Design of centrifugal impeller blades
A 1939 NASA technical report on the design of centrifugal impeller blades, a dense engineering document of mathematical analysis and plotted results prepared for aeronautical and mechanical engineers. The two pictures are graphs of radial functions plotted against radius from about 0.3 to 0.7 metres, and a pair of long numbered equations for velocity components. A designer can take from them only the restrained look of technical plots: thin black axes, grid lines, and one smooth curve per graph.
