visualisation of the lift distribution over a wing

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
If there is no downwash, it will not fly. No.
You are arguing a point not under contention (at least with respect to
heavier-than-air aircraft.)

See everyone: this is why understanding of the actual facts is
required.
The ground isn't required. Air has inertia, and it's just as much a part
of the earth as dirt and rocks are. So why are you fixated on the
earth's solid surface? It compresses too, you know. You could argue that
the downforce travels through the whole planet and back into the
atmosphere in China.

You simply haven't really read anyone else's posts to understand what
they
are stating.
The previous poster just said:

"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?"

She ("Beryl"?)
A mineral

is clearly implying that such an hypothetical craft could remain airborne
without downwash.
No, I only asked.

How else can it be read?
Read it as a question.
So what is your answer? Can the postulated craft fly if there is no
downdraft?
The inflow strikes the underside of the conventional rotor disk, but
strikes the topside of the centrifugal fan disk. That's all!

I'm betting you'll find a way to avoid answering...
I did.


No surprise there.

So where are we? Your downward accelerated air might continue traveling
until it's stopped by the earth's surface, which is the only thing that
can stop it. But it isn't simply thrown down. Much of the finite energy
put into to the air is "wasted" in spinning it. Kinetic energy becomes heat.

And now you're just ducking.

Like you do, every time it's pointed out that when air is pushed down,
an equal volume of air must go UP? You then avoid saying "air flow" and
start grasping for other terms.

So how far down do you think air can flow before the ground is out of
reach? Forever?

In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
If there is no downwash, it will not fly. No.
You are arguing a point not under contention (at least with respect to
heavier-than-air aircraft.)

See everyone: this is why understanding of the actual facts is
required.
The ground isn't required. Air has inertia, and it's just as much a part
of the earth as dirt and rocks are. So why are you fixated on the
earth's solid surface? It compresses too, you know. You could argue that
the downforce travels through the whole planet and back into the
atmosphere in China.

You simply haven't really read anyone else's posts to understand what
they
are stating.
The previous poster just said:

"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?"

She ("Beryl"?)
A mineral

is clearly implying that such an hypothetical craft could remain
airborne
without downwash.
No, I only asked.

How else can it be read?
Read it as a question.
So what is your answer? Can the postulated craft fly if there is no
downdraft?
The inflow strikes the underside of the conventional rotor disk, but
strikes the topside of the centrifugal fan disk. That's all!

I'm betting you'll find a way to avoid answering...
I did.


No surprise there.

So where are we? Your downward accelerated air might continue traveling
until it's stopped by the earth's surface, which is the only thing that
can stop it. But it isn't simply thrown down. Much of the finite energy
put into to the air is "wasted" in spinning it. Kinetic energy becomes
heat.

And now you're just ducking.

Like you do, every time it's pointed out that when air is pushed down,
an equal volume of air must go UP? You then avoid saying "air flow" and
start grasping for other terms.

Eventually it must go up. After it has transferred its momentum to the
earth.

I'm sorry, but that is the reality of the situation.


So how far down do you think air can flow before the ground is out of
reach? Forever?

Essentially, yes. The fact is that if the aircraft and the Earth are to
remain the same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium by
which the aircraft can transmit that push.

And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that enters
downward gets turned to go sideways. That 90 degree turn can only be
accomplished by the a push upward from the aircraft and thus the air
must push down on the system with an equal but opposite force.

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

Alan Baker wrote:
Jim Logajan wrote:
Because the airplane and the Earth have zero relative vertical
velocity during straight and level flight, conservation of momentum
requires the net vertical flow of air to also be zero.

Therefore in subsonic flows where the fluid is assumed
incompressible, to the extent any fluid is moving downward,
conservation of mass requires an equal amount of mass must be moving
upward (the continuity requirement.)

Hence airplanes must cause air to move in circles.

Nope. Wrong.

The aircraft is experience an force upward the entire time it is in
flight. That force means there must be an equal force acting on the
air, and since the air was not moving vertically (in our idealized
case for this discussion) before the aircraft arrived, the force
exerted on it must mean that it is moving downward afterward it has
passed.

