Crossfeed

[Silviu250]

I only want to ask what crossfeed is, what it does and if it's good?

[Foxster]

1 hour ago, Silviu250 said:

I only want to ask what crossfeed is, what it does and if it's good?

A coupler part and such by default doesn't allow fuel to pass. Turning crossfeed on means it does. 

It is subtly different to using a duct. A duct allows fuel to pass only one way. Crossfeed through a coupler allows fuel to pass both ways, which I find usually worse that useless and it can mess up your staging and your dV readings. 

Personally I rarely use crossfeed and just stick to using ducts. 

[Curveball Anders]

18 minutes ago, Foxster said:

A coupler part and such by default doesn't allow fuel to pass. Turning crossfeed on means it does. 

It is subtly different to using a duct. A duct allows fuel to pass only one way. Crossfeed through a coupler allows fuel to pass both ways, which I find usually worse that useless and it can mess up your staging and your dV readings. 

Personally I rarely use crossfeed and just stick to using ducts. 

You can adjust the flow by setting the priority of each tank.

So it allows for various forms of aspargus without the need of ducts.

 

[Foxster]

Just now, Curveball Anders said:

You can adjust the flow by setting the priority of each tank.

So it allows for various forms of aspargus without the need of ducts.

 

I appreciate that but a common problem is with multiple stages. An outer set of tanks+engines will run on the fuel in the outer tanks as they have the higher priority. When those tanks are empty the outer engines then draw their fuel from the inner tanks. This is not usually what you want, you want the outer engines to run until their attached tanks are empty and then those engines shut down and you stage them away. 

This is particularly bothersome when using a mod to automate staging as it won't stage when the outer tanks are empty. 

[Geonovast]

12 minutes ago, Foxster said:

This is particularly bothersome when using a mod to automate staging as it won't stage when the outer tanks are empty. 

Which is where SmartParts is really handy.  I always let a SmartPart module stage outer tanks.

 

I do really, really wish that you could set crossfeed on decouplers to only go one way.

[Snark]

10 hours ago, Silviu250 said:

I only want to ask what crossfeed is, what it does and if it's good?

As discussed here, it allows, for example, setting up asparagus without needing fuel ducts. I use it all the time, works great.

Advantage: more convenient construction, save the weight and drag of ducts.

Disadvantage: no automatic protection against "backflow", as Foxster points out, so you have to watch the fuel tank and activate staging when it empties, though the SmartParts mod can handle that for you if you use it.

Both methods work just fine. Which one is "better" depends on your preferences. Some folks like one, some like the other. (Myself, I love the crossfeed and hardly ever use fuel ducts anymore.)

 

[FloppyRocket]

On 2/23/2019 at 8:54 AM, Curveball Anders said:

You can adjust the flow by setting the priority of each tank.

So it allows for various forms of aspargus without the need of ducts.

 

Near-novice question when it comes to cross-feed:

How does one "set the priority of each tank"? All I see is an enable/disable option.

Edited February 25, 2019 by FloppyRocket

[Geonovast]

4 minutes ago, FloppyRocket said:

Near-novice question when it comes to cross-feed:

How does one "set the priority of each tank"? All I see is an enable/disable option.

You need to enable Advances Tweakables.  It's in your difficulty settings.

Higher numbers drain first.

[GoatRider]

4 minutes ago, FloppyRocket said:

Near-novice question when it comes to cross-feed:

How does one "set the priority of each tank"? All I see is an enable/disable option.

In the settings, there is an option called "advanced tweakables". It turns on things like tank priority, and autostruts.

[FloppyRocket]

@GoatRider, @Geonovast, thanks for the tip. Lots of goodies hiding in "advanced tweakables", I've never been in there.