Mxsmanic , IFR sensations, and some other stuff

On May 23, 9:32*am, "Capt. Geoffrey Thorpe" The Sea Hawk At Wow Way
D0t C0m wrote:


You can use either Newton or Bernoulli to explain lift, but the correct
way to explain it is to explain how both are correct.

That's because Bernoulli's equation is nothing more than Newtons law
(conservation of momentum) applied to a streamline. It's not that hard to
derive Bernoulli's equation from Newtons...

Nope. It's an energy equation, not inertial.

Cheers

Dudley Henriques wrote:

Any article that "discounts Bernoulli" as having anything to do with
lift is incorrect. I just can't understand why there is so much trouble
in the pilot community understanding that Newton and Bernoulli do NOT
conflict in any way whatsoever, and that each explanation is correct in
itself. Newton AND Bernoulli are BOTH present simultaneously on th wing
at any moment lift is being created. EACH creates the other and EACH is
a complete explanation for how lift is created.

You can use either Newton or Bernoulli to explain lift, but the correct
way to explain it is to explain how both are correct.
In other words, anytime you have lift being created you have a Newton
explanation AND a Bernoulli explanation occurring at the SAME TIME!

Most people seem to want simple, one size fits all answers to
everything and forget that most real life things, e.g. what causes
lift and what causes cancer, are complex and can't be boiled down
into a 10 second sound bite.


--
Jim Pennino

Remove .spam.sux to reply.

wrote:
Dudley Henriques wrote:

Any article that "discounts Bernoulli" as having anything to do with
lift is incorrect. I just can't understand why there is so much trouble
in the pilot community understanding that Newton and Bernoulli do NOT
conflict in any way whatsoever, and that each explanation is correct in
itself. Newton AND Bernoulli are BOTH present simultaneously on th wing
at any moment lift is being created. EACH creates the other and EACH is
a complete explanation for how lift is created.

You can use either Newton or Bernoulli to explain lift, but the correct
way to explain it is to explain how both are correct.
In other words, anytime you have lift being created you have a Newton
explanation AND a Bernoulli explanation occurring at the SAME TIME!

Most people seem to want simple, one size fits all answers to
everything and forget that most real life things, e.g. what causes
lift and what causes cancer, are complex and can't be boiled down
into a 10 second sound bite.


This is exactly correct.

Lift explanation in it's true form is an extremely complicated issue.
Attempts to explain it in one simple sentence is usually very confusing
to a new student pilot.
The closest thing to a one sentence explanation I have seen is that lift
is created by turning an airflow.
Of course this covers Newton and leaves Bernoulli out there to be
discovered later on as one finally comes to realize that you can't turn
the airflow without having the pressure difference :-)

The best way to handle the lift question is to openly discuss both
Newton and Bernoulli and how they interact to create each other while
creating what we call lift.

--
Dudley Henriques

"Dudley Henriques" wrote

Lift explanation in it's true form is an extremely complicated issue.
Attempts to explain it in one simple sentence is usually very confusing
to a new student pilot.
The closest thing to a one sentence explanation I have seen is that lift
is created by turning an airflow.
Of course this covers Newton and leaves Bernoulli out there to be
discovered later on as one finally comes to realize that you can't turn
the airflow without having the pressure difference :-)


I hadn't looked into this much in recent years and the article rekindled
some interest. I hadn't even heard of the "equal transit theory" before you
mentioned it, but a short search brought up a detailed explanation of
exactly what you are talking about, and turning the airflow is ultimately
what it's all about for both Bernoulli and Newton.

BDS

On May 22, 10:15 am, wrote:
Dudley Henriques wrote:
Snipped

Most people seem to want simple, one size fits all answers to
everything and forget that most real life things, e.g. what causes
lift and what causes cancer, are complex and can't be boiled down
into a 10 second sound bite.

--
Jim Pennino

Remove .spam.sux to reply.

Careful there; next you'll be telling us that we shouldn't nationalize
the oil companies, tax all profits and generally use a Marxist
economic system in an effort to 'simplify' our complex energy issues.

wrote:
On May 22, 10:15 am, wrote:
Dudley Henriques wrote:
Snipped

Most people seem to want simple, one size fits all answers to
everything and forget that most real life things, e.g. what causes
lift and what causes cancer, are complex and can't be boiled down
into a 10 second sound bite.

--
Jim Pennino

Remove .spam.sux to reply.

