Effect of roughness on properties of airfoils
This is a 1926 NACA technical memorandum on how surface roughness changes the performance of aircraft airfoils, issued by the US National Advisory Committee for Aeronautics for aerodynamic engineers and researchers. The three plates are plain line drawings: two airfoil cross-sections dimensioned with rows of small circles marking roughness elements, and a graph of lift-type coefficients plotted against angle of attack on a gridded field with several curves. A designer might take from them the clean technical-diagram conventions of early engineering reports, with dimension lines, numbered labels and dense plotted curves.
