Metal-truss wing spars
A 1931 NACA technical note from the NASA Technical Reports Server on metal-truss wing spars, written for aircraft engineers and aeronautical researchers. Its figures are engineering diagrams: truss members in tension and compression, deflection curves with labelled points, and cross-section sketches of a spar under load. A designer might take from them only the schematic vocabulary of structural diagrams, such as dashed deflection lines beside solid members, tidy labelled grids, and shaded section profiles.
