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Old 14th December 2007, 03:14 AM   #61
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Great explanation from expander;;;
but it does assume there is a very close anology between lift annd drag relatiopn ships for wings/fins nd to that of planing surfaces.(Which has been in doubt in a few posts)

Not sure its anything to do with it but;

An aircraft wing will give lift at a zero angle of attack.(Bernouli /venturi principle;ie air over top surface travels much further than that underneath; creates pressure difference between upper and lower surfaces and cause luift.

A planing surface (ie a board) will not create any lift at zero angle of attack because at zero AoA there iis no momentum exchange.Board /hull or any planing surface needs to be at a slight angle to direction of travel. (Ie even flat slalom boards are sat deeper at tail than front edge)

Taking all this into account dont really think we can assume wing anolgy is a good one. (Especially when we are making conclusions based on them)
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Old 14th December 2007, 03:55 AM   #62
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...a planing surface (ie a board) will not create any lift at zero angle of attack because at zero AoA there iis no momentum exchange.Board /hull or any planing surface needs to be at a slight angle to direction of travel...
--

As I've written in previous post, "...in these context, in air or in water, an HIGHER Aspect Ratio has pratical effect of increasing LIFT (above all when angle of attack increases)..."

And when a windsurfing board runs on water it always (and inevitably) assumes a certain Angle of Attack for board design (scoop line).

Last edited by Expander; 14th December 2007 at 03:30 PM.
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Old 15th December 2007, 02:16 AM   #63
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With all repect expander thats been crux of thread for a while.
We know some have said high aspect is more efficient; some have said more efficient in certain situations and a couple have said Aspect ratio does not affect overall lift.
If Floyd`s quotes (from some Scientuific papers; listed in post) are taken to have any substance then overrall lift for a planing body is simply a matter of area.
Your post implies a longer leading edge gives more lift.
If planing is a result of momentum exchange over entire area there is no reason to just assume high aspect is any more efficient.(It would simply be matter of max area for minimum leading edge/trailng edge)
On the other hand if planing is a result of lift generated by leading edge then it stands to reason higher aspect would generate more lift.
Nobody has actually said its one or the other (for a fact) with evidence.(Infact evidence provided is contadictory)
Personally reckon leading edge argument is flawed for reasons mentioned in my last post.(ie boards do not have flow over top surface so wing anology is very weak)
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