In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
Beryl wrote:
Alan Baker wrote:
Beryl wrote:
Alan Baker wrote:
Beryl wrote:
Alan Baker wrote:
It's like the downwash argument. You can say "IT DOESN'T
MATTER", when people argue that the air behind an
aircraft is not deflected downward, but it *does* matter.
Having an accurate understanding of the physical
processes of flight matters.
It isn't really deflected downward, not for long anyway.
It's churning in a torus. Like a smoke ring.
No.

It really *is* deflected downward.

The edges of the deflected area churn, and the air that is
deflected ends up getting diffused among all the other air
below *it*, but it really is deflected downward.

And eventually, that downward deflection makes it way until
it -- very diffusely -- impacts upon the surface of the
earth. That is the only thing that finally stops it.

After more than 100 years of flight, the atmosphere still
hasn't been pushed down to the earth's surface.

Sorry, Beryl, but you're just wrong.

As I said, the atmosphere isn't getting any shorter. Do you
disagree with that? Repeating that "the net flow is downward" isn't
making progress.
The net flow is downward until it hits the ground and the momentum is
transfer to the earth.
Has to be an equal upward flow. Somewhere. Where?

Imagine riding in a C-130 Hercules. You're flying an RC model airplane
in the cabin! (That's why I picked a C-130)
The model's weight is applied to the cabin floor, of course, but the
"downwash" from the model's wing doesn't pile up on the floor.

http://www.efluids.com/efluids/galle...s/Morris_4.jsp
The column of downward flow in the center doesn't really flow down so
far, does it?
Yes, it does.

All the way to the ground.

Spread out among lots and lots of air, but that's where the momentum
*has* to go.
Say where the _air_ has to go.
The aircraft starts the air moving downward. Net downward momentum.

The ground stops that net downward motion.
What if there were no ground? Jupiter has atmosphere, gravity, and I
don't see why a solid surface below is required for flight.

Look, the aircraft imparts downward momentum to the air. If only air is
encountered by that air, the momentum cannot be go away, so it keeps
moving downward. As more air shares the momentum, it moves more slowly,
but it still moves until eventually, the air encounters the Earth.

There, the momentum it imparts downward to the earth is match by the
momentum imparted upward by the force of gravity that the aircraft
exerts on the earth; balancing out the system.

On Earth, the gravity of the planet far outweighs the gravity of our
atmosphere and thus essentially all the momentum of the moving
atmosphere must reach the ground to react out, but on Jupiter it's all
atmosphere and so eventually gravity acting on that atmosphere reacts
out the momentum.

After an airplane lands, and the weight is on its wheels, a bunch of
compressed air jumps off the ground back up to the altitude where it
came from. Ready for re-use.

Nope.


Let's talk about helicopters. We can replace that rotor with a squirrel
cage fan. Air is drawn down into the fan as before, and most of the
pressure differential is due to lowering pressure above the fan. As
before... except that now the air is exhausted out the periphery of the
centrifugal-flow squirrel cage fan, not down as it was with the old
axial-flow rotor. Will it fly? Where's the downwash?

If there is no downwash, it will not fly. No.

See everyone: this is why understanding of the actual facts is required.

The for the aircraft to experience an upward force from the air (the
only thing in contact with it), it must exert a downward force on the
air. Because the air is not a rigid body in contact with the earth (the
source of the downward force of gravity on the aircraft), a force
applied to the air must -- M-U-S-T-! -- cause it to move downward. That
downward momentum must eventually be transferred to the source of the
downward force on the plane for the system to remain in equilibrium.

--
Alan Baker
Vancouver, British Columbia
http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg