Interestingly enough, if the occupants weren't looking outside, a "1G roll" would feel almost the same as level flight; here's a video showing how "gravity" seems to invert along with the plane:
The article quotes the pilot, Tex Johnston, saying something similar,
"The airplane does not recognize attitude, providing a maneuver is conducted at one G. It knows only positive and negative imposed loads and variations in thrust and drag. The barrel roll is a one G maneuver and quite impressive, but the airplane never knows it’s inverted.”
Problem is, it isn't actually a 1G manoeuvre. You can only have a constant 1G if you are in straight and level flight. If you perform a gentle turn, you will have very slightly more than 1G as you bank around the turn.
With roll, if you pull positive 1G while inverted, the plane will effectively be accelerating towards the ground twice as much as if it was in free fall. When the roll is over, in order to regain straight and level flight, more than 1G must be pulled to counteract the groundwards velocity that has been accumulated.
Of course. Level flight isn't exactly 1G either because of small amounts of turbulence. The point is that the load is arbitrarily close to 1G, given a slow enough roll (and enough altitude).
Yes, you can do a descending turn, with <= 1G. However, you will then come out of it going down, and unless you want to fly into the cumulogranite you will need to pull > 1G in order to level out again.
If you really want to be pedantic, going east in level flight you are at less than 1G due to orbital momentum and in vary small part due to altitude. So, in theory you could do all of this and stay under 1G.
PS: The weight thing can be significant for hypersonic+ aircraft. Also, you use slightly less fuel going east than west due to earth’s rotation, though winds are going to be far more important.
To be truly pedantic, you could be landing and execute a slow sinking flare, which can be < 1G right up until the moment the wheels contact the pavement and the momentum of the aircraft results in > 1G force - but then you aren't flying any more!
https://www.youtube.com/watch?v=pMWxuKcD6vE
This is also why pilots can become spatially disoriented:
https://en.wikipedia.org/wiki/Spatial_disorientation