what the heck is lift?

On Fri, 09 Sep 2005 10:47:52 -0400, T o d d P a t t i s t
wrote:


A change in height is not an indication that the vertical
component of the total aerodynamic force is less or more
than weight. Only an accelerating change in height
indicates an imbalance in forces. Constant climbs, constant
descents, fully developed spins, etc. all have the vertical
component equal to weight.



Sorry, I wrote before I thought. I meant "no change in acceleration"
and didn't catch that he had stated "Steady sinking" and "fully
developed"

He's right. I'll go crawl away now...


Jim

http://www.unconventional-wisdom.org

"T o d d P a t t i s t" wrote in message
...
"Dudley Henriques" dhenriques@noware .net wrote:

both descriptions (often referred to as the Bernoulli
and Newton descriptions) are 100% correct

Not AGAIN!!!!!!!!!
Dudley

Now Dudley, you don't say that to every new student who
tries to steer with the yoke while taxiing, do you? OMG,
not another student who's got it wrong -when will it ever
end!

Similarly, there is an endless supply of people who haven't
yet figured out what "lift" is. It will never ever stop.
The best we can do is to do a better job of teaching it at
the pilot level (the quality of instruction on this is
abysmal), and a better job of answering the questions that
arise. :-)

Just an attempt at a small bit of "inside" humor here...obviously misguided.
Dudley Henriques

Peter Duniho wrote:
Hilton wrote:
Todd's reply to this clearly shows why Roger's statement is wrong.

No, it doesn't. See my reply to Todd and Stefan's reply here to
understand
what we are all talking about.

You wrote "Had his definition of lift been correct, he would have been
exactly correct." Ummm, OK. But lift is well-defined and it is not
defined as the force that opposes weight. So, you can redefine whatever you
want, doesn't make it right.

Hilton

"Hilton" wrote in message
ink.net...
You wrote "Had his definition of lift been correct, he would have been
exactly correct." Ummm, OK. But lift is well-defined

Actually, part of the problem is that "lift" is poorly defined. It means
different things in different contexts.

and it is not
defined as the force that opposes weight.

Actually, most basic aviation texts written for pilots DO define lift as
"the force that opposes weight". You should not be faulted for having never
read one; after all, the texts certainly gloss over many important facts,
and it's not necessary to have studied one to become a pilot. But many
pilots DO use them as a reference, and they DO define lift in exactly the
way you seem to think they do not.

So, you can redefine whatever you want, doesn't make it right.

I'm not the one doing the "redefinition". The word "lift" is simply not a
technical term. You can get closer by using the phrase "aerodynamic lift",
but ultimately you simply need to know in what context you're using the
word.

Pete

Hilton wrote:

But lift is well-defined and it is not
defined as the force that opposes weight.

That's the way Jeppesen describes it.

George Patterson
Give a person a fish and you feed him for a day; teach a person to
use the Internet and he won't bother you for weeks.

Nothing about curvature, nothing about pressure. My point exactly.

OK check this out...

http://scienceworld.wolfram.com/phys...lliEffect.html

I think this makes my point.

G

"Hilton" wrote in message
ink.net...
Peter Duniho wrote:
Hilton wrote:
Todd's reply to this clearly shows why Roger's statement is wrong.

No, it doesn't. See my reply to Todd and Stefan's reply here to
understand
what we are all talking about.

You wrote "Had his definition of lift been correct, he would have been
exactly correct." Ummm, OK. But lift is well-defined and it is not
defined as the force that opposes weight. So, you can redefine whatever
you
want, doesn't make it right.

Hilton

I would tend to agree with you on this point, but with a caveat.
Unfortunately for many student pilots searching for information on lift,
many of the data sources in use at the student pilot level present subjects
like lift improperly in my opinion anyway.
Rather than state a definition of lift, the "definition" actually passes
that stage and presents what lift DOES! It's a fine point, but it is worthy
of note for the more "scientific minds" among us :-)
I've always STARTED an explanation of lift by presenting it initially as the
aerodynamic force that opposes the relative wind, NOT the force that opposes
gravity or weight. (That comes later :-)))
Again, it's a fine point, and there are many ways to discuss definition, and
if nothing else, what you are discussing here with others on the group helps
demonstrate why the subject of lift is so misunderstood by the student pilot
community. (Not your fault BTW :-)
I think I've spent more time discussing lift with students through the years
than any other single aspect of flight. Part of the reason for that is the
confusion caused by the community's seeming insistence on presenting lift in
a non standard written form.
Dudley Henriques

buttman opined

I have always been under the impression that lift is the product of
airspeed and angle of attack, and that lift is the measure of upward
force acting on the plane at a given time. For instance, if you are
doing slow flight, your wings are producing the same amount of life
that you would be if you were cruising, GIVEN that you did not lose or
gain any altitude during the maneuver.

My instructor, which is a very knowledgable guy tried telling me that
lift has nothing to do with airspeed. He said that lift is directly and
soley related to AOA and AOA only. So if you are doing slow flight, you
are producing more life than you are when you're cruising. I overheard
a ATP guy who flies King Air's say that this huge 20 ton military plane
he used to fly would fly approaches at 110 knots, and I heard him say
"It is able to do this because it producing so much lift", which I took
as him defining lift as my instructor does.

So whats the deal here? Are we just thinking of two diffrent concepts?

Lift = Cl(AOA) * Area * V^2


-ash
Cthulhu in 2005!
Why wait for nature?

The distinction is really a thought convenience to help us talk about
what is going on and not a real physical difference. Lift is really
drag directed upwards.

--

Roger Long

Stall is not loss of lift but loss of stability in the airstream.
Stability is the ability to reach a steady state. A fully stalled
wing will develop just as much lift as an unstalled one but will seek
an angle of attack that will result in a steady state by sinking
faster. This makes most aircraft head nose first for the ground which
feels like loss of lift.

For a more complete explanation:

http://www.avweb.com/news/airman/184307-1.html

--

Roger Long