Backwash Causes Lift?

Mxsmanic wrote in
:

writes:

Lemme see: People have been building flying machines since the late
1800's, about 125 years now, and none of them have been interested
enough in the phenomenon of lift to do the physics?

The physics seems simpler than it is, and the explanation of the
physics depends hugely on one's frame of reference.

However, the practical reality is simple: an airfoil with an angle of
attack greater than zero and less than the critical (stall) angle will
produce lift. This is completely reliable, and it's all a pilot needs
to know (although, oddly enough, many pilots don't know this).

Many of the contributors here have been flying much longer
than you have likely been alive and have studied this in detail, and
some of them might even have doctorates in the subject.

See above.

We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.

Students only need to know about the angle of attack, if theory is
required. Or you can simply teach them by rote, which is even easier
albeit somewhat less safe.




You have no idea what you are talking about.

You don't fly and you never will, mercifully.

Bertie

On Oct 3, 10:34 am, wrote:
Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 3, 10:34 am, wrote:
Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.


Couldn't be clearer and it's really all you need to know.

Go out and fly now. If you ask any more questions I'l just hand you over to
Anthony from now on.



Tough love.


Bertie

On Oct 3, 12:05 pm, Bertie the Bunyip wrote:
Le Chaud Lapin wrote roups.com:

On Oct 3, 10:34 am, wrote:
Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

Couldn't be clearer and it's really all you need to know.

Go out and fly now. If you ask any more questions I'l just hand you over to
Anthony from now on.

I don't think actually flying an airplane will explain the
aerodynamics of lift any more than driving a car will help with
understanding of rack-and-pinion. Yes, there will be an an intuition
that will develop, but that's going to happen anyway, and that would
have happened even if I were a 16-year-old sitting in pilot's seat.
Doesn't mean that 16-year-old is going to understand aerodynamics.

Let's face it. A large pecentage of people walking this planet think
there is a "suction" force. I was watching the History Channel one
day, and the narrator actually used that term - a "suction" force, and
he did not mean the force that is on the other side of the barrier
where the "suction" force was being applied. I've also seen countless
erroneous explantions on the same channel about electronics which I do
know about. Typically the narrator will say voltage when he meant
current, or energy when he meant power.

I'm more of a mind-over-matter type. I'll get my license and fly
around and develop the intuition that you mention, certainly, but
that's not enough.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
ups.com:

On Oct 3, 12:05 pm, Bertie the Bunyip wrote:
Le Chaud Lapin wrote
roups.com:

On Oct 3, 10:34 am, wrote:
Both Newton and Bernoulli are correct. Even inside a pipe
the
static pressure drops as velocity increases. That's why your
bottom table jumps as you yank off the top one: you accelerated an
airflow. And in generating lift there's a displacement of air.
Can't escape that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

Couldn't be clearer and it's really all you need to know.

Go out and fly now. If you ask any more questions I'l just hand you
over to Anthony from now on.

I don't think actually flying an airplane will explain the
aerodynamics of lift any more than driving a car will help with
understanding of rack-and-pinion.

Well, then you're a lost cause.

Ask Anthony and be damned, then

Bertie

On Oct 3, 10:56 am, Le Chaud Lapin wrote:
On Oct 3, 10:34 am, wrote:

Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

-Le Chaud Lapin-

See http://www.petester.com/html/bachap02.html or
Google yourself using terms like static, dynamic pressures, kinetic
energy, converging or diverging ducts, net energy, and so on. If we
have gas flow in a pipe, and if we had a static gauge and a dynamic
pressure gauge (airspeed), we would see the static pressure fall as
the airspeed rose. If the no-movement static pressure was 29.92" hg,
the dynamic pressure would be zero. As the speed comes up to, say,
10" hg on the dynamic, the static will fall 10" to 19.92. There is no
free lunch. The static and dynamic always add up to the same figure as
speed increases or decreases, unless there is further energy input as
in a turbine combustion section.
As I said, it's not intuitive. Converging and diverging ducts
do different things than you'd expect, but we know they work because
the turbine engine uses their principles, and wouldn't work without
them.

Dan

On Oct 3, 1:33 pm, wrote:
On Oct 3, 10:56 am, Le Chaud Lapin wrote:

On Oct 3, 10:34 am, wrote:

Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

[explanation of Bernoulli's principle clipped].

I did not mean that I did not understand Bernoulli's principle.

What I am saying is that I do not believe that the bottom table jumps
because of airflow acceleration. In fact, if I were to use tables
with circular faces, and put the entire apparatus in a giant
cylindrical tube, and pull up on the top table, assuming that the very
bottom of the tube were open-ended, the bottom table would follow the
top table upward, no matter how fast any air inside the tube were
moving. I could move the top table one molecular diameter every
10,000,000 years, and after the top table has moved, say, 0.5 meters,
the bottom table will follow. This assumes, of course, that the
appartus is airtight, that no air from outside the tube can squeeze in
between the walls of table and tube to fill the void that was created.

