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Lift - Newton/Bernoulli ratio...



 
 
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  #41  
Old May 25th 11, 03:03 AM posted to rec.aviation.piloting
a[_3_]
external usenet poster
 
Posts: 562
Default Lift - Newton/Bernoulli ratio...

On May 24, 10:35*am, Dudley Henriques
wrote:
On May 23, 9:31*pm, a wrote:









On May 22, 10:02*pm, brian whatcott wrote:


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

*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.

What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!

It's nice to see a real aviation topic here, isn't it?

  #42  
Old May 25th 11, 03:16 AM posted to rec.aviation.piloting
Dudley Henriques[_3_]
external usenet poster
 
Posts: 66
Default Lift - Newton/Bernoulli ratio...

On May 24, 10:03*pm, a wrote:
On May 24, 10:35*am, Dudley Henriques
wrote:









On May 23, 9:31*pm, a wrote:


On May 22, 10:02*pm, brian whatcott wrote:


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
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.

What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. *I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. *My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!

It's nice to see a real aviation topic here, isn't it?


I don't know what "literature" you're referring to that doesn't
mention Bernoulli when discussing lift, but I'd avoid that literature
if I were you. It's incomplete! :-))
DH
  #43  
Old May 25th 11, 07:36 AM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

In article 6469c134-67e0-4ca9-8dd1-
, , a says...

On May 24, 10:35*am, Dudley Henriques
wrote:
On May 23, 9:31*pm, a wrote:









On May 22, 10:02*pm, brian whatcott wrote:


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
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.

What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!

It's nice to see a real aviation topic here, isn't it?


Have a look at this one that I found late last night - check the section
out on Wing Efficiency - and the sections beyond it... comments welcomed


http://home.comcast.net/~clipper-108/lift.pdf

--
Duncan.
  #44  
Old May 25th 11, 02:06 PM posted to rec.aviation.piloting
Dudley Henriques[_3_]
external usenet poster
 
Posts: 66
Default Lift - Newton/Bernoulli ratio...

On May 25, 2:36*am, Dave Doe wrote:
In article 6469c134-67e0-4ca9-8dd1-
, , a says...











On May 24, 10:35*am, Dudley Henriques
wrote:
On May 23, 9:31*pm, a wrote:


On May 22, 10:02*pm, brian whatcott wrote:


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
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.


What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. *I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. *My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!


It's nice to see a real aviation topic here, isn't it?


Have a look at this one that I found late last night - check the section
out on Wing Efficiency - and the sections beyond it... comments welcomed


http://home.comcast.net/~clipper-108/lift.pdf

--
Duncan.


I didn't have to get past the first several paragraphs to see what was
going on here with this paper. It becomes apparent with the sentence,
"Bernoulli relies on equal transit times". This statement is false on
premise so all that comes after it has to be flawed.
Bernoulli absolutely and most certainly does NOT rely on equal
transit. Equal transit is incorrect in ALL explanations on lift
development and in fact is probably responsible for more
misunderstanding about Bernoulli that anything else.
This paper represents just more of the misunderstanding surrounding
lift. It looks good on the face, is well written, but misses the basic
point that you don't need equal transit to prove Bernoulli.
The main point this paper makes is that if you believe you need equal
transit to prove Bernoulli you need to dig into lift development a bit
deeper, especially the Bernoulli end of things.
Point of note;
Be wary of any and all papers on this subject written by individuals.
Be wary of me as well. Do some SERIOUS homework on this if you are
really interested.

One of the most credible, if not THE most credible text ever written
on these subjects is the bible I have used myself all through my
career, and recommended to every instructor and pilot who has ever
crossed my path. The book is well worth the money and every serious
pilot should own a copy. It's a bit heavy on math but crystal clear on
explanation.
Get a copy of "Aerodynamics For Naval Aviators" by Hurt. Read the
section on lift and you will never again have any doubt at all about
either Newton or Bernoulli being a 100% explanation for how lift is
createdi.
Dudley Henriques
  #45  
Old May 25th 11, 05:45 PM posted to rec.aviation.piloting
Dylan Smith[_2_]
external usenet poster
 
Posts: 53
Default Lift - Newton/Bernoulli ratio...

On 2011-05-25, a wrote:
What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!


The reason why is that you have tradeoffs - long and slender wings
won't work so well for a much heavier plane (more heavy structure) that has
to go much faster (more form drag). Even performance gliders are slow
compared to, say, a Beech Bonanza (I got all excited about flying
a Discus, now I could transit across areas of sink at a whopping 90
knots or so).

