Longitudinal stability in relation to the use of an automatic pilot
A 1938 NACA technical note on longitudinal stability and automatic pilot use, issued by the National Advisory Committee for Aeronautics for aeronautical engineers and researchers. The pictures are plain engineering graphs of Routh's discriminant and damping against control parameters for the Fairchild 22 airplane, drawn as black lines on gridded white paper, with a designer able to take from them a clean, minimal chart style for technical data.
