Barrel rolls by big aircraft and large formations
Have a look at this earlier pprune series ....
http://www.pprune.org/military-aircr...nk-please.html
A barrel roll to the left usually starts from initial level flight with a gentle descending turn to the right to pick up speed. At about 30 deg right bank the roll starts to reverse to the left, 'g' increases, and the nose is pulled up to start a flight path which describes the perimeter of a barrel.
Slight positive g is maintained at the apex of the 'barrel' albeit pulling the aircraft downwards as the aircraft (one or a formation) are nose high upside down at this cardinal point. The roll continues to the left, the nose slowly drops towards the horizon at the 270 degree point, the roll continues to a slightly nose low finish which becomes level flight once more as the aircraft (or formation) completes the full 360 degree rotation.
A barrel roll by say a B-707 or an aerobatic team will describe similar flight paths. The 707 has lowish structural limits and a formation team needs to keep the 'g' lowish to enable safe close formation flying, particularly by the outer and inner wing men in large formations.