| The plane survived but it was not certified or engineered to do a barrell-roll - it was foolish. I do not know specific limitation of the aircraft other than there was grave concern the engine mounts would fail. It may have been the mounts were not designed for compression force. In normal flight the mounts would never be exposed to compression. In inverted flight it becomes a possibility if not a certainty.

The engine mounts see no forces in a barrel roll they don't see in normal flight. A barrel roll is a 1 g maneuver. Which means, from the aircrafts point of view, the aircraft sees the floor as down for the whole maneuver. There are countless of not aerobatic type aircraft doing barrel rolls while people hold or pour some sort of fluid on youtube. It's a thing. Planes don't fall out of the sky performing them.

The aircraft was never inverted from its point of view. The mounts saw no compressive force. The never even saw 0 force. Everything in the aircraft was loaded toward the floor like normal.

Bob hoover drinking tea while inverted is a video you can look for.

I do not really want to argue this anymore. But if I am wrong, please let me know.