Airplane Pilot's As Physicists

Hi All,

There is a long discussion ongoing in rec.aviation.piloting about what
causes lift on a plane. You can read from the link below. Please
note that about 80% of the post are mostly ad hominem attacks and
should be ignored. There are some small bits of real discussion.

http://groups.google.com/group/rec.a...11fa289cd7864a

I am an electrical engineer with experience in analag design and
software, with math and physics background that you would expect of an
electrical engineer.

There are many points made in the discussion, but I would like to
focus on one in particular for the sake of progress.

There are people in the pilot's group, who think that lift on a wing
is analyzed as such:

1. There is air on outside of top of wing that is pushing down, but
reduced because of aerodynamics.
2. The *inside* of the wing contains air pushing up against the
underside of top of wing .
3. Let us ignore that the same air inside the wing pushes down on the
overside of bottom part of wing.
3. The difference in pressure against the underside of the top wing on
the inside of wing and top of wing on outside, is what gives plane
lift.

Note that they ignore the pressure inside the wing that pushes
downward on the wing.

I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing. Lift is caused by a
difference in pressure between the underside of the bottom of the
wing, and the overside of the top of the wing.

I count 8-9 people in the group who are utterly convinced that I am
inept at physics, mathematics, etc.

Note that some of these people have been flying aircraft for years,
even decades, while I am still a student pilot.

Comments from anyone who knows physics welcome.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ps.com:

Hi All,

There is a long discussion ongoing in rec.aviation.piloting about what
causes lift on a plane.


No, there isn't. There are people who know perfectly well how it works
trying to tell a ccouple of k00ks who think they know


Bertie

On Oct 9, 4:08 pm, Le Chaud Lapin wrote:
Hi All,

There is a long discussion ongoing in rec.aviation.piloting about what
causes lift on a plane.

Heh. I know the argument. I think it's broken out here (sci.physics)
many times.

(a) It's the Bernoulli effect due to the shape of the
wing cross-section, the way we were all taught as kids.

(b) No, it's just the angle of attack.

I'm no expert, but I heard enough in similar arguments here
to convince me that the angle-of-attack people are right and
the shape of the wing has more to do with controlling
turbulence.

There are people in the pilot's group, who think that lift on a wing
is analyzed as such:

1. There is air on outside of top of wing that is pushing down, but
reduced because of aerodynamics.
2. The *inside* of the wing contains air pushing up against the
underside of top of wing .

Er... that's a new one. OK, I haven't heard this argument
then.

3. Let us ignore that the same air inside the wing pushes down on the
overside of bottom part of wing.
4. The difference in pressure against the underside of the top wing on
the inside of wing and top of wing on outside, is what gives plane
lift.

You can consider that last just a definition of lift. You
won't get lift unless the upward forces are stronger than
then downward forces.

Note that they ignore the pressure inside the wing that pushes
downward on the wing.

A wing doesn't need to be hollow to fly.

I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing. Lift is caused by a
difference in pressure between the underside of the bottom of the
wing, and the overside of the top of the wing.

I count 8-9 people in the group who are utterly convinced that I am
inept at physics, mathematics, etc.

Note that some of these people have been flying aircraft for years,
even decades, while I am still a student pilot.

Comments from anyone who knows physics welcome.

As I said, I lean toward the angle-of-attack arguments now. Take
a flat rectangle, tilt it into the wind. The wind blows against the
front which is also the bottom, not the back/top. So the
forces are on the bottom.

Why does that translate into lift? I forget the exact arguments
but from first principles if the effect is to change the direction
of the incoming air molecules, then by conservation of
momentum that translates into equal and opposite change
of momentum of the surface, i.e. pressure with an upward
component.

- Randy

Randy Poe wrote in
oups.com:

On Oct 9, 4:08 pm, Le Chaud Lapin wrote:
Hi All,

There is a long discussion ongoing in rec.aviation.piloting about
what
causes lift on a plane.

Heh. I know the argument. I think it's broken out here (sci.physics)
many times.

(a) It's the Bernoulli effect due to the shape of the
wing cross-section, the way we were all taught as kids.

(b) No, it's just the angle of attack.

I'm no expert, but I heard enough in similar arguments here
to convince me that the angle-of-attack people are right and
the shape of the wing has more to do with controlling
turbulence.

There are people in the pilot's group, who think that lift on a wing
is analyzed as such:

1. There is air on outside of top of wing that is pushing down, but
reduced because of aerodynamics.
2. The *inside* of the wing contains air pushing up against the
underside of top of wing .

Er... that's a new one. OK, I haven't heard this argument
then.

3. Let us ignore that the same air inside the wing pushes down on the
overside of bottom part of wing.
4. The difference in pressure against the underside of the top wing
on
the inside of wing and top of wing on outside, is what gives plane
lift.

