General Considerations on the Flow of Compressible Fluids
This is a 1936 NACA technical memorandum on the flow of compressible fluids, issued by the National Advisory Committee for Aeronautics for aerodynamics engineers and researchers. Its pictures are plain line diagrams: a Mach-wave cone with circles expanding from a moving source, and parallel streamlines bending over an angled shock or disturbance at a surface. A designer could take from them the clean, schematic style of technical drawing, with thin black linework, lettered labels and simple arrows.
