Disabling Liquid Fuel Crossfeed

[Leafbaron]

I was trying to build a a space plane last night and for the life of me I could not keep the LF from the rocket tanks from feeding into the Jet Engines. This was very problematic. I tried even attaching the rocket tanks via a coupler and disabling crossfeed to no avail. I was just curious is there a way to do this without changing fuel flow priorities? or is that the only way?

Thanks in advance,

Leafy

[Sir_Robert]

That sounds exactly what fuel priority is designed for. Why do you want to do it without that?

[Leafbaron]

I just thought that there might be an easier way to do it than set each tanks fuel priority in such a fashion that LF is drawn only when the primary tank is empty. 

[Terwin]

Why not just increase the priority of the primary tank?

So long as the number on the primary tank is higher than the number on the rocket fuel tanks, the exact values do not matter.

[DocMoriarty]

Disabling crossfeed should have worked. It's a BUG.

[Leafbaron]

@DocMoriarty it could be.

@Terwin I'm not exactly sure how the fuel flow priority works and what weight the values for priority carry. When i did some initial testing when 1.2 first came out. it appeared that constant fuel flow was still happening across all tanks. For example if i set the fuel flow priority higher one tank than another both tanks were still drained, just one tank at a lower rate. If someone knows how it works more precisely please chime in!

 

What happens when fuel flow priority is set to 0?

What happens when fuel flow priority is set to a negative value?

What kind of ratios on fuel flow priority are needed to have one tank drain before another is used?

Edited November 4, 2016 by Leafbaron

[Tyko]

IIRC fuel priority numbers matter only in relation to other tanks' priority numbers. It doesn't matter if it's zero or a negative value, the system just starts with the highest numbered tank(s) and then works its way down.

Edited November 4, 2016 by tjt

[Leafbaron]

I will test tonight when I get home from work. Ill report back with my findings. 

[Renegrade]

19 minutes ago, Leafbaron said:

 I'm not exactly sure how the fuel flow priority works and what weight the values for priority carry. When i did some initial testing when 1.2 first came out. it appeared that constant fuel flow was still happening across all tanks. For example if i set the fuel flow priority higher one tank than another both tanks were still drained, just one tank at a lower rate. If someone knows how it works more precisely please chime in!

There's no magic to the fuel priority system at all.  A higher priority number drains before a lower priority number. end of story.   The specific numbers don't matter, just their relative order (1 is bigger than 0, which is bigger than -1, which is bigger than.. etc).  There are NO magic numbers with special meanings.  It works that way on jets and rockets both.

An important thing to note is that only the number on the left (the one without brackets around it) is the one to worry about.  It's the sum of your adjustment, plus the automatic number assigned by the fuel low system.  The number on the right is your adjustment ONLY.  So a tank that's "19 (-1)" will drain before a tank that's "12 (+2)" and also before a tank that's "10 (+20)".   In those three cases, the original numbers were 20, 10, and -10, but the user subtracted 1, added 2, and 20, respectively.

[SpacedCowboy]

I'm inclined to agree with Doc. However, this whole situation could be cured by the implementation of fuel tanks being controlled by action groups. A simple "on or off" of liquid and or oxygen tanks would be a godsend!

One can only hope.

[Foxster]

Couldn't you just toggle off the tanks until you want to use them?

[Terwin]

@Leafbaron It maybe different for jet engines, but for rocket engines, it is just as @Renegrade said, a tank at 3 will fully drain before before a tank at 2 which will in turn fully drain before a tank at 1 and so on for any integer numbers(the only kind you can set)

[FancyMouse]

I worried about the same thing initially when I start building my spaceplanes, and not long after I just decided it was too much to worry about, and I let all the engines share all LF ever since.

For the decoupler approach - I think you need to do the opposite - try attach jet engine to the stage 0, and put LF tanks to stage 1 (i.e. LFO main tank and LF drop tank, just to fool the jet fueling rule - I'm not saying to actually decouple LF tanks).

(and I remember there's a mod to make fuel enable/disable into action groups - I forgot the name but I know it exists)

Edited November 5, 2016 by FancyMouse