visualisation of the lift distribution over a wing
Stealth Pilot
admittedly it is an FA18 but it still comfirms classic lift theory
http://www.airshowaction.com/axalp07/axalp07_227.jpg
Stealth Pilot
4p1e
wrote:
> admittedly it is an FA18 but it still comfirms classic lift theory
>
> http://www.airshowaction.com/axalp07/axalp07_227.jpg
>
> Stealth Pilot
Stealth - I have posted the site address to
http://eng-tips.com/viewthread.cfm?qid=251055&page=1 for their
viewing.
Thanks - good stuff.
Wright1902glider
> On Aug 1, 7:59 am, Stealth Pilot <notranspon...@aeroplanes.com.au>
> wrote:
>
> > admittedly it is an FA18 but it still comfirms classic lift theory
>
it creates a difference in airspeed between the air on top of the wing
and the air underneath it (relative to gravity or G-forces) which
creates the difference in air pressure which causes what we call
"lift". On hot humid days, reducing air pressure enough can cause
condensation to form. Some people say it even causes clouds.
Now before you flame me, remember that I did not say that a wing does
not deflect some air downward (assuming down is the side toward the
gravity). Only that thats not the primary source of "lift". Which of
course has been known to science since two guys stuck a fan in the end
of a box and blew around a bunch of old hacksaw blades.
Harry Frey
vaughn
"Wright1902glider" <wright19...@aol.com> wrote in message
news:aa5b89e2-c650-43cb...@m7g2000prd.googlegroups.com...
>
>Amen! I say to thee, a wing does NOT fly by pushing air down. Rather,
>it creates a difference in airspeed between the air on top of the wing
>and the air underneath it (relative to gravity or G-forces) which
>creates the difference in air pressure which causes what we call
>"lift".
I decided years ago to "stop deciding" and just believe that life comes
from both theories. If you only look at the picture that started this
thread, you will be left with no doubt about classic lift theory, but if you
had spent as many hours as I have at the back end of a glider tow rope, you
would know that the wake of an airplane is strongly deflected (accelerated)
downward. (New airplane pilots learn about wake turbulence from pictures in
books, but glider CFIs must take their students into the real thing on a
daily basis.) Flying a short distance behind a tow plane, I am always
flying in clean air unless I fly considerably *below* the tow plane.
Even though I know better, from inside a glider on tow it sure looks like
an airplane's lift comes from pushing air down.
Vaughn
Dan D
"vaughn" <vaughnsimo...@gmail.FAKE.com> wrote in message news:h5d55v$5ps$1...@aioe.org...
Hope to do the glider rating thing next year. Sounds like a good add on and BFR resetter...
Equal and opposite reaction, momentum theory, etc. The low pressure on top causes the air to deflect down...and I go up!
Nothing like 720 power turns bumping through the second 360 as you go through your own wake...
Orval Fairbairn
<aa5b89e2-c650-43cb...@m7g2000prd.googlegroups.com>,
Wright1902glider <wright19...@aol.com> wrote:
Actually, both models describe the same phenomenon. The Bernoulli
principle explains the detailed mechanics of lift, while the momentum
exchange model explains the end product physics of lift. After all, a
symmetric airfoil generates lift by angle of attack, as does the "flat
plate" airfoil, with zero camber.
--
Remove _'s from email address to talk to me.
Alan Baker
<aa5b89e2-c650-43cb...@m7g2000prd.googlegroups.com>,
Wright1902glider <wright19...@aol.com> wrote:
You are -- I regret to tell you -- entirely wrong.
Lift is only created if air is deflected downward.
--
Alan Baker
Vancouver, British Columbia
<http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
Stealth Pilot
although that all happens as you describe it is the air below pushing
you up that lifts the wing.
Stealth Pilot
Jim Logajan
> Amen! I say to thee, a wing does NOT fly by pushing air down. Rather,
> it creates a difference in airspeed between the air on top of the wing
> and the air underneath it (relative to gravity or G-forces) which
> creates the difference in air pressure which causes what we call
> "lift".
Well then, you'd better contact NASA and tell them they need to correct the
following:
"Lift occurs when a moving flow of gas is turned by a solid object. The
flow is turned in one direction, and the lift is generated in the opposite
direction, according to Newton's Third Law of action and reaction."
Quoted from:
http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
"Lift is created by deflecting a flow of air,"
Quoted from:
http://www.grc.nasa.gov/WWW/K-12/airplane/momntm.html
> On hot humid days, reducing air pressure enough can cause
> condensation to form. Some people say it even causes clouds.
Inserting the word "adiabatically" right after the word "pressure" make the
above a more reasonable assertion.
> Now before you flame me,
Too late! :-)
> remember that I did not say that a wing does
> not deflect some air downward (assuming down is the side toward the
> gravity). Only that thats not the primary source of "lift". Which of
> course has been known to science since two guys stuck a fan in the end
> of a box and blew around a bunch of old hacksaw blades.
Different physical situations. Incorrect analogy.
brian whatcott
>
> Wright1902glider <wright19...@aol.com> wrote:
>> Amen! I say to thee, a wing does NOT fly by pushing air down. Rather,
>> it creates a difference in airspeed between the air on top of the wing
>> and the air underneath it (relative to gravity or G-forces) which
>> creates the difference in air pressure which causes what we call
>> "lift". .....
>> Harry Frey
>
> Actually, both models describe the same phenomenon. The Bernoulli
> principle explains the detailed mechanics of lift, while the momentum
> exchange model explains the end product physics of lift. After all, a
> symmetric airfoil generates lift by angle of attack, as does the "flat
> plate" airfoil, with zero camber.
>
What he said
Brian W
brian whatcott
> /snip/ it is the air below pushing
> you up that lifts the wing.
