Energy & Industry / Transport & Mobility

Wing Theory & Boundary Layer (Prandtl)

Ludwig Prandtl explained in 1904 why air clings to a surface in a thin layer, and by 1918 had a working theory of lift and drag on a wing, so engineers could calculate an aircraft before building it.

In August 1904 Prandtl told the mathematics congress in Heidelberg that air next to a surface sticks to it in a thin boundary layer; this explains friction drag and, when the layer peels away, stall. In 1907 he began building a wind-tunnel institute at Göttingen, and with Albert Betz and Max Munk he published the lifting-line theory in 1918-1919, which shows how wingtip vortices cause drag and that an elliptical lift distribution gives the least of it for a given span. These theories let designers analyse a wing before building it, and in 1926 A. A. Griffith used aerofoil theory to show that compressor blades must be wing-shaped, a step toward the jet engine.