Some 4 seat planes have longer, higher aspect ratio wings than was
traditional, for instance the Diamond DA-40 which has trouble fitting
in a lot of T-hangars due to its wingspan of 40-odd feet. However I suspect
much beyond that wingspan you're going to start losing more than you
gain in parasitic drag and extra structural weight to have a very
long, slender wing in a 4 seat plane that goes more than 140 knots in
cruise.

  #46  
Old May 25th 11, 09:29 PM posted to rec.aviation.piloting
george
external usenet poster
 
Posts: 803
Default Lift - Newton/Bernoulli ratio...

On May 26, 1:06*am, Dudley Henriques
wrote:
On May 25, 2:36*am, Dave Doe wrote:



In article 6469c134-67e0-4ca9-8dd1-
, , a says....


On May 24, 10:35*am, Dudley Henriques
wrote:
On May 23, 9:31*pm, a wrote:


On May 22, 10:02*pm, brian whatcott wrote:


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
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls.. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D..


What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. *I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. *My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!


It's nice to see a real aviation topic here, isn't it?


Have a look at this one that I found late last night - check the section
out on Wing Efficiency - and the sections beyond it... comments welcomed


http://home.comcast.net/~clipper-108/lift.pdf


--
Duncan.


I didn't have to get past the first several paragraphs to see what was
going on here with this paper. It becomes apparent with the sentence,
"Bernoulli relies on equal transit times". This statement is false on
premise so all that comes after it has to be flawed.
Bernoulli absolutely and most certainly does NOT rely on equal
transit. Equal transit is incorrect in ALL explanations on lift
development and in fact is probably responsible for more
misunderstanding about Bernoulli that anything else.
This paper represents just more of the misunderstanding surrounding
lift. It looks good on the face, is well written, but misses the basic
point that you don't need equal transit to prove Bernoulli.
The main point this paper makes is that if you believe you need equal
transit to prove Bernoulli you need to dig into lift development a bit
deeper, especially the Bernoulli end of things.
Point of note;
Be wary of any and all papers on this subject written by individuals.
Be wary of me as well. Do some SERIOUS homework on this if you are
really interested.

One of the most credible, if not THE most credible text ever written
on these subjects is the bible I have used myself all through my
career, and recommended to every instructor *and pilot who has ever
crossed my path. The book is well worth the money and every serious
pilot should own a copy. It's a bit heavy on math but crystal clear on
explanation.
Get a copy of "Aerodynamics For Naval Aviators" by Hurt. Read the
section on lift and you will never again have any doubt at all about
either Newton or Bernoulli being a 100% explanation for how lift is
createdi.
Dudley Henriques

Yup
Or "Flight without Formulae" for simple easy to understand reading to
prepare one for the more complex explanations out there...
  #47  
Old May 25th 11, 11:55 PM posted to rec.aviation.piloting
Dave Doe
external usenet poster
 
Posts: 378
Default Lift - Newton/Bernoulli ratio...

In article 47971036-2b4d-4297-bcbf-
, ,
Dudley Henriques says...

On May 25, 2:36*am, Dave Doe wrote:
In article 6469c134-67e0-4ca9-8dd1-
, , a says...











On May 24, 10:35*am, Dudley Henriques
wrote:
On May 23, 9:31*pm, a wrote:


On May 22, 10:02*pm, brian whatcott wrote:


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
*theories
anyone here really believe there is no change in air density as if
flows at speeds of a hundred miles an hour past an airfoil? The
equation works well for water flow in pipes and around boat hulls. It
does not do such a good job of predicting pressures along an airfoil.
Stick with Newtonian Physics and the gas laws.


