So, i've been building a new version of the DX-185 Deathstalker II. I've given it some stuff at the end, and a new, much smoother cockpit then previous versions.

The problem is here:
When i spawn it in, it does really weird stuff:
If i spawn it on land, it just sinks to the ground, explodes, then SP commits game crash.
If i airstart it, it just seems that most major pieces and a few minor ones just get detached from the plane, then its forms a replica of the Hell Kraken from Kerbal Space Program (seriously, both velocity and altitude are just "NaN", much like KSP's version.)

Link to the broken aircraft:
trust me again, it's NOT a rick roll