It seem that the bombers are
way too armored, and takes too many bullets to bring them down. In actual WWII, I don't think many bombers went down missing a wing, however that seems to be the case in Aces High. If bombers were this tough to take out, it would have been impossible for the British in the Battle of Britain to take out any of the bombers with those .303's. Instead, it's almost a requirement to have a 30mm to take out Bombers. Bombers are usually thought as reletivly easy targets, and only lethal in large groups. If a trio of B-17's spotted a 109 comming in, they'd probably be pretty worried. In AH, the 109 could be pasted well before any damage was delt.
I haven't really done research on it, but it seems like bombers would be more likely to go down for these reasons in no particular order:
1) Crew was too injured or killed. Structurally, the bombers were very tough, but they had little or no protection for the crew itself, thus they died quite easily. In AH, unless you get a dead on shot, you don't do much damage to the crew, especially the pilots.
2) Fires are a big hazard. Especially if the bombs are still in the bomb bay.

Of course if the fire is on the player bomber, you got a problem. With the drones though, they could burn all day. That could stand to be changed.
3) Control cables and junk inside the bomber could be damaged fairly easily. However, in AH, the only thing you can do to simulate this is to actually knock the control surface off. I'd think if you took a hit, there should be a fair chance that your control cables could be damaged, resulting in A. Mushy control, B. Limited control, or C. Loss of control to the respecive control surfaces the cables were connected to. This could also stand to be implemented on fighters as well. That way, you also don't have to blow off a guys wing or pop off his tail to bring him down. Even in WWII footage, blowing off wings wasn't
that common.
Like I said, I didn't do any research on this, so correct me if I'm wrong, or if you can add in anything else.