ok, nobody explained why ucd3d set up as a trainer still isn't a trainer...

a trainer has some degree of self righting ability, and usually isn't too happy inverted anyway.

a 3d plane does not do this, and will happily bury itself into the ground at any angle it pleases.

(All this is assuming it has very small control movements, like a trainer, otherwise that plane is going to go in REALLY quick!!)