Calculation of wing spars
A 1921 technical report from the NASA Technical Reports Server on calculating aircraft wing spars, a structural engineering treatise for aeronautical engineers and designers. Its pictures are plain line diagrams: a loaded beam with distributed load and supports labelled MA and MB, a graphical construction with vectors and a labelled moment envelope, and a stepped beam with segment lengths marked S1 and S2. A designer could take the clean, labelled schematic style for showing load and stress diagrams.
