On Oct 7, 12:15 pm, Le Chaud Lapin wrote:

An airplane can stay aloft if rarefication is somehow created above
the wing. This is what's happening with the blow-over-paper trick.
The air below the wing remains more or less steady at ambient
atmosphere. The air above the wing is rarefied and therefore causes
less force above the wing. The net result of the difference between
the full force below the wing and the reduced force above the wing,
minus the weight of the paper due to gravity, results in an upward net
force on the paper, causing it to rise. As soon as you stop blowing,
the ambient atmosphere works to replenish the rarefied air above the
paper to its natural state, which causes a net force on the paper due
to pressures above the paper and below the paper to equalize [taking
normal vectors into account, yada..], and gravity becomes the
determining force, causing the paper to flop back down.

"Rarefaction" again. I don't see that term used by
aerodynamicists, unless they're dealing with supersonic or hypersonic
flight, and I think that's where you are haywire. (Google "aerodynamic
rarefaction" to see what comes up.) Bernoulli said that as velocity
increases, static pressure decreases. We can measure this phenomenon
inside a pipe that has no change in cross-section. As velocity
increases, the dynamic pressure increases and therefore subtracts from
the static pressure to keep the total pressure the same. On an
airfoil, the lowest pressures are found where the velocity is highest,
just atop the leading edge, where we'd expect COMPRESSION to be
happening, not rarefaction. LIFT IS GENERATED BY LOWERED STATIC
PRESSURE, NOT LOWERED DENSITY. Until you get that through your head,
you will waste years trying to prove everyone else wrong. You are, as
the NASA site says, mistakenly applying the physics of solids to the
problem, not the physics of gases.
The air moves to fill any void over a wing in subsonic
flight. It moves far more quickly that you could generate any
significant rarefaction above a wing.

From that site:

"For example, from the conservation of mass, a change in the
velocity of a gas in one direction results in a change in the velocity
of the gas in a direction perpendicular to the original change. This
is very different from the motion of solids, on which we base most of
our experiences in physics.

Dan