In 1925, Prandtl became the Director of the Kaiser Wilhelm Institute for Fluid Mechanics. His discovery in 1904 of the Boundary Layer which adjoins the surface of a body moving in a fluid led to an understanding of skin friction drag and of the way in which streamlining reduces the drag of airplane wings and other moving bodies. His work on wing theory, published in 1918 - 1919, followed that of F.W. Lanchester (1902-1907), but was carried out independently and elucidated the flow over airplane wings of finite span.

Prandtl's work and decisive advances in boundary layer and wing theories became the basic material of aeronautics. He also made important contributions to the theories of supersonic flow and of turbulence, and contributed much to the development of wind tunnels and other aerodynamic equipment. In addition, he devised the soap-film analogy for the torsion of non-circular sections and wrote on the theory of plasticity and of meteorology.