Fuel flow from outside to center tutorial (COM solution)

[Tripzter]

As we all know originally fuel flows from the front to the rear of the ship. This causes rather big problems with center of mass as the fuel gets used up. When i first started my plane would be leveled and then 10 minutes into the flight the nose would not stand down. Well i've figured out the routing to prevent that.

For my example i will use my plane. The B2. The plane has 1 jet engine and 2 Aerospike engines. The Jet engine is to be used on the planet and the aerospike engines are to be used in space.

So lets get started. In my plane i have a fuel tank in the front, a large fuel tank in the middle and at last a fuel tank in the rear. Now this is important as the center tanks cannot store the oxidizer from the outside tanks however they can take the liquid fuel part from them. The aerospike engines cannot run without oxidizer. Actually worse. Once you run out of oxidizer they will take the remaining fuel and use it up in seconds.

Anyways without further delay i will explain. You want a fuel line from the front one to the center tank and another fuel line from the rear tank to the center one. This is the yellow lines. This will keep the fuel in the center and use it up from the ends. Now with just those fuel lines it will run however once you use up the rear tank it will stop therefore you need a fuel line from the center fuel tank to the engine. This is the blue arrow. At last the green fuel lines. You want those as a backup. Yes you want both a fuel line in each direction, let me explain. Say you're on the planet using your jet engine. The bottom green lines will feed the fuel to the center tank. Anyways after 20 minutes you're in space and you shut down the jet engine. At this point your outside tanks will be near empty. If you turn on your Aerospike engines they cannot run without liquid fuel and will use up any oxidizer you have in seconds. This is where the upper set of green lines comes in to play. It will take the necessary fuel it needs from the center tank and supply it to the aerospike engines.

TL;DR? Just do your fuel lines like they are in the picture.

I hope this explains it.

Tripzter.

Edited August 9, 2013 by Tripzter
Added further info.

[Exothermos]

Hmm so essentially you can think of it as the center most fuel tank is the bottom, and you set it up so that fuel flows down hill, and your jets pull from that tank.

[Tripzter]

Fuel flows to the center so your center of gravity stays pretty much the same so your ship remains the same as fuel gets used up.

[Dkmdlb]

Those fuel lines going in both directions don't cause problems for you?

[Tripzter]

Those fuel lines going in both directions don't cause problems for you?

No, just the opposite, they solve problems. When you're using the jet engine liquid fuel goes from those tanks to the center tank. So eventually they will empty from the liquid fuel. Say you're ready to switch to the rocket engines, if you do not have the 2nd line the rocket engines will flush the oxidizer in seconds and then you're screwed. Sure you can transfer fuel and you'll be ok but thats an extra step you HAVE to remember to do. Having the opposite fuel line will feed the rocket engines the necessary fuel they need so you dont need to do a fuel transfer or anything like that. The rocket engines will just take the necessary liquid fuel from the center tank.

Edited August 22, 2013 by Tripzter