visualisation of the lift distribution over a wing

In article ,
cavelamb wrote:

Jim Logajan wrote:
Alan Baker wrote:
Look if you think that conservation of *mass* plays any role in this,
you're missing out from the start. It's conservation of *momentum*
that's in play here.

It appears you have never studied fluid dynamics (maybe elementary fluid
statics?) and I doubt that you own any books on the subject.

The aircraft has a force exerted on it equal to its weight. That means
that the aircraft must be exerting a force on the air in the opposite
direction.

In other news, 1 + 1 = 2.

That means that there is a constant change of momentum being done on
the air by the aircraft. That means air *must* be moving down (net)
after the aircraft has passed.

You must have a devil of a time figuring out what keeps balloons afloat,
what with no handy downward moving air!

(Just FYI, imagine a ~957 kg (Fg ~= 9379 N) helicopter dropped from a
balloon from 3,000 m altitude (rho ~= 0.83 kg/m^3) and it's engine
immediately started. After a small drop it levels out and maintains a
downwash of air moving through its 6 m diameter disk (A ~= 28 m^2)
at, say, 20 m/s. (So m_dot ~= 469 kg/s and hence Fe = Fg.)

It would take ~150 s for that downwash to reach the ground if it
maintained that speed. In the mean time, once the helicopter stopped
descending, conservation of mass in an incompressible fluid seems to
require an equal volume of air to have an upward vector of 20 m/s. So
the surface of earth appears to be irrelevant for over two minutes.)
Nope.

Dang - I try to use real numbers to establish a baseline example, and you
manage to use a single word to demolish my attempts! Really helpful
mathematical counter-example you produced - not.

The conservation of momentum says that there cannot be an equal amount
of air moving upward at an equal speed.

I don't know what your problem is - maybe you are thinking this is a
rocket problem where no external fluids are involved and you can't get
your mind around the fact that THIS ISN'T A BLOODY ROCKET PROBLEM.
Whatever the case, you seem to be fixated on applying one conservation
law to one element in the entire system to the exclusion of everything
else.

Best of luck to you.



Two dimensional Newtonian thinking in a three dimensional non-Newtonian world.

LOL

Sorry, caveman....


But conservation of momentum works well enough at the speeds at which
aircraft operate.

And Newton's laws tell us all we need to know.

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

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
...
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.
Oh, it was simply interesting to you that the vortex goes off into the
distance, right out the bottom of the picture.

No. That shows that the air continues to move downward far below the
small portion of the vortex which is moving up.

No it doesn't. Perspective shows nothing. If the camera was above the
approaching airplane and looking down at it, the picture would show that
the air continues to move upward far above the small portion of the
vortex which is showing up.

Alan Baker wrote:

It's true that the exhaust stream doesn't directly push on the inner
surface of a rocket engine.

Yeah, I like that aerospike design, the inside-out nozzle thing.

wing encounters some unmoving air, and the wing then throws the air
downwards, the velocity of the air has been changed, and the wing
will experience an upwards reaction force. At the same time, a
downwash- flow is created.

The wing, remember, is moving forward. "Downwards" is one component of
circulation.

Alan Baker wrote:
In article ,
Jim Logajan wrote:

You must have a devil of a time figuring out what keeps balloons afloat,
what with no handy downward moving air!

I have no trouble figuring that out at all. A gas of a different density
within the balloon causes the net upward force on the balloon exerted by
the air outside the balloon to be greater than the net downward force on
it.

Nope! The "gas of a different density" inside does not cause the
differential forces exerted by the air outside. Whether the balloon is
filled with phlogiston or concrete, the difference between upward and
downward forces exerted by the air outside depends on the height of the
balloon. That's what my goofy 10,000 foot thick wing was, that would
take off with no airspeed or power. A balloon.

In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:
...
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.
Oh, it was simply interesting to you that the vortex goes off into the
distance, right out the bottom of the picture.

No. That shows that the air continues to move downward far below the
small portion of the vortex which is moving up.

No it doesn't. Perspective shows nothing. If the camera was above the
approaching airplane and looking down at it, the picture would show that
the air continues to move upward far above the small portion of the
vortex which is showing up.

LOL

Perspective would show the same amount of movement at greater and
greater distances as less and less absolute distance on the picture.

But the downward flow goes right off the bottom of the page...

