A few years ago, I made some 2.5D models in 1/700 scale for the Axis & Allies Naval Miniatures game.
See:
Axis & Allies Naval Miniatures: War at Sea | Board Game | BoardGameGeek
The planes on the left are my paper planes(IJN Kates) and the planes on the right are the commercial planes(TBD Devastators) which are used as playing pieces in the game.
Are 2.5D models eligible for the Smallest Aircraft Competition ?