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Bug #3477

Closed-cycle engines drawing from jet fuel tanks can draw oxidizer from unconnected tanks.

Added by aureus about 10 years ago. Updated over 8 years ago.

Status:
Closed
Severity:
Normal
Assignee:
-
Category:
Gameplay
Target version:
-
Start date:
11/08/2014
% Done:

100%

Version:
Platform:
Any
Expansion:
Language:
English (US)
Mod Related:
No
Votes:
Arrow u r green
Arrow d r red

Description

A little background: I was flying a spaceplane with a fuel configuration that looked something like the following and noticed that when I switched the RAPIER engines to closed-cycle, the center engine was running out of oxidizer before the side engines.

After a bit of testing, I have determined the following:
- Engines drawing fuel from jet fuel tanks can draw oxidizer from unconnected tanks. (see attached Oxidizer Testbed I craft file)
- The illegal tanks must be an ancestor of the jet fuel tank in the craft's part tree or in the same stack as an ancestor. (see Oxidizer Testbed II and III)
- Drawing fuel from a liquid fuel+oxidizer tank that contains fuel but no oxidizer does not cause this bug. (see Oxidizer Testbed IV)
- This will occur even after the jet fuel tank runs out of fuel. (see Oxidizer Testbed V)
- The oxidizer will be pulled from the (hierarchically?) furthest tank that meets the above conditions. (see Oxidizer Testbed V and note while the engines are firing that the oxidizer in the smaller and larger tanks of the center stack will deplete simultaneously)

Some additional notes:
- This will occur even without the modular girder segments. Those are present just to make it clear how the tanks are connected.
- The Mk2 Liquid Fuel Fuselage and Mk2 Liquid Fuel Fuselage Short parts exhibit the same behavior as the Mk1 Fuselage - Jet Fuel shown.

Oxidizer Testbed I.craft (16.5 KB) Oxidizer Testbed I.craft aureus, 11/08/2014 03:34 AM
Oxidizer Testbed II.craft (16.5 KB) Oxidizer Testbed II.craft aureus, 11/08/2014 03:34 AM
Oxidizer Testbed III.craft (16.6 KB) Oxidizer Testbed III.craft aureus, 11/08/2014 03:34 AM
Oxidizer Testbed IV.craft (16.8 KB) Oxidizer Testbed IV.craft aureus, 11/08/2014 03:34 AM
Oxidizer Testbed V.craft (23.9 KB) Oxidizer Testbed V.craft aureus, 11/08/2014 03:34 AM

History

#1 Updated by Padishar about 10 years ago

This is a well understood and well documented (here: http://forum.kerbalspaceprogram.com/threads/64362-Fuel-Flow-Rules-%280-24-2%29) consequence of how the "fuel flow" mechanism works (and how some rather surprising parts are "crossfeed capable").

#2 Updated by aureus about 10 years ago

I still think this is a bug: it only occurs with jet fuel tanks, and the affected engines can only draw oxidizer from the unconnected tanks, not liquid fuel.

#3 Updated by Padishar about 10 years ago

Basically, parts that are surface mounted to their parent can draw resources from the parent except when the part contains the type of resource being drained. So a LF only fuel tank that is surface attached to its parent can draw oxidiser from its parent but can not draw liquid fuel from it. While you may think that the behaviour is not logical (and you would have a point), it is working as intended, so it is not really a bug, as such. It is highly unlikely that this behaviour will be changed though a related issue where radial decouplers allow resources to flow across them may, possibly, be fixed.

#4 Updated by TriggerAu over 8 years ago

  • Status changed from New to Needs Clarification

#5 Updated by TriggerAu over 8 years ago

  • Status changed from Needs Clarification to Closed
  • % Done changed from 0 to 100

Closing this report out for now. If you find it is still occuring in the latest version of KSP please open a new report (and this one can be linked to it.) For best results, the wiki contains really useful info for when creating a report http://bugs.kerbalspaceprogram.com/projects/ksp/wiki.

You can also ask questions about the bug cleanup in the forum here: http://forum.kerbalspaceprogram.com/index.php?/topic/143980-time-to-clean-up-the-bug-tracker/ and tag @TriggerAu to get my attention

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