> Stealth Pilot
In most circumstances, suction on the upper surface contributes about
2/3 rds of the lift, and pressure on the lower surface contributes about
1/3 rd.
That's one reason which rib stitching for rag wings is a biggy.
Brian W
cavelamb
At high angle of attach - maybe 1/3 on the bottom.
Especially along the leading edge.
At cruise, I believe the lower surface is closer to ambient pressure.
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
Ummmm...
It sort of depends what you mean.
If you mean that suction is actually providing an upward force, you're
quite mistaken.
If you mean that the difference in pressure between upper and lower
surfaces is 2/3 the result of lower pressure on the upper surface, then
you might be right. I don't know.
brian whatcott
> In article <ZNSdnV72vMzGVIzW...@giganews.com>,
> brian whatcott <bet...@sbcglobal.net> wrote:
>
>> Stealth Pilot wrote:
>>> /snip/ it is the air below pushing
>>> you up that lifts the wing.
>>> Stealth Pilot
>> In most circumstances, suction on the upper surface contributes about
>> 2/3 rds of the lift, and pressure on the lower surface contributes about
>> 1/3 rd.
>> That's one reason which rib stitching for rag wings is a biggy.
>>
>> Brian W
>
> Ummmm...
>
> It sort of depends what you mean.
>
> If you mean that suction is actually providing an upward force, you're
> quite mistaken.
>
> If you mean that the difference in pressure between upper and lower
> surfaces is 2/3 the result of lower pressure on the upper surface, then
> you might be right. I don't know.
>
Interesting comment: what would YOU call it when the fabric on the upper
wing surface wants to pull away from the ribs?
Brian W
Scott
It's the "wind" blowing through the bottom surface, inflating the wing
like a balloon ;)
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
Air pressure from inside the wing pushing up on it more than the air
above is pushing down...
Morgans
"Alan Baker" <alang...@telus.net> wrote
> Air pressure from inside the wing pushing up on it more than the air
> above is pushing down...
I hope you are pulling someone's leg, and that your are not that inept in
the field of aerodynamics and physics.
--
Jim in NC
Alan Baker
"Morgans" <jsmo...@charterJUNK.net> wrote:
No, I'm quite serious.
The reduction in *pressure* on the upper surface of the wing cannot
produce any force except downward. A perfect vacuum over the entire
upper surface wouldn't produce any upward force, but simply *zero*
force; allowing the upward force on the lower surface to act alone.
Anyone who thinks that the pressure of a fluid on a surface can act in
any direction but towards the surface is simply wrong.
brian whatcott
>>>
>> Interesting comment: what would YOU call it when the fabric on the upper
>> wing surface wants to pull away from the ribs?
>
> Air pressure from inside the wing pushing up on it more than the air
> above is pushing down...
>
Let me take a wild guess here: you did physics for an uundergraduate
degree. Is that right?
Brian W
Steve Hix
brian whatcott <bet...@sbcglobal.net> wrote:
> Alan Baker wrote:
>
> >>>
> >> Interesting comment: what would YOU call it when the fabric on the upper
> >> wing surface wants to pull away from the ribs?
> >
> > Air pressure from inside the wing pushing up on it more than the air
> > above is pushing down...
For a couple of seconds, perhaps.
Wings aren't typically hermetically sealed.
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
No. But it doesn't matter.
If the fabric is moving upward, it can only be because there is more
pressure on its bottom surface than there is on its top surface.
cavelamb
I'll take Physics Majors for $500, Alex!
cavelamb
> In article <AKmdnVkk8d03gI7W...@giganews.com>,
> brian whatcott <bet...@sbcglobal.net> wrote:
>
>> Alan Baker wrote:
>>
>>>> Interesting comment: what would YOU call it when the fabric on the upper
>>>> wing surface wants to pull away from the ribs?
>>> Air pressure from inside the wing pushing up on it more than the air
>>> above is pushing down...
>>>
>>
>> Let me take a wild guess here: you did physics for an uundergraduate
>> degree. Is that right?
>>
>> Brian W
>
> No. But it doesn't matter.
>
> If the fabric is moving upward, it can only be because there is more
> pressure on its bottom surface than there is on its top surface.
>
I'm kind of curious about how that higher pressure got on the bottom
of that wing though...
brian whatcott
> In article <AKmdnVkk8d03gI7W...@giganews.com>,
> brian whatcott <bet...@sbcglobal.net> wrote:
>
>> Alan Baker wrote:
>>
>>>> Interesting comment: what would YOU call it when the fabric on the upper
>>>> wing surface wants to pull away from the ribs?
>>> Air pressure from inside the wing pushing up on it more than the air
>>> above is pushing down...
>>>
>>
>> Let me take a wild guess here: you did physics for an uundergraduate
>> degree. Is that right?
>>
>> Brian W
>
> No. But it doesn't matter.
>
> If the fabric is moving upward, it can only be because there is more
> pressure on its bottom surface than there is on its top surface.
>
It seems that you are uncomfortable with the entire concept of suction.
For example, how do you suppose suction cups work?
Or how about a suction pump that happens to be limited to a 30 ft lift?
Well duh, it's also atmospheric pressure that enables suction pumps and
suction cups etc., etc. Yes indeed , but it's an academic issue at
the junior high level, isn't it?
Brian W
Morgans
"Alan Baker" <alang...@telus.net> wrote
>
> Anyone who thinks that the pressure of a fluid on a surface can act in
> any direction but towards the surface is simply wrong.
I see. You are not lookng at the wing as a system, but taking an
observation at one point only, without reguard to what is happening around
it.
Point made.