Nothing you wrote in your paragraph contradicts anything in my
paragraphs. So I'm at a loss therefore as to what specific statements you
claim are wrong. So how about I break it down into smaller claims and you
tell me which of these statements you agree with and which you disagree
with:

1) Conservation of momentum requires that at all times during flight that
net vertical momentum of the total system must be zero. Agree or
disagree?

2) We can treat air as incompressible, so conservation of mass means the
net vertical mass flow of the system during level flight must be zero.
Agree or disagree?

3) Therefore if, say, the downwash is 1 kg/s at any given instant due to
the wing, somewhere else in the fluid there must be an upwash at that
same instant of 1 kg/s. Agree or disagree?

4) Because upwash mass rate equals downwash mass rate, at some point the
downward flow reverses direction and becomes the upwash. Agree or
disagree?

Yes some deflection downward occurs. But I don't know that it could
be said to "diffuse" in any sense due to conservation of mass and
momentum requirements.

As the air the plane has forced downward encounters more air, the
momentum is diffused so that a greater and greater mass of air moves
downward at smaller and smaller velocities (net)...

...until it encounters the ground.

Keep in mind that balloons need no downwash to stay aloft. Yet we know
from conservation laws that the *static* pressure on the surface of the
earth must be increase due to their presence. Nothing you've written
rules out the possibility that the *dynamic* pressure of the downwash
translates into a *static* pressure increase well before the downwash
reaches the surface of the earth. The physics of the situation do not
seem to rule out that a priori.

In article ,
Jim Logajan wrote:

Alan Baker wrote:
Jim Logajan wrote:
Because the airplane and the Earth have zero relative vertical
velocity during straight and level flight, conservation of momentum
requires the net vertical flow of air to also be zero.

Therefore in subsonic flows where the fluid is assumed
incompressible, to the extent any fluid is moving downward,
conservation of mass requires an equal amount of mass must be moving
upward (the continuity requirement.)

Hence airplanes must cause air to move in circles.

Nope. Wrong.

The aircraft is experience an force upward the entire time it is in
flight. That force means there must be an equal force acting on the
air, and since the air was not moving vertically (in our idealized
case for this discussion) before the aircraft arrived, the force
exerted on it must mean that it is moving downward afterward it has
passed.

Nothing you wrote in your paragraph contradicts anything in my
paragraphs. So I'm at a loss therefore as to what specific statements you
claim are wrong. So how about I break it down into smaller claims and you
tell me which of these statements you agree with and which you disagree
with:

1) Conservation of momentum requires that at all times during flight that
net vertical momentum of the total system must be zero. Agree or
disagree?

2) We can treat air as incompressible, so conservation of mass means the
net vertical mass flow of the system during level flight must be zero.
Agree or disagree?

Agree, but that system needs to include the Earth itself, doesn't it?


3) Therefore if, say, the downwash is 1 kg/s at any given instant due to
the wing, somewhere else in the fluid there must be an upwash at that
same instant of 1 kg/s. Agree or disagree?

Agree. At the surface of the Earth.

4) Because upwash mass rate equals downwash mass rate, at some point the
downward flow reverses direction and becomes the upwash. Agree or
disagree?

Agree. At the surface of the Earth.


Yes some deflection downward occurs. But I don't know that it could
be said to "diffuse" in any sense due to conservation of mass and
momentum requirements.

As the air the plane has forced downward encounters more air, the
momentum is diffused so that a greater and greater mass of air moves
downward at smaller and smaller velocities (net)...

...until it encounters the ground.

Keep in mind that balloons need no downwash to stay aloft. Yet we know
from conservation laws that the *static* pressure on the surface of the
earth must be increase due to their presence. Nothing you've written
rules out the possibility that the *dynamic* pressure of the downwash
translates into a *static* pressure increase well before the downwash
reaches the surface of the earth. The physics of the situation do not
seem to rule out that a priori.

Conservation of momentum does.

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

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
If there is no downwash, it will not fly. No.
You are arguing a point not under contention (at least with respect to
heavier-than-air aircraft.)

See everyone: this is why understanding of the actual facts is
required.
The ground isn't required. Air has inertia, and it's just as much a part
of the earth as dirt and rocks are. So why are you fixated on the
earth's solid surface? It compresses too, you know. You could argue that
the downforce travels through the whole planet and back into the
atmosphere in China.

