Backwash Causes Lift?

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 writes:

For example, as I mentioned earlier, I am reading Jeppesens Private
Pilot manual, and there are clearly errors in concept the manual
(energy being created by engine, for example), even though Jeppensen
probably has access to as many Ph.D. laureates as they want.

Describe the errors in a letter and send it to them. Good technical
publishers are always willing to accept corrections.

Le Chaud Lapin wrote in
oups.com:

On Oct 3, 10:34 am, wrote:
On Oct 3, 8:15 am, Le Chaud Lapin wrote:

Actually I did because every book I read about flying skimped on
the
subject. I'm going to hop over to MIT's OpenCourseWare later this
week and download their most basic course on aero/astro.
Benoulli's
principle is toss around as if it were facecloth, but I'm getting
the
feeling that no one is really doing the physics.

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? How old are you,
anyway? 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. The subject
of
lift has been beaten to death on this forum and if you Googled it
you'd find some good information.

I want to be clear. I did not me to say "no one" is doing the
physics. Obviously there are aero/astro scientists all over the
world. What I mean to say is that there seems to be a lot of *pilots*
who are using Bernoulli's principle somewhat carelessly, IMO. Some of
these people are CFI's. Please don't ask me to name individuals, but
I know with certainty that there are at least 2 living, breathing
CFI's who do not understand where 29.92 Hg comes from, or does not
understand it well enough to make it make sense to a student. The
might have understood it at one point, but they don't now. I know
because I asked them. My feelings about teaching is that if you are
not very certain about something, you do more damage than talking
about it. Of course, this leads to the conundrum of having to explain
to a student why a plane stays in the air without providing erroneous
information. If I were a CFI, I would simply say that the aerodynamics
result in pressure below plane is sufficient to counteract pressure
above planes for force of gravity.

That's not enough either.

you need to know how and why lift varies throughot the flight envelope,
but after th ebook learning, it's mostly intuitive and the intuition
comes from experience.

Bertie

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

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-

"Le Chaud Lapin" wrote in message

I'm saying that, if you take a plane with certain critical angle,
throw away engine, put on an engine that can generate 10x the thrust,
the plane should still fly, even if you exceed critical angle.

These books imply that the critical angle is angle at with bad things
happen above the wing, and because of that, the plane will fall. I'm
saying that, you can have all the bad things happen above the wing and
still be able to keep the plane aloft due to compression that occurs
beneath the wing.

Of course, I have only been doing this officially 7 weeks, so I might
be wrong.

You are.

With a stronger engine, the wing would still be stalled. You would be
flying on the thrust of the engine.

Disruption of the flow on the top side of the wing is what defines a stall.
The wing would create only a fraction of the list that it would, unstalled.
--
Jim in NC