Fuel flow issues

[bsalis]

I'm trying to get the fuel flow here to work in ways I think KSP just does not like. However I thought I would put this out there to see if anyone can (or has already) cracked this. Here's a pic from the VAB showing one of many attempted solutions...

So... this orbiter/lander has a detachable tank+leg+aerospike setup on the side. You can see this craft without any attempt at fuel crossflow...

Problem is that without any crossflow, once the 400 units tanks are gone, that's it for the aerospikes. I want to be able to draw from the 3200s and detach the aerospikes when I don't need the TWR any more. However, no matter the fuel crossflow arrangement and tweaking of tanks, I can't seem to get the result I want. That is to have the 400s drained early then have the aerospikes draw from the 3200s until detached.

Another requirement is to have the central stage tanks not drain until the outer stage of 3200s are detached. So far this has been done simply be disabling the central 3200. That above Laythe ascent being an example of where this has worked fine.

[sloth]

If you stick something that doesnt feed fuel between the aerospikes and the 400s and then place a fuel line from the 400s to the 3200s and then from the 3200s to the aerospikes, then I think the 400s should drain first, followed by the 3200s until such a time as you ditch the aeros. Does that fix your problem or am I misunderstanding it?

[Temstar]

You have to put a decouper between 400L tank and aerospike as well. Pump the fuel from 400L to 3200L tank and then pump fuel from 3200L tank directly into aerospike.

I use to have a craft like that, the spacing for the fuel lines can get a bit tight. Alternatively why not just have the 400L tanks and aerospikes on radial mount?

[bsalis]

Yeah - I can move the decouper so that only the aerospike is on it. I can do that as a backup. However I would like to detach the whole tank+leg+engine assembly.

[sloth]

I dont think its possible to fix with fuel lines alone without adding/moving parts.

Another reason why I would like interconnected tanks to drain in order of staging but thats a whole other debate

[Temstar]

Yeah - I can move the decouper so that only the aerospike is on it. I can do that as a backup. However I would like to detach the whole tank+leg+engine assembly.

Nono, don't just move the decouper, add a new decouper so it's:

tricoupler

decoupler

400L tank with leg

decouper

aerospike

When you stage, decouple the upper and lower decoupler at the same time.

[bsalis]

Nono, don't just move the decouper, add a new decouper

Yeah, you are right. It adds a little more weight, but that's I think as good as it gets. Better than anything I have thought of so far.

Now I just need to rework some other things. A couple of the aerospikes are melding with parts of the booster stage and is...

Nothing that I can't resolve. Thanks for the help everyone

Edited October 15, 2012 by bsalis

[EndlessWaves]

the right to left fuel line in that first picture is the wrong way round which is likely why the small tanks are draining first as they're at the end of the fuel line chain (so each aerospike is actually draining the next tank along, not the one above it).

[Qumefox]

He's wanting the small outlying tanks drained first.

[sal_vager]

Hmmm, try running the fuel lines from the small tanks up to the big ones, then from the big tanks to the engines, you might need decouplers between the aerospikes and tanks for this.

What should happen is the small tanks are emptied first into the large tanks, so you can then jettison them and their aerospikes while keeping the big tanks fully fueled

[Fried]

[ATTACH=CONFIG]34843[/ATTACH]I'm having flow troubles with my space plane no mater how I hook it up the engens die at different times. [ATTACH=CONFIG]34843[/ATTACH]

[bsalis]

Hmmm, try running the fuel lines from the small tanks up to the big ones, then from the big tanks to the engines, you might need decouplers between the aerospikes and tanks for this.

Yep - I did that as per me previous post. You do need decouplers at both ends of the tank. If you don't have one between the tank and engine some very odd draining happens (ie. it's bugged).

I'm having flow troubles with my space plane no mater how I hook it up the engens die at different times.

Have you tried simply having fuel lines from where there is more fuel to less? By the look of it, from the inner stacks to outer. If theres a path from fuel to an engine it should keep running.

[Fried]

Yes if i do that the center engen dies followed by the next and so on its vary anoying because that should work. is there any mod that alows me to see whats going to happen. I need this because once finished im off to the poles. I have spent a lot of time balancing this plane for that flight and the fule + structural saved me from having to put some system of lower down gear or over weighted nose. also im resistant to make many modifications to the body because it has crashd 15 times and not one kerbal has died.(True Story).

Edited October 16, 2012 by Fried

[r_rolo1]

@bsalis

You should never, ever, do anything with the fuel lines that:

a) goes from the center to the outside and then comes to the center again

something that creates a circular hose system in the ship

Both are prone to creating weirdness. In your case it was , since your pretty x-shaped system was creating a bunch of loop systems ( 2 around the whole ship and one for each aerospike + tank ). Adding the decouplers solves the issue, but, and just as curiosity, do you really need those tanks with fuel ? I see you are using then as structural parts to have where to put the landing legs as well, but if you could live without that fuel, there are far lighter alternatives ( from structural fuselages to wings ... )

P:S I was editing my post , Fried I had given a incomplete and misleading answer to bsalis issue that I wanted to correct

Edited October 16, 2012 by r_rolo1

[Qumefox]

put the engines on decouplers to isolate them from the fuel stacks. Plumb the outer fuel stacks to the center one, then plumb the center stack to each engine. That way, all engines will be feeding from the same tank, instead of drawing from the stacks they're attached to.

[nhnifong]

That's a pretty interesting design. I never thought about mixing engine types on one tricoupler but you've got them arranged in such a way that it's still symmetrical.

[Fried]

I did what was asked and now nomatter what i do it has a constant drag to one side or the other.

[Max Schram]

This Plugin lets you disable engines as well as fuel tanks:

http://kerbalspaceprogram.com/forum/showthread.php/22951-MajiirKerbalLib-0-2-1-Engine-toggles-high-Isp-prioritization-stock-part-fixes

[A Fat Pokemon]

Run the fuel lines directly to the engines, not on the fuel tank, and it should draw from the 400 before moving to the 3200