Backwash Causes Lift?

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

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.

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, 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

Le Chaud Lapin writes:

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

You can only push the wing upward if something else is pushed downward. Thus,
the wing generates lift only to the extent that it diverts a substantial mass
(of air) downward. No downwash, no lift.

wrote in message
oups.com...
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.

I SWEAR to you guys, somebody sounding conspicuously like him was out here
within the last couple of months refuting Bournoulli and referring to
pressure under the wing, making plywood fly, etc. Sounds awful familiar.

-c

On Oct 5, 4:42 pm, "Gatt" 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.

I SWEAR to you guys, somebody sounding conspicuously like him was out here
within the last couple of months refuting Bournoulli and referring to
pressure under the wing, making plywood fly, etc. Sounds awful familiar.

It's familiar because there are many out there who don't
understand or don't agree with the textbooks. Even among experts
there's disagreement. Every so often one of them makes an issue of it.
It's quite normal, especially if they don't use the Google Groups
Search function first to see what the previous arguments have been on
the subject on a particular newsgroup.
It annoys some of us because the same arguments are put forth
repeatedly and we can't figure out why some don't get it. But it's no
different than my classroom, in which every new batch of students
brings the same misunderstandings and doubts and arguments. We were
young once, too, and didn't believe much of what our teachers were
trying to tell us.
Bernoulli said that moving air has a lower pressure than
static air. The air over the top of the wing is moving considerably
faster than that underneath, so it has lower pressure. It's not
rarefaction; it's the increase in dynamic pressure (velocity) that
subtracts from static pressure, the same phenomenon that makes a
turbine engine work so well.
Newton said that for every action there's an equal and
opposite reaction. If you look at the diagrams of airflow here,
http://www.av8n.com/how/htm/airfoils.html
scrolling down to Figure 3.2, you'll see that there's upwash ahead of
the wing as well as downwash behind it. the upwash is generated by the
approaching low pressure area above the wing. As the wing passes, the
upwash is converted to downwash; if this isn't Newton at work, I don't
know what is. Newton would be just another dead guy.
For the average PPL or CPL this should be sufficient. It's true
enough, even if it doesn't give the detail that the physicist would
like. As I said, most pilots have other careers and interests and they
find that Newton and Bernoulli jibe with what they experience in the
air, so they're satisfied. Making textbooks thicker or filling them
with competing theories does nothing but confuse these people.
If a student wants to argue that the physics as presented are
all wrong he should do extensive research and publish a book on the
subject, not argue with pilots who have been trusting their soft pink
bodies to Bernoulli and Newton for decades.

Dan

"Gatt" wrote

I SWEAR to you guys, somebody sounding conspicuously like him was out here
within the last couple of months refuting Bournoulli and referring to
pressure under the wing, making plywood fly, etc. Sounds awful familiar.

You don't have to convince me. This one is as bad a K00K as has been here
for a while, and that's saying something.

He can say he has not changed his handle until he is blue in the face, and I
won't believe it.
--
Jim in NC