Max M Munk at Langley (1926). Photo courtesy of NASA History Office
The contributions of Max Munk to aerodynamics could be summed up by his own statement. He came of age at the beginning of aeronautics and started his work with Prof Ludwig Prandtl at Göttingen, where he earned his doctorate. The wind tunnel at Göttingen was the first in Germany, “primitive and slow”, but that was enough at the time: “You can learn so much when you start from ignorance (Munk, 1981, recollections).
Munk’s most outstanding contributions are in the field of theoretical aerodynamics, and include a wide variety of problems. His works were classified under WWI by the German army, but they leaked out to the English speaking countries soon after.
After WWI (in 1921) Munk moved to the US, were he held jobs at both NACA (as chief aerodynamicist) and the Catholic University of America, Washington, DC. He was one of first of a long series of aerodynamicists to leave Germany.
Some of his contributions are: airship theory (moments and forces), the theory of induced drag (his own definition), airfoil theory (with the definition of the center of pressure), interference aerodynamics of multi-body lifting systems (with 3 stagger theorems), a general theory of the biplane, non planar wing systems (twisted wings), propeller and windmill theory, the apparent mass theory (1923), and the variable density wind tunnel (NACA TN 60, 1923).
The invention of the variable density wind tunnel was not a small thing. In fact, by compressing air, one could increase the Reynolds number without needing to increase the model size. Conversely, at high densities, say 10 bars, the model needed for a given Reynolds number would be 1/10 of the size in atmospheric conditions.
The figure below is a sketch based on the variable speed wind tunnel built at NACA by Munk. The pressurized air is circulated through an annular duct.
Fig. 2: NACA Variable Speed Wind Tunnel designed/built by M. Munk