The critical velocity of a body towed by a cable from an airplane
This is a 1937 NACA technical memorandum, issued by the National Advisory Committee for Aeronautics as a research report for aeronautical engineers, on the critical velocity of a body towed on a cable behind an airplane. Its pictures are line diagrams of relative velocity, angle of attack and forces acting on the body, plus a photograph of towed test models with a gauge, all in plain drafting-room style that a designer could use for schematic linework or technical annotation.