You can consider that last just a definition of lift. You
won't get lift unless the upward forces are stronger than
then downward forces.

Note that they ignore the pressure inside the wing that pushes
downward on the wing.

A wing doesn't need to be hollow to fly.

I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing. Lift is caused by a
difference in pressure between the underside of the bottom of the
wing, and the overside of the top of the wing.

I count 8-9 people in the group who are utterly convinced that I am
inept at physics, mathematics, etc.

Note that some of these people have been flying aircraft for years,
even decades, while I am still a student pilot.

Comments from anyone who knows physics welcome.

As I said, I lean toward the angle-of-attack arguments now. Take
a flat rectangle, tilt it into the wind. The wind blows against the
front which is also the bottom, not the back/top. So the
forces are on the bottom.

Why does that translate into lift? I forget the exact arguments
but from first principles if the effect is to change the direction
of the incoming air molecules, then by conservation of
momentum that translates into equal and opposite change
of momentum of the surface, i.e. pressure with an upward
component.

- Randy



Well, thanks be to god that that';s been authoritatively setttled.


Bertie

On Oct 9, 3:22 pm, Randy Poe wrote:
On Oct 9, 4:08 pm, Le Chaud Lapin wrote:

Hi All,

There is a long discussion ongoing in rec.aviation.piloting about what
causes lift on a plane.

Heh. I know the argument. I think it's broken out here (sci.physics)
many times.

(a) It's the Bernoulli effect due to the shape of the
wing cross-section, the way we were all taught as kids.

(b) No, it's just the angle of attack.

I'm no expert, but I heard enough in similar arguments here
to convince me that the angle-of-attack people are right and
the shape of the wing has more to do with controlling
turbulence.

There are people in the pilot's group, who think that lift on a wing
is analyzed as such:

1. There is air on outside of top of wing that is pushing down, but
reduced because of aerodynamics.
2. The *inside* of the wing contains air pushing up against the
underside of top of wing .

Er... that's a new one. OK, I haven't heard this argument
then.

3. Let us ignore that the same air inside the wing pushes down on the
overside of bottom part of wing.
4. The difference in pressure against the underside of the top wing on
the inside of wing and top of wing on outside, is what gives plane
lift.

You can consider that last just a definition of lift. You
won't get lift unless the upward forces are stronger than
then downward forces.

Note that they ignore the pressure inside the wing that pushes
downward on the wing.

A wing doesn't need to be hollow to fly.

I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing. Lift is caused by a
difference in pressure between the underside of the bottom of the
wing, and the overside of the top of the wing.

Thanks Randy,

But before we talk about what causes lift on the plane, we should
clear up the basic physics 1st. Note that what I have described above
has nothing to do with airplanes really.

If you read carefully, the premise of what they are saying is that, if
you have, for example, a sealed jar with air in it, you are permitted
to consider the air on the _inside_ of the jar, pushing up on the lid
as contributing to a force to lift the jar off the ground, but you are
not allowed to consider the air on the _inside_ of the jar, pushing
down on the jar un the upper surface of the bottom of the jar.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 9, 3:22 pm, Randy Poe wrote:
On Oct 9, 4:08 pm, Le Chaud Lapin wrote:

Hi All,

There is a long discussion ongoing in rec.aviation.piloting about
what
causes lift on a plane.

Heh. I know the argument. I think it's broken out here (sci.physics)
many times.

(a) It's the Bernoulli effect due to the shape of the
wing cross-section, the way we were all taught as kids.

(b) No, it's just the angle of attack.

I'm no expert, but I heard enough in similar arguments here
to convince me that the angle-of-attack people are right and
the shape of the wing has more to do with controlling
turbulence.

There are people in the pilot's group, who think that lift on a
wing
is analyzed as such:

1. There is air on outside of top of wing that is pushing down, but
reduced because of aerodynamics.
2. The *inside* of the wing contains air pushing up against the
underside of top of wing .

Er... that's a new one. OK, I haven't heard this argument
then.

3. Let us ignore that the same air inside the wing pushes down on
the
overside of bottom part of wing.
4. The difference in pressure against the underside of the top wing
on
the inside of wing and top of wing on outside, is what gives plane
lift.

You can consider that last just a definition of lift. You
won't get lift unless the upward forces are stronger than
then downward forces.

Note that they ignore the pressure inside the wing that pushes
downward on the wing.

A wing doesn't need to be hollow to fly.

I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing. Lift is caused by
a
difference in pressure between the underside of the bottom of the
wing, and the overside of the top of the wing.

Thanks Randy,

But before we talk about what causes lift on the plane, we should
clear up the basic physics 1st. Note that what I have described above
has nothing to do with airplanes really.

