Fuel drain rates unexpectedly different.

[Gravitas Shortfall]

I've got a jumbo-64 with a mainsail beneath it, 6 more jumbo-64s with mainsail radially attached, and then to each of the radial jumbo-64s, I have 3 T800s each with an LV-T30. No fuel lines. Now if I just looks at each of these engines and corresponding fuel tank individually, then MechJeb tells me I should get 58s of thrust for all of them, but when I put it all together and launch, what happened is that first the radial mainsails run out of fuel, then a little later the central one, and then finally the TV-T30s. Now all I can figure is that is happening because my T800s are actually attached by means of a tail connector for reasons of prettiness, and since the model snaps together in such a way that the TV-T30s appear below the jumbo-64, they're somehow drawing fuel from the 64s first rather than the T800s.

So I guess my question is what determines which tank an engine first draws fuel from, and how might I get around this particular problem? I tried adding fuel lines from the T800s straight to the LV-T30s, but they still seemed to be draining the jumbos first.

[Dkmdlb]

Can you post a picture? It's a lot easier to figure out if we can see exactly how it is arranged.

[stupid_chris]

Yeah we'd really need to see pictures else it's kinda hard to see what's wrong. We could probably spot the problem easier this way

[capi3101]

Pics would help.

From the sound of it, though, your problem is indeed the tail connectors. Tail connectors allow fuel crossfeed, and an engine always draws fuel from the available source that's furthest away from it first - in the case of your -30s, since they can draw from the Jumbo and it's furthest away, that's where they'll draw first. Your best bet is to attach the 800s directly to the jumbos or, if that doesn't solve the problem (or if the VAB barfs at that idea), with radial decouplers (even if you don't intend to use them).

[Gravitas Shortfall]

Pics would help.

From the sound of it, though, your problem is indeed the tail connectors. Tail connectors allow fuel crossfeed, and an engine always draws fuel from the available source that's furthest away from it first - in the case of your -30s, since they can draw from the Jumbo and it's furthest away, that's where they'll draw first. Your best bet is to attach the 800s directly to the jumbos or, if that doesn't solve the problem (or if the VAB barfs at that idea), with radial decouplers (even if you don't intend to use them).

Shouldn't that go both ways, though? If the tail connector is a crossfeed, then shouldn't my mainsails and -30s just all share the same fuel supply, and shut down at the same time?'

Will try to add some pics once I get back to my main computer.

[capi3101]

Well, see fuel flow only goes one way. It's part of the nature of how KSP puts together rockets - its a tree-like structure, you have a root part and branches off of a part. I'd bet good money that you put the Tail Connector on the Jumbo before you added the FL-T800s, right? Well, as far as the game's concerned, the LV-T30s is a branch of the FL-T800 is a branch of the Tail connector is a branch of the Jumbo 64. The Mainsail is a branch of the Jumbo 64, and since it is on a separate branch from the Tail Connectors, it has no association with the FL-T800s. Thus, the furthest connecting fuel supply for the LV-T30s is the Jumbo64, and the furthest connecting fuel supply for the Mainsails (again, considering this root-branch relationship structure) is also the Jumbo64.

Again I think that's what's going on; we'd all need to see a screenshot or a posted craft file to be absolutely 100% sure.

Fuel lines from the 800s to the 64 incidentally will not solve the issue - thought I'd through that in there real quick. You wind up with a fuel loop as a result and KSP really doesn't know what to do with thems; you could get any kind of behavior out a loop, most often the fiery and destructive kind that makes Jeb happy then dead.