I'm not sure if this is a bug, or a feature. With the 2.11 update, if I enter the game with a Mosquito that does not have internal ordnance, the bomb bays no longer function. If I try to open them, the game says "Your plane doesn't have a bomb bay".
The bombless Mosquito has the same weight as a Mosquito which has dropped its bombs, and appears to be the exact same model. It's a picky point, because there isn't much need for the bomb bay doors if you have no bombs, except as a really naff speed brake, but it seems an odd feature. At the very least it's a shame that the bayless Mosquito isn't slightly lighter (if only for the lack of a knob on the dashboard), or more functional in some way.
PS. In fact this seems to be the case with all aircraft that have a bomb bay, and an option for no internal bombs (e.g. the Ju88, Boston etc). If internal ordnance is selected, and then dropped, the bay doors continue to function even when empty.
