Have you ever seen this?
Perfect 1G Barrel Roll in Airplane - Truveo Video Search
Also here is an explanation off a site I copied:
Imagine your in space. A 1G roll would be a perfect circle with a
constant 1G acceleration.
Now bring that path into the Earth's gravity well. Now the 1G roll is
all messed up by the Earth's 1G. How can we fix that? Just like the
Vomit Comet does, by accelerating down at 9.8m/s^2. Superimpose a roll
on top of a parabolic descent and you have the path of a theoretical
airplane in a 1G roll.