If you roll the aircraft without a change in altitude, the magnitude
of the G force can be held constant.


Even this is only partly true - you do need to impose
acceleration forces on the aircraft and pilot to produce the
torque required to start and finish the axial rotation of
the aircraft as it makes a roll.

Okay, but then...

Unlike the impossible roll question originally asked, the
loop problem is sort of interesting. Let's assume the
pilot has to feel a steady unchanging 1G and look at what
has to happen in the level flight start case. Initially he
feels that 1G straight down. Now we want to start a loop.
The 1G vector has to tilt back, so we have to reduce the
straight down force of gravity by allowing the aircraft to
descend.

Tilting the 1G vector back, the nose comes up. This requires rotational
acceleration just like the roll, only on a different axis. Sauce for
the goose and all.

You just can't easily raise the nose and
make the aircraft descend.

Reduce engine power, the aircraft descends. Raise the nose, the
aircraft ascends (at least in the short term). Do them both so that the
two cancel out, and you've achieved your goal.

Jose
--
He who laughs, lasts.
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