Thanks @ItsAMysteriousOfficial !!!
One model had 83.000 vertices instead of 10.000. I had to remodel quite a bit and it doesn't look so good but it works :-) .
BTW do you now if its possible to have multiple textures for one model like exterior.png and interior.png?
The mod is called "MCHeli Mod"and its basically the Flans mod without bugs (no planes stuck on the roof or in the floor :-D ) and way better.
Seriously try it!!! It's one of the best mods but pretty unknown (from a Japanese guy).
I'm only making a Content Pack for it.
Yes it is. I can tell you much more about the possibilities you have with .obj models if you want, just add me on skype(itsamysterious)!!
Oh and i work on a Mod called Real Life Mod, you might be interested in it, cuz it adds Ultra Realistic Cars and stuff to the game, here is a link: http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/2196915-real-life-mod-taken-from-reality-directly-into