Page 9 - Understanding Flight

FM_Anderson 11/14/00 12:40 PM Page ix

Introduction

Forget Bernoulli’s theorem
WOLFGANG LANGEWIESCHE, STICK AND RUDDER, 1944

here are few physical phenomena so generally studied which are
as misunderstood as the phenomenon of flight. Over the years
Tmany books have been written about flight and aeronautics (the
science of flight). Some books are written for training new aeronauti-
cal engineers, some for pilots, and some for aviation enthusiasts.
Books written to train engineers often quickly delve into complicated
mathematics, which is very useful for those who wish to make
detailed calculations. But the necessary formalism is often achieved at
the expense of a fundamental understanding of the principles of flight.
Books written for pilots and enthusiasts try to explain flight principles
but frequently fudge the physics to simplify the explanation.

Unfortunately, the books that do address the principles of
flight more often than not propagate long-held myths. We say Sometime between the 1940s
long-held, but it is interesting to note that if one looks at the and now the explanations of lift
description of flight in books written in the 1930s and 1940s have gone astray from reality
one finds essentially the correct explanation. Those and have become much more
discussions focused on the angle of attack and Newton’s complex, nonintuitive, and
principles. Somehow between then and now the explanations frequently wrong.
have gone astray from reality and have become much more
complex, nonintuitive, and frequently wrong.

One common myth is the “principle of equal transit times” which
states that the air going around a wing must take the same length of
time, whether going over or under, to get to the trailing edge. The
argument goes that since the air goes farther over the “hump” on
the top of the wing, it has to go faster, and with Bernoulli’s principle
we have lift. But in reality, equal transit times hold only for a wing
without lift. Another common misconception is that the shape of the

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