[slavak]

First, this video is amazing.

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.

[FabHK]

True. Needn't be much though: to put it into a 2 m/s climb (400 ft/min), you'd just need to hold 1.1 G over two seconds.