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

In article ,
Beryl wrote:

Alan Baker wrote:

It's true that the exhaust stream doesn't directly push on the inner
surface of a rocket engine.

Yeah, I like that aerospike design, the inside-out nozzle thing.

wing encounters some unmoving air, and the wing then throws the air
downwards, the velocity of the air has been changed, and the wing
will experience an upwards reaction force. At the same time, a
downwash- flow is created.

The wing, remember, is moving forward. "Downwards" is one component of
circulation.

Those weren't my words.

Yes, but Newton's laws tell us that there is a net force down on the
air. No net force down on the air, no net force up on the plane.

Force is change of momentum with respect to time.

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

In article ,
Beryl wrote:

Alan Baker wrote:
In article ,
Jim Logajan wrote:

You must have a devil of a time figuring out what keeps balloons afloat,
what with no handy downward moving air!

I have no trouble figuring that out at all. A gas of a different density
within the balloon causes the net upward force on the balloon exerted by
the air outside the balloon to be greater than the net downward force on
it.

Nope! The "gas of a different density" inside does not cause the
differential forces exerted by the air outside. Whether the balloon is
filled with phlogiston or concrete, the difference between upward and
downward forces exerted by the air outside depends on the height of the
balloon. That's what my goofy 10,000 foot thick wing was, that would
take off with no airspeed or power. A balloon.

You're wrong.

The "net downward force" includes the force of gravity. Which is
lessened because a gas of lower density..

....I can't believe I have to explain things so basic.

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

In article ,
Alan Baker wrote:

In article ,
Beryl wrote:

Alan Baker wrote:

It's true that the exhaust stream doesn't directly push on the inner
surface of a rocket engine.

Yeah, I like that aerospike design, the inside-out nozzle thing.

wing encounters some unmoving air, and the wing then throws the air
downwards, the velocity of the air has been changed, and the wing
will experience an upwards reaction force. At the same time, a
downwash- flow is created.

The wing, remember, is moving forward. "Downwards" is one component of
circulation.

Those weren't my words.

Yes, but Newton's laws tell us that there is a net force down on the
air. No net force down on the air, no net force up on the plane.

Force is change of momentum with respect to time.

BTW, the man whom you are contradicting is Scott Eberhardt, Bachelors &
Masters Degrees in Aeronautics and Astronautics from MIT, Ph.D. in the
same field from Stanford, research scientist at the NASA Ames Research
Center, faculty of the University of Washington.

But... ...really...

http://books.google.com/books?id=wmu...T5&dq=Scott+Eb
erhardt+aeronautics+and+astronautics&source=bl&ots =skN-zbDvej&sig=msQ-_Im
p6t-P62ehNWIld7RRYWs&hl=en&ei=GgEeS4f4AYzStgPB5eiCCg&s a=X&oi=book_result&
ct=result&resnum=6&ved=0CBsQ6AEwBQ#v=onepage&q=dow nwash&f=false

....what would *HE* know about it compared to you?

LOL

--
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:
...
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.
Oh, it was simply interesting to you that the vortex goes off into the
distance, right out the bottom of the picture.
No. That shows that the air continues to move downward far below the
small portion of the vortex which is moving up.
No it doesn't. Perspective shows nothing. If the camera was above the
approaching airplane and looking down at it, the picture would show that
the air continues to move upward far above the small portion of the
vortex which is showing up.

LOL

Perspective would show the same amount of movement at greater and
greater distances as less and less absolute distance on the picture.

You're talking about a vanishing point. Has nothing to do with this.

But the downward flow goes right off the bottom of the page...

Because the viewer is looking up at it!

Look!!!
http://www.efluids.com/efluids/galle...essnajet_1.htm
OMG the downward flow went up!!!

Alan Baker wrote:
In article ,
Beryl wrote:

Alan Baker wrote:

It's true that the exhaust stream doesn't directly push on the inner
surface of a rocket engine.
Yeah, I like that aerospike design, the inside-out nozzle thing.

wing encounters some unmoving air, and the wing then throws the air
downwards, the velocity of the air has been changed, and the wing
will experience an upwards reaction force. At the same time, a
downwash- flow is created.
The wing, remember, is moving forward. "Downwards" is one component of
circulation.

Those weren't my words.

What do you suppose happens to "downwash" when it goes up? Say, pulling
positive G force at the top of a loop? Now you lost the surface of the
earth, the only thing that, according to you, finally stops it.