OK, I'll buy this. I should remind everyone that I am still
talking about an infinite wing, having no induced drag.

I claim that my statement is generally true, and does not require an
infinite wing, just an infinite air field (as per the example I'm
developing).

However, air will still have to be accelerated downwards to
keep the airplane from succumbing to gravity.


No it won't. Now we have no acceleration of the plane
upwards. It's true that the wing must still throw air down,
but now it's catching the air that is rising ahead of the
wing, and throwing it down at a speed that exactly matches
the rising speed of the air. Thus, the net downward speed
of the air is zero and the wing leaves undisturbed air
behind it..

Yes, it will.

The rising air in front of the wing doesn't rise by magic. It doesn't
rise before the wing does its thing (though it may rise before the wing
gets there); it rises =because= the wing is doing its thing, which is
throwing the air down (where it pushes the other air aside, and that
other air has to go somewhere).

Think about it. There's no earth, just this "magic plane gravity" which
pushes the airplane down. Something has to push up on the plane to keep
it in the air. The air can't push up (the way the runway can) because
the air is fluid - it smooshes out of the way and lets the plane
through. The only way the air can push up is by being thrown down -
accelerated at a rate that matches the acceleration due to "magic plane
gravity".

A wing not only keeps the plane away from the earth, it keeps the earth
away from the plane. If you could measure the total forces on the earth
due to everything on top of it (essentially making the earth a giant
bathroom scale), the reading would not change when an airplane takes
off. Even though the plane is not touching the earth, it is throwing
air down at the earth, and that impact registers as weight.

Jose
--
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