The transformation of heat in an engine
A 1929 NACA technical memorandum from the NASA Technical Reports Server, a government aeronautical research series issued for engineers studying engine thermodynamics. Its pictures are plain line diagrams: pressure-volume cycle graphs, turbine diagrams and a fuel consumption curve, drawn in black on white with lettered points and hatched areas. A designer could take from them the clean, labelled graph style of early engineering documentation.
