what the heck is lift?

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?

"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

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

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

Not according to the Jepp Private Pilot's Manual.

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.