does fuel line work?

@Toinkove @Zenithspeed thx for help

idk what I did, but fuel line is now works

Interesting design for sure!
………
1. Make sure fuel in tanks are same as what the engine is set to use.
2. Check connections and insure the engine is connected to the “surface” of the fuel tank or nose cone
3. I once saw someone unknowingly set the engine to an activation group so it wasn’t starting in staging (they had to use the AG to start engine). See if that’s the case
…….
Beyond that I’d have to take a look at the craft myself and see what was going on.

@StephanieBread weird
well, i can't help any further, it's an issue that i have no knowledge of

@Zenithspeed
I tried to create simplest rocket with 3 parts, as I described in question: I tried to enable fuel line on everything and that's not works...

@Toinkove
sorry, when I said engines on rotators, I mean this:

https://cloud.disroot.org/s/yD3XwjcGk9mZt3G

engine > fuel tank > rotator > fuel tank with more fuel for this engine
I enabled fuel line everywhere I can, and that's not working,,,

Ok somehow I didn’t compute the part about "engines on rotators" ….. I’ve ALWAYS had to attach engines to “fuel tanks”. You can run fuel through a “strut” and a "rotator" (I have done it myself) but there needs to be fuel tank (and it can be a relatively small tank) on the other side to hold some fuel. Then connect the engine to that small tank. I think that should work.

my solution is to just turn on fuel line on everything
if that doesn't work, then idk

@CloakPin rotators works normal, but fuel line is not..

You might need a battery for rotators.