what the heck is lift?

On Sat, 10 Sep 2005 20:48:51 -0700, Bob Fry
wrote:

"private" == private writes:

private A - The aerodynamic resultant reaction of an airfoil
private pulling air downward.

private B - The flight physics teaching concept that an aircraft
private (in unaccelerated flight) must generate a force (lift,
private thrust ,drag) that balances its (apparent) weight.

The problem with restricting your example to unaccelerated flight is
that the resulting definition of lift will almost surely be incorrect,
by not being general. Imagine for example an airplane in a
continuously positive-g loop. Neither definition A or B are valid,
yet lift from the wing always occurs.

So what do we call the aerodynamic force on the horizontal tail that
forces the back of the airplane downward to keep the airplane from
diving into the ground? If it were acting upward we'd easily refer to
it as lift, but it acts downward. Is that lift?

Of course this same force is upward when it's on an airplane with a
canard. I guess that then it qualifies as lift.

What about the aerodynamic force on the vertical tail/rudder that
controls yaw? It's acting sideways. And what about the aerodynamic
force created by the propeller, which is a wing after all?

RK Henry