You simply haven't really read anyone else's posts to understand what
they
are stating.
The previous poster just said:

"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?"

She ("Beryl"?)
A mineral

is clearly implying that such an hypothetical craft could remain
airborne
without downwash.
No, I only asked.

How else can it be read?
Read it as a question.
So what is your answer? Can the postulated craft fly if there is no
downdraft?
The inflow strikes the underside of the conventional rotor disk, but
strikes the topside of the centrifugal fan disk. That's all!

I'm betting you'll find a way to avoid answering...
I did.

No surprise there.

So where are we? Your downward accelerated air might continue traveling
until it's stopped by the earth's surface, which is the only thing that
can stop it. But it isn't simply thrown down. Much of the finite energy
put into to the air is "wasted" in spinning it. Kinetic energy becomes
heat.
And now you're just ducking.
Like you do, every time it's pointed out that when air is pushed down,
an equal volume of air must go UP? You then avoid saying "air flow" and
start grasping for other terms.

Eventually it must go up. After it has transferred its momentum to the
earth.

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.

I'm sorry, but that is the reality of the situation.

Pressure waves can reach the ground, without the air in the column
descending to the ground.

So how far down do you think air can flow before the ground is out of
reach? Forever?

Essentially, yes.

How? A wing doesn't keep pushing down on a parcel of air forever. It
gives that air a shove, then it moves on. That downward-shoved air
pushes the air below it out of the way, not just down, but sideways.
Then the sideways-moving air shoves its neighboring air out of the way,
not just sideways, but down and up. Add all the "downs" and subtract all
the "ups" until there's nothing left.

The fact is that if the aircraft and the Earth are to remain the same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium by
which the aircraft can transmit that push.

Right. And I can push against the hill across the road with my voice.
Not much, but enough to move the diaphragm in a microphone over there,
in a split second. The air expelled from lungs is never going to make it
across the road.

And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that enters
downward gets turned to go sideways. That 90 degree turn can only be
accomplished by the a push upward from the aircraft and thus the air
must push down on the system with an equal but opposite force.

But is that 90 degree turn *exactly* the same as a 180 degree turn that
directs incoming air back in the opposite direction? No, so I'll just
turn my squirrel cage upside down with 180 degree flow redirection, and
get lift with no net downwash.

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:
In article ,
Jim Logajan wrote:

Alan Baker wrote:
If there is no downwash, it will not fly. No.
You are arguing a point not under contention (at least with respect
to
heavier-than-air aircraft.)

See everyone: this is why understanding of the actual facts is
required.
The ground isn't required. Air has inertia, and it's just as much a
part
of the earth as dirt and rocks are. So why are you fixated on the
earth's solid surface? It compresses too, you know. You could argue
that
the downforce travels through the whole planet and back into the
atmosphere in China.

You simply haven't really read anyone else's posts to understand
what
they
are stating.
The previous poster just said:

"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?"

She ("Beryl"?)
A mineral

is clearly implying that such an hypothetical craft could remain
airborne
without downwash.
No, I only asked.

How else can it be read?
Read it as a question.
So what is your answer? Can the postulated craft fly if there is no
downdraft?
The inflow strikes the underside of the conventional rotor disk, but
strikes the topside of the centrifugal fan disk. That's all!

I'm betting you'll find a way to avoid answering...
I did.

No surprise there.

So where are we? Your downward accelerated air might continue traveling
until it's stopped by the earth's surface, which is the only thing that
can stop it. But it isn't simply thrown down. Much of the finite energy
put into to the air is "wasted" in spinning it. Kinetic energy becomes
heat.
And now you're just ducking.
Like you do, every time it's pointed out that when air is pushed down,
an equal volume of air must go UP? You then avoid saying "air flow" and
start grasping for other terms.

Eventually it must go up. After it has transferred its momentum to the
earth.

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.

You've seen the edges curling back up. For anything with downward
momentum to start moving upward, something else has to start moving
downward.

Have you heard of "Conservation of Momentum"?


I'm sorry, but that is the reality of the situation.

Pressure waves can reach the ground, without the air in the column
descending to the ground.