--
Jim in NC
Beryl
He looked inside the wing, at the entire upper surface, at the lower
surface... that pretty much covers most of it. Air can't be in tension.
cavelamb
> Alan Baker wrote:
>> In article <AKmdnVkk8d03gI7W...@giganews.com>,
>> brian whatcott <bet...@sbcglobal.net> wrote:
>>
>>> Alan Baker wrote:
>>>
>>>>> Interesting comment: what would YOU call it when the fabric on the
>>>>> upper wing surface wants to pull away from the ribs?
>>>> Air pressure from inside the wing pushing up on it more than the air
>>>> above is pushing down...
>>>>
>>>
>>> Let me take a wild guess here: you did physics for an uundergraduate
>>> degree. Is that right?
>>>
>>> Brian W
>>
>> No. But it doesn't matter.
>>
>> If the fabric is moving upward, it can only be because there is more
>> pressure on its bottom surface than there is on its top surface.
>>
Have you ever seen the top surface of a fabric covered wing?
The skin does not bulge upwards.
Not usually anyway.
Jim Logajan
> Air can't be in tension.
If it had a stressful day it might become tense. Air can be under a lot of
pressure at times, and work can cause it to get hot. Put under too much
pressure, air can blow a gasket.
That's why it's best to let air blow off steam after a hard day at work and
maybe offer it a smoke with a gin and tonic to cool off:
cavelamb
I think it's about time for a little remedial aerodynamics for the group.
http://www.messybeast.com/dragonqueen/liftdemon.htm
LIFT DEMONS AND THRUST PIXIES
Title of Paper: The Role of Lift Demons and Thrust Pixies in Heavier Than Air Flight
Publication Date: 2004
Abstract: The role of Lift Demons in aeronautics was first explained in 1994 by
Mary Shafer (NASA). Since then, Shafer's work has been explored and revised.
This paper summarises advances in Lift Demon technology over the last decade.
Keywords: Lift Demons, Thrust Pixies, lemon fondant
Authors: Sarah Hartwell, DEF Smith, Peter Rieden, Gavin Bull
Morgans
"Beryl" <fo...@road.net> wrote
>
> He looked inside the wing, at the entire upper surface, at the lower
> surface... that pretty much covers most of it. Air can't be in tension.
Yes, but the person that observed that the pressure on the bottom was one
third responsible (for lift) and the low pressure on top was responsible for
two thirds of the lift is also correct, when you look at the wing as a whole
system, even if those fractions are approximate.
I think his view of individual points of observations are splitting
toadstools.
But that is my opinion, and like everyone, we all have but-holes and
opinions.
--
Jim in NC
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
If the curvature of the upper surface lowers the pressure, then even if
the pressure on the lower surface is just the ambient pressure, it will
be *higher* than the upper surface.
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
> Alan Baker wrote:
> > In article <AKmdnVkk8d03gI7W...@giganews.com>,
> > brian whatcott <bet...@sbcglobal.net> wrote:
> >
> >> Alan Baker wrote:
> >>
> >>>> Interesting comment: what would YOU call it when the fabric on the upper
> >>>> wing surface wants to pull away from the ribs?
> >>> Air pressure from inside the wing pushing up on it more than the air
> >>> above is pushing down...
> >>>
> >>
> >> Let me take a wild guess here: you did physics for an uundergraduate
> >> degree. Is that right?
> >>
> >> Brian W
> >
> > No. But it doesn't matter.
> >
> > If the fabric is moving upward, it can only be because there is more
> > pressure on its bottom surface than there is on its top surface.
> >
>
> It seems that you are uncomfortable with the entire concept of suction.
> For example, how do you suppose suction cups work?
The pressure outside the cup keeps it in place.
> Or how about a suction pump that happens to be limited to a 30 ft lift?
Because a vacuum cannot do any actual pulling, you can only lift water
as far as the pressure allows, right.
>
> Well duh, it's also atmospheric pressure that enables suction pumps and
> suction cups etc., etc. Yes indeed , but it's an academic issue at
> the junior high level, isn't it?
Yup.
Alan Baker
"Morgans" <jsmo...@charterJUNK.net> wrote:
Nope.
I'm making the point that the upper surface contributes absolutely *no*
lifting force.
None.
Zero.
In fact, it provides a downward force. Every time.
Alan Baker
"Morgans" <jsmo...@charterJUNK.net> wrote:
> "Beryl" <fo...@road.net> wrote
> >
> > He looked inside the wing, at the entire upper surface, at the lower
> > surface... that pretty much covers most of it. Air can't be in tension.
>
> Yes, but the person that observed that the pressure on the bottom was one
> third responsible (for lift) and the low pressure on top was responsible for
> two thirds of the lift is also correct, when you look at the wing as a whole
> system, even if those fractions are approximate.
Which I correctly identified if the OP meant it in the appropriate terms.
>
> I think his view of individual points of observations are splitting
> toadstools.
>
> But that is my opinion, and like everyone, we all have but-holes and
> opinions.
--
cavelamb
> In article <A0IQm.72135$W77....@newsfe11.iad>,
> "Morgans" <jsmo...@charterJUNK.net> wrote:
>
>> "Alan Baker" <alang...@telus.net> wrote
>>> Anyone who thinks that the pressure of a fluid on a surface can act in
>>> any direction but towards the surface is simply wrong.
>> I see. You are not lookng at the wing as a system, but taking an
>> observation at one point only, without reguard to what is happening around
>> it.
>>
>> Point made.
>
> Nope.
>
> I'm making the point that the upper surface contributes absolutely *no*
> lifting force.
>
> None.
>
> Zero.
>
> In fact, it provides a downward force. Every time.
>
Sorry, Alan, old boy, I find must disagree.
In actuality, BOTH surfaces are below ambient pressure.
