In article ,
vincent p. norris wrote:

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.

Indeed. And when you do that, you observe positive G's all the way
around an aileron roll (in the aircraft I fly, at least). I do a bit of
aerobatics photography, and I'm absolutely required to be able to
anticipate G forces to keep the camera from smashing into something else
(or myself).

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.)

Indeed. And an aircraft in an aileron roll changes direction constantly
as it describes a ballistic corkscrew-like path (S&G).

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.

Indeed.

That is, the nose of the
airplane must "rise"--in relation to the airplane-- to provide more
than 1G of positive acceleration.

Or the corkscrew motion of an aileron roll must provide enough "outward"
(normal) force to counteract the downward force of gravity. Which it
does.... We're not doing a slow roll here, so the longitudinal axis of
the aircraft describes a circle around the axis of the maneuver itself.
The maneuver starts with a pullup, and that pullup is never really lost.

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.

At the start of most aileron rolls the stick *is* pulled back -- to get
you to the magic 30 degree point with a small 2G pullup. Then by the top
of the roll the nose is trending down, with enough normal force from the
corkscrew motion to keep the G's positive. Once again, as described by
Szurovy & Goulian (quoted in the bits you snipped) and nearly every text
or reference I can find, and my own experience, a simple aileron roll is
one of the canonical positive G maneuvers (unlike the slow roll, which
can result in negative G's in many aircraft).

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.

*Nothing* in an Aerobat is fast :-). But in fact, since the aileron roll
(as described by S & G, again...) is a positive G maneuver, you can do
it without worrying about the fuel feed (or the oil). You can certainly
screw up an aileron roll and get non-postive G's (as I've discovered
:-)), but it takes extra effort (or forgetting to keep the ailerons
fully deflected...).

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.

Which, if done as slowly as I do them, will result in non-positive
G's... it takes only a second or two to make the Aerobat stutter.

Hamish