I've literally got no idea whats going on with the contact points and getting this thing working. Here's the Blend file and the OTX, some help would be greatly appreciated.



OTX: https://www.dropbox.com/s/03li0dg2wpxyldg/jet.Ali.otx

Blend: https://www.dropbox.com/s/ganizqosk0d9hh1/jet2.blend



Under you have two types of Contact points:type="BOGEY": These are used to define the contact surface/point of each wheel, the lower part of the wheel. See green helpers:type="STRUCTURE": These are used to define the collision points of the fuselage (at the moment they collide only with the terrain). See green helpers:And about the Center of Gravity, I suggest you to find the most realistic place for it, I think it should be somewhere under the wings, but not at the same height as the wheels. Of course you can change it from FDM, but first it's better to have the pivot point where the CG should be. The CG will be affected by the Fuel tanks as well. These are located under and you can add as many as you need. But you have to distribute the total weight somehow because you have, and eachthat will add to the overall weight of your plane.Your Pivot point:How it should be (It could be moved a bit backward and/or upward, but I think you have to do a research and figure out where it is on the real thing, and of course the CG will vary with the fuel tanks, if they are not filled proportionally, the CG will be moved even on the sides...):So... I took a quick look at your airplane, and tweaked some basic things in the FDM so now you can move the aircraft and steer. It can take off, but a bit hard because of the weight's distribution and quantity I think. You have to tweak some values like where are the fuel tanks and how much fuel on each tank, also the position of each turbine, add more collision points, correct the position of the wheels in type="BOGEY", and so on. I think the wheels are sinking a bit, so you have to script the wheels to act in concordance with the suspension, it's not so hard, you also can take a look at the Basler bt67's Script & FDM. Inside the script I added some basic comments so you can understand a bit easier what each part does.If you still having questions, feel free to ask