what the heck is lift?

Roger Long wrote:
Lift in a fully developed spin or steady sinking mush is also exactly
the same as in level flight.

Not even close!

Hilton

"Hilton" wrote in message
. net...
Roger Long wrote:
Lift in a fully developed spin or steady sinking mush is also exactly
the same as in level flight.

Not even close!

He's quite close. See Todd' post.

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.

Pete

On Fri, 9 Sep 2005 10:51:23 -0700, "Peter Duniho"
wrote in
::

But any unaccelerated flight means
lift equals weight, and that includes the "fully developed spin" and "steady
sinking mush"

Isn't there acceleration in a sinking mush? If the aircraft is
descending, does lift equal weight?

Peter wrote:
Hilton wrote:
Roger Long wrote:
Lift in a fully developed spin or steady sinking mush is also exactly
the same as in level flight.

Not even close!

He's quite close. See Todd' post.

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.

Todd's reply to this clearly shows why Roger's statement is wrong. A large
percentage of the upward force in a spin is drag. The extreme case is a
parachutist coming straight down in one of those old round parachutes. In
this case, the 'aircraft' has zero lift and DRAG == WEIGHT.

Lift, drag, and thrust can be pointed in any direction; the only constant is
weight which always points towards the center of the earth.

Hilton

"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.

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.

"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

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

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