[PSUBS-MAILIST] Re: []

[Danny Campbell <danny.campbell@usa.net>]

I beg to differ with you over your statement about pressure differences
between the top and bottom of flow over an airfoil shape being used in water. 
True, water for all intents and purposes is incompressible, that does not say
that the lift is due to the fluid being compressed.  Bernoulli's Law applies
in water just as in air... If two particles hit the leading edge of a foil
section and separate, one going over the top and one going along the flat
bottom, the one that has to travel the greater distance must travel faster to
meet up with the other particle at the trailing edge.  The faster the flow the
lower the pressure.

Rudders and things like that are typically symmetrical since you're not trying
to get lift per se, just a force due to redirecting the mass flux of the water
going by.  I've never looked into it but I'm sure there are applications for
true foil sections used while submerged, whether it be for "flying" a
submarine or for the lifting wings of a hydrofoil.

Hope that answers your question Dale.  We'd love to see some more pictures of
your boat and know how your adventures are going!

Danny

"Dale" <heinzind@cadvision.com> wrote:

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I have a question for the group..

I am a pilot, and know the theory behind lift on the wing..I noticed on some
posts, that there were airfoil shapes being used, to produce lift (in a
downward direction) on submarines, submersibles  etc..   my question is , how
does that work??  Water will not compress, or expand, being a liquid, 
therefore the pressure difference between the top of the "wing" and the bottom
of the wing will be the same, there fore no lift..  or am I missing
something??

dale.


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