what the heck is lift?

T o d d P a t t i s t wrote:

I'd say it's the other way around: Lift creates the pressure differential.

The pressure differential is caused by the motion of the air
as the wing moves through the air.

Well how will that work. The air on top is set into motion as a result
of the wing pulling on it and the air on bottom is set into motion as a
result of the wing pushing on it. How can the motion of the air on the
top and bottom of the wing cause a pressure differential? It can't.
The pressure differentials are actually caused by the wing pulling and
pushing on the air and the air pushing and pulling back. Low pressure
does very little to generate lift directly. Example. A ball will
suspend in an upward airflow from an air hose. This causes the not to
bright people at the NASA web sight to jump to the large and mostly
inaccurate conclusion that it is sucked in to the low pressure flow or
pushed into it by the higher atmospheric pressure. This is disproved
by the fact other shaped object do not seem to be sucked into the flow
at all.


The shape of the wing,
particularly, the upper surface, strongly affects the motion
of the air and thereby strongly affects the amount of lift
and drag produced.



The shape of the wing (the top or bottom) strongly affects the
direction of the motion of influenced air. Thereby strongly affecting
the amount of lift produced. Example One of the airfoil shapes that
generates the most lift at zero degrees angle of attack is the under
cambered. It uses shape on top and bottom to divert the low-pressure
air.

Dudley Henriques wrote:


"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'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 :-)))
Dudley Henriques

Lift opposes the Relative Wind?

How does lift (and I assume you are talking wing lift here since you mention
gravity/weight) *oppose* the relative wind?

What do you mean when you use the word "oppose"?

Or were you speaking of prop lift?

--
Saville

Replicas of 15th-19th century nautical navigational instruments:

http://home.comcast.net/~saville/backstaffhome.html

Restoration of my 82 year old Herreshoff S-Boat sailboat:

http://home.comcast.net/~saville/SBOATrestore.htm

Steambending FAQ with photos:

http://home.comcast.net/~saville/Steambend.htm

"gregg" wrote in message
...
Dudley Henriques wrote:


"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'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 :-)))
Dudley Henriques

Lift opposes the Relative Wind?

This should read "Lift is the component of aerodynamic force perpendicular
to the relative wind.", and not "opposes". My error in presentation.
DH

Dudley,

As usual, excellent post - I totally agree.

Hilton

Roger Long wrote:
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.

I have absolutely no idea what you mean. I have never seen lift described
as "drag directed upwards". Please explain.

Hilton

Peter,
Todd wrote:
Pete, in your reply above, you did the same thing Roger did,
(and what I often do too,) you equated the vertical
component of aerodynamic force to "lift."
[zap]
The real issue here is whether lift changes according to airspeed. The
generic idea of lift (as in, the force that keeps airplanes aloft) versus
the specific physics definition of lift is inconsequential in that
context,
and not one I feel is worth nitpicking over.

It is *exactly* worth discussing and it is not nitpicking. Lift as DEFINED
is completely different to the force pointing upwards and there are many
examples where they all completely different; some example: spins, steep
turns, a plane climbing vertically, a flat spin, the F-18 slow pass...

OK, quick question: how much 'lift' (your definition) is an aircraft
producing in a 45 degree bank? Equal to the weight? If so, why does my
stall speed increase? Nitpicking? Well this nitpicking kills a lot of
pilots including very experienced ones.

How would you explain to a pilot that even though lift equals weight in a
steep turn (your definition), the stall speed increases?

Hilton

"Hilton" wrote in message
k.net...
It is *exactly* worth discussing and it is not nitpicking.

Not in this context. Still, you have demonstrated you are happy to continue
to do so, so please...knock yourself out.

The hardest thing about teaching someone about lift and drag in trying
to unlearn them the misconceptions they have already learned. The Nasa.
Gov web pages are a poster boy for this misconception. They define lift
and drag and thrust with narrow-minded characterizations that do not
differentiate one from the other. Example lift is THE force that
supports the aircraft in flight. Drag opposes the forward motion of an
aircraft thru the air. Thrust causes the forward motion of the
aircraft. They exclusively refer to drag as resistance force when the
major use of lift in aeronautics is to resist gravity. How stupid do
they think people are?

I am a member in model airplane club whose members are made up mostly
by retired pilots (commercial and private). I make it a point to ask
any pilot I meet what is the difference between lift and drag and I
have never Got a correct answer except for I don't know.

I hate it when some one says it's just a matter of semantics. Words
are useless without meaning and the words that have simple and accurate
definitions are the most useful. Glider pilots look for lift when they
fly their craft. But the upward aerodynamic force they are looking for
to accelerate their craft upward as a result of this lift is called
drag.
I like to discuss aerodynamics with people of authority. Please do not
think I am picking on you because I think you are one of the smarter
people in this group. I find it hard to argue with you because I agree
with so much of what you say. I sound like I am on a soap box don't
I?

"Dudley Henriques" dhenriques@noware .net wrote in message
hlink.net...
snip
This should read "Lift is the component of aerodynamic force perpendicular
to the relative wind.", and not "opposes". My error in presentation.
DH

Hello Dudley,

Nicely stated,

Are we not really looking at two different concepts of lift here?

A - The aerodynamic resultant reaction of an airfoil pulling air downward.

B - The flight physics teaching concept that an aircraft (in unaccelerated
flight) must generate a force (lift, thrust ,drag) that balances its
(apparent) weight.

ISTM that A is the description of the dynamics of motion through a fluid
and B is the description of the dynamics of motion of a mass. The fact
that the mass is moving through a fluid makes it a complex problem that is
straining our definitions, and perhaps is more of a problem of conceptual
semantics.


In regards to "not AGAIN", here in Canada we have an ongoing debate on
Quebec nationalism/referendum that we wags refer to as the "neverendum".

regards,

"Ash Wyllie" wrote in message
...
snip
Lift = Cl(AOA) * Area * V^2
snip

I believe this is more correctly stated as

Lift = Cl(AOA and some other stuff including shape) * Area * P/2 * V^2