I've seen some awful diagrams of the aircrafts supposed position during barrel rolls. Henry's isn't so bad but I don't think many underpowered trainers could start from "A" without falling out at the top.
I did a few in a Victa, completing the barrel shape regardless of where the a/c was this way or the other. Started with the nose on a feature, dived and turned to arrive at Henry's "A" with a bit of speed up, probably already at 90deg by C, falling to D at upright and pulling back to A to finish. Rough and self taught, but my instructor wouldn't sign my log book for barrel rolls because, "you can do them better than me." Mind you, he signed for everything else.
