tisdag 7 augusti 2012

Text Book: The Simple Science of Flight

Henk Tennekes is Director of Research Emeritus at the Royal Netherlands Meteorological Institute, Emeritus Professor of Meteorology at the Free University (VU) in Amsterdam, and Emeritus Professor of Aerospace Engineering at Pennsylvania State University. He is the coauthor of A First Course in Turbulence (MIT Press, 1972) and The Simple Science of Flight:
  • An investigation into how machines and living creatures fly, and of the similarities between butterflies and Boeings, paper airplanes and plovers.
  • A leisurely introduction to the mechanics of flight and, beyond that, to the scientific attitude that finds wonder in simple calculations, forging connections between, say, the energy efficiency of a peanut butter sandwich and that of the kerosene that fuels a jumbo jet.
Let us check out how Tennekes describes the "simple science of flight": 
  • Unfortunately, most of us learned in high school that one needs the Bernoulli principle to explain the generation of lift. Your science teacher told you that the upper surface of a wing has to have a  convex curvature, so that the air over the top has to make a longer journey than that along the bottom of the wing.
  • Polite fiction, indeed. It does not explain how stunt planes can fly upside down....
  • We will have to do better. I will use a version of Newton's 2nd Law. I will also appeal to Newton's 3rd Law, which says that action and reaction are equal and opposite.
  • Applied to wings these two laws imply that a wing produces an amount of lift that is equal to the downward impulse given to the surrounding air.
  • The lift of a wing is proportional to angle of attack x density x speed^2 x wing area.  
This is all Tennekes has to say about the "simple science of flight". Simple indeed: Upward lift on the wing is balanced by a downward force on the air from the wing! And the formula is just trivial similarity and an assumption pulled out of the pocket that lift scales with the angle of attack  

What Tennekes offers the general reader in "college-level courses for senior citizens" is non-sensical triviality instead of enlightening simplicity, as if the senior citizens are all Alzheimer patients.  

The book, written by an author who describes himself as a turbulence specialist, gives yet another indication of the collapse of theory in the century of aerodynamics.

Tennekes was forced out of office because he expressed skepticism to climate alarmism and so his critique of Bernoulli was not the only case where "he was right after all".

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