Bug with jet fuel useage ingnoring cross fuel settings

[Vorg]

Was trying to make a jet for a mission. A row if the second size tanks for the center with an LTV30 on the back, then 2 tanks, one each side with the basic jet engine. No parts between the center tanks and the side tanks and no fuel lines. The jets pulled from all the tanks including the center line tanks. But the rocket engine could only access center tanks. Also could not transfer fuel to center tanks.

Edited May 6, 2015 by Supernovy

[Vareo]

I have been experiencing the same thing. It seems like every single part on a Spaceplane has fuel crossfeed. When I use a jet engine it drains the fuel equally out of every single tank on the plane, regardless how the tank is connected to the engine thats running. At first I thought this might be intended, because I had the tanks next to the one that the engine was supposed to run of, but it always does that, no matter with what you have connected the extra tanks. Now I have the tanks connected with structural pylons where the description clearly states "no fuel crossfeed" and it still drains the liquid fuel out of those tanks.

And to make this a proper Bug Report:

KSP Version: 1.0.2 (Steam)

System: Windows 7 64 Bit

Screenshot: Edit: at least for me the image does not seem to show, so if thats the case use this http://imgur.com/TjbXwyn

I think that this is a specific issue just for spaceplanes and crafts from the SPH.

No crash reports to be had and I don't think that the system specs are of any use here.

And last I just want to say, that I don't want to sound like I'm just a complainer, because KSP and the 1.0 release have been awsome. Thanks for that great game!

Edited May 5, 2015 by Vareo
image not loading

[Red Iron Crown]

This is intended behavior, air breathing engines now draw fuel from all tanks in a stage equally, starting with the highest stage. Stage is determined by the number of decouplers between the tank and root part, not the staging icon list. The idea is that aircraft will remain more balanced than if the typical front-to-back fuel crossfeed was used.

You can get tricky with decouplers to make tanks drain in the order you prefer.

[sal_vager]

Jet engines will draw from all liquid fuel in the same stage now, you can use decouplers and edit the stage list to control jet fuel draw to some extent (they should drain one stage at a time).

He wears