As for a request of I am posting on how I made the Dispensable Trail Nozzle.
The mechanics is quite simple actually if you know how the game works.

Alright let's start.

Let's begin with a detacher. Put a detacher (attach the backside) on the block. This prevents the detacher, along with the rocket, from separating.

As shown, I just strapped a rocket underneat and a standard block at its back.

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Edit the XML Value of the rocket
Mass Scale=0
No Collision=True
selfDestructTimer=99999999999999
burnTimer=0.001

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Disable the AG group of the detacher and set detach force to 0. Also set No Collision to true but always set mass scale to 1(do this to all detachers)

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And basically you are done!

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In order to make it disposable you have to attach a bomb and another detacher.

Attach it as shown:
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This is the main attachment point.
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Nudge the parts...
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There you have it, a dispensable smoke trail!
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I just showed the simple mechanics behind this simple build. And it only takes 5 main parts...
I didn't include the part that requires to alter some stuff in the SP files. There I used a pylon to hold the bomb instead of a detacher. Let's just say it connects a block and a bomb on the same pylon.

I think I should post on forums more often.
Just tell me if you want to know how I made my stuff. And I'll post it right away.

This is my first forum post by the way.
In case you haven't seen me in this site, I build weapons, engines, gizmos or any type of subassembly for any type of vehicles.

Check my account if you're free.

Thank you and have a good day.