[quote=@Burning Kitty]
Would a transformable mecha be acceptable?

Fighter Jet to Robot Mecha
[/quote]

Yep. One of the models available for use at the moment, the Raptor, is exactly that. It's worth noting that they're not very advanced yet; transformable frames, in universe, are pretty new. Midair conversion and such is pretty limited by lack of flight capabilities in mecha mode.