The Aerodynamic Characteristics of a Slotted Clark Y Wing as Affected by the Auxiliary Airfoil Position
A 1932 NASA technical report on wind-tunnel tests of a slotted Clark Y airfoil, with the slot position varied to measure how it changed lift and drag. Its pictures are plain engineering graphics: line charts of lift coefficient against angle of attack, a test-setup diagram, and photographs of the cut wing sections. A designer could take the clean charts and the stripped-down diagram style as a model for technical figures.