Careful there; next you'll be telling us that we shouldn't nationalize
the oil companies, tax all profits and generally use a Marxist
economic system in an effort to 'simplify' our complex energy issues.

Or add ethenol to gasoline to free use from oil imports.

--
Jim Pennino

Remove .spam.sux to reply.

"BDS" wrote:
There is an interesting article in Flying magazine by Peter Garrison
that talks about lift theory.

[...]

Oh yeah, the article also pretty much discounts Bernoulli as having
anything to do with why a wing produces lift.

The Bernoulli equations aren't wrong. It is a simply a case that they apply
ONLY to a set of streamlines. Once the streamlines are determined, the
Bernoulli equation should be able to tell you the lift of an airfoil.
Explanations that point to Bernoulli and then fail to discuss how and
whence the streamlines are determined for a problem are bound to lead to
confusion and misunderstanding.

BDS writes:

I agree that a flat wing will produce lift at a positive AOA even without an
airfoil shape - it just won't be as efficient as it would otherwise be if it
were shaped like an airfoil, and talk about pitch divergent...

Non-flat airfoil shapes help to increase the range of usable AOAs and reduce
drag, but a positive AOA is still required to generate lift.

Oh yeah, the article also pretty much discounts Bernoulli as having anything
to do with why a wing produces lift.

It is a common misconception.

BDS wrote:
There is an interesting article in Flying magazine by Peter Garrison that
talks about lift theory.

I thought that one of the most interesting points he made was that the
lift force generated by an airfoil is greater at the optimum angle of
attack than would be the force imparted to it if you were to move it
through the air perpendicular to the air flow at the same speed.

I first experienced this as a kid, sticking my hand out the car window with
the thumb as a leading edge, forming a crude airfoil.

When at the right shape and angle of attack, the lift is amazingly strong.
I always found it remarkable that when my hand was completely
perpendicular to the wind, the force didn't seem as strong.

Definitely a visceral lesson in lifting versus stalling.

On May 22, 5:36 pm, Some Other Guy wrote:
BDS wrote:
There is an interesting article in Flying magazine by Peter Garrison that
talks about lift theory.

I thought that one of the most interesting points he made was that the
lift force generated by an airfoil is greater at the optimum angle of
attack than would be the force imparted to it if you were to move it
through the air perpendicular to the air flow at the same speed.

I first experienced this as a kid, sticking my hand out the car window with
the thumb as a leading edge, forming a crude airfoil.

When at the right shape and angle of attack, the lift is amazingly strong.
I always found it remarkable that when my hand was completely
perpendicular to the wind, the force didn't seem as strong.

Definitely a visceral lesson in lifting versus stalling.

I have a copy of that article here. Very, very good. The
coefficient of lift, as he described it, was a ratio related to the
lift generated by a unit area of wing compared to the flat-plate drag
created by the same unit area perpendicular to the airflow. The Wright
brothers did this in their wind tunnel, so they were able to develop
efficient airfoils. A common airfoil (NACA 23012, IIRC) has a max lift
coefficient of 1.8 , which means that it generates 1.8 times the lift
as the drag of the perpendicular surface of the same area.
He made things really clear when he pointed out that this is why
boats and ships no longer use paddlewheels. The wheel will produce
forward thrust equivalent to the power required to force the paddle
back through the water, while the propeller (they call it a "screw")
will produce much more forward thrust for the same torque required by
the paddlewheel.
So it's a process to cause the air to exert a force in a
direction perpendicular to the airflow. It fools the air, if you like,
which is why we call it an "air foil." A foil is a device to deceive.
Bernoulli is right, and so is Newton. There's a pressure
difference because of the difference in airspeeds between top and
bottom, and there's a movement of air downward to which there's an
upward reaction. The equal-transit time theory is bogus, since the
airfoil is much more efficient than that theory would imply. See this
page:
http://www.av8n.com/how/htm/airfoils.html
And, again, Mxmanic has declared, for about the 12th time, that
positive AOA is necessary for lift. If this was so, and it isn't, and
he has been shown many times that it isn't, then airfoils like the
Clark Y wouldn't generate lift at AOAs as low as -4 degrees. That's
negative 4 degrees, airfoil chord pointing downward. A graph can be
found a third of the way down this page: http://lpmpjogja.diknas.go.id/kc/a/air/airplane.htm
That page also deals properly with both Newton and Bernoulli.

Dan