Fuel tanks not dispersing fuel right.

[a-rod48]

I have a Mun base I need to get back into orbit for various reasons. It has an X shape to it, with a command pod in the middle, and four fuel tanks/engines/docking ports attached radially to the outside using I-beams. The tanks are the FL-T400 tanks, then below that is an inline clamp-o-tron, below that a lv-909 engine (on top i have a medium sized RCS tank, but I don't think that matters). I have fuel lines attaching the fuel tanks diagonally to two engines (the one to it's left and the one to it's right.)

Now that I have that explained, here is my problem. It takes off and about 6 seconds into flight I can't control it because each engine is using an uneven amount of fuel. I never had this problem when i was landing it. All of the engines are at 100 power and all of the fuel tanks are completely full. If you look at it from the top, the engines on the top-right and bottom-right use fuel twice as fast as the ones on the left.

[Streetwind]

Make sure that each engine can only draw fuel from one single tank.

You might get the idea to connect multiple tanks to each engine for redundancy, but this will screw things up because ultimately, what draws fuel from where in which order is a round-robin operation. First one engine gets its fuel and computes its action for a physics tick, then the next one, then the next one and so on. And each engine gets to decide individually from which tank it draws. Now if there happens to be a rule in the game logic that says "always draw from the tank that is the furthest down in the Unity part tree first", then multiple engines may decide to drain from the same tank instead of splitting it evenly.

EDIT: I think Kasuha made a guide on fuel flow logic, you can try and see if that answers your question.

Edited March 12, 2014 by Streetwind

[FREEFALL1984]

Are you running any mods or just the vanilla game?

[Kasuha]

The thread about how fuel distribution works is here. Possible reasons are:

- problem with fuel flow (you can find some examples of the "If the ship is symmetric, it will draw fuel symmetrically" fallacy in the thread)

- problem with engines, such as one tweaked to lower power

- problem with mods redistributing fuel in an unwanted way

- problem with balance (such as an off-center extra part mounted/attached somewhere)

Screenshot of the craft, or your persistence file (if you don't use modded parts) would probably help.

[Superfluous J]

Also, if your engines are gimbaling and above your Center of Mass, they may be incorrectly correcting drift. Try turning off gimbaling, and hope you have RCS or reaction wheels to turn

[Navy2k]

Please consider also, the order in which the fuel lines where attached to the craft influence the order from which tank fuel is used first. So if you first attach all left hand side tanks and then all right hand tanks it should be ok.

Ben

[a-rod48]

what draws fuel from where in which order is a round-robin operation. First one engine gets its fuel and computes its action for a physics tick, then the next one, then the next one and so on. And each engine gets to decide individually from which tank it draws. Now if there happens to be a rule in the game logic that says "always draw from the tank that is the furthest down in the Unity part tree first", then multiple engines may decide to drain from the same tank instead of splitting it evenly.

Thank you. I will try to avoid that in future designs. (Of course now I am stuck with a half finished mun base.)

I apologize for not knowing where to look for this information, I am relatively new to this.

[Claw]

Thank you. I will try to avoid that in future designs. (Of course now I am stuck with a half finished mun base.)

I apologize for not knowing where to look for this information, I am relatively new to this.

No need to apologize.

Welcome to the forums. I hope you never hesitate to poke around or ask a question if you want to know something. There isn't exactly a manual for the game yet, so don't be afraid to ask (or experiment yourself!)

Good luck