what the heck is lift?

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?

I don't follow the point you are trying to make here. The
increased lift does affect the RW. As the glider
accelerates upwards, it begins to match the upward motion of
the air, changing the RW back to the previous RW. I
attribute the upward acceleration mostly to the increased
lift and only partly to the increased drag. You claim that
the vertical component of lift is unchanged.
issued with the Curtis-Wright flyer)

When the motion of an object is caused by lift it will never reduce the
relative airflow that initially caused that motion it will increase the
speed and change the direction of it. This is why wind powered vehicles
can move faster than the wind they are powered by. When the motion of
an object is caused by drag the faster it moves the less drag it
generates because the less relative airflow it generates. It is
impossible for the increased lift to do anything but increase the
relative airflow if that object is allowed to move as a result of it
(lift). If the glider accelerates upward and relative airflow decreases
the only aerodynamic force that can cause that is drag. You claim that
the increased lift does affect the RW but it actually will affect it
the complete opposite way that you say it does if the upward
acceleration were due to lift.

Lets say you are holding a propeller in the wind. The relative airflow
caused by the wind causes the propeller to tend to rotate. If the
propeller were to be allowed to rotate as a result of this lift the
relative airflow now influencing the prop is still all of the wind plus
the relative airflow caused by its motion. The relative airflow is
made up by the actual motion of the air (Wind) plus the motion of the
propeller thru the wind. Objects that move as a result of drag don't
move thru the air they move with the air.

T o d d P a t t i s t wrote:
wrote:

When the motion of an object is caused by lift it will never reduce the
relative airflow that initially caused that motion it will increase the
speed and change the direction of it.

You're making the same argument here that you made before -
you are separating the vector components of the new RW into
two parts, the original RW and the new vector component of
RW comprising a vertical RW due to rising air. Then you
ignore the original component and make arguments about the
other component in isolation. It's obviously true that if
there were no wind other than the vertically rising air,
then all the aircraft vertical acceleration would be due to
drag from that rising air. That's not what's happening
though.

There is no wind other than the vertically rising air, the rest of the
relative airflow is caused by the motion of the glider thru the still
air. The difference between the two is that to move thru the air you
must over come drag and to remain still in moving air you must overcome
drag. This makes them easy to separate. The glider uses inertia to
overcome drag from the lift (a meteorological term for rising air). I
did not use the term vertical acceleration I said upward acceleration
witch did not include the gliders downward deceleration from the
thermal. I believe that when the gliders downward motion stops it is
slightly less influenced by the downward motion thru the air.
You said after the flight stabilizes to a steady climb at the original
constant speed in the rising air The glider will continue in
unaccelerated flight and the only difference will be that the glider
is now in a steady unaccelerated climb instead of a steady
unaccelerated descent. Here is another difference. The lift and drag go
from resisting downward motion to causing upward motion among other
things.

The validity of your argument depends on the ability to
separate the RW into two non-orthogonal vector components
and attribute lift and drag separately to each, then add up
the lift and drag from each component. That's what's wrong.
You can't treat your vector components independently, as you
are doing.

So my argument is not valid due to the many and obvious shortcoming of
mathematical formula. You cannot explain it mathematically so it's
not true or does not exist or even more absurd metrological lift causes
vertical aerodynamic lift. This does not make what I said true but sure
is a good sign that it is. Save the math to balance your checkbook not
to distort actual occurrences in the real world. This is not rocket
science you simply have to apply a little common sense and logic. You
know I am wrong but you do not know why.