visualisation of the lift distribution over a wing

In article ,
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.

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

Alan Baker schreef:

No.

Yawn.

Alan Baker wrote:
In article ,
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.

Ok, so there is a low pressure field above the wing,
and the wing is pressed up from underneath.

So, just out of curiosity, what happens to the air
that was in the low pressure field above the wing -
after the wing passes?

Does it just magically co back to it's old ways
(and places)?

And the air that was in the high pressure field under
the wing?

After the wing passes, is it unaffected as well?

cavelamb wrote:
Ok, so there is a low pressure field above the wing,
and the wing is pressed up from underneath.

So, just out of curiosity, what happens to the air
that was in the low pressure field above the wing -
after the wing passes?

Does it just magically co back to it's old ways
(and places)?

And the air that was in the high pressure field under
the wing?

After the wing passes, is it unaffected as well?

It's all a slowly descending smoke ring. If the earth was "the only
thing that finally stops it" as Alan says, none of the ring's energy
would be lost as it pushes through the surrounding air to reach the earth.

http://www.av8n.com/how/htm/airfoils.html#sec-circulation-vortices
Figure 3.27 ties the wingtip vortices in with the rest of the
circulation pattern, showing the whole smoke ring in red.

Also look up at section Section 3.11,
http://www.av8n.com/how/htm/airfoils.html#sec-spinners
Add the Fluttering Card circulation, Figure 3.25, to familiar tip
vortices, and you get the whole ring.

Other articles do a nice job explaining tip vortices or downwash behind
the wing as isolated subjects, but that's where they end their stories.

Alan Baker wrote:
Jim Logajan wrote:
Alan Baker wrote:
Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.

That assertion is incorrect. You are no dummy so I'm sure you'll
correct it when you realize the errors.

Sorry, but it's not. Pressure is created by particle collisions.

Brian Whatcott already addressed one of the errors I had in mind. The other
I had in mind was your incorrect assertion "*by definition*". You should
have asserted "*by derivation*". College level texts on statistical and
thermal physics *derive* the gas laws from statistical mechanics; they do
not present them as true "by definition." (Though that would make for short
textbooks!)

Alan Baker wrote:
In article ,
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.

It's also deflected upward. ;-)

Here's why:
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.

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.

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.

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.

That assertion is not true in general. What appears to happen instead is
that any downward deflection is quickly reversed, leading to what is
known as a shed vortex. Here are some links on the subject:

http://www.grc.nasa.gov/WWW/K-12/airplane/shed.html
http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

While the deflected flow doesn't need to reach the surface of the earth
for the airplane to stay aloft, an increase in air _pressure_ would
eventually make its way to the surface.

Beryl wrote:
cavelamb wrote:
Ok, so there is a low pressure field above the wing,
and the wing is pressed up from underneath.

So, just out of curiosity, what happens to the air
that was in the low pressure field above the wing -
after the wing passes?

Does it just magically co back to it's old ways
(and places)?

And the air that was in the high pressure field under
the wing?

After the wing passes, is it unaffected as well?

It's all a slowly descending smoke ring. If the earth was "the only
thing that finally stops it" as Alan says, none of the ring's energy
would be lost as it pushes through the surrounding air to reach the earth.

http://www.av8n.com/how/htm/airfoils.html#sec-circulation-vortices
Figure 3.27 ties the wingtip vortices in with the rest of the
circulation pattern, showing the whole smoke ring in red.

Also look up at section Section 3.11,
http://www.av8n.com/how/htm/airfoils.html#sec-spinners
Add the Fluttering Card circulation, Figure 3.25, to familiar tip
vortices, and you get the whole ring.

Other articles do a nice job explaining tip vortices or downwash behind
the wing as isolated subjects, but that's where they end their stories.


I've seen the results first hand.

Flying along just above a smooth cloud surface at high subsonic,
the "wake" behind the leader makes a shallow trough in the cloud,
then the edges swirl back up into the tip vortices.

The high pressure air underneath rebounds up, and the low pressure
field above the wing rebounds back down.

Net result = zero.

In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
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.

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

In article ,
cavelamb wrote:

Beryl wrote:
cavelamb wrote:
Ok, so there is a low pressure field above the wing,
and the wing is pressed up from underneath.

So, just out of curiosity, what happens to the air
that was in the low pressure field above the wing -
after the wing passes?

Does it just magically co back to it's old ways
(and places)?

And the air that was in the high pressure field under
the wing?

After the wing passes, is it unaffected as well?

It's all a slowly descending smoke ring. If the earth was "the only
thing that finally stops it" as Alan says, none of the ring's energy
would be lost as it pushes through the surrounding air to reach the earth.

http://www.av8n.com/how/htm/airfoils.html#sec-circulation-vortices
Figure 3.27 ties the wingtip vortices in with the rest of the
circulation pattern, showing the whole smoke ring in red.

Also look up at section Section 3.11,
http://www.av8n.com/how/htm/airfoils.html#sec-spinners
Add the Fluttering Card circulation, Figure 3.25, to familiar tip
vortices, and you get the whole ring.

Other articles do a nice job explaining tip vortices or downwash behind
the wing as isolated subjects, but that's where they end their stories.


I've seen the results first hand.

Flying along just above a smooth cloud surface at high subsonic,
the "wake" behind the leader makes a shallow trough in the cloud,
then the edges swirl back up into the tip vortices.

The high pressure air underneath rebounds up, and the low pressure
field above the wing rebounds back down.

Net result = zero.

Sorry, but wrong.

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