Are you picking up the collision? Select the VehicleBody node, on the right go to the "Node" tab. Double click on "body_entered(body: Node)", select your VB script. That gets you this:
apply_central_impulse(Vector3.UP * 10000)
printt("Weeeeeeeeeeeee! I hit ", body.name)
Obviously just add whatever linear algebra you need to get the behaviour you're after.
If you want to do something more advanced you can use
_integrate_forces(state). I used it for an amphibious craft so you can newtonian gravity / buoyancy / thrust from the rotating outboard motor etc. Unfortunately there's no visualisation in the editor so this is advanced. You probably just want a simple impulse.