[EMAIL PROTECTED] wrote:
> Are you referencing Bernoulli’s Principle?
No, I'm not.
> Really not applicable to lift. The real answer you want has more to do
> with Angle of Attack.
This is in line with the answer offered here before, but no matter what,
no angle of attack by itself will make a sail drive a boat upwind if the
only forces acting on the sail are 'pushing' forces, that is to say
forces that would tend to increase air pressure at or very near the
sail, such as you would get on the face of a flat surface facing the
wind tilted at an 'angle of attack'.
There is more to it than that.
And just because a bunch of folks say "it is not Bernoulli's principle"
doesn't necessarily make that so, either! Not saying that is what it is
or is not.
What it is, is negative and positive vector forces summed, not just
positive vectors as in air pressure on the bottom of a wing at a given
angle of attack.
The trick is, how do you get negative vectors (forces that act like
'suction' or 'pulling') on a sail going upwind that are bigger than the
positive ('pushing') vectors?
Because when you think about it, the only forces acting on the bottom of
a wing at an angle of attack are 'pushing' forces, and the wind cannot
'push' a boat so it moves in the direction opposite that in which it is
'pushed'.
So something, but not the force on the bottom of the wing (or windward
side of the sail), is acting to 'pull' the boat so that it moves upwind,
or against the wind (and the forces from the wind).
Right? -Ken
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