Zero, you can make a static afterburner animated with thust vectoring nozzles:
http://en.wikipedia.org/wiki/Thrust_vectoring

It's more realistic than the ship trails like in wipeout since this system would be the one used to turn the ship, even when stopped.
In planes it's used for pitch, but if you turn the engine sideways you get yaw.
This is the F-22's engine:
Attachment 2825

This can be easily done in a 3D program, you just have to make unity accept transparent materials and add a shine shader of sorts.