I never said that the particular molecules that the aircraft touches are
the ones that have to reach the ground.


So how far down do you think air can flow before the ground is out of
reach? Forever?

Essentially, yes.

How? A wing doesn't keep pushing down on a parcel of air forever. It
gives that air a shove, then it moves on. That downward-shoved air
pushes the air below it out of the way, not just down, but sideways.
Then the sideways-moving air shoves its neighboring air out of the way,
not just sideways, but down and up. Add all the "downs" and subtract all
the "ups" until there's nothing left.

Look up "Conservation of Momentum" and get back to me.


The fact is that if the aircraft and the Earth are to remain the same
distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium by
which the aircraft can transmit that push.

Right. And I can push against the hill across the road with my voice.
Not much, but enough to move the diaphragm in a microphone over there,
in a split second. The air expelled from lungs is never going to make it
across the road.

No, sorry. You don't push the hill with your voice. The pressure waves
contain both positive and negative phases.


And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that enters
downward gets turned to go sideways. That 90 degree turn can only be
accomplished by the a push upward from the aircraft and thus the air
must push down on the system with an equal but opposite force.

But is that 90 degree turn *exactly* the same as a 180 degree turn that
directs incoming air back in the opposite direction? No, so I'll just
turn my squirrel cage upside down with 180 degree flow redirection, and
get lift with no net downwash.

No, you won't.

No downwash, no lift. No go learn something.

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

Alan Baker wrote:
In article , Beryl
wrote:
...

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.

You've seen the edges curling back up.

That photo shows ALL of the flow curling back up. The bottom of the
vortex couldn't be any clearer, and there's nothing extending further
down underneath it.

Pressure waves can reach the ground, without the air in the column
descending to the ground.

I never said that the particular molecules that the aircraft touches
are the ones that have to reach the ground.

You said "The net flow is downward until it hits the ground and the
momentum is transfer to the earth."

The molecules that "reach" the ground are the ones that
were *already there* at ground level.

The fact is that if the aircraft and the Earth are to remain the
same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium
by which the aircraft can transmit that push.

Right. And I can push against the hill across the road with my
voice. Not much, but enough to move the diaphragm in a microphone
over there, in a split second. The air expelled from lungs is never
going to make it across the road.

No, sorry. You don't push the hill with your voice.

Of course I do.

The pressure waves contain both positive and negative phases.

So you think that a positive won't push because a negative will be
coming along shortly?

And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that
enters downward gets turned to go sideways. That 90 degree turn
can only be accomplished by the a push upward from the aircraft
and thus the air must push down on the system with an equal but
opposite force.
But is that 90 degree turn *exactly* the same as a 180 degree turn
that directs incoming air back in the opposite direction? No, so
I'll just turn my squirrel cage upside down with 180 degree flow
redirection, and get lift with no net downwash.

No, you won't.

No downwash, no lift. No go learn something.

Let's learn here. From you. Is that 90 degree turn *exactly* the same as
a 180 degree turn that directs incoming air back in the opposite direction?

In article ,
Beryl wrote:

Alan Baker wrote:
In article , Beryl
wrote:
...

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.

You've seen the edges curling back up.

That photo shows ALL of the flow curling back up. The bottom of the
vortex couldn't be any clearer, and there's nothing extending further
down underneath it.

Sorry, but you're wrong.

First of all, the downward motion of the vortex clearly carries right
out the bottom of the frame. Second, I've stated all along that as time
passes the momentum is diffused among more and more air.



Pressure waves can reach the ground, without the air in the column
descending to the ground.

I never said that the particular molecules that the aircraft touches
are the ones that have to reach the ground.

You said "The net flow is downward until it hits the ground and the
momentum is transfer to the earth."

And it is: the *net* flow.


The molecules that "reach" the ground are the ones that
were *already there* at ground level.

I never implied that the same molecules are the ones that eventually
strike the ground.


The fact is that if the aircraft and the Earth are to remain the
same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium
by which the aircraft can transmit that push.

Right. And I can push against the hill across the road with my
voice. Not much, but enough to move the diaphragm in a microphone
over there, in a split second. The air expelled from lungs is never
going to make it across the road.

No, sorry. You don't push the hill with your voice.

Of course I do.

