Hi Dion,
I just quickly made some screenies.
The X-1 is not a second model, it loads together with the B-29 as the first model.
Dropping is very easy: just climb with the B-29 up to a reasonable hight, push the release button (same as hook) and fire up the thrusters of the X-1. It then rushes away with a nice flame at its tail. Really cool.
When the X-1 is free, you can steer it with the normal controls, so you are controlling the B-29 and the X-1 at the same time. But as the X-1 reacts much quicker you can controll it without losing control over the B-29. Sounds difficult but is really easy.
Cheers,
Lego