Variable pitch propeller
This is a 1923 technical report from NASA's Technical Reports Server on variable pitch propellers, with its engineering charts plotted against altitude and time. The pictures are plain black-and-white line graphs: the first plots power-to-altitude curves labelled by engine conditions, and the second plots altitude against time for several flight profiles, with dashed and solid lines and lettered labels. A designer might take from them the clean, sparse grid-and-curve vocabulary of early technical diagrams.
