I’ve some problems with layers in jmonkey.
The flame is always infront of the ship.
How can I change it that the flame is always behind the ship and not at the front site?
You can see here the front site of the ship:
The flame should be behind the ship…
Looks like you need to put a z-buffer state on that flame 
Also, if your flame is actually part of the model (and is transparent) you may not be able to solve it unless you make the flame a separate model…