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Lift - Newton/Bernoulli ratio...



 
 
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  #1  
Old May 22nd 11, 11:15 AM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?

I appreciate this is not a static figure - but say a yer average C-172,
or perhaps a 737.

I would hazard a semi-educated guess that lift is *primarily* produced
by angle of attack (or deflection if you like) - Newton's Laws - and by
a much lesser degree by Bernoulli's Law. I would guess that Bernoulli's
principle might create 20% of the lift a wing generates. A friend
believes it would be much lesser - about 5%.

--
Duncan.
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  #2  
Old May 22nd 11, 07:08 PM posted to rec.aviation.piloting
Orval Fairbairn
external usenet poster
 
Posts: 824
Default Lift - Newton/Bernoulli ratio...

In article ,
Dave Doe wrote:

Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?

I appreciate this is not a static figure - but say a yer average C-172,
or perhaps a 737.

I would hazard a semi-educated guess that lift is *primarily* produced
by angle of attack (or deflection if you like) - Newton's Laws - and by
a much lesser degree by Bernoulli's Law. I would guess that Bernoulli's
principle might create 20% of the lift a wing generates. A friend
believes it would be much lesser - about 5%.


Newton and Bernoulli approach the idea of lift generation from two
different perspectives -- both correct.

Newton's laws explain lift as an exchange of energy and momentum -- a
craft flying through the air imparts some of its momentum to the
vertical axis, which manifests itself as "lift."

Bernoulli explains the fluid mechanics of lift generation via pressure
distribution, to create "lift."

Newton explains why we get a downdraft as a plane flies overhead.
  #3  
Old May 23rd 11, 12:04 AM posted to rec.aviation.piloting
Mxsmanic
external usenet poster
 
Posts: 9,169
Default Lift - Newton/Bernoulli ratio...

Dave Doe writes:

Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?


All lift is produced by Newton's third law of motion. Air is forced downwards
by the wings, and this produces an equal and opposite force that attempts to
raise the wings, and that is lift. How the air is forced downwards is
irrelevant, as long as it happens. In practice, principles discovered by
Bernoulli and others play a role in diverting the air flow when this is
accomplished by an airfoil.
  #4  
Old May 23rd 11, 03:02 AM posted to rec.aviation.piloting
Brian Whatcott
external usenet poster
 
Posts: 915
Default Lift - Newton/Bernoulli ratio...

On 5/22/2011 5:15 AM, Dave Doe wrote:
Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?

I appreciate this is not a static figure - but say a yer average C-172,
or perhaps a 737.

I would hazard a semi-educated guess that lift is *primarily* produced
by angle of attack (or deflection if you like) - Newton's Laws - and by
a much lesser degree by Bernoulli's Law. I would guess that Bernoulli's
principle might create 20% of the lift a wing generates. A friend
believes it would be much lesser - about 5%.


Think of it this way:
Newton: force is proportional to the mass and its acceleration.

In this context, the meaning is, to produce the aircraft's weight in
lift i.e. upwards , an airmass has to move with sufficent acceleration
to provide that up force.

Bernoulii: the mass of air flowing through a channel times its speed
gives the same product even if the channel then narrows to a waist:
the air mass has to flow faster, but its pressure drops..

In this context: air flowing in an airstream over a wing sees it bulging
(or waisting) and so that it needs to speed up, and pressure drops over
the upper wing. Arguments of this type can be used as evidence that 2/3
of the wing lift is produced at the upper surface, and 1/3 at the lower
wing surface.


The larger truth: air pressure drops over the upper surface of a wing,
and increases over the lower surface of a wing, and the resultant
downflow balances the lift on the wing.

Brian W
  #5  
Old May 23rd 11, 04:04 AM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

In article [email protected]
216.pools.spcsdns.net, , Orval Fairbairn
says...

In article ,
Dave Doe wrote:

Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?

I appreciate this is not a static figure - but say a yer average C-172,
or perhaps a 737.

I would hazard a semi-educated guess that lift is *primarily* produced
by angle of attack (or deflection if you like) - Newton's Laws - and by
a much lesser degree by Bernoulli's Law. I would guess that Bernoulli's
principle might create 20% of the lift a wing generates. A friend
believes it would be much lesser - about 5%.


Newton and Bernoulli approach the idea of lift generation from two
different perspectives -- both correct.

Newton's laws explain lift as an exchange of energy and momentum -- a
craft flying through the air imparts some of its momentum to the
vertical axis, which manifests itself as "lift."

