what the heck is lift?

Peter Duniho wrote:

Are you relying on the part of that manual that you quoted elsewhere?

No. In a spin, at least one wing is at least partially stalled. According to
Jepp, this "results in a loss of lift in the area of the wing where it is taking
place."

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.

Peter Duniho wrote:

I wrote "straight and level flight" simply because that was the scenario
being discussed in the original post. But any unaccelerated flight means
lift equals weight, and that includes the "fully developed spin" and "steady
sinking mush" Roger described.

It depends on how you define "lift". If every upward pointing force is
lift, you're correct. If however you make a difference between, hmmm,
let's call it "true" lift created by the airfoil and drag that's just
incidentally pointing upwards, then you're not.

Stefan

Klein wrote:

In a somewhat more extreme example, when I pull my 400 hp Sukhoi into
a nearly vertical attitude, the rate of climb decreases to essentially
zero, i.e., the airplane hovers. In this case, the wings are
providing essentially no lift and the airplane is being supported by
almost totally by thrust.

In this situation, you might call that trust lift produced by the
propellor blades.

Stefan

George Patterson wrote:

Not according to the Jepp Private Pilot's Manual.

Which is the authoritative physics textbook ;-)

Stefan

Peter Duniho wrote:

"buttman" wrote in message
ups.com...

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


Your instructor is wrong, and should not be instructing.

In straight and level flight, lift equals weight. Unless your weight
changes, lift does not change, regardless of airspeed. What *can* change is
the lift coefficient, which is determined by the angle of attack. But lift
itself remains static.

Slight addition ... lift remains static in unaccelerated flight.

Matt

"T o d d P a t t i s t" wrote in message
...
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."

I made the assumption that when I wrote "See Todd's post" people would. You
clarified that quite well there, and I didn't see any reason to try to use a
finer brush than what started the thread.

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.

If you'll note, I also wrote "He's quite close". Had his definition of lift
been correct, he would have been exactly correct. Again, referencing your
post explains the minute detail where he was incorrect, and I didn't feel a
need to delve more deeply.

Frankly, I think this might be one of the reasons so many pilots don't
understand lift. As soon as the discussion turns technical, many people
want to make sure every last detail is just perfectly right. But in
reality, one can gain a very useful and practical understanding of lift
without ever knowing that lift is perpendicular to relative wind. Jumping
right into the minutiae of relative wind, vertical components, etc. just
makes some people's eyes glaze over, and they don't learn anything at all,
not even that lift is relatively constant over all unaccelerated flight,
regardless of airspeed.

Pete

"Hilton" wrote in message
ink.net...
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.

"George Patterson" wrote in message
news:bWkUe.743$626.107@trndny08...
No. In a spin, at least one wing is at least partially stalled. According
to Jepp, this "results in a loss of lift in the area of the wing where it
is
taking place."

That still does not contradict Roger's post.

IMHO, by "lift" Roger clearly meant "the force acting against gravity".
This is a fairly common (though not aerodynamically correct) definition of
"lift", and in fact is the one the Jepp training book uses (assuming it
hasn't changed much in the 15 years since I used it). That is, they have
the classic "lift, weight, thrust, drag" picture with the two pairs of
opposing arrows.

If Roger had meant by "lift", the "aerodynamic force created by the wing as
a result of relative wind" (or something similar), then he would have been
incorrect. But given that that definition makes his post incorrect, and
given that there's another widely accepted definition that does not, it
seems fair to give him the benefit of the doubt and assume he was using the
definition that's consistent with his post.

Now, granted, this *is* Usenet after all, and everyone seems to think it's
their job to point out why everyone else is wrong. So maybe I'm all wet in
my thinking. But that's my thinking, nonetheless.

Pete

"Stefan" wrote in message
...
In this situation, you might call that trust lift produced by the
propellor blades.

You might. But then you get into trouble in straight and level flight when
those propeller blades are still producing that lift. Then the total lift
greatly exceeds the airplane's weight.

Pete

On Fri, 09 Sep 2005 10:51:57 -0400, T o d d P a t t i s t
wrote:

Jimbob wrote:

He is describing the traditional airfoil theory which is correct. It
is the most efficient method as it produces lift with minimal drag.
That's what most people are taught.

There is another mode that is related to the force of the air
impacting on the bottom of the wing at high AOA producing lift as
well.

You make it sound like there are two effects, one that
applies in some cases and one that applies in other cases.
The reality is that both descriptions apply in all cases.
They are alternative descriptions of the same thing, and
both "explain" the effect 100%


You are correct. Both are consequences of Bernoulli.

However, I am trying to explain it to people that may not be versed in
the the conservation of energy in fluids, conservation of momentum and
Newton's #3.

Sometimes it helps to view it from bernoulli some times form Newton.
To the layman, they they don't care. They just have a simple question
they want answered.




Jim

http://www.unconventional-wisdom.org