"Technical progress is made by integration, not differentiation."
Max M. Munk, physicist and mathematician
Early airplane engineers based their flying machines on the flight of birds. It soon became clear, however, that this method was limited. When a bird is in flight, air flows over its wings, and engineers realized that the flow of air over an airplane's wings would need to be simulated in order to uncover the secrets of flight.
Early simulation methods included the whirling arm in which a wing was attached to a pole and rotated. Shortly after, Frank Wenham (1824-1908) designed a crude wind tunnel in which a fan channeled air down a tube.-This produced a controlled airflow, and harnessing this led to the first variable- density wind tunnel of Max Munk (1890-1986).
Munk moved from Germany to the United States in 1920 to work for the National Advisory Committee for Aeronautics. He decided to improve the modeling of air flow in early wind tunnel designs so they could recreate the conditions experienced by a full-sized plane at high altitude. The breakthrough came with his idea of increasing the density of the air in the tunnel by compressing it. This laid the groundwork for the first variable-density closed-circuit wind tunnel, which went into operation in 1923 and revolutionized aircraft and automobile design.
