That demonstrates that there are no negative G forces. It doesn't demonstrate that it's 1G.
I'm a private pilot who has done aerobatics, exactly 1G doesn't work - and it's completely unnecessary (though you can stay pretty close to it, so that someone with their eyes closed would not know they were rolled).
But just about the video as "proof of 1G":
As long as you stay positive you are fine, even psychologically with passengers not used to it. The real turning point, in real effects as well as psychologically, is when you approach 0G, the feeling only starts at less than 0.5G when you begin to feel more and more weightless.
When you go even slightly negative it becomes a completely different matter, both in terms of real effects (fuel, oil, lose stuff flying around the cabin) as well as psychologically: Even though you made the harness extra tight with as much force as you could muster in preparation for an aerobatic flight with negative G forces, when you get here it feels as if you hang upside down in the harness and the seat is miles away from you, as if you dropped a few centimeters and now literally just hang in the airplane.
I (in my small and somewhat underpowered aircraft) go below 1G when I get close to the top, because if I tried to maintain 1G the nose of the airplane would have to drop (towards the earth in that position), and I want to keep that at a minimum, so that I don't end the roll with the nose in too much of a nose-down attitude from which I will have to pull out.
EDIT: (after reading some comments) To me a roll is over when the airplane is back to straight and level, after 360 degrees. So my statements are for that interpretation of the word "roll". And my frame of reference for g-forces are the people on board the aircraft.
But as the video demonstrates quite well, the first phase of a barrel roll requires pitching up into a gentle climb. This is physically impossible without exceeding 1g at any point.
I love that video. I've got an autographed pencil sketch of Bob's P-51 (autographed by both the artist and Bob!). And while watching him fly, the only explanation I could come up with that explains how effortless he makes it look is that he was actually a bird in an earlier lifetime.
I'm a private pilot who has done aerobatics, exactly 1G doesn't work - and it's completely unnecessary (though you can stay pretty close to it, so that someone with their eyes closed would not know they were rolled).
But just about the video as "proof of 1G":
As long as you stay positive you are fine, even psychologically with passengers not used to it. The real turning point, in real effects as well as psychologically, is when you approach 0G, the feeling only starts at less than 0.5G when you begin to feel more and more weightless.
When you go even slightly negative it becomes a completely different matter, both in terms of real effects (fuel, oil, lose stuff flying around the cabin) as well as psychologically: Even though you made the harness extra tight with as much force as you could muster in preparation for an aerobatic flight with negative G forces, when you get here it feels as if you hang upside down in the harness and the seat is miles away from you, as if you dropped a few centimeters and now literally just hang in the airplane.
I (in my small and somewhat underpowered aircraft) go below 1G when I get close to the top, because if I tried to maintain 1G the nose of the airplane would have to drop (towards the earth in that position), and I want to keep that at a minimum, so that I don't end the roll with the nose in too much of a nose-down attitude from which I will have to pull out.
Here is an image from my flying some years ago, in a Grob 115C Acro (rented from Attitude Aviation, Livermore, CA, ca. 2002): http://i.imgur.com/Rd5VW3R.jpg (the inside of this airplane: http://i.imgur.com/4bwJn13.jpg)
EDIT: (after reading some comments) To me a roll is over when the airplane is back to straight and level, after 360 degrees. So my statements are for that interpretation of the word "roll". And my frame of reference for g-forces are the people on board the aircraft.