Bug #4796

Unexplained fuel drain

Added by Ecthelon almost 5 years ago. Updated over 3 years ago.

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In the attached ship file, the fuel in the tanks of the second stage up inexplicably drain when the first stage is activated on takeoff.

This is very easy to replicate, as you can see that they drain upon launch for no reason, and those 3 outer engines have no fuel when their stage is started.

Have tried connecting lower stages with different parts and removing engines but tanks still drain.

Seem to split evenly between the tanks below them somehow.

Has happened since previous version when I first made this ship, only now annoyed me enough to report it when it didn't fix with the update (sorry!).

Race mk3.craft (532 KB) Race mk3.craft The effected ship Ecthelon, 04/28/2015 07:28 PM
Structural Fuselage.craft (15.9 KB) Structural Fuselage.craft Shows bug in small craft. zhollett, 04/29/2015 03:42 AM
screenshot0.jpg (312 KB) screenshot0.jpg Shows fuel draining from wrong tank. zhollett, 04/29/2015 03:51 AM


#1 Updated by zhollett almost 5 years ago


I can confirm this bug. The parts in question are the Structural Fuselage combined with either the TT-38K or the TT-70 radial decouplers.
I have attached a new .craft file which displays this bug as described by the OP but in a much smaller example :)

Steps to reproduce:
  1. Launch the attached craft file called "Structural Fuselage.craft"
  2. The craft starts off with the Structural Fuselage attached to the TT-38K.
  3. Stage the engine and you will notice the fuel drains from the tank under the Command Pod in Stage 1, which it should not do.
  4. Revert back to VAB and move the Structural Fuselage (and everything below it) to the Structural Pylon and re-launch the craft
  5. Upon staging, you will see the expected behaviour (the fuel tank below the command pod stays full)

Notes from testing:
(Note to OP: An interim fix for your craft would be to use Structural Pylon's instead of TT-38K's)

If you place any other piece above the tank in stage 0 instead of the Structural Fuselage, you get the expected results, the fuel will not drain from the tank under the command pod.
(Note to OP: This is another interim fix for you, I got the best weight results by replacing the Structural Fuselage with EMPTY MK1-Liquid Fuel Fuselage's)

#2 Updated by Kasuha almost 5 years ago

Technically not a bug - the fact that a part which is not a fuel tank drains fuel from its parent part is intended behavior. Radial engines rely on that. But could be improved by disabling fuel crossfeed on radial decouplers.

#4 Updated by Squelch over 4 years ago

  • Platform Win32 added
  • Platform deleted (Windows)

#5 Updated by TriggerAu over 3 years ago

  • Status changed from Confirmed to Needs Clarification
  • % Done changed from 10 to 0

#6 Updated by TriggerAu over 3 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

You can also ask questions about the bug cleanup in the forum here: and tag @TriggerAu to get my attention

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