The dangerous flat spin and the factors affecting it
A 1931 NASA Technical Reports Server scientific paper on aircraft flat spin, a dangerous stall condition, presented as an aeronautical research report for engineers and pilots. Its pictures are plain technical line graphs of lift and drag coefficients against angle of attack, plus one three-dimensional diagram of aircraft axes and notation, so a designer might take only the sparse, labelled chart style and the clean monochrome linework of engineering diagrams.
