torsdag 2 augusti 2012

Text Book: Not Understanding Flight

The text book Understanding Flight by David Anderson and Scott Eberhardt, presented as "the simplest, most intuitive book on the toughest lessons of flight--addresses the science of flying in terms, explanations, and illustrations that make sense to those who most need to understand: those who fly", seek to fill its mission with the following proclamations:
  • There are few physical phenomena so generally studied which are as misunderstood as the phenomenon of flight.
  • Books written to train engineers often quickly delve into complicated mathematics....the necessary formalism is often achieved at the expense of a fundamental understanding of the principles of flight.
  • A shortcoming of many books on the topic of aeronautics is that the information is presented in a very complicated manner, often mistaking mathematics for a physical explanation. 
  • In fact, we believe that if something can only be described in complex mathematical terms it is not really understood. To be able to calculate something is not the same as understanding it.
  • Teachers and students who are looking for a better understanding of flight will find this book useful. Even students of aeronautical engineering will be able to learn from this book, where the physical descriptions presented will supplement the more difficult mathematical descriptions of the profession.
  • The mathematical description of lift is a general term for the analysis tools of classical aerodynamics and computation aerodynamics. If the objective is to accurately compute the principle or aerodynamics of a wing, these are the tools to use, though the aerodynamic description is mathematical and not physical. This is a point lost on many of its proponents. Fortunately, the physical description of lift, presented here, does not require complicated mathematics.
  • The physical description of lift is based primarily on Newton's three laws and a phenomenon called the Coanda effect. This description is uniquely useful for understanding the phenomena associated with flight.
  • So why do fluids tend to bend around a solid object?
  • The answer is viscosity, that characteristic that makes a fluid thick and makes it stick to a surface. When a moving fluid comes into contact with a solid object, some of it sticks to the surface. 
Comment: We read that Anderson-Eberhardt informs us that (i) mathematics of flight is one thing, which is difficult to understand, and (ii) physics of flight is another thing, which is easy to understand: The Coanda effect resulting from the viscosity of air.

Yes, (i) is correct, the mathematics of flight of Kutta-Zhukovsky-Prandtl is not understood by any living scientist.  But (ii) is plain wrong. Lift is not an effect of viscosity, but results from the fact that air has very small viscosity, as shown by the New Theory of Flight.  The book shows that the authors do not understand flight and so the book should more correctly be titled Not Understanding Flight.

An unsuccessful attempt to discuss the themes of the book is recorded in an interview with Anderson-Eberhardt.

Only when mathematics and physics come together is science created. Understanding in physics means understanding of a mathematical model describing real physics.  Pseudo-science is characterized by mathematics separated from physics, as in the Kutta-Zhukovsky circulation theory.

1 kommentar:

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