Fuel/Oxidizer Inbalance

[LMC]

I have a bizarre situation with my latest SSTO. It's basically laid out like the Ravenspear Mk4 (stock) with a central body and two outrigger engines, the major difference being the outriggers are separated and supported by 'chime' wings along the central body and I am using Rapier engines. The central body has 2 engines and the outriders have 1 apiece, and each section has an equal amount of Fuel/LOX to support each engine (the center has twice as much fuel as it supports 2 engines.) and some extra fuel in each section for the air breathing part of the mission. The setup works great during the air breathing section of the mission, as each section uses the spare fuel provided there for same. My problem starts after the engines switch to closed cycle, the center uses all its oxidizer (while ignoring the Fuel), and the outriggers use the Fuel up (while ignoring the Oxidizer), and as there is some extra fuel in each section the center engines cut out first (for lack of oxidizer) while the outriggers keep running thanks to the spare fuel from the air breathing part of the mission. There are no fuel lines between the sections, so how the heck is this happening, and how do I stop it?!

Thanks for any reply.

[Crown]

My first thought is of symmetry. If the plane isn't build with the symmetry tool there might be fuel draining problems.

Can you give us some pictures or the .craft file so we can take a look at it?

[rodion]

i can think of two ways to help alleviate this problem: one is by running the very useful TAC Fuel Balancer mod to make sure that all tanks (and by extension engines) have an equal share of the resources in the craft, the other is using the tweakables menus in the SPH to change the fuel/oxidizer balance in the tanks to represent your best guess as to what the flight profile demands (with a SABRE/RAPIER that usually just means 10% or so less oxidizer, if i recall), so you don't end up with any excess resources left over in your tanks.

[Padishar]

This thread describes the fuel flow rules in detail. I suspect the issue is that a fuel tank that does hold a particular resource does not draw that resource from its parent if it is surface attached (not node to node, e.g. any tank attached to a wing) but a tank that does not hold a particular resource will draw that resource from the parent. So, if you use any parts that just hold liquid fuel then they can draw fuel through the wings from the main body.

Pictures (or better, your craft file) would be a big help in diagnosing the exact cause. You will probably have to add some fuel lines to force the fuel to drain in the way you want (and you may need to reorganise some of the part connections too).

[LMC]

Looks like a recursive search error. Here's a link to the pic and ship file.

https://onedrive.live.com/redir?resid=90F455F2BB5B921!150&authkey=!ADQd-SRKdDeHyPU&ithint=file%2ccraft

It looks real pretty, but it's not really worth the bother of fixing I think, I made a drone that does the job for a fraction the cost. Interesting to know what the error is though.

Edited November 2, 2014 by LMC
Picture link didn't work... :(