Question on Fuel flow mechanics

[ghost314]

I have discovered through experimentation that if I place a radially mounted engine onto a radial decoupler which is attached to a barrel of fuel, the radial engine will work without requiring an external fuel duct connection from the engine to the fuel barrel (the fuel apparently travels horizontally through the radial decoupler). However when placing two fuel barrels side by side, and engine mounted to the bottom of one barrel can't access fuel from the other side barrel. Now I'm confused and wondering what exactly are the rules for how fuel flows through components, since it looks like it can travel radially but not if the radial component is another fuel tank, which seems rather arbitrary to me.

**Edit**

I mentioned that an engine on the bottom of one fuel barrel can't access fuel from a radially mounted barrel, apparently this is only half true, you can still manually transfer fuel between the two barrels, allowing the engine to access fuel from the side barrel by funneling it through the middle one.

Edited January 5, 2014 by ghost314

[Smidge204]

Check this:

http://forum.kerbalspaceprogram.com/threads/64362-Fuel-Flow-Rules-%280-23%29

=Smidge=

[Kasuha]

it looks like it can travel radially but not if the radial component is another fuel tank, which seems rather arbitrary to me.

Your observation is correct (it applies if the part is fuel tank for the requested type of fuel, so if it is e.g. liquid fuel-only tank, it will pass oxidizer request radially but not liquid fuel request - [see here]).

If it was not that way, any standard staging (central tank -> radial decoupler -> stage tank) would pull the fuel from the central fuel tank first and the central engine would lose all its fuel before the stage you're willing to drop first. Similarly how it happens in [this example].

Rules were set up to support usual rocket designs. That means some unusual designs may run into problems or unexpected effects. Unexpected if you don't understand the fuel distribution.

Edited January 5, 2014 by Kasuha