Differential equations in airplane mechanics
A 1922 technical report on differential equations of airplane mechanics, issued by NASA's Technical Reports Server as a digitised scan of an early aeronautical research paper for engineers and mathematicians. The single picture is a hand-drawn diagram of nested closed curves spiralling around a centre point, with straight axes and dashed lines crossing them, showing a phase-plane style trajectory analysis. A designer might take from it the graphic power of concentric spirals and crosshair axes as a simple abstract motif, drawn in fine single-weight pen lines on plain paper.
