On Thu, 19 Aug 2004 at 08:11:24 in message
, Todd Pattist
wrote:
True, but so what? The same thing is true of a wing. You
never hear of downwash or wingtip vortices *above* the wing,
yet it's still true that most of the lift from the wing
comes from the top surface, not the bottom surface. The
pressure difference relative to static is still greatest
above the wing. You're confusing where the air comes from
with the force produced by deflecting that ai

Right. The only way forces can be applied to a wing or a prop is by
differential air pressure on the component itself.

The generation of such forces can only occur when a momentum change is
produced on the air.

The only way you can jump off the ground is by applying an equal force
to the ground and to the bottoms of your feet. You also have to provide
energy to create the change of momentum that gives you a vertical
velocity. This is not quite the same as the wing or prop but I am trying
to reinforce the principle that forces that move or support objects must
be applied directly to the object.

Some things may seem different (like magnetic levitation), but it is
just that the force is supplied by a force field.
--
David CL Francis