphs plotting aerodynamic coefficients against angle of attack in degrees, with families of labelled curves for varying parameters and a comparison of theory against experiment for a single wing. A designer might take from them the clean, restrained look of engineering charts: dense grid paper, labelled curves fanning out, and a few bold reference lines.
