[solved] Tri-Coupler allows fuel flow in one direction only

[Darbin Giesorg]

Solved: Intended behaviour to prevent fuel flow between parallel stacks. Fuel ducts necessary (from tanks to coupler). Lack of description was the culprit.

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KSP Version: Steam v1.0.5.1028 vanilla | Windows 7 x64

Description: TVR-1180C Mk1 Stack Tri-Coupler does not deliver fuel from big end (3 attachment points) to small end (1 attachment point).

Reproduction:

• In VAB, place Tri-Coupler.
• Place rocket fuel tank below.
• Flip liquid fuel engine upside-down, place above.

• Engineers report fuel missing and unused.

• Place fuel tank above, flip engine, place below.

• Engineers report no problem.

More Info: I don't know if this is intended or a bug. I wanted to hook an engine up with 3 fuel tanks but couldn't. The description says nothing about only delivering fuel in one direction, so I assumed it was a bug.

Edited February 20, 2016 by Darbin Giesorg
Solved.

[sal_vager]

Hi Darbin, please use fuel lines to connect the tanks to the adapter.

Also because the nodes on the adapter will not connect to both nodes of multiple stacks of fuel tanks you will need a strut on each unconnected point.

This will mean those unconnected nodes are treated as exposed to air flow, this is a limitation of the tree system used for part hierarchy.

[sebi.zzr]

Actually,this is intended behavior,and applies to all six "couplers/adapters"(3 large and 3 small (bi,tri,quad)).
It's defined in parts *.cfg:

NoCrossFeedNodeKey = bottom

If you whant to change that and you using Module Manager ,use this patch to allow fuel crossfeed in any orientation:

@PART[*]:HAS[#NoCrossFeedNodeKey[bottom]]:AFTER[Squad]
{
 !NoCrossFeedNodeKey = DELETE
}

 

Edited February 11, 2016 by sebi.zzr

[Claw]

Yes, it's intended. Otherwise engines hanging down one "leg" of a multi-coupler would be capable of stealing fuel from a stack hanging down another leg. So fuel can flow from the top node down to the bottom nodes, but not from the bottom nodes up (either through to the top node or another bottom node).

I also see that the (lack of) description is misleading.

Edited February 20, 2016 by Claw

[Darbin Giesorg]

7 hours ago, Claw said:

Yes, it's intended. Otherwise engines hanging down one "leg" of a multi-coupler would be capable of stealing fuel from a stack hanging down another leg. So fuel can flow from the top node down to the bottom nodes, but not from the bottom nodes up (either through to the top node or another bottom node).

Makes sense now and I'm using fuel ducts for everything since being told that. And yes, I'm sure I wouldn't have asked if the description had hinted at fuel flow only being allowed in one direction. This is similar to me assuming that struts wouldn't be usable with decouplers because it wasn't specifically mentioned they'd disappear on decoupling a stage. I assumed they'd just persist, so I had no idea how to deal with wobbly stages.

Bi-/tri-couplers are weird anyway. Putting tri-/bi-couplers on both sides of a stack cluster doesn't seem to be intended as only one node is ever connected. Which is a damn shame. I had plans...

Thanks, man. Great job on the stock bug fixes, by the way. Appreciated.

[Claw]

Just now, Darbin Giesorg said:

Putting tri-/bi-couplers on both sides of a stack cluster doesn't seem to be intended as only one node is ever connected.

Yes, unfortunately this is a limitation of the way the game engine works. The craft are built as a "tree" structure, where things can branch out, but branches can never loop back together. So the only (stock) way to deal with that is to use struts, or some clever docking port tricks (if you haven't seen that).

And thanks. Hopefully there will be even less need for them in the next update.

[Darbin Giesorg]

1 minute ago, Claw said:

or some clever docking port tricks (if you haven't seen that)

Dude.

Wow.