Plane falls through the ground

[Slipp]

I'm trying to make a flyable Mirage-2000, everything works alright with the exception that it's wheels don't hold the plane on the ground. When I try ramp start, the plane falls down and explodes.

 

Any ideas?

 

Here is the dl for my current state of the mod:

http://www.filedropper.com/mirage2000-5

[Sukhoi25]

Will take a look to it...