Re: 15 minute classroom version...

[David_Anderson <dfa@FNAL.GOV>]

There is some bouncing off the bottom of the wing.  In fact, simulations
show that almost 1/2 of the lift on a barn door in flight (and your hand
out the car window) is due to the air interacting with the bottom.  Of
course, it is a little hard to directly detect the force caused by the
lowering of the pressure on the back of the hand.  It would feel like a
force on the palm.

David Anderson
dfa@fnal.gov




On Tue, 24 Aug 1999, Ludwik Kowalski wrote:

> I support this naive point of view. Why is it a "misconception"?
> What happens to the air encountered by the bottom of the wing?
> How can the absence of "bouncing down" be demonstrated?
>
> OK, I see. You are not denying bouncing, you are saying it is
> not the cause of the lift force. In my opinion it is also the cause.
> The faster air from above should contribute more than slower
> air from below but that is a different story. The statement "air
> pushed down  cause the lift" simply avoids this issue.
>
> William Beaty wrote:
>
> > ... The idea that lift occurs because air bounces off the bottom of the wing
> > is a typical misconception that children aquire (I myself figured it out
> > as a kid from experimenting with hands out the car window, also by analogy
> > with sprayers on hoses deflected from the hand.)  In reality, most of the
> > lift appears because the flow of the air "attaches" to the upper surface
> > of the wing and is guided downwards because the trailing edge of the wing
> > is angled downwards.  It's called "flow attachment", also "the Coanda
> > Effect." The air "bounces off" the upper surface of the wing, but the
> > "bounce" is reversed, it is like an attraction, and when the air is thrown
> > down, the wing must experience an upwards-directed force. ....


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                               David F. Anderson
                    Fermi National Accelerator Laboratory
                              PO Box 500,  MS-220
                               Batavia, IL 60510
                     (630) 840-3471; FAX (630) 840-6039
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