('splain why?)
But without that reduction of the pressure across the top curve of the wing,
the pressure below it can't do much at all, can it?
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
> Alan Baker wrote:
> > In article <A0IQm.72135$W77....@newsfe11.iad>,
> > "Morgans" <jsmo...@charterJUNK.net> wrote:
> >
> >> "Alan Baker" <alang...@telus.net> wrote
> >>> Anyone who thinks that the pressure of a fluid on a surface can act in
> >>> any direction but towards the surface is simply wrong.
> >> I see. You are not lookng at the wing as a system, but taking an
> >> observation at one point only, without reguard to what is happening around
> >> it.
> >>
> >> Point made.
> >
> > Nope.
> >
> > I'm making the point that the upper surface contributes absolutely *no*
> > lifting force.
> >
> > None.
> >
> > Zero.
> >
> > In fact, it provides a downward force. Every time.
> >
>
>
> Sorry, Alan, old boy, I find must disagree.
Disagree all you want, it won't make the upper surface of the wing
experience anything but a downward force.
>
> In actuality, BOTH surfaces are below ambient pressure.
> ('splain why?)
Bernoulli.
>
> But without that reduction of the pressure across the top curve of the wing,
> the pressure below it can't do much at all, can it?
Which I never disagreed with.
But anyone who thinks the upper surface of the wing is experiencing
anything but a downward force is just sadly misinformed.
cavelamb
Ok, be that way.
I actually see what you are trying to say.
And, have no real issues with it.
Myopic, but not technically incorrect.
Richard
(That's just my own opinion, but it works for me)
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
Be what way: accurate? Thanks, I think I will.
>
> I actually see what you are trying to say.
> And, have no real issues with it.
Then why say: "I find I must disagree".
>
> Myopic, but not technically incorrect.
Not myopic: accurate. Understand the world AS IT IS.
>
> Richard
>
> (That's just my own opinion, but it works for me)
--
cavelamb
Einstein's greatest gift what that of Relativity.
Each has his own unique perception based on location
relative to an event.
Each sees something different - but ALL can understand
the other's perceptions.
And here you are claiming all truth...
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
Nope. Not *all* truth. One truth:
The top of a wing doesn't *pull* an aircraft up, it just pushes down
less than the bottom surface pushes up.
And that is the truth. Period. Full stop.
brian whatcott
> Have you ever seen the top surface of a fabric covered wing?
>
> The skin does not bulge upwards.
>
> Not usually anyway.
I find your tone impertinent.
Brian W
brian whatcott
Now can we go back to using terms like suction the way 99.99% of the
technical and scientific population understands it? :-)
Brian W
brian whatcott
> Nope.
>
> I'm making the point that the upper surface contributes absolutely *no*
> lifting force.
>
> None.
>
> Zero.
>
> In fact, it provides a downward force. Every time.
>
...and you are making the point that when you are breathing in, you are
not SUCKING air at all. It's atmospheric pressure on your chest that
inspires the air. Wow! Who would have guessed? :-)
Brian W
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
No one understands "suction" to actually mean a pulling force. Not since
they tried to pump water out of mines and discovered that they could
only "pull" it a certain number of feet, but no further.
et
> In article <RbidncVwS5G6847WnZ2dnUVZ_rCdn...@earthlink.com>,> > > In article <A0IQm.72135$W77.27...@newsfe11.iad>,
> > > "Morgans" <jsmor...@charterJUNK.net> wrote:
>
> > >> "Alan Baker" <alangba...@telus.net> wrote
>
> - Show quoted text -
When I fly my Cheerokee I can detect a slight bulge in the upper
skin. For what it's worth.
Ed
Alan Baker
<fc7e9944-c2ab-4401...@v15g2000prn.googlegroups.com>,
et <etje...@gmail.com> wrote:
Great. Do you think that is caused by the air above the skin pulling on
it?
brian whatcott
> No one understands "suction" to actually mean a pulling force.
Remember folks: no more talk of sucking soda through a straw!
Just suck it up!
Brian W :-)
et
Has to be a pressure differental I would think.
Ed
Alan Baker
<fd25718d-b15a-4ef5...@x25g2000prf.googlegroups.com>,
et <etje...@gmail.com> wrote:
Then you understand reality.
:-)
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
Talk about it all you want...
...just don't pretend that there is a force acting upward on the surface
of the liquid inside the straw...
...because you'll be wrong.
:-)
brian whatcott
>
>>> No one understands "suction" to actually mean a pulling force.
>>
>> Remember folks: no more talk of sucking soda through a straw!
>> Just suck it up!
>
>
> ...because you'll be wrong.
>
>
impressive in Junior High science classes, and paradoxically is quite
correct but trivial. Get over it.
Just so you can savor the general idea - let me phrase the general
concept so it won't trip your OC reaction:
In the general case, two thirds of the lift provided by a wing is due to
the depression over the upper surface - (actually towards the front...)
and a third due to the air flow over the lower surface.
THERE. Are you happy now?
Brian W
Dan_Thom...@yahoo.com
> > > Nope.
>
> > > I'm making the point that the upper surface contributes absolutely *no*
> > > lifting force.
>
> > > None.
>
> > > Zero.
>
> > > In fact, it provides a downward force. Every time.
>
> > Sorry, Alan, old boy, I find must disagree.
>
> Disagree all you want, it won't make the upper surface of the wing
> experience anything but a downward force.
>
>
>
> > In actuality, BOTH surfaces are below ambient pressure.
> > ('splain why?)
>
> Bernoulli.
>
>
>
> > But without that reduction of the pressure across the top curve of the wing,
> > the pressure below it can't do much at all, can it?
>
> Which I never disagreed with.
