Characteristics of an Airfoil as Affected by Fabric Sag
This 1932 NACA Technical Note from the National Advisory Committee for Aeronautics reports wind-tunnel tests of an airfoil whose fabric covering sags, comparing it with a smooth surface for aircraft designers and engineers. The pictures are plain engineering graphs of lift, drag and moment coefficients against angle of attack, plus a photograph of a grey metal wing model with ribbed, rippled skin and a mounting rod, which a designer might take as a reference for how wavy surfaces change aerodynamic curves.