The pressure waves contain both positive and negative phases.

So you think that a positive won't push because a negative will be
coming along shortly?

I think their will be no net push, yes.

See the difference: sound waves, no net flow: no net push.


And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that
enters downward gets turned to go sideways. That 90 degree turn
can only be accomplished by the a push upward from the aircraft
and thus the air must push down on the system with an equal but
opposite force.
But is that 90 degree turn *exactly* the same as a 180 degree turn
that directs incoming air back in the opposite direction? No, so
I'll just turn my squirrel cage upside down with 180 degree flow
redirection, and get lift with no net downwash.

No, you won't.

No downwash, no lift. No go learn something.

Let's learn here. From you. Is that 90 degree turn *exactly* the same as
a 180 degree turn that directs incoming air back in the opposite direction?

Read this:

"To determine [the angle represented by a greek letter in the original
text], we observe that no downwash is generated when the wing generates
no lift."

http://www.aoe.vt.edu/~cwoolsey/Cour...al/Aerodynamic
Properties.pdf

Read it over and over again until you get it.

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

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article , Beryl
wrote:
...

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.
You've seen the edges curling back up.
That photo shows ALL of the flow curling back up. The bottom of the
vortex couldn't be any clearer, and there's nothing extending further
down underneath it.

Sorry, but you're wrong.

First of all, the downward motion of the vortex clearly carries right
out the bottom of the frame.

Are you impaired? The airplane is approaching the camera. The camera is
looking up at the airplane. The bottom of the frame contains the distant
background. Objects farther than the airplane appear lower in the frame.
If the camera was above the approaching airplane and looking down at
it, distant objects would appear higher in the frame than the airplane.

Second, I've stated all along that as time passes the momentum is diffused among more and more air.

Yes, you don't explain much, but you do stick to whatever you've said.

Pressure waves can reach the ground, without the air in the column
descending to the ground.
I never said that the particular molecules that the aircraft touches
are the ones that have to reach the ground.
You said "The net flow is downward until it hits the ground and the
momentum is transfer to the earth."

And it is: the *net* flow.

The "net" flow is circulating air. Circulation circulates. It doesn't go
somewhere and stay there. The "net" displacement is zero.

The molecules that "reach" the ground are the ones that
were *already there* at ground level.

I never implied that the same molecules are the ones that eventually
strike the ground.

So then, the net flow stops when "it" hits the ground.
"It" isn't the molecules that the wing touches.
Would "it" be the molecules at the bottom of the air column? (they're
already on the ground)
Identify "it" and maybe we'll know when the flow stops.

The fact is that if the aircraft and the Earth are to remain the
same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium
by which the aircraft can transmit that push.
Right. And I can push against the hill across the road with my
voice. Not much, but enough to move the diaphragm in a microphone
over there, in a split second. The air expelled from lungs is never
going to make it across the road.
No, sorry. You don't push the hill with your voice.
Of course I do.

The pressure waves contain both positive and negative phases.
So you think that a positive won't push because a negative will be
coming along shortly?

I think their will be no net push, yes.

There will be two pushes. There will be no net displacement.

See the difference: sound waves, no net flow: no net push.

"No net push" doesn't make much sense here. There are opposing pushes,
but at _different_ times. That's the difference. By your reasoning,
microphones wouldn't work because the diaphragms inside won't move.

And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that
enters downward gets turned to go sideways. That 90 degree turn
can only be accomplished by the a push upward from the aircraft
and thus the air must push down on the system with an equal but
opposite force.
But is that 90 degree turn *exactly* the same as a 180 degree turn
that directs incoming air back in the opposite direction? No, so
I'll just turn my squirrel cage upside down with 180 degree flow
redirection, and get lift with no net downwash.
No, you won't.

No downwash, no lift. No go learn something.
Let's learn here. From you. Is that 90 degree turn *exactly* the same as
a 180 degree turn that directs incoming air back in the opposite direction?

Read this:

"To determine [the angle represented by a greek letter in the original
text], we observe that no downwash is generated when the wing generates
no lift."

I'm not disagreeing with that. I'll rephrase it, and say no circulation
is generated. It is not even relevant.

http://www.aoe.vt.edu/~cwoolsey/Cour...al/Aerodynamic
Properties.pdf

Read it over and over again until you get it.