Bernoulli explains the fluid mechanics of lift generation via pressure
distribution, to create "lift."

Newton explains why we get a downdraft as a plane flies overhead.


Thanks for the reply - looking for numbers, not the physics behind it.
IE looking for the percentage of lift obtained by each - and as I said,
although this is variable dependent no doubt on the plane and the
airspeed - just trying to get a rough idea (hence, say a C-172 or a
737).


--
Duncan.
  #7  
Old May 23rd 11, 05:46 AM posted to rec.aviation.piloting
Dudley Henriques[_3_]
external usenet poster
 
Posts: 66
Default Lift - Newton/Bernoulli ratio...

On May 22, 7:04*pm, Mxsmanic wrote:
Dave Doe writes:
Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?


All lift is produced by Newton's third law of motion. Air is forced downwards
by the wings, and this produces an equal and opposite force that attempts to
raise the wings, and that is lift. How the air is forced downwards is
irrelevant, as long as it happens. In practice, principles discovered by
Bernoulli and others play a role in diverting the air flow when this is
accomplished by an airfoil.


Actually, if I'm reading you right, I would rephrase this just a bit,
as it feeds into the problems we as instructors have in "re-
explaining" lift to students.
STRESSING either Newton or Bernoulli in the lift explanation causes
more than a modicum of confusion UNLESS it's done by including BOTH
theories in the explanation. You've done that actually. I would just
enhance things a bit more :-)
Read what Orval says above. He is absolutely correct. BOTH Newton and
Bernoulli are COMPLETE explanations for lift, which is interesting in
another respect, as neither man had lift in mind with their work.
The simple truth of it is that each explanation is totally correct and
is interchangeable with the other. Each explains the same thing
without relying on the other and BOTH are occurring simultaneously.
It's a common misconception that Bernoulli and Newton EACH contribute
INDIVIDUALLY to form a TOTAL of the lift produced. This explanation is
incorrect and should be discouraged.
When I dealt with the lift issue with instructors in seminar, my
personal approach was to favor the Newtonian explanation as in my
opinion student pilots can grasp Newton a lot easier than Bernoulli,
but I've ALWAYS made it habit NEVER to leave Bernoulli out in the
cold.
The correct way to deal with the lift issue is to explain to those
asking that BOTH explanations are complete by themselves, and Newton
might be the easier of the two to explain.
Dudley Henriques
  #8  
Old May 23rd 11, 06:06 AM posted to rec.aviation.piloting
Private
external usenet poster
 
Posts: 188
Default Lift - Newton/Bernoulli ratio...


"Dave Doe" wrote in message
...
In article ,
, Mxsmanic says...

Dave Doe writes:

Does anyone have any figures and references for about what ratio lift
is
produced by Newton's Laws and Bernoulli's Laws?


All lift is produced by Newton's third law of motion. Air is forced
downwards
by the wings, and this produces an equal and opposite force that attempts
to
raise the wings, and that is lift. How the air is forced downwards is
irrelevant, as long as it happens. In practice, principles discovered by
Bernoulli and others play a role in diverting the air flow when this is
accomplished by an airfoil.


As said in other reply - not looking for a run-down on the physics -
looking for the *ratio* of lift obtained by each.

--
Duncan.



Simple answer, there is no "ratio" -
Newton 100% + Bernoulli 100%, total = 100%

It really is a "chicken or egg" question.

Google "Newton vs. Bernoulli"
and "Newton vs. Bernoulli" NASA

I recommend
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

and much more
http://www.grc.nasa.gov/WWW/K-12/airplane/short.html

When done you can also work (troll?) on other important old disputes
regarding -
high wing vs. low wing,
track up vs. north up,
and slip vs. crab with a kick.

Happy landings,


  #9  
Old May 23rd 11, 08:40 AM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

In article 4f56d67d-f259-46e7-8e3f-
, ,
Dudley Henriques says...

On May 22, 7:04*pm, Mxsmanic wrote:
Dave Doe writes:
Does anyone have any figures and references for about what ratio lift is
produced by Newton's Laws and Bernoulli's Laws?


All lift is produced by Newton's third law of motion. Air is forced downwards
by the wings, and this produces an equal and opposite force that attempts to
raise the wings, and that is lift. How the air is forced downwards is
irrelevant, as long as it happens. In practice, principles discovered by
Bernoulli and others play a role in diverting the air flow when this is
accomplished by an airfoil.


