Lift - Newton/Bernoulli ratio...

Dave Doe writes:

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.

An airfoil doesn't need a specific shape to produce lift, as long as it's
reasonably flat. The lift is ALWAYS produced by diverting the flow of air, no
matter what the camber of the airfoil. And in airfoils, Bernoulli's effect
ALWAYS has a hand in diverting the air flow, again no matter what the camber
of the airfoil.

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.

The distinction you are making doesn't exist.

A plank of wood is an airfoil when air flows over it and it has a positive
angle of attack. Newton and Bernoulli are always involved. There is no lift
without positive angle of attack. No special shape is necessary for the plank,
but it should be relatively flat and roughly edgewise to the air flow (apart
from the positive angle of attack, which is mandatory).

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

Because no additional lift is obtained. It's impossible to dissociate
Bernoulli from Newton for airfoils. The lift always comes from Newton, the
diversion of airflow that invokes Newton is due to Bernoulli (and other
effects, depending on how one looks at things).

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).

A flat sail will produce lift just as well as a curved sail.

And I don't want to get stuck on the pedantics of Newtonian physics
encompassing the Bernoulli effect ...

Perhaps that explains why you haven't thus far understood the explanations
you've received.

On 2011-05-23, Dave Doe wrote:
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

100% Newton
100% Bernouilli

b) a plank of wood that is an airfoil - and is getting lift from both
angle of attack and the Bernoulli effect.

100% Newton
100% Bernouilli

In article , , Dylan Smith
says...

On 2011-05-23, Dave Doe wrote:
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

100% Newton
100% Bernouilli

b) a plank of wood that is an airfoil - and is getting lift from both
angle of attack and the Bernoulli effect.

100% Newton
100% Bernouilli

Thanks - I will try and fire back a reply after our next argument over
this

--
Duncan.

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.
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

Dudley, here are some more links I've found - only what I consider to be
the good stuff

http://www.physicsforums.com/showthread.php?t=19014

Nice thread that leads to this *cool* diagramatic animated page...

http://www.diam.unige.it/~irro/profilo_e.html

And I thought this was good too...

http://www.askamathematician.com/?p=1736

and this...
http://blog.sciencegeekgirl.com/2008...airplanes-fly/

*But* - I still want to know what this is (in the last link, the last
comment)...
"Nice distinction, jim-bob. The bernouilli principle does indeed play a
role. "

How much of a role??? Gimme some numbers! Gimme some percentages!



--
Duncan.

Dudley Henriques writes:

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 :-)

Agreed.

The problem is that all these effects interact, and explaining lift is often a
matter of preferred viewpoint, as you imply.

But it is true that lift always involves the acceleration of an air mass,
which is a matter of Newton's third law. How this acceleration is accomplished
is irrelevant, provided that it occurs. Bernoulli's effect and many other
effects help to explain why air flowing over an airfoil with a positive angle
of attack is accelerated at right angles to the direction of flow, but these
effects don't produce the lift directly, it's the acceleration that produces
the lift.

If you build something that accelerates an air mass in the same way without
any connection to Bernoulli et al., it will still fly. On the other hand, if
you build something that demonstrates Bernoulli's effect but does not
accelerate air perpendicular to its flow, no lift results.

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.

Lift is produced by diverting the air flow, thanks to Newton. The diversion in
an airfoil is in part produced thanks to Bernoulli.

On May 23, 5:20*pm, Mxsmanic wrote:
Dudley Henriques writes:
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 :-)

Agreed.

The problem is that all these effects interact, and explaining lift is often a
matter of preferred viewpoint, as you imply.

But it is true that lift always involves the acceleration of an air mass,
which is a matter of Newton's third law. How this acceleration is accomplished
is irrelevant, provided that it occurs. Bernoulli's effect and many other
effects help to explain why air flowing over an airfoil with a positive angle
of attack is accelerated at right angles to the direction of flow, but these
effects don't produce the lift directly, it's the acceleration that produces
the lift.

If you build something that accelerates an air mass in the same way without
any connection to Bernoulli et al., it will still fly. On the other hand, if
you build something that demonstrates Bernoulli's effect but does not
accelerate air perpendicular to its flow, no lift results.

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.

Lift is produced by diverting the air flow, thanks to Newton. The diversion in
an airfoil is in part produced thanks to Bernoulli.

Again correct but with a slightly different approach from me. It's
fine to quote the need for an accelerated air mass (relative wind
actually) as a necessity for lift creation. The statement is
absolutely correct, but again we have to be careful when dealing with
someone wishing to dissect Bernoulli and Newton.
The plane simple truth of it is that YES, we need relative wind to
create lift, and YES, we also need a positive angle of attack to
create lift. An airfoil no matter how efficient, at rest with no
relative wind in play, creates no lift. Same for the plank of wood.
Produce a relative wind on either and introduce a positive angle of
attack and INSTANTLY you have lift that can be explained completely
EITHER by Bernoulli or by Newton.
All we do when we stipulate that a relative wind must be present for
lift to be created is to stipulate the CONDITION under which Bernoulli
and Newton require for either to produce and explain lift.
It's a round robin that always ends up with both of these guys staring
us right in the puss with neither of them winning OVER the other .
Bernoulli 100% Newton 100% Newton the easier of the two to use as an
explanation, but NOT at the expense of Bernoulli! :-))
Dudley Henriques
Dudley Henriques

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On 5/23/2011 4:20 PM, Mxsmanic wrote:

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.

Dealt with lift - with instructors - in seminar?

Do tell! :-)

Brian W

On May 28, 2:27*pm, brian whatcott wrote:
On 5/23/2011 4:20 PM, Mxsmanic wrote:

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.

Dealt with lift - with instructors * - in seminar?

Do tell! * *:-)

Brian W

Not sure I understand where you're going with this. I used to give
seminars with instructors in attendance. Simple!
DH

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