>
> But anyone who thinks the upper surface of the wing is experiencing
> anything but a downward force is just sadly misinformed.
>
> --
> Alan Baker
> Vancouver, British Columbia
> <http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg>
Unfortunately for you, Alan, I have some actual observations of a
fabric-covered wing in flight. My Jodel, being a fabric-covered low-
wing aircraft, has a top surface easily observed during flight. The
fabric actually pulls up between the ribs in flight. It actually does.
And near the trailing edge, it's pushed down just a little between the
ribs. Which agrees perfectly with the distribution of lift on airfoil
diagrams.
And don't give me any baloney about pressure inside the wing bulging
the fabric.If that was the case, it would all bulge, not just the 90%
aft of the leading edge.
I have a picture here of a biplane that had a poor fabric job. The
fabric hadn't been tensioned properly during application, and the view
from above of the wing in flight showed the fabric bulging upward
between the ribs quite amazingly. Positive pressure on the top surface
sure isn't going to do that.
There really isn't much substitute for actual observation. Flights of
imagination are usually way out to lunch. We have a few guys of in
homebuiltairplanes.com who are similarly convinced that all the
experts are wrong and have been for 150 years.
Dan
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
I was happy to begin with. Read my initial reply:
"Ummmm...
It sort of depends what you mean.
If you mean that suction is actually providing an upward force, you're
quite mistaken.
If you mean that the difference in pressure between upper and lower
surfaces is 2/3 the result of lower pressure on the upper surface, then
you might be right. I don't know."
You see, I never had any problem sorting out the "minutiae" from the
important. But a whole bunch of people (well, *some* people) jumped in
and certainly made statements that they actually believe the air was
pulling up on the wing.
Alan Baker
<a19350de-73f4-48ce...@v25g2000yqk.googlegroups.com>,
Dan_Thom...@yahoo.com wrote:
And it is only deflected upward by the fact that the air *pushing* on
the bottom of the fabric's surface is doing so with greater force than
the air *pushing* down from above.
>
> And don't give me any baloney about pressure inside the wing bulging
> the fabric.If that was the case, it would all bulge, not just the 90%
> aft of the leading edge.
I would only bulge where the air is at lower pressure than the air
inside the wing.
>
> http://www.cartage.org.lb/en/themes/sciences/physics/FluidDynamics/FlyingDynam
> ics/Aerodynamics/SelectedTopics/Velocity/Velocity/Velocity.htm
>
> I have a picture here of a biplane that had a poor fabric job. The
> fabric hadn't been tensioned properly during application, and the view
> from above of the wing in flight showed the fabric bulging upward
> between the ribs quite amazingly. Positive pressure on the top surface
> sure isn't going to do that.
Not on it's own, no. But greater positive pressure on the bottom surface
than on the top surface sure is and does.
>
> There really isn't much substitute for actual observation. Flights of
> imagination are usually way out to lunch. We have a few guys of in
> homebuiltairplanes.com who are similarly convinced that all the
> experts are wrong and have been for 150 years.
Observation can lead you astray: and that is clearly the case here if
you actually think that air can *pull* on a surface.
Alan Baker
Alan Baker <alang...@telus.net> wrote:
> > > > But without that reduction of the pressure across the top curve of the
> > > > wing,
> > > > the pressure below it can't do much at all, can it?
> > >
> > > Which I never disagreed with.
> > >
> > > But anyone who thinks the upper surface of the wing is experiencing
> > > anything but a downward force is just sadly misinformed.
> > >
> >
BTW, Brian:
This is precisely why I bother with "minutiae". The PP clearly believes
that the air is actually pulling...
Scott
>
> This is precisely why I bother with "minutiae". The PP clearly believes
> that the air is actually pulling...
>
I'm with Einstein. It's relative. If I'm floating above a wing in
flight and the wing is "climbing" it looks like it's being sucked toward
me. If I'm floating below a wing in flight and the wing is "climbing"
it looks like it's being pushed away from me.
In all reality, as an airplane USER, I don't really care what is really
happening. I know how to manipulate the controls I have to make it do
what I want it to do.
Scott
>
> Observation can lead you astray: and that is clearly the case here if
> you actually think that air can *pull* on a surface.
>
Why can't air PULL on a surface? Air is made up of molecules.
Molecules have mass. Anything with mass can attract anything else with
mass, can't it?
Alan Baker
Scott <acepilo...@bloomer.net> wrote:
Gravity?
You're not serious.
Ed
<bet...@sbcglobal.net> wrote:
>Stealth Pilot wrote:
>> /snip/ it is the air below pushing
>> you up that lifts the wing.
>> Stealth Pilot
>
>In most circumstances, suction on the upper surface contributes about
>2/3 rds of the lift, and pressure on the lower surface contributes about
>1/3 rd.
>That's one reason which rib stitching for rag wings is a biggy.
>
>Brian W
I have never noticed the fabric lifting on my wings, however I have
seen the fuel siphon out of a wing tank due to an improperly applied
fuel cap.
Alan Baker
Ed <ebs...@sbcglobal.net> wrote:
And greater pressure in the tank than outside of it...
Scott
> In article <F_-dnaufgMTclYjW...@bright.net>,
> Scott <acepilo...@bloomer.net> wrote:
>
>> Alan Baker wrote:
>>
>>> Observation can lead you astray: and that is clearly the case here if
>>> you actually think that air can *pull* on a surface.
>>>
>> Why can't air PULL on a surface? Air is made up of molecules.
>> Molecules have mass. Anything with mass can attract anything else with
>> mass, can't it?
>
> Gravity?
>
> You're not serious.
>
something?
