what the heck is lift?

"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.

Pete

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

--

Roger Long

On Fri, 09 Sep 2005 11:12:36 GMT, "Roger Long"
wrote:

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


Hmm. If lift was equal to weight in level flight the forces are
equal, thus no change in height.

How do you reconcile this with a mush or spin? Height is changing,
thus left is less than weight.



Jim

http://www.unconventional-wisdom.org

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

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