If you read carefully, the premise of what they are saying is that, if
you have, for example, a sealed jar with air in it, you are permitted
to consider the air on the _inside_ of the jar, pushing up on the lid
as contributing to a force to lift the jar off the ground, but you are
not allowed to consider the air on the _inside_ of the jar, pushing
down on the jar un the upper surface of the bottom of the jar.



Oh for ****'s sake.

You push on something it moves, right?

Everone already knows that, Stephen hawkings.


While you're trying to agitate in a physics froup why don;'t you ask
them how it's physically possible to get your head that far up your own
ass.

Bertie

On Oct 9, 3:31 pm, Sam Wormley wrote:
Ref:http://www.physlink.com/Education/AskExperts/ae627.cfm

Question:
If an airplane wing provides lift (an airfoil), how does a plane fly
upside down?

Asked by: Lee Hathcox

Answer:
The same way that your hand gets pulled upwards if you stick it out the
car window and tilt it. The lift of an airfoil is determined by two
things - the shape of the wing, and it's angle of attack. Angle of
attack is the angle between the flat surface of the wing, and the
oncoming air stream. So when I roll the airplane upside down... if I
push the stick forward, that pushes the nose of the plane towards the
sky, and increases my angle of attack, even though I'm upside down. So,
the shape of the wing doesn't change, and it pulls me down, but the
angle of attack I control, and I can make it push me up. So when the
lift from angle of attack in the up direction, exceeds the lift from
the shape of the wing, in the down direction, you can balance the force
of gravity acting on the plane. You can see the influence of angle of
attack, because even if your hand isn't shaped like a wing, you can see
how the angle and the force of the air push it in whichever direction
you choose.

Even though this (new) thread is not about what causes a wing to lift,
I just wanted to say for the record that I agree with this answer,
that it is both AoA and curvature of the wing.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
oups.com:

On Oct 9, 3:31 pm, Sam Wormley wrote:
Ref:http://www.physlink.com/Education/AskExperts/ae627.cfm

Question:
If an airplane wing provides lift (an airfoil), how does a plane fly
upside down?

Asked by: Lee Hathcox

Answer:
The same way that your hand gets pulled upwards if you stick it out
the
car window and tilt it. The lift of an airfoil is determined by two
things - the shape of the wing, and it's angle of attack. Angle of
attack is the angle between the flat surface of the wing, and the
oncoming air stream. So when I roll the airplane upside down... if I
push the stick forward, that pushes the nose of the plane towards the
sky, and increases my angle of attack, even though I'm upside down.
So,
the shape of the wing doesn't change, and it pulls me down, but the
angle of attack I control, and I can make it push me up. So when the
lift from angle of attack in the up direction, exceeds the lift from
the shape of the wing, in the down direction, you can balance the
force
of gravity acting on the plane. You can see the influence of angle of
attack, because even if your hand isn't shaped like a wing, you can
see
how the angle and the force of the air push it in whichever direction
you choose.

Even though this (new) thread is not about what causes a wing to lift,
I just wanted to say for the record that I agree with this answer,
that it is both AoA and curvature of the wing.



Quick, call NASA.



Bertie

Le Chaud Lapin wrote:
I am trying to convince them that, if there is air on the inside of
the wing, it pushes against all sides of the inside of the wing,
including both top underside and bottom overside, and thereby
nullifying any effect it would have on the wing.

You are trying to convince one person - there is no plural.

Just for the record, I pointed the OP at the following NASA web pages and
after first thanking me, has decided NASA's explanation is somehow suspect:

http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html
http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
http://www.grc.nasa.gov/WWW/K-12/airplane/downwash.html

Note follow-ups set to sci.physics only.

Randy Poe writes:

As I said, I lean toward the angle-of-attack arguments now. Take
a flat rectangle, tilt it into the wind. The wind blows against the
front which is also the bottom, not the back/top. So the
forces are on the bottom.

The essential feature of an airfoil is that it twists the flow of air as it
passes (or as the airfoil passes through still air, which is equivalent, and
that's how it works in airplanes). The air is accelerated downward, and this
engenders an equal and opposite force that is lift.

So how does a wing produce lift? By twisting air downwards, creating a
downwash. Accelerating a mass of air downwards tends to accelerate the wing
upwards, and there's your lift.

The theory gets more complicated when you try to explain exactly how and why
airfoils twist an airflow. Just looking at a flat board with a positive angle
of attack, you'd think that it would twist the air, and that's exactly what it
does. But the devil is in the details.

Fortunately, aviators don't have to know or care about the details. All they
need to know is that a wing with a positive angle of attack (and below the
stall angle) will generate lift.

Lift, like so many other phenomena in physics, can be analyzed and explained
in a number of different, equally valid ways, depending on one's point of
view. All analyses and explanations converge on the same reality. Of course,
some explanations of lift are just plain incorrect, and unfortunately a few of
them are quite widespread.