Uneven Fuel Use Messing with CoM

[Clipperride]

So, I tend to build my rockets with a central fuel tank with engine at the bottom then radially attach 3 or 4 tanks the next diameter down, with engines on each of those. I then attach fuel lines from each radial tank to the main central tank as well as from the central tank to each of the radial tanks. Most of the time this works fine with a nicely balanced fuel load throughout the flight.

Because I play KSP on a inherited "vintage" laptop (OK so its not that old, but it's a little below minimum specs for the game) I've had to turn all the graphics down to the minimum settings (but the game is so awesome I'm just happy to be able to play at all). At those settings the game plays rather well, a little lag on liftoff and when docking large craft, but my LKO station now has 500 parts and it's still possible to dock without the lag becoming much of a pain.

One issue I've had is landing somewhere new, with no idea of the height of the local terrain. It only becomes obvious you're near the ground when you are really close, which means a conservative, fuel wasting decent or suicide burn with fingers crossed. My "bright idea" was to loose the central engine on my landers and replace it with a decoupler and a small, light, fuel tank. Once I've finished my gravity turn and I'm heading pretty much straight down, I drop the tank and note the distance it travels before becoming one with the body I'm landing on (ie crashes). It gives a reasonable guide to how far I've left to travel before touchdown.

But, this method also seems to mess with the fuel flow. I keep finding myself having to balance out the fuel load or, worse, not noticing and having my ship twist and turn all over the place during burns. Previously sound vechiles, when reloaded and refitted with my "distance to destruction" dropable parts suddenly become unbalanced in their fuel use.

Do I need to redo the fuel lines on all my vechiles when changing something, or is there something I'm overlooking?

Edited September 1, 2015 by Clipperride

[Steelsunoa]

Without seeing the craft, I'd say you have the fuel lines crossed somewhere. I'm not sure I understand what you mean by ..." as well as from the central tank to each of the radial tanks." That part seems unnecessary to me, link the lines to eventually end at the tank that has the final stage of rockets.

[The_Rocketeer]

Having fuel lines that 'loop' can cause issues with uneven draining - a simple loop would be tank 1 > hose to tank 2 > tank 2 > hose to tank 1, but it could be much more complex and still loop. In your case it sounds like u have three such loops that share a common 'tank 1'.

[A_name]

My advice would be to lock the fuel tank you're going to be dropping or remove its fuel altogether before flight. Are you already doing that?

[Clipperride]

Yep, there is definite looping going on! Let's call the central tank 1 and the radials a,b,c. The lines currently run;

1 -> a

1 -> b

1 -> c

As well as

a -> 1

b -> 1

c -> 1

It was a habit I got into when I first unlocked fuel lines in Science mode. It's my first ever game of KSP and I've been playing about a month. Before reading this excellent forum, I was having trouble correctly placing fuel lines and so took the "overkill" route.

Hopefully dropping the connection back to 1 will solve the problem.

As for the drop tank for altitude assessment - There are no fuel lines to or from it, so the decoupler stops it being part of the troublesome system and I do usually launch with it empty. I never remembered to shuffle the fuel about before dropping it, so just emptied it in the VAB

Thanks all :-)

Edited September 1, 2015 by Clipperride