Originally Posted by
3664shaken
...I suggest the following books that all explain why lift increases in ground effect.
Fundamentals of Aerodynamics – John Anderson
The Illustrated guide to Aerodynamics – H. C. “Skip” Smith
Low Speed Aerodynamics – Joesph Katz & Allen Plotkin
An Introduction to Aircraft Performance – Mario Asselin
Theory of Wing Section – Ira Abbott & A. E. von Doenhoff...[/COLOR]
Fundamentals of Aerodynamics by John Anderson resides on my bookshelf and I used it extensively for aerodynamics in college. I used to borrow Theory of Wing Sections by Ira Abbott & A. E. von Doenhoff from a professor, and as a classic work on the subject it predates high-speed aerodynamics but it is useful.
As for the other ones, I have equivalents: Low Speed Aerodynamics by Joesph Katz & Allen Plotkin is equally treated in Aerodynamics for Engineers by John J. Bertin. I personally studied under one of the contributors to the latter, a Mr. Robert J. Englar.
An Introduction to Aircraft Performance by Mario Asselin is equally treated in Aircraft Performance and Design by John D. Anderson. I always like Anderson's writing, he is a very good writer in addition to a leading scholar. He is getting on in years now, so we may lose him at any time. These are all great books. Do you have an AE degree? Seems like maybe you do having a book list like that. Engineering texts are pretty expensive.
So we both have good books. But you are not reading them very well on this particular subject. You missed the section on circulation when it explains that in ground effect the wing vortices “see” a mirror image of themselves underground and the effect is felt all the way up to the wing. It is a mathematical fact although obviously there is nothing going on under the ground. The net effect is a reduction in downwash and an increase in angle of attack in ground effect. I never said otherwise- by the time I wrote my last post I was no longer saying without qualification that a wing produces less lift in ground effect, I was saying that when you account for the change in effective angle of attack caused by ground effect there is no increase in lift. I also extended it to an explanation of why low wing airplanes settle faster, but I admit I do not have any data on that it was just my practical experience. The theory is correct, however.
I read your links by NASA article and SE Technology and they do not contradict this in the least. They simply do not mention that the extra lift is from a change in effective angle of attack and that effective angle of attack is what counts bar none. You want me to contradict all those sources but they are not speaking to this issue at all. If you reduce the angle of attack the amount the reduction in downwash does to decreases it you have a wing that is producing less lift.
And why do STOL airplanes hate to use a low-wing configuration?