The ideal gas law still applies. Compressing airflow does indeed
complicate Bernoulli as do the density changes involved but Bernoulli
still holds up. Both theories remain correct even with compressible
flow. But you are correct in that the Newton explanation is FAR easier
of the two for people to deal with and understand. The only caveat I
stress to instructors when getting into the lift issue is that they
NEVER explain lift using ONLY one theory without mention of the other,
as student pilots, once exposed to the lift question will invariably
find through a credible source that BOTH Newton and Bernoulli are
correct and that each can explain exactly the same thing to the 100%
point.
Lift can be explained to death. The deeper one goes into the
explanation the more complicated it can get. Denigrating Bernoulli due
to changing density and airflow speeds causing compression factors is
NOT the way to present lift. Bernoulli stands. It's the math that gets
harder when you compress the flow that's all. All this can be avoided
by simply explaining to students that lift results when an airflow is
TURNED, and BOTH Newton and Bernoulli can be shown to cause the
airflow to turn as lift is being produced. Circulation, density,
vortices..........all part of it, but it's the turning of that airflow
that produces lift force and BOTH Bernoulli and Newton are working
equally to produce that force, only doing it differently.
Dudley Henriques


Actually, a quick meander through the literature will not find
Bernoulli mentioned: in 2 D airflow studies it's gas laws and
Newtonian physics, with a heavy emphasis on experimental results.
These days, numerical methods -- what we used to call difference
equations -- seem to yield results that seem to come pretty close to
predicting experimental results. Notice especially in experiments that
chord sections have end plates so that flow really is confined to 2 D.


What is really interesting is that high performance glider wings are
long and slender: that's how they get the most efficient use of
potential energy in the form of altitude and turn it into range. *I
don't know of any 4 seat complex SEL that uses the same principle and
am not sure why. *My Mooney gets 20 mpg or so, sure would enjoy seeing
that change to 30!


It's nice to see a real aviation topic here, isn't it?


Have a look at this one that I found late last night - check the section
out on Wing Efficiency - and the sections beyond it... comments welcomed


http://home.comcast.net/~clipper-108/lift.pdf

--
Duncan.


I didn't have to get past the first several paragraphs to see what was
going on here with this paper. It becomes apparent with the sentence,
"Bernoulli relies on equal transit times". This statement is false on
premise so all that comes after it has to be flawed.
Bernoulli absolutely and most certainly does NOT rely on equal
transit. Equal transit is incorrect in ALL explanations on lift


I don't think you read or understood the paper very well. The author is
saying that that is the common misconception - he terms it, "Popular
Description" - which he points out is incorrect - as you do.

--
Duncan.
  #48  
Old May 26th 11, 01:17 AM posted to rec.aviation.piloting
Dudley Henriques[_3_]
external usenet poster
 
Posts: 66
Default Lift - Newton/Bernoulli ratio...

On May 25, 6:55*pm, Dave Doe wrote:
In article 47971036-2b4d-4297-bcbf-
, ,
Dudley Henriques says...











On May 25, 2:36 am, Dave Doe wrote:
In article 6469c134-67e0-4ca9-8dd1-
, , a says....


On May 24, 10:35 am, Dudley Henriques
wrote:
On May 23, 9:31 pm, a wrote:


On May 22, 10:02 pm, brian whatcott wrote:


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.

  #49  
Old May 26th 11, 02:20 AM posted to rec.aviation.piloting
Dudley Henriques[_3_]
external usenet poster
 
Posts: 66
Default Lift - Newton/Bernoulli ratio...

On May 25, 6:55*pm, Dave Doe wrote:
In article 47971036-2b4d-4297-bcbf-
, ,
Dudley Henriques says...











On May 25, 2:36 am, Dave Doe wrote:
In article 6469c134-67e0-4ca9-8dd1-
, , a says....


On May 24, 10:35 am, Dudley Henriques
wrote:
On May 23, 9:31 pm, a wrote:


On May 22, 10:02 pm, brian whatcott wrote:


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.

  #50  
Old May 26th 11, 03:20 AM posted to rec.aviation.piloting
Mxsmanic
external usenet poster
 
Posts: 9,169
Default Lift - Newton/Bernoulli ratio...

Dave Doe writes:

If you are right, I'd expect to see planes with the airfoil upsidedown
(with the increased camber on the bottom), but that's not the case (and
I'm talking about the *wings* here, not the horizontal stabiliser


Actually it is. NASA has tested airfoils with a camber on the bottom, and they
fly just as well as airfoils with a camber on the top. I don't know what
became of the research, though. As a I recall, they had some airfoils that
were very good at preventing stalls, but I suppose they had other
disadvantages (drag problems?).

I think you have explained though, that the Bernoulli effect occurs with
a barn door too at an angle of attack - however it is a lot less
*efficient* without that camber (which will continue to 'suck' air down
- as the camber continues to change direction - and therefore drag the
viscous air around it with it). I hope you'll agree with that.


Good airfoil designs can reduce drag and improve stall characteristics, but
generating lift requires only a positive angle of attack.
 




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