Today, Max Munk and aimful thinking. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

In 1981, I read a wonderfully odd autobiographical article by Max Munk, and I never forgot it. Munk was then 91 years of age. He'd begun a brilliant career during WW-I -- a young engineer, working for German aerodynamics pioneer Ludwig Prandtl. When the war ended, Prandtl's lab was light years ahead of anyone else's.

Twenty-seven years later, after another war, the Germans again had certain technology that we didn't; but this time we were ready. We went in with teams to locate documents and people. A program called Operation Paperclip brought an army of high-level engineers back here. I worked with many who'd stayed and become citizens. 

We'd been a lot less clever back in 1918. Prandtl's funding was slashed and Munk was out of a job. He found temporary work in the Zeppelin dirigible works. But it was soon clear that prospects were better in America. He finally applied for work with the NACA. 

NACA was NASA's predecessor -- the National Advisory Committee on Aeronautics. And Munk had to pull strings to get there. He finally said that he'd invented a new kind of wind tunnel. We could have it as a bonus. Munk had realized that, if he used high-pressure air in a wind tunnel, he could model real airplanes with small models, or with lower airspeeds. 

NACA hired Munk and soon had a disaster on its hands. Personalities clashed. When one of their engineers proposed a wind tunnel similar to his, Munk accused him of theft. But Munk was only thirty, and he was caught in a major cultural readjustment. Historian Max Eckert remarks that the revolt, which rose up against him, overshadowed the fact that he was leaving a permanent imprint.

Munk set up an entire experimental and mathematical apparatus for understanding aerodynamics. Variable density wind tunnels became important tools. A new understanding of airfoil theory was put to use. So were Munk's mathematical modeling methods. 

Now this article by an aged Munk: He's watched airplanes passing the sound barrier and astronauts walking on the moon. His style is blunt and economical -- self-effacing and self-promoting at the same time. In a few brief pages he speaks of his work on how fish swim, on turbulence, linguistics, and wing theory. He finishes with a brief would-be proof of Fermat's last theorem. 

And one phrase keeps recurring. It is aimful thinking. Research must be aimful. Never mind that the word was not used before or since. It's self-explanatory and it works. Munk praises two former friends who, though very different, embodied the virtue of aimful thinking. They were Ludwig Prandtl and Orville Wright.

Aimful thinking is what William Blake meant when he said, "I will not cease from mental fight." It's the difference between creative dabblers and people who produce things. It is that quiet guidance system to be found in the back of a few peoples' minds -- no matter how high or how far their flights of fancy take them. 

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

M. M. Munk, My Early Aerodynamic Research -- Thoughts and Memories. Annual Review of Fluid Mechanics. Vol. 13, 1981, pp. 1-7. 

M. Eckert, Strategic Internationalism and the Transfer of Technical Knowledge: The United States, Germany, and Aerodynamics after World War I. Technology and Culture, Vol. 46, No. 1, January 2005, pp. 104-131 (see especially, pp. 120-124).

J. H. Lienhard, Prandtl, Ludwig. Dictionary of Scientific Biography, Vol. XI, (C.C. Gillespie, ed.) (Chas. Scribner and Sons, New York, 1975).

Munk's wind tunnel idea depended on what we call Reynolds Number similarity. As long as the Reynolds Number, Re = rhoVL/µ, is the same for the model a nd prototype the aerodynamic behavior will be the same. (rho is the air density, V is the air velocity, L the size of the model, and µ the viscosity of the air.) Pressurizing the air hardly affects µ and it greatly increases rho. Thus, to keep Re the same in a pressurized tunnel, the size or the velocity must be reduced. This idea would be well within the grasp of a first semester fluid mechanics student today. 

Some standard forms of cambered airfoil sections as they had finally evolved before WW-II. The Göttingen form is one that evolved out of Prandtl's Laboratory at the University of Göttingen. It and the NACA 6049 shape could both be ones that Munk helped to develop.