The flight of an autogiro at high speed
A 1933 NASA technical report on autogiro flight at high speed, issued as a scientific engineering study for aeronautical engineers and researchers. Its four pictures are engineering graphs plotting power ratios against airspeed in km/h and m/s for varying solidity, blade angle and advance ratio, plus one geometric diagram of rotor blade velocity vectors around a circle. A designer could take the restrained, labelled plotting style: thin black curves, dashed secondary lines, tick-marked axes and small handwritten-style value labels on a white field.