Get what? It's about wings and geometry. Find something about air moving
through air.

In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
In article , Beryl
wrote:
...

You've seen pics of it curling right back up.
http://www.efluids.com/efluids/gallery/gallery_pages/Morris_4.jsp
It hasn't bounced off the ground.
You've seen the edges curling back up.
That photo shows ALL of the flow curling back up. The bottom of the
vortex couldn't be any clearer, and there's nothing extending further
down underneath it.

Sorry, but you're wrong.

First of all, the downward motion of the vortex clearly carries right
out the bottom of the frame.

Are you impaired? The airplane is approaching the camera. The camera is
looking up at the airplane. The bottom of the frame contains the distant
background. Objects farther than the airplane appear lower in the frame.
If the camera was above the approaching airplane and looking down at
it, distant objects would appear higher in the frame than the airplane.

None of which refutes what I said.


Second, I've stated all along that as time passes the momentum is diffused
among more and more air.

Yes, you don't explain much, but you do stick to whatever you've said.

Because it's the truth.

Look up "conservation of momentum".


Pressure waves can reach the ground, without the air in the column
descending to the ground.
I never said that the particular molecules that the aircraft touches
are the ones that have to reach the ground.
You said "The net flow is downward until it hits the ground and the
momentum is transfer to the earth."

And it is: the *net* flow.

The "net" flow is circulating air. Circulation circulates. It doesn't go
somewhere and stay there. The "net" displacement is zero.

No. If there were no net displacement, there would be no net change in
momentum. No net change in momentum means no force down on the air by
the aircraft. No force down on the air means no force up on the aircraft.


The molecules that "reach" the ground are the ones that
were *already there* at ground level.

I never implied that the same molecules are the ones that eventually
strike the ground.

So then, the net flow stops when "it" hits the ground.
"It" isn't the molecules that the wing touches.

Correct.

Would "it" be the molecules at the bottom of the air column? (they're
already on the ground)
Identify "it" and maybe we'll know when the flow stops.

The movement of air downward is "it".


The fact is that if the aircraft and the Earth are to remain the
same distance apart, the plane must "push" against the Earth
with a force equal to the force of gravity. The air is the medium
by which the aircraft can transmit that push.
Right. And I can push against the hill across the road with my
voice. Not much, but enough to move the diaphragm in a microphone
over there, in a split second. The air expelled from lungs is never
going to make it across the road.
No, sorry. You don't push the hill with your voice.
Of course I do.

The pressure waves contain both positive and negative phases.
So you think that a positive won't push because a negative will be
coming along shortly?

I think their will be no net push, yes.

There will be two pushes. There will be no net displacement.

See the difference: sound waves, no net flow: no net push.

"No net push" doesn't make much sense here. There are opposing pushes,
but at _different_ times. That's the difference. By your reasoning,
microphones wouldn't work because the diaphragms inside won't move.

And to explain to you why your hypothetical craft with the radial
exhaust of air from a centrifugal fan won't work. The air that
enters downward gets turned to go sideways. That 90 degree turn
can only be accomplished by the a push upward from the aircraft
and thus the air must push down on the system with an equal but
opposite force.
But is that 90 degree turn *exactly* the same as a 180 degree turn
that directs incoming air back in the opposite direction? No, so
I'll just turn my squirrel cage upside down with 180 degree flow
redirection, and get lift with no net downwash.
No, you won't.

No downwash, no lift. No go learn something.
Let's learn here. From you. Is that 90 degree turn *exactly* the same as
a 180 degree turn that directs incoming air back in the opposite
direction?

Read this:

"To determine [the angle represented by a greek letter in the original
text], we observe that no downwash is generated when the wing generates
no lift."

I'm not disagreeing with that. I'll rephrase it, and say no circulation
is generated. It is not even relevant.

http://www.aoe.vt.edu/~cwoolsey/Cour...al/Aerodynamic
Properties.pdf

Read it over and over again until you get it.

Get what? It's about wings and geometry. Find something about air moving
through air.

"To determine [the angle represented by a greek letter in the original
text], we observe that no downwash is generated when the wing generates
no lift." isn't about air moving?

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