Jim Logajan wrote
Most everyone agrees that keeping the coffee in the cup is possible.
What some people don't seem to believe is possible is that the force
felt by the pilot (or tea/coffee) can be 1 gee during the entire roll.
They believe it has to vary during the roll. I'm hesitant to name
names. ;-)

My name is Bob Moore :-)

Just what is a barrel roll has been debated between "Big John", Dudley,
and myself at least twice in the past. It IS difficult to describe
without having a model airplane in one's hand and flying it through the
maneuver.

How come you don't seem to belive the following from Wikipedia?

Barrel roll
From Wikipedia, the free encyclopedia

This article is about the aerial sport. For the military operation, see
Operation Barrel Roll.
A barrel roll occurs when an object (usually an airplane or roller coaster)
makes a complete rotation on its longitudinal axis while following a
helical path, approximately maintaining its original direction. The G load
is kept positive (but not constant) on the aircraft throughout the
maneuver, commonly not more than 2-3 G.

In aviation, the maneuver includes a constant variation of attitude in all
three axes, and at the midpoint (top) of the roll, the aircraft is flying
inverted, with the nose pointing at a 90-degree angle ("sideways") to the
general path of flight. The term "barrel roll" is frequently used,
incorrectly, to refer to any roll by an airplane (see aileron roll), or to
a helical roll in which the nose remains pointed generally along the flight
path. In fact, the barrel roll is a specific and difficult maneuver; a
combination of a roll and a loop. It is not used in aerobatic competition.

From:
http://acro.harvard.edu

The Barrel Roll is a not competition maneuver. The barrel roll is a
combination between
a loop and a roll. You complete one loop while completing one roll at the
same time.
The flight path during a barrel roll has the shape of a horizontal cork
screw. Imagine a big
barrel, with the airplanes wheels rolling along the inside of the barrel in
a cork screw path.
During a barrel roll, the pilot experiences always positive G's. The
maximum is about 2.5 to
3 G, the minimum about 0.5 G.