Understanding flight Anderson D.F., Eberhardt S.

Anderson D.F., Eberhardt S.
Год: 2001
Издательство: The McGraw-Hill Companies
Город: New York
Количество страниц: 249
Язык: Английский
Формат: DJVU / RAR

Формат файла: RAR

Forget Bernoulli's theorem Wolfgang Langewiesche, Stick and Rudder, 1944
There are few physical phenomena so generally studied which are as misunderstood as the phenomenon of flight. Over the years many books have been written about flight and aeronautics (the science of flight). Some books are written for training new aeronautical 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 long-held, but it is interesting to note that if one looks at the description of flight in books written in the 1930s and 1940s one finds essentially the correct explanation. Those discussions focused on the angle of attack and Newton's principles. Somehow between then and now the explanations 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 wing is the dominant characteristic in determining lift. Actually, the shape of the wing is one of the least significant features when understanding lift. The principles of lift are the same for a wing flying right side up or in inverted 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. This is of little use to one seeking a clear understanding of the basic principles. It is our belief that all fundamental concepts in aeronautics can be presented
in simple, physical terms, without the use of complicated
mathematics. 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.
The object of this book is to provide a clear, physical description of lift and of basic aeronautical principles. This approach is useful to one who desires a more intuitive understanding of airplanes and of flight. This book is written for those interested in airplanes in general, and those interested in becoming more proficient pilots. 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 first chapter, "Basic Concepts," is an introduction to a basic set of terms and concepts. This will give the reader and the authors a common set of tools with which to begin the discussion of flight and aeronautics.
The next chapter, "How Airplanes Fly," is where we get into lift and flight. We believe that this chapter gives the most complete and correct physical description of lift to date. Like many before us, we describe lift using Newton's three laws. But, unlike anyone to our knowledge, we take this description and use it to derive almost all aspects of flight. It allows us to intuitively explain aspects that most aeronautical engineers can only explain mathematically. It will become clear to the reader why one increases the angle of the wing when the airplane slows down or why lift takes less power when the airplane goes faster. It will be obvious why airplanes can have symmetric wings or fly upside down.
The third chapter is "Wings." Here we will explain why wings look the way they do and what tradeoffs take place in their design. When you fly on a commercial jet and see all the changes that are made to the wing on landing, you will have a clear understanding of what is going on and why. A natural follow-on to "Wings" is a chapter on "Stability and Control." Airplane stability is presented and the distinction is made between stable and balanced flight. The concept of fly-by-wire and the role of the computer are also discussed.
Among other things, the chapter on "Propulsion" explains how a jet engine works and why they have gotten so large. Would you believe that there is essentially a propeller in front of the jet engine on that Boeing 777?
The following chapter on "High-Speed Flight" discusses the interesting phenomena associated with flying faster than the speed of sound and why these airplanes look as they do. Chapter 7, "Airplane Performance," discusses such aspects of flight as the climb, cruise, and landings.
The final chapter on "Aerodynamic Testing" addresses wind-tunnel testing and flight testing. The principles of wind tunnels are presented in some detail. Some examples of flight testing as it pertains to the previously introduced concepts are presented.
This work is presented on two levels. The bulk of the material is addressed to the general reader. Here a minimum of experience is assumed. At times it will be desirable to make clarifying comments by insertion of a short topic, which may be somewhat removed from the main train of thought. These insertions are printed on a colored background. They may be skipped over without any loss of continuity or understanding of the main text.