An Introduction to the Laws of Air Resistance of Aerofoils
This is a technical report from the 1920s-era National Advisory Committee for Aeronautics, published in 1920 and issued for engineers and aeronautical researchers studying drag on wing sections. The pages carry numbered line diagrams of airflow vectors around aerofoil profiles, force-direction sketches, and small coordinate plots of resistance curves, all drawn in plain black ink on cream paper.