Actually, if I'm reading you right, I would rephrase this just a bit,
as it feeds into the problems we as instructors have in "re-
explaining" lift to students.
STRESSING either Newton or Bernoulli in the lift explanation causes
more than a modicum of confusion UNLESS it's done by including BOTH
theories in the explanation. You've done that actually. I would just
enhance things a bit more :-)
Read what Orval says above. He is absolutely correct. BOTH Newton and
Bernoulli are COMPLETE explanations for lift, which is interesting in
another respect, as neither man had lift in mind with their work.
The simple truth of it is that each explanation is totally correct and
is interchangeable with the other. Each explains the same thing
without relying on the other and BOTH are occurring simultaneously.
It's a common misconception that Bernoulli and Newton EACH contribute
INDIVIDUALLY to form a TOTAL of the lift produced. This explanation is
incorrect and should be discouraged.


While it's true that the Bernoulli effect is part of Newtonian mechanics
- I want to know what the ratio of (gonna have to rephrase this aren't
I) is:
* an airfoil where the camber on both sides is equal and opposite
(mirroed)
vs
* an airfoil that is shaped to produce lift via Bernoulli effect.

When I dealt with the lift issue with instructors in seminar, my
personal approach was to favor the Newtonian explanation as in my
opinion student pilots can grasp Newton a lot easier than Bernoulli,
but I've ALWAYS made it habit NEVER to leave Bernoulli out in the
cold.
The correct way to deal with the lift issue is to explain to those
asking that BOTH explanations are complete by themselves, and Newton
might be the easier of the two to explain.
Dudley Henriques


I'll rephrase it a second time. What percentage of extra lift is gained
from:
a) a plank of wood (can only produce lift via angle of attack)
vs
b) a plank of wood that is an airfoil - and is getting lift from both
angle of attack and the Bernoulli effect.

I hope that is clearer.

Here are some articles - but they produce no data to show the
addidtional lift obtained by the Bernoulli effect.

http://en.wikipedia.org/wiki/Airfoil

http://en.wikipedia.org/wiki/NACA_airfoil

http://en.wikipedia.org/wiki/Lift_(force)

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

And here is a third re-phrase...
* A yacht that has a sail made of unbendable stiff material
(will not point as high and go as fast as)...
* A yacht that has a sail of normal material and has an effective
airfoil shape and produces lift perpendicular to the sail (via the
Bernoulli effect).

Is it not a simple enough question? - I mean, really. While results
will undoubtably vary among plane types and airspeed - I'm just looking
for an approximate percentage.

Do read that: http://en.wikipedia.org/wiki/NACA_airfoil page!

And I don't want to get stuck on the pedantics of Newtonian physics
encompassing the Bernoulli effect - just really looking at, as said
(rephrase #4)...
- lift produced by an airfoil that has a mirrored camber top and bottom
(the zero lift line is the same as the chord line)
vs
- lift produced by a traditional airfoil

--
Duncan.
  #10  
Old May 23rd 11, 09:40 AM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

In article , er, Private
says...

"Dave Doe" wrote in message
...
In article ,
, Mxsmanic says...

Dave Doe writes:

Does anyone have any figures and references for about what ratio lift
is
produced by Newton's Laws and Bernoulli's Laws?

All lift is produced by Newton's third law of motion. Air is forced
downwards
by the wings, and this produces an equal and opposite force that attempts
to
raise the wings, and that is lift. How the air is forced downwards is
irrelevant, as long as it happens. In practice, principles discovered by
Bernoulli and others play a role in diverting the air flow when this is
accomplished by an airfoil.


As said in other reply - not looking for a run-down on the physics -
looking for the *ratio* of lift obtained by each.

--
Duncan.



Simple answer, there is no "ratio" -
Newton 100% + Bernoulli 100%, total = 100%


So a wing generates as much lift upside down?

What I want, is half the difference between a wing up the right way, and
the wing up the wrong way. That is, I presume, the additional lifting
force from the Bernoulli effect vs a wing with a mirrored camber
(obtaining no lift due to the Bernoulli effect).


It really is a "chicken or egg" question.

Google "Newton vs. Bernoulli"
and "Newton vs. Bernoulli" NASA


Perhaps it is. I have googled.


I recommend
http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html

Been there.


and much more
http://www.grc.nasa.gov/WWW/K-12/airplane/short.html


And there.


When done you can also work (troll?) on other important old disputes
regarding -
high wing vs. low wing,
track up vs. north up,
and slip vs. crab with a kick.

Happy landings,


Not interested in trolling. If you think I am, please do not reply, or
reply and say so, and I will do as such.

--
Duncan.
 




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