Backwash Causes Lift?

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.
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.
The stagnation point on a leading edge isn't right at the front.
It's slightly below the wing, and as AOA increases it moves back
underneath quite a bit. It's not all intuitive, you see, and that
intuitive understanding of some of this stuff is where people get all
messed up and think they have the answers that have escaped all the
other experts all these years. We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.

Dan

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.

It is the removal of air from above the table that causes the lift.

If a person sucks on a straw, thus removing air from the inside of the
straw, the fluid rises into the straw from the container do to the air/
fluid system outside the straw. This is the same phenomenon that is
occurring in my table scenario. In fact, I could enclose the entire
table scenario inside a tube, and cause the bottom table to rise up
off the ground. This has nothing to do with the velocity or
acceleration of air.

The stagnation point on a leading edge isn't right at the front.
It's slightly below the wing, and as AOA increases it moves back
underneath quite a bit. It's not all intuitive, you see, and that
intuitive understanding of some of this stuff is where people get all
messed up and think they have the answers that have escaped all the
other experts all these years. We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.

I do rely on intuition to figure things out, but most importantly, I'd
rather actually understand, than except shallow explanations.

I never attempted to contradict either Bernoulii or Newton. What I
keep saying is that I have seen too many situations where someone will
rattle of "Bernoulli's Principle" and not really understand it
themselves.

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.

-Le Chaud Lapin-

Le Chaud Lapin wrote in
oups.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.

It is the removal of air from above the table that causes the lift.

If a person sucks on a straw, thus removing air from the inside of the
straw, the fluid rises into the straw from the container do to the
air/
fluid system outside the straw. This is the same phenomenon that is
occurring in my table scenario. In fact, I could enclose the entire
table scenario inside a tube, and cause the bottom table to rise up
off the ground. This has nothing to do with the velocity or
acceleration of air.

The stagnation point on a leading edge isn't right at the
front.
It's slightly below the wing, and as AOA increases it moves back
underneath quite a bit. It's not all intuitive, you see, and that
intuitive understanding of some of this stuff is where people get all
messed up and think they have the answers that have escaped all the
other experts all these years. We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.

I do rely on intuition to figure things out, but most importantly, I'd
rather actually understand, than except shallow explanations.

I never attempted to contradict either Bernoulii or Newton. What I
keep saying is that I have seen too many situations where someone will
rattle of "Bernoulli's Principle" and not really understand it
themselves.

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.



Yes, well, you obviously need to write a good old fashioned, angry,
frothng at the mouth letter to Jeppeson. I'm sure Elry will be suitably
rattled.


Bertie

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.

On 3 Oct, 17:56, Mxsmanic wrote:
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.

Thus the pile of "thank you for your input" letters.

Froootloop.

Bertie

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.
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.
The stagnation point on a leading edge isn't right at the front.
It's slightly below the wing, and as AOA increases it moves back
underneath quite a bit. It's not all intuitive, you see, and that
intuitive understanding of some of this stuff is where people get all
messed up and think they have the answers that have escaped all the
other experts all these years. We run into this attitude rather
frequently in the flight training industry. It tends to make the
student unteachable.

I think the main issue is that it doesn't require a Phd in physics to
fly an airplane and the explanations of lift, stall, drag, etc.
for pilots tend to be highly simplified, and rightfully so.

A full explanation that would satisfy a physisicist would likely
cause exterme eye glaze in the average pilot.

If one want's that level of insight, I would suggest they go read
a good aerodynamics text and not expect to find it in a couple of
paragraphs in a USENET posting.

--
Jim Pennino

Remove .spam.sux to reply.

jimp wrote

I think the main issue is that it doesn't require a Phd in physics to
fly an airplane and the explanations of lift, stall, drag, etc.
for pilots tend to be highly simplified, and rightfully so.

A full explanation that would satisfy a physisicist would likely
cause exterme eye glaze in the average pilot.

If one want's that level of insight, I would suggest they go read
a good aerodynamics text and not expect to find it in a couple of
paragraphs in a USENET posting.

Exactly.

To learn to fly, it is important to understand aerodynamics to the point of
knowing what you can do to mess them up, and what you can do to fix things.
Only the most basic understanding of the subject is needed to achieve these
goals.
--
Jim in NC

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. If they wanted to know more, I'd
direct them to book on aerodynamics.

Can you fly without understanding many of these things? Certainly.
But personally, I would feel a lot better in a cockpit if I did. The
more I know, the more confident I am, and if something goes wrong, the
added perspective will allow me to quickly eliminate those things
which I am certain is not root of problem. This reminds me of
incident about year ago when I was fixing a neighbor's car, and
another neighbor kindly ask me if we needed to borrow jumper cables,
even though she had heard the engine turn over with no problem many
times. Someone who understands how automobile works would have known
that it is highly unlikely that there was problem with battery with
such robust cranking. [Turned out to be fuel line].

-Le Chaud Lapin-

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.