Thrusting or Sucking (where's Howard Stern when we need him.)

Schroedinger says yes! and no!
"Shawn" sdotherecurry@bresnannextdotnet wrote in message
...
Don Johnstone wrote:
I think you can also obtain books that prove the earth
is flat and the Holocaust never happened. Oh and I
forgot there are several that prove global warming
:-)

"Climate Change" C'mon don, get with the times. "Global Warming" is so
1997.
;-)
BTW, was the Earth flat before Magellan sailed around it?

Shawn

On Mon, 9 Jan 2006 19:05:38 UTC, Don Johnstone
wrote:

: I think you can also obtain books that prove the earth
: is flat and the Holocaust never happened. Oh and I
: forgot there are several that prove global warming
: :-)

Indeed. Any book which explains why Bernouilli doesn;t work was
written by someone who doesn;t understand what Bernouilli's theorem
say in the first place, or when and how it is applied.

Ian


--

Ken,
Howard Stern is on Sirius Satellite radio... Channel 100... first day
today! Channel 101 replay for West Coasters ..... LOL

Ken Kochanski (KK) wrote:

OK, what is the better explanation to give fledgling students. Should
you say the wing deflects/pushes/thrusts the air down to hold the
aircraft up ... or should you say the wing/airflow creates a low
pressure area that sucks the wing/aircraft upwards.

I suggest you tell them to hold their hand out a car window like a wing,
and experiment with the angle of attack. Anything more complicated than
that isn't going to help them fly a glider better. You don't have to
understand the physics to fly well, as ras demonstrates repeatedly, and
I don't see how explaining it with Bernoulli's theorem, or f=ma, or
pressure differentials is an aid to flying. It's hard enough to get
across the idea of angle of attack for stalling, much less Bernoulli or
Newton.

Like many people, Bernoulli was the initial and only explanation I was
aware of ... but I now think it is easier and more accurate to explain
that a wing/airfolil pushes the air downward. Yes, you do have
pressure differences, but that is just an artifact of the process.

And this illustrates part of the problem. Ken, whom I believe to be a
good instructor, wants to explain it to the student, but he doesn't
understand it either (I'm not suggesting I do, either). Nonetheless, his
students can fly well, because you have to know what to do at the right
time, and (fortunately) you don't have to figure it out from an
explanation of the physics involved.

Pragmatically, telling the student whatever explanation makes them happy
is probably good enough, but maybe referring the really interested to
good book like "Fundamentals of Sailplane Design" would be a good idea.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Wrote
"You don't have to understand the physics to fly well, as ras demonstrates
repeatedly"

In terms of agreeing with Eric's two cents worth on the phsyics and
aerodynamics of it all...I tend to agree...I still find myself clueless as
to how the toilet actually flushes...and yet it's use, I accomplish rather
handily.

Please...I beg....don't explain the whole physics issues...I'll sleep
soundly, knowing that...
" It just swirls around...and then disappears down that hole there..."




Happily clueless.


Steve.

Spell checking is left as an excercise for the reader.
"Ken Kochanski (KK)" wrote in message
oups.com...

OK, what is the better explanation to give fledgling students. Should
you say the wing deflects/pushes/thrusts the air down to hold the
aircraft up ... or should you say the wing/airflow creates a low
pressure area that sucks the wing/aircraft upwards.

Like many people, Bernoulli was the initial and only explanation I was
aware of ... but I now think it is easier and more accurate to explain
that a wing/airfolil pushes the air downward. Yes, you do have
pressure differences, but that is just an artifact of the process.

A Bernoulli based explanation seems to create some inconsistencies.


Berhoulli's equation (pressure + (1/2 *density* velocity squared)
+(densty*g*elevation) = constant) is simply a special case of Newtons law
applied to ideal gasses under specific circunstances.

So, no inconsistancies, no problems.

Air is deflected. Delta pressures are created.


--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail

Bernoulli is not explaining 70% of the lift an ordinary airfoil
generates. Bernoulli completely fails when using a flat plate which
creates plenty of lift at normal angles of attack. Newton, bah humbug!
The key to understanding lift is circulation, nothing else gives
compliance with wind tunnel and test data.
Problem is that it takes about 20 minutes to read through the whole
story and many people give up before they understand. Here is by far
the best explanation I have found:
http://www.av8n.com/how/htm/airfoils.html
This guy put an entire book about flight training on the web, God bless
him!
He disposes with many myths that simple minded and uneducated wannabe
physicists promote, you gotta love it!
Ken, I know you as a reasonably smart guy, you're gonna figure it out!

Herb, J7

Capt. Geoffrey Thorpe wrote:
Spell checking is left as an excercise for the reader.
"Ken Kochanski (KK)" wrote in message
oups.com...

OK, what is the better explanation to give fledgling students. Should
you say the wing deflects/pushes/thrusts the air down to hold the
aircraft up ... or should you say the wing/airflow creates a low
pressure area that sucks the wing/aircraft upwards.

Like many people, Bernoulli was the initial and only explanation I was
aware of ... but I now think it is easier and more accurate to explain
that a wing/airfolil pushes the air downward. Yes, you do have
pressure differences, but that is just an artifact of the process.

A Bernoulli based explanation seems to create some inconsistencies.


Berhoulli's equation (pressure + (1/2 *density* velocity squared)
+(densty*g*elevation) = constant) is simply a special case of Newtons law
applied to ideal gasses under specific circunstances.

So, no inconsistancies, no problems.

Air is deflected. Delta pressures are created.


--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail

What ??? Bernoulii works great for flat plate airfoils ! Or are you
confusing the real Bernoulli with the bogus equal transit time BS that
some "dumb the truth down for the stupid pilots" wiseass created ?

The site has a good and complete explanation.

Todd Smith, 3S

"toad" wrote in message
oups.com...
What ??? Bernoulii works great for flat plate airfoils ! Or are you
confusing the real Bernoulli with the bogus equal transit time BS that
some "dumb the truth down for the stupid pilots" wiseass created ?

Does anyone know who the aforementioned wiseass was? Or when this myth was
invented?

--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

On Mon, 9 Jan 2006 23:27:10 UTC, "1MoClimb"
wrote:

: Bernoulli is not explaining 70% of the lift an ordinary airfoil
: generates. Bernoulli completely fails when using a flat plate which
: creates plenty of lift at normal angles of attack.

Rubbish. Bernouilli explains it perfectly well, as long as you have
the right velocity distribution. What Bernouilli's theore, does /not/
do is predict velocity distributions, and certainly not thos ebased on
fatupus ideas like "it's the different lengths of the top and bottom
surfaces that matter."

As you go on to say, rightly, it;s circulation that matters, and one
you know how big the bound vortex is a simply momentum equation on a
cylindrical control volume around the vortex/wing produces the
Kutta-Joukowski Theorem: lift = free stream velocity x circulation x
density. But do do that, no need the pressure distribution on the
control surface. Guess how you do that?

Yup. Bernouilli.

Ian

--