Are you aware of the Delta3D engine? I don't know if switching engines is a useful option at this point, or if Delta3D has the features you need, but if you're interested, you can make all the changes you want to the engine. The license is LGPL, which means you can build a proprietary game or application on top of the engine if you want to, but any changes you make to the engine itself have to be distributed under the LGPL (so any improvements you make will be available to everyone else who uses the engine). The URL is http://www.delta3d.org/. There's a feature list here. 
  
Also, do you need 3-view plans for any fighters? I have a book that contains 3-views for all kinds of fighters, many of which didn't get beyond the prototype stage. It includes 3-views of the DFW T 28 Floh and the Lohner 10.20A, among many others that are even less well-known. It also has plenty of photographs. If there's anything in particular you're looking for, I can scan it for you. I'd offer to help with programming, modelling, or skinning if I had much experience in any of those areas. I'm currently making my first attempts at skinning, and I may eventually be of some use in that area. Good luck with your game.