Does the water spill because the aileron roll is *not*
a positive-G maneuver, or because the forces on it are not balanced
laterally or longitudinally? (I can't do the experiement because there's
nowhere to put the glass in the plane I fly).

If you can tie or tape a string with a small weight on the end to the
top of your canopy or windshield, you could use that.

Let's take a snapshot of the airplane at the moment it is inverted.

At that instant, (as at all other times), gravity is exerting a force
of 1 G on the airplane, down toward the earth--in other words "upward"
in relation to the airplane. What we normally call one negative G.

Now, as Einstein pointed out, "acceleration" is a force
indistinguishable from gravity. In this context, acceleration does
not mean "increasing speed," it means "changing direction." (As the
acceleration of a steep turn exerts Gs on the airplane.)

To counteract the one negative G now being exerted on the airplane by
gravity, plus a little more to make it a positive G maneuver, we must
have acceleration, of the sort experienced when pulling out of a dive
or in a loop--although not that much. That is, the nose of the
airplane must "rise"--in relation to the airplane-- to provide more
than 1G of positive acceleration.

If the stick is over to one side, but not pulled back, how is that
acceleration provided? I do not see the nose of the airplane "rise"
while I'm inverted in an aileron roll.

Or do it in a Cessna Aerobat -- which requires a positive G force to
keep the oil and fuel running. I can get the engine to stutter in a
second or two in a slow roll (more like a slowish roll in an Aerobat,

I've never flown an Aerobat, but if it aileron rolls as fast as an
SNJ, then the engine won't stutter simply because the maneuver doesn't
last long enough. No SNJ I've flown stutters even in a properly done
slow roll--in which the stick is moved *forward* to keep the nose up
(in relation to the horizon) while inverted.

vince norris