There are 14.7 lbs per square inch of pressure pressing upward against
the underside of the bottom table. The yanking of the top table
creates a vacuum between the two faces of the table. The lack of
pressure on the top of the bottom table leaves nothing to counteract
the pressure pressing upward on the underside of the bottom table.
Then the only thing holding the bottom table on the floor is gravity.
Assuming that the table is a typical table of typical weight and size,
one is guranteed that the impulse net pressure of 14.7lbs / in^2 is
enough to overcome gravity and lift the bottom table off the floor.

Note that this really has nothing to do with Bernoulli's principle or
dynamic pressures.

If it is still not clear, put the assembly in a tube again, anchor the
bottom table with a tie wire so it cannot move upward, and using a
hydraulic jack, pull the top table upward, then stop, wait a minute,
have a Coke (sipping with a straw of course), then take cutters and
snap the wire holding the bottom table to the floor.

At the precise moment that the wire is snapped, there is no movement
of anthing at all. There is no Bernoulli action.

The bottom table will rush up toward the top table, even slamming
against it quite hard if the coefficient of sliding friction between
table-side and tube wall is low enough.

-Le Chaud Lapin-

On 3 Oct, 21:11, Le Chaud Lapin wrote:
On Oct 3, 1:33 pm, wrote:

On Oct 3, 10:56 am, Le Chaud Lapin wrote:

On Oct 3, 10:34 am, wrote:

Both Newton and Bernoulli are correct. Even inside a pipe the
static pressure drops as velocity increases. That's why your bottom
table jumps as you yank off the top one: you accelerated an airflow.
And in generating lift there's a displacement of air. Can't escape
that at all.

Also, if you don't mind, I would like to understand what you mean
here.

It's not clear to me.

[explanation of Bernoulli's principle clipped].

I did not mean that I did not understand Bernoulli's principle.

What I am saying is that I do not believe that the bottom table jumps
because of airflow acceleration. In fact, if I were to use tables
with circular faces, and put the entire apparatus in a giant
cylindrical tube, and pull up on the top table, assuming that the very
bottom of the tube were open-ended, the bottom table would follow the
top table upward, no matter how fast any air inside the tube were
moving. I could move the top table one molecular diameter every
10,000,000 years, and after the top table has moved, say, 0.5 meters,
the bottom table will follow. This assumes, of course, that the
appartus is airtight, that no air from outside the tube can squeeze in
between the walls of table and tube to fill the void that was created.

There are 14.7 lbs per square inch of pressure pressing upward against
the underside of the bottom table. The yanking of the top table
creates a vacuum between the two faces of the table. The lack of
pressure on the top of the bottom table leaves nothing to counteract
the pressure pressing upward on the underside of the bottom table.
Then the only thing holding the bottom table on the floor is gravity.
Assuming that the table is a typical table of typical weight and size,
one is guranteed that the impulse net pressure of 14.7lbs / in^2 is
enough to overcome gravity and lift the bottom table off the floor.

Note that this really has nothing to do with Bernoulli's principle or
dynamic pressures.

If it is still not clear, put the assembly in a tube again, anchor the
bottom table with a tie wire so it cannot move upward, and using a
hydraulic jack, pull the top table upward, then stop, wait a minute,
have a Coke (sipping with a straw of course), then take cutters and
snap the wire holding the bottom table to the floor.

At the precise moment that the wire is snapped, there is no movement
of anthing at all. There is no Bernoulli action.

The bottom table will rush up toward the top table, even slamming
against it quite hard if the coefficient of sliding friction between
table-side and tube wall is low enough.


Whoowh!
Zero point energy!

In my own kitchen!

I can tell the electric company to **** off now.


Bertie

On Oct 3, 4:14 pm, Bertie the Bunyip
wrote:
Whoowh!
Zero point energy!


Surely, you must be joking. The exposition I wrote above is nothing
more than high school physics.

Where do you see me implying zero point energy?

I know my physics. Do you? There is no "zero point" energy.

Plain and simple:

If a person sucks on a straw, the reason the fluid rises has *NOTHING*
to do with Bernoull's principle. It has to do with the balance in
force being eliminated. In particular, the air in the straw is
removed, so the 14.4lbs/square in will lift the fluid in the straw.

This should be familiar to you, since you are a pilot. Where do you
think 29.92 Hg comes from? It comes from the height that a column of
mercury will rise in a complete rarefied tube in STP, which just
happens to be 29.92.

Both you and Mxmanic are wrong.

-Le Chaud Lapin-

Le Chaud Lapin wrote:

Both you and Mxmanic are wrong.

-Le Chaud Lapin-

ooooo.....wait for it.....here it comes....

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