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Title: Stop Abusing Bernoulli!: How Airplanes Really Fly by Gale M. Craig ISBN: 0-9646806-2-9 Publisher: Regenerative Press Pub. Date: 01 January, 1998 Format: Paperback Volumes: 1 List Price(USD): $17.00 |
Average Customer Rating: 3.47 (15 reviews)
Rating: 5
Summary: A Long Overdue Book
Comment: Stop Abusing Bernoulli! properly presents aerodynamics of airfoils, wings and airplanes in terms of Newtonian physics. In 1972, NASA scientist Norman K. Smith wrote in The Physics Teacher: "For explaining dynamic lift, the result of an encounter between a fluid and a lifting device, Newton's laws must be used. Consolidation of all dynamic forces produced in a fluid-- propulsion, lift, control, etc.-- under Newton's third law is not only correct physics but also makes the whole business far easier to teach and to learn." More recently, in a paper presented to the 2001 meeting of the American Institute of Aeronautics and Astronautics, Dr. Jaako Hoffren, of the Helsinki University of Technology, also proposed teaching more directly in Newtonian terms.
This reader concurs with the review provided by Erik Zapletal from Maroota, Australia. It is complete, factual and extensive, and favors Newtonian based aerodynamics teaching. However, some of the other reviews are not accurate, and deserve comment. A few reviewers have not really read the book, are incapable of understanding it, or are prejudiced with vested interest. Richard Asher's review has mostly only vague generalities, with only one specific but erroneous statement-- that the author claims Bernoulli's laws are contradicted by Newton's laws. In fact, the author derives Bernoulli's equation from Newtonian principles, beginning on page 139. Asher should have found this if he really read the book. Also, beginning on page 129, the lift equation is derived logically and methodically from Newtonian principles, producing exactly the same result as classically derived from Bernoullian considerations. Contrary to Asher's claim, these derivations confirm agreement between Newtonian and Bernoullian concepts.
The Scott Johnson review, applauded by Asher, and the Jan-Orlov and Jeff Noall reviews, deny the reality of circulation, claiming it to be a fiction of classical aerodynamics for mathematical purposes. Although the classical explanation of how circulation is produced is fictional, the circulation is in fact real, as Newtonian principles and common sense demand. Reacting to force of pressure difference, air ahead of a lifting wing accelerates upward around the leading edge, away from higher pressure below and toward lower pressure above. This upward movement is the basis of stall warning systems. Above the leading edge, air accelerates rearward into reduced pressure, while below the leading edge air accelerates forward, away from increased pressure. Behind the wing, air following the surfaces is left with downward movement. Thus instantaneous air movements occurring in still air around a passing wing include upward movement ahead, downward movement behind, rearward movement above and forward movement below. Overall, this movement is of circulatory nature around the wing, and is appropriately referred to as "circulation." Pitot instrumentation evidence on page five of the book supports circulation as fact. The classical explanation, using fictional induction to explain circulation, rather than Newtonian principles of force, mass and acceleration, apparently leaves Asher and others believing circulation is not real.
Aerodynamics must be treated open-mindedly as science, not as dogma or unquestionable religion. The most popular layman-level theory of wing operation, religiously taught to pilots and public school students for about 100 years, falsely claims transit time of flows above and below a wing must be equal. This, if true, would require flow over a curved upper surface to be faster than that at a more flat, and therefore shorter, lower surface. Hence, Bernoulli's law would require pressure above to be less than that below so as to produce lift. Indeed upper surface flow is faster, but much faster than equal transit time would require or even permit. This most popular but false teaching of lift is an abuse of Bernoulli's law. That abuse is alluded to in the book title.
Rating: 5
Summary: Reply to Richard Asher's Review
Comment: Mr. Richard Asher's pompous negative "review" of "Stop Abusing Bernoulli!" consists of generalities with nothing specific other than stating that the book's author "claims" Bernoulli's laws contradict Newton. He says "It is thus absurd to suggest that a explanation of wing theory using Bernoulli's laws contradicts a Newtonian explanation as the author of this book claims."
Clearly this person has not really read the book. There is no such claim. The author only demonstrates that wing operation can be described in Newtonian terms without involving Bernoulli. This in no way suggests Bernoulli's law is wrong.
Asher also complains vaguely about the mathematics. In the book the lift equation is produced from Newtonian momentum considerations, rather than from Bernoulli. The result coincides precisely and logically with the derviation involving Bernoulli. Without proper mathematics, and physics, this result would be quite improbable.
Mr. Asher is the second "expert" to publish a pompous and erroneous review after perhaps glancing through the book and finding it contains material beyond his understanding.
Rating: 1
Summary: The Ideas taught in this book are not correct.
Comment: I am a aerodynamisist working at Pratt & Whitney (maker of jet engines), and have a graduate degree in mechanical engineering, specializing in fluid mechanics. I design airfoils for the turbo-machinery in the jet engines we design.
As an aerodynamisist, I can attest that if the author's (Mr. Craig) speculative ideas were indeed correct, then jet engines simply would not work! We have a wealth of experimental data which demonstrate that the author's explanations of how airfoils work are simply not correct.
I read Mr. Craig's book out of a sense of curiosity. I was very disappointed to find how completely bogus the book is. I noticed several mathematical flaws in the author's derivations, but in going to write this review I noticed another reviewer (Mr. Scott Johnson) has already addressed the same topic (Please refer to Mr. Johnson's excellent review. You must select to read all the reviews to see Mr. Johnson's review since it was written a couple of years ago).
I will not repeat the same material as Mr. Johnson wrote. Instead I would like to bring out an additional point. Only those who lack an understanding of fluid mechanics would seek to argue whether the principles of Newton or Bernoulli accurately account for how wings generate lift. Bernoulli's laws do not contradict Newton's laws and visa versa. Any results derived from Bernoulli's laws will satisfy all of Newton's laws of motion. Newton's laws of motion are very general laws applicable to an incredible variety of situations. It is this generality that makes Newton's laws so powerful. Bernoulli's laws are much less general (they apply only to fluids), but they give additional insights, which Newton's laws don't provide, about how fluids behave. Bernoulli's principles give us more information about how fluids obey Newton's laws of motion. It is thus absurd to suggest that a explanation of wing theory using Bernoulli's laws contradicts a Newtonian explanation as the author of this book claims.
Unless you are looking for a reading in science-fiction, I do not recommend this book.
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