Jim Logajan writes:

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. ;-)

It has to vary during the roll, because the constant 1 G acceleration due to
gravity does not change. The net acceleration of the aircraft must always be
at least one G in consequence, and if the aircraft begins a climb or ends a
descent, it _must_ be greater than +1.0 G.