Currently, despite the fact of helicopter and airplane controls being differentiated, we cannot set different keybindings for the "turn left"/"turn right" action.
In airplane it steers you roll axis. In helicopter it steers your roll and yaw axis. When flying on the mouse in helicopter, I prefer to use my pedals with Q and E, so I unbind the turn left/right keys to do that and just steer my pitch and roll with the mouse.
But then when I jump into a fixed wing aircraft, I find myself unable to steer my roll using the mouse.