what the heck is lift?

On Fri, 09 Sep 2005 10:59:00 -0400, T o d d P a t t i s t
wrote:

"Brian" wrote:

Generally speaking lift = AOA * Airspeed.

Not quite. Generally speaking lift is proportional to AOA *
(Airspeed squared).

Except when accerlating or decelerating up or down (i.e Beginning or
ending a climb or descent) the lift = weight of the airplane.

This is close and is often a reasonable approximation, so
I'm not really disagreeing, just expanding. However, lift
is actually defined as a force perpendicular to the flight
path, so in climbs, some weight is supported by thrust, and
in descents, some weight is supported by drag. Lift is
slightly reduced in both cases.

In a somewhat more extreme example, when I pull my 400 hp Sukhoi into
a nearly vertical attitude, the rate of climb decreases to essentially
zero, i.e., the airplane hovers. In this case, the wings are
providing essentially no lift and the airplane is being supported by
almost totally by thrust. Actually, you should imagine Sean Tucker
doing this as I don't do it all that well. ;-)

Klein