Scott
> In article <k2qah594pkehush2u...@4ax.com>,
> Ed <ebs...@sbcglobal.net> wrote:
>
>> On Sat, 28 Nov 2009 19:07:16 -0600, brian whatcott
>> <bet...@sbcglobal.net> wrote:
>>
>>> Stealth Pilot wrote:
>>>> /snip/ it is the air below pushing
>>>> you up that lifts the wing.
>>>> Stealth Pilot
>>> In most circumstances, suction on the upper surface contributes about
>>> 2/3 rds of the lift, and pressure on the lower surface contributes about
>>> 1/3 rd.
>>> That's one reason which rib stitching for rag wings is a biggy.
>>>
>>> Brian W
>> I have never noticed the fabric lifting on my wings, however I have
>> seen the fuel siphon out of a wing tank due to an improperly applied
>> fuel cap.
>
> And greater pressure in the tank than outside of it...
>
fuel out of the vent since air can't PULL it out?
Alan Baker
Scott <acepilo...@bloomer.net> wrote:
Because the push is caused by the impact of countless air molecules with
the surface of wing. If those collisions fall to zero (i.e. in a perfect
vacuum) then there is zero push.
But there is no set of circumstances that can make the number of
collisions be negative.
Jim Logajan
> Alan Baker wrote:
>> In article <F_-dnaufgMTclYjW...@bright.net>,
>> Scott <acepilo...@bloomer.net> wrote:
>>
>>> Alan Baker wrote:
>>>
>>>> Observation can lead you astray: and that is clearly the case here
>>>> if you actually think that air can *pull* on a surface.
>>>>
>>> Why can't air PULL on a surface? Air is made up of molecules.
>>> Molecules have mass. Anything with mass can attract anything else
>>> with mass, can't it?
>>
>> Gravity?
>>
>> You're not serious.
>>
> Anti-gravity in this case. If air can push something, why can't it
> pull something?
No need to postulate anti-gravity to find a case where air can "pull" on a
surface - just invoke van der Waals force! :-)
Alan Baker
Scott <acepilo...@bloomer.net> wrote:
First of all, the tank is not completely sealed. If it were, the fuel
pumps would soon have difficult pumping the fuel out of the tank.
So, yes, the greater pressure inside the tank is pushing the fuel out.
Alan Baker
Jim Logajan
> Because the push is caused by the impact of countless air molecules
> with the surface of wing. If those collisions fall to zero (i.e. in a
> perfect vacuum) then there is zero push.
>
> But there is no set of circumstances that can make the number of
> collisions be negative.
Pedantically speaking, outgassing would occur for a while that would create
a force on your wing surface when it is exposed to a vacuum. Pedantically
speaking, I don't see why those couldn't be called negative collisions.
(Last worked on a fancy high-vaccum system back in college, wherein my lab
mate and I attempted to replicate the Lamb-Retherford experiment.)
Alan Baker
Jim Logajan <Jam...@Lugoj.com> wrote:
> Alan Baker <alang...@telus.net> wrote:
> > Because the push is caused by the impact of countless air molecules
> > with the surface of wing. If those collisions fall to zero (i.e. in a
> > perfect vacuum) then there is zero push.
> >
> > But there is no set of circumstances that can make the number of
> > collisions be negative.
>
> Pedantically speaking, outgassing would occur for a while that would create
> a force on your wing surface when it is exposed to a vacuum. Pedantically
> speaking, I don't see why those couldn't be called negative collisions.
The force they'd create would be in the same direction as the force of
regular collisions: toward the surface. If the outgassing molecules have
momentum away from the surface then the surface must experience a change
in momentum in the opposite direction.
Dan_Thom...@yahoo.com
> >> Scott <acepilotREM...@bloomer.net> wrote:
>
> >>> Alan Baker wrote:
>
> >>>> Observation can lead you astray: and that is clearly the case here
> >>>> if you actually think that air can *pull* on a surface.
>
> >>> Why can't air PULL on a surface? Air is made up of molecules.
> >>> Molecules have mass. Anything with mass can attract anything else
> >>> with mass, can't it?
>
> >> Gravity?
>
> >> You're not serious.
>
> > Anti-gravity in this case. If air can push something, why can't it
> > pull something?
>
> No need to postulate anti-gravity to find a case where air can "pull" on a
> surface - just invoke van der Waals force! :-)
I think I see what Alan is getting at: While there is low pressure
on the top of the wing, there is still pressure. There isn't an
absolute vacuum, so some pressure is there. But its a lot less than
that below the wing, so the wing moves upward. As he says, air can't
suck the wing upward, but its pressure can be reduced enough that the
pressure below displaces the wing upward.
Semantics. We argue about downwash (Newton) and pressure
differential (Bernoulli) but they're just two symbiotic approaches to
the same phenomenon. Shoot, the air flowing off the top of the wing is
accelerated and moving downward with respect to the flight path, so
downwash is to be expected.
But there's no downwash when a balloon rises. Just displacement.
Dan
Jim Logajan
> Because the push is caused by the impact of countless air molecules
> with the surface of wing. If those collisions fall to zero (i.e. in a
> perfect vacuum) then there is zero push.
I don't see what a change in air density (such as taking the extreme case
of a vacuum) has to do with lift. Unless you are claiming density change as
a requirement?
I believe lift can be reasonably computed using inviscid _incompressible_
flow theory (e.g. as far back as Kutta's 1902 dissertation,) so I don't see
why any change in _density_ - much less the vacuum edge case - needs to be
invoked.
Beryl
> Alan Baker <alang...@telus.net> wrote:
>> Because the push is caused by the impact of countless air molecules
>> with the surface of wing. If those collisions fall to zero (i.e. in a
>> perfect vacuum) then there is zero push.
