Why does this lifter drain fuel assymetrically?

[Klingon Admiral]

Sup spacefriends,

While lifting a station component into orbit I ran into the problem that this lifter:

The lifter itself is pretty standard asparagus-staging, but the first set of asparagus-boosters is draining fuel from the payloads's tanks. But for some reason, one of the boosters runs out of fuel before the other one, forcing me to eject the first set of boosters early to avoid a mission failure (luckily this thing was quite over-engineered). The thing I don't understand is why it drained fuel in that way.

Edited July 29, 2013 by Klingon Admiral

[Procyon]

I think going from one tank into 2 doesn't work very well, least I seem to remember reading that somewhere, run the line from the top tank to the bottom see if that works.

[Captain Sierra]

Uhm, you could always manually transfer the fuel out of the payload when you get down to your center tanks. I'm not sure how the fuel is actually running. What version is this on and are you willing to share a .craft file?

EDIT: Disregard the version question, you appear to be running 21.1 am I correct?

[sojourner]

I think going from one tank into 2 doesn't work very well

This. You can go from 2 to 1, but going from 1 to 2 usually ends up with assymetric usage.

[stupid_chris]

Actually the problem comes from a fuel loop. Going from a tank to many isn't a problem, and going from many tanks to one isn't, but here, fuel flows from the center stack, out to the first set of boosters, then the second, and then back to the center stack. Even though they're separated, the fuel flow logic is quite cringy with those.

So basically, you can have this ---<=== and you can have this ===>---, but you can't have this ---<===>---

[hanvyj]

Not sure if it makes a difference, but when I do asparagus staging I have the fuel lines go from outer tank to inner engine. Always works to me.

[KrazyKrl]

As long as you have all your first stage engines identical, you just need one fuel line per outer tank to drain into the center tank. The outer engines will draw from the outer tanks at the same rate. The inner engine will draw from the inner tank, then the inner tank will draw fuel via the fuel lines from the outer tanks. You do not ususally need more than one "parent to child" relationship in a series of tanks. The fuel lines should always be set up to prioritize what tanks you drain from and jettison first.

[Nurph]

I believe you could get around the flow logic problem by waiting to activate the center engine until the payload tanks are empty.

[Eric S]

I believe you could get around the flow logic problem by waiting to activate the center engine until the payload tanks are empty.

That might work. I've seen this problem come up in rockets where you have two possible paths from an engine to a fuel tank, so if the center engine isn't running until after the payload fuel tank is empty, that could avoid that.

[Klingon Admiral]

I believe you could get around the flow logic problem by waiting to activate the center engine until the payload tanks are empty.

This worked perfectly, many thanks.

[Epic DaVinci]

I believe you could get around the flow logic problem by waiting to activate the center engine until the payload tanks are empty.

This is an inefficiant method though, the center stack will be dead weight that will have to be lifted by the outer stacks, Plus without the center engine fireing untill you drop your outer tanks, there is no point using asparagus staging.

[Eric S]

This is an inefficiant method though, the center stack will be dead weight that will have to be lifted by the outer stacks, Plus without the center engine fireing untill you drop your outer tanks, there is no point using asparagus staging.

I think you're misunderstanding this suggestion. They're not saying don't fire the center engine until the side tanks drop, they're saying don't fire the center engine until the payload stage fuel tank is empty, and with the way the fuel is routed, it will be the first tank to empty.