well you are asking the right person
through my encounters of downloadable aircraft, where's what most airtists (note spelling) do
Shift + E - your normal door
Shift + E + 2 - cargo doors on default aircraft and some downloadable
Shift + T (tailhook) this sometimes opens cargo doors
wing fold/unfold (I use Ctrl + shift + w, may be diff. on your system) this opens cargo doors, and is flying a 747, opens the nose and huge side cargo doors.
glad to be of service
