The issue with adapting existing models to IL-2 is many-fold;
1. The overall D0 model cannot exceed 20,000 polys (this is not a hard and fast rule, but in the interests of performance, 20,000 polys is the upper end of optimal for close up work)
2. The model must then be easily separable into different parts (Fuselage Nose, Mid section, aft section, air brakes, inner, mid and outer wings, ailerons, flaps, flaperons, spoilers etc...) with each part not exceeding 3000 polys. (This is a hard and fast rule, due to the exporter, IIRC)
3. You then need to make damage models based on the D0. There can be up to 3 damage levels (I think) and then damage caps for when the part is finally shot off.
4. Then on top of this, you need to make LOD meshes for each of teh parts of the D0 model, the D1 (damage level 1) model, the D2 model and so on...
5. Then comes the shadow model which is a simplified version of the D0 model.
6. Then comes the cockpit model so that you can actually fly the damned thing.
7. Of course, mixed into this you need to think about the skin, as there is no guarantee the skin you have is suitable for IL-2
8. Then comes the black art of importing and adding hooks, clips, collision boxes, the flight model, the weapon loadouts, the dreaded hier.him and also the java animation for the landing gear and air brakes.
9. Not to mention the shit that I don't even know about...
It really isnt so simple as finding a model on the net and importing it, no sir...