>
> I don't see what a change in air density (such as taking the extreme case
> of a vacuum) has to do with lift.
I'm going to build a thick wing, real thick! About 10,000 feet thick.
While the bottom surface of the wing sits at 29.92" sea level
atmospheric pressure, the upper surface will be *way* up there, in a
lower-pressure area. This airplane is gonna to lift off the ground at
zero airspeed with no power.
Steve Hix
Scott <acepilo...@bloomer.net> wrote:
It does, but the tiny resulting forces are completely swamped by things
like van der Waals force, static electric charges, magnetic fields, and
any number of things that are usually quite happily ignored by us in
normal life.
Steve Hix
Beryl <fo...@road.net> wrote:
Only if you make it from monatomic Unobtanium. Only thing light enough
for the job.
Alan Baker
Jim Logajan <Jam...@Lugoj.com> wrote:
Any change in pressure is *by definition* a change in the number of
particles in the fluid that are impacting the surface.
I never mentioned density.
brian whatcott
/snip/
>>>> I have never noticed the fabric lifting on my wings, however I have
>>>> seen the fuel siphon out of a wing tank due to an improperly applied
>>>> fuel cap.
>>> And greater pressure in the tank than outside of it...
>>>
>> Right, but in a sealed metal tank, is all that other fuel PUSHING the
>> fuel out of the vent since air can't PULL it out?
>
> First of all, the tank is not completely sealed. If it were, the fuel
> pumps would soon have difficult pumping the fuel out of the tank.
>
> So, yes, the greater pressure inside the tank is pushing the fuel out.
>
Hmmm...it probably goes more like this: there's a 100 mph? wind past an
open port, with some venturi effect certainly, but plenty of
turbulence. If you beat up the surface with a gusty blow, it gets
wavelets which can lap the filler and blow out the fuel.
Which reminds me of that trick that suction pumps use for high lift.
As you probably know, if you pump down even to a vacuum above a tall
3water pipe, the water will not rise more than about 30 ft - (if it were
mercury, it would not rise more than 29.92 inches on a standard day,
remember?)
Anyway, the mine engineers who want to pump up water MORE than 30 ft,
say 40 ft without placing a force pump at the foot of the head, blow air
into the water column which has the effect of reducing the density of
the mix. If the relative density goes down from 1.0 to 0.5 they COULD
pump up to nearer 60 ft. How bout that!
Brian W
Scott
> any number of things that are usually quite happily ignored by us in
> normal life.
EXACTLY!! ;) I don't have to know if air pushes or sucks (although I'm
quite sure it SUCKS in L.A.) to control the airplane to do what I want
it to do.
Jim Logajan
> In article <Xns9CD4D48B2DC8...@216.168.3.30>,
> Jim Logajan <Jam...@Lugoj.com> wrote:
>
>> Alan Baker <alang...@telus.net> wrote:
>> > Because the push is caused by the impact of countless air molecules
>> > with the surface of wing. If those collisions fall to zero (i.e. in
>> > a perfect vacuum) then there is zero push.
>>
>> I don't see what a change in air density (such as taking the extreme
>> case of a vacuum) has to do with lift. Unless you are claiming
>> density change as a requirement?
>>
>> I believe lift can be reasonably computed using inviscid
>> _incompressible_ flow theory (e.g. as far back as Kutta's 1902
>> dissertation,) so I don't see why any change in _density_ - much less
>> the vacuum edge case - needs to be invoked.
>
> 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.
> I never mentioned density.
Sorry, but you used the word "vacuum." The notable characteristic of a
vacuum is that its density is zero.
Robert Bonomi
Quote: "There are two things you need to know to be an engineer:
1) F = M x A
2) you can't push on a rope."
Your question involves a violation of rule #2.
brian whatcott
>
> Quote: "There are two things you need to know to be an engineer:
> 1) F = M x A
> 2) you can't push on a rope."
>
> Your question involves a violation of rule #2.
>
>
Hehe... If you push downwards on a tight rope carefully enough,
you can qualify as a tightrope walker?? :-)
Brian W
Alan Baker
Jim Logajan <Jam...@Lugoj.com> wrote:
> Alan Baker <alang...@telus.net> wrote:
> > In article <Xns9CD4D48B2DC8...@216.168.3.30>,
> > Jim Logajan <Jam...@Lugoj.com> wrote:
> >
> >> Alan Baker <alang...@telus.net> wrote:
> >> > Because the push is caused by the impact of countless air molecules
> >> > with the surface of wing. If those collisions fall to zero (i.e. in
> >> > a perfect vacuum) then there is zero push.
> >>
> >> I don't see what a change in air density (such as taking the extreme
> >> case of a vacuum) has to do with lift. Unless you are claiming
> >> density change as a requirement?
> >>
> >> I believe lift can be reasonably computed using inviscid
> >> _incompressible_ flow theory (e.g. as far back as Kutta's 1902
> >> dissertation,) so I don't see why any change in _density_ - much less
> >> the vacuum edge case - needs to be invoked.
> >
> > 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.
>
> > I never mentioned density.
>
> Sorry, but you used the word "vacuum." The notable characteristic of a
> vacuum is that its density is zero.
That is *a* notable characteristic.
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
How about it? It still doesn't change the physical reality that air
doesn't *pull* on the wings.
brian whatcott
> In article <Xns9CD55D0FE89...@216.168.3.30>,
> Jim Logajan <Jam...@Lugoj.com> 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.
Hmmm...looks like Jim expected too much from you: the kinetic theory of
gases has it that pressure may be computed from the temperature AND the
density of gases... that is to say, by retaining the SAME molar quantity
of gas, and raising its temperature (which translates to a higher
velocity), the pressure is increased P.V = R.t and all that....
Put it another way: each "hotter" molecule reverses direction at a
surface with greater force.
Brian W
brian whatcott
>>>>>> I have never noticed the fabric lifting on my wings, however I have
>>>>>> seen the fuel siphon out of a wing tank due to an improperly applied
>>>>>> fuel cap.
>>>>> And greater pressure in the tank than outside of it...
/snip/
>>> So, yes, the greater pressure inside the tank is pushing the fuel out.
>>>
>> Hmmm...it probably goes more like this: there's a 100 mph? wind past an
>> open port, with some venturi effect certainly, but plenty of
>> turbulence. If you beat up the surface with a gusty blow, it gets
>> wavelets which can lap the filler and blow out the fuel.
> How about it? It still doesn't change the physical reality that air
> doesn't *pull* on the wings.
>
You're still singing the last hymn, Alan.
We are now discussing how an open tank, with a 100 mph wind blowing over
its top, can lose its fuel over the top. Do you think the tank has
GREATER pressure due to the venturi effect of the airflow?
Brian W
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
I'm perfectly aware of that, but that hardly matters for the scope of
our discussion of the effect of pressure on a wing. The point I'm making
is that all else being equal, more collisions means higher pressure and
fewer means lower pressure, but that pressure is therefore always a
positive value that acts toward the surface to which it is applied.
It is *never* acting away from that surface; i.e. "pulling".
That is the only reason I mentioned a vacuum, because it is a situation
in which there is *by definition* zero absolute pressure.
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
No. I think that the venturi effect lowers the pressure below the
pressure that already exists in the tank. Contrary to what the PP wrote,
a tank cannot be sealed if you are to pump fuel out of it. If it were
the pump would have to work against a rising pressure difference as it
removed fuel from the tank. Hence we know the tanks pressure must be
allowed to equalize.
If the pressure over an open filler is less than that in the tank -- and
assuming the filler is not simply pulling from the air/fuel vapor
mixture, then it will pull fuel from the tank if the pressure difference
is sufficient to lift the fuel the from its level in the tank to the
level of the open filler.
But it is being *pushed* out by higher pressure inside, not pulled.
brian whatcott
/snip/
>>>>> 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.
>> Hmmm...looks like Jim expected too much from you: the kinetic theory of
>> gases has it that pressure may be computed from the temperature AND the
>> density of gases... that is to say, by retaining the SAME molar quantity
>> of gas, and raising its temperature (which translates to a higher
>> velocity), the pressure is increased P.V = R.t and all that....
>>
>> Put it another way: each "hotter" molecule reverses direction at a
>> surface with greater force.
>>
>> Brian W
>
> I'm perfectly aware of that...
It took me too long to realise the problem: you have a problem with
saying: "Oh yes, I got it worng."
People who WON'T do that in technical discussions qualify as people who
are just happy to stir up heated debate.
I am going to leave this thread now: wrasslin' with pigs gets the
hands jest too soiled...
Brian W
Alan Baker
brian whatcott <bet...@sbcglobal.net> wrote:
> Alan Baker wrote:
> /snip/
> >>>>> 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.
>
> >> Hmmm...looks like Jim expected too much from you: the kinetic theory of
> >> gases has it that pressure may be computed from the temperature AND the
> >> density of gases... that is to say, by retaining the SAME molar quantity
> >> of gas, and raising its temperature (which translates to a higher
> >> velocity), the pressure is increased P.V = R.t and all that....
> >>
> >> Put it another way: each "hotter" molecule reverses direction at a
> >> surface with greater force.
> >>
> >> Brian W
> >
> > I'm perfectly aware of that...
>
> It took me too long to realise the problem: you have a problem with
> saying: "Oh yes, I got it worng."
I didn't get anything wrong.
I am and was perfectly aware of the fact that the temperature of a gas
indicates a different average speed for the gas molecules and thus a
different momentum when the strike a surface.
>
> People who WON'T do that in technical discussions qualify as people who
> are just happy to stir up heated debate.
I agree. What of it.
>
> I am going to leave this thread now: wrasslin' with pigs gets the
> hands jest too soiled...
You can go.
cavelamb
I feel the same as Brian.
This had not been a discussion as much as a troll.
OF BLOODY COURSE, the high pressure area under the wing pushes up.
So what.
It couldn't possibly do that without the reduction of pressure on the top.
That's where all the magic is.
And you, sir, are a bloody bore.
So now, please also dismiss me.
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
Look, I started out to clarify the point for those who have the wrong
perception of the situation...
...and it turned that there were such people.
I explicitly stated that if the OP meant that the low pressure above the
wing is responsible for two thirds of the pressure *difference* then he
was on solid ground (while allowing as how I didn't know what the
precise figures actually were).
Ever since then, types like you have been coming in and saying "IT
DOESN'T MATTER", when very clearly (because there are people who don't
understand the situation) it does.
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.
Beryl
>
> 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.
Alan Baker
Beryl <fo...@road.net> wrote:
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.
jan olieslagers
> No.
Yawn.
Beryl
> In article <6MadnfORp9stB4XW...@posted.toastnet>,
> Beryl <fo...@road.net> 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.
cavelamb
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?
Beryl
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.
Jim Logajan
> Jim Logajan <Jam...@Lugoj.com> wrote:
>> Alan Baker <alang...@telus.net> 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!)
Jim Logajan
> In article <6MadnfORp9stB4XW...@posted.toastnet>,
> Beryl <fo...@road.net> 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.
cavelamb
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.
Alan Baker
Beryl <fo...@road.net> wrote:
Sorry, Beryl, but you're just wrong.
Alan Baker
cavelamb <cave...@earthlink.net> wrote:
Sorry, but wrong.