fuel crossfeeding

[kurja]

I don't understand how to use fuel crossfeed. I made a lander using a 2-kerbal lander can, with a fuel tank under it, on top center I put a docking port and around that 8 small trusses and 8 of those small grey cylindrical fuel tanks on those, and then radial engines on the sides of the lander can - and the engines aren't getting any fuel. I was able to get fuel from top tanks by running a fuel line from each to the lander can, but for some reason I couldn't put a fuel line from bottom tank to lander can so I tried placing a truss on each and then a fuel line to those but that doesn't work... What am I doing wrong? Why isn't fuel flowing from tanks to engines through the lander can, or the cubic trusses?

Edited July 17, 2013 by kurja

[Cashen]

I'm not sure if the lander can or the cubic trusses are cross-feed capable? I'd have to check. Parts that allow fuel to flow through them typically specifically say this in the part description. It's possible the lander can allows it but the trusses don't?

[dave4002000]

The cubics definitely allow fuel transfer. I use them to mount KAS winches all the time. All command pods are also crossfeed capable. I think a picture of your rocket would help tremendously here.

[Johnno]

Why isn't fuel flowing from tanks to engines through the lander can, or the cubic trusses?

Fuel flows through stacks and won't flow radially on its own. As soon as you put trusses, I-beams or even just attachs tanks radially straight onto the center stack the fuel in those won't flow to the center stack. And the opposite, the center stack fuel won't get out radially onto tanks/engines that are mounted off it radially.

Radial engines get fuel from a tank if they're attached straight to it, otherwise they need a fuel line (or be attached onto something in the centerstack). Anything in the centerstack with fuelcrossfeed will crossfeed. I just did a quick test and radial engines straight onto the landercan will get fuel through the landercan itself from the fueltank below it (since they count as centerstack).

[kurja]

I'm not attaching radially, well except for the radial engines. Small fuel tanks are on top, however not on the can's own attachment node, but on trusses because the tanks wouldn't attach on the lander can's roof on their own. Do tanks need to be attached on a node on the center stack for fuel to flow?

The bottom tank is however attached node-to-node on the lander can's belly, but still my radial engines attached on the can won't get fuelled for some reason.

I'll post a picture of it later when I get home.

[kurja]

ach, I forgot I had a stack separator between the can and tank. So no cross feed through that. However, I expected to be able to get fuel to those radial engines when I put trusses on tank and can, connected with a fuel line. Isn't that supposed to work? VAB won't let me draw a fuel line directly from that tank to the lander can, either.

From the top tanks, I get fuel if I put a fuel line form each to the can. Is there a cleaner way to do this?

This seems unnecessarily complicated right now

Picture of it:

[Johnno]

However, I expected to be able to get fuel to those radial engines when I put trusses on tank and can, connected with a fuel line. Isn't that supposed to work?

It simply won't work because those trusses count as being attached radially so they themselves won't crossfeed. One way around this is to attach a oscar-b (or any other) fuel tank to one of the trusses and lead fuel through it.

From the top tanks, I get fuel if I put a fuel line form each to the can. Is there a cleaner way to do this?

Nope, those top tanks don't count as being stacked onto the landercan, so they're the same as radially attached, won't transfer fuel unless you put fuel lines onto them.

This seems unnecessarily complicated right now

Well it's only as complicated as you want it to be. There's plenty of inspiration to be found in the spacecraft exchange subforum, I recall a lander specific thread. But to get you started here's some from my personal collection.

My first manned Mün lander design

Second manned Mün lander design

Third (current, sorta) manned Mün lander design

[Skorpychan]

When it comes to parts on landers, less is more. Can you replace that pile of small tanks with one big one?

[kurja]

When it comes to parts on landers, less is more. Can you replace that pile of small tanks with one big one?

Well it's supposed to have a docking port on the top, and there's ample empty space around it so I wanted to use that space, also keeping the rocket shorter... I could put a tank between the crew module and the docking port, but all properly fitting fuel tanks are larger than I need so it would make the ship heavier too. The bottom tank is larger than I need as well, I wish there were shorter tanks in this diameter.

I guess I'll have to use some radial tanks.