Gale M. Craig informs us in Physical Principles of Winged Flight that:
- Popular explanations of how wings work are often erroneous and scientifically unsound. Wrong explanations may be given by well-meaning teachers and others, but false teaching may sometimes be just for convenience.
- Many years ago, a famous aerodynamicist, Dr. Theodore Von Karman, instructed his assistant: When you are talking to technically illiterate people you must resort to the plausible falsehood instead of the difficult truth.
- Falsehood, whether intentional or not, is still being taught.
- Curvature of flow and resulting pressure gradients is the source of lift for heavier than air aerodynamic flight. Description of lift as due to pressure gradients in curvature of above-wing and below-wing flows was given by Otto Lilienthal in his 1889 book titled Birdflight as the Basis of Aviation.
- Unfortunately that has been neglected for well over a century in favor of pseudoscientific descriptions.
- The recirculation around an airfoil or wing is termed circulation, and is, in classical theory, the cause of faster above-wing flow as compared to below-wing flow. As described by Lanchester (1868-1945) in his 1907 book, Aerodynamics, circulation is essential to lift.
- The concept of superimposed circulation may seem a bit abstract but circulation is a real rotational movement that travels through the air with the wings of an airplane in flight.
- Fallacies of popular aerodynamic teachings based on misapplication of Bernoulli's law are revealed, and more appropriate description of wing operation is presented in terms of Newton's laws.