what the heck is lift?

Buttman,

This guy is an amazing instructor.


Apparently.

--
Thomas Borchert (EDDH)

Generally speaking lift = AOA * Airspeed.

Except when accerlating or decelerating up or down (i.e Beginning or
ending a climb or descent) the lift = weight of the airplane. Check out
the 1st few pages of any physic book to verify this. Another way of
thinking about it is that the tension on an elevator (Building elevator
not an airplane elevator) cable always equals the weight of the
elevator and occupants even if the elevator is moving. It changes only
as the elevator accelerates or decelerates.

so since the lift seldom changes the only other 2 variables are AOA
and Airspeed. If you slow down you must increase the AOA to maintain
lift. If you decrease the AOA you must increase airspeed to maintain
lift.

The Rate of Climb indicator directly show excess or Power in a climb or
insufficent power (to maintain alt) in a descent.
Movement of the Rate of climb needle (decreasing or increasing) shows
changes in the amount of lift generated.
A G Meter will directly show the amount of lift being Generated. i.e.
2G = 2x gross weight of the airplane is being generated.

Hope that helps a little

Brian
CFIIG/ASEL

buttman wrote:

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

Nonsense. Don't listen to what any of these people are saying here.
Lift is produced by the action of millions of tiny gnomes standing on
each other's shoulders. The thing is they're not too strong so you have
to keep moving because each gnome can only hold you up for a brief
instant and pass you on to the next one. Larger wings allow you to
spread the load out over more gnomes, thus creating more "lift." Spins
happen when you move the controls the wrong way and scare the gnomes.
Some people don't accept this because they can't see the gnomes, well,
you can't see air particles either. Even the Ph.D. guys can't explain
it, but any fool can see that planes fly. Gnomes!

-cwk.

buttman wrote:

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.

No. From the Jeppesen Sanderson "Private Pilot Manual" -- "Lift can be increased
in two ways; by increasing the forward speed of the airplane or by increasing
the angle of attack."

And elsewhere -- "When an aircraft is in straight and level flight, .... lift
equals weight ..."

So, you have no more lift when you are cruising level than if you're in level
slow flight.

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.

buttman opined

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?

Lift = Cl(AOA) * Area * V^2


-ash
Cthulhu in 2005!
Why wait for nature?

"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

buttman wrote:


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.

Uh-huh. So if you use a crane to lift up the nose of a 747 sitting on
the ramp, your instructor believes it will be generating the same
amount of lift as it would at that AOA and 400 knots. Detach the crane
and the 747 will just stay there in a nose up attitude without any
visible means of support. Or maybe your instructor has a poor
understanding of lift.

Lift is actually a mathematical formula: L = 1/2 air density * velocity
squared * area of the wing * coefficient of lift for that wing. Your
instructor should know that; it is on both the commercial and flight
instructor written exams.

You generally can't do much about the air density, but you usually can
change your velocity and the coefficient of lift. The coefficient of
lift for most wings increases with AOA, peaking at the critical AOA and
dropping off sharply at higher AOA after that. Some flaps and other
devices (variable geometry wngs come to mind) can change the area of
the wing and/or its coefficient of lift. Also, "the area of the wing"
is not quite right; it really is a reference area which might have
little to do with the actual wing size. A helicopter, for example, uses
a reference area equal to the entire disk, not just the blades. The
same rule applies to propellers. The reference area on a fixed wing
plane includes the area through the fuselage, as if the wing was all
one piece.

You can use either sq. feet or sq. meters (or, heck, sq. rods if you
want to) for the reference area; it all works out as long as you use
the same type of units all through the calculation, including air
density.

http://www.allstar.fiu.edu/aero/airflylvl3.htm


Regards, Ross
C-172F 180HP
KSWI


buttman wrote:
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?