Airplane drag
This is a 1929 NACA technical memorandum, No. 544, issued by the National Advisory Committee for Aeronautics and preserved through NASA's Technical Reports Server, written for aeronautical engineers studying aircraft drag. Its pages are black-and-white line diagrams of wings and lift distribution. A designer could take from them the clean, schematic way engineering diagrams label forces with arrows, plus the elliptical lift shape and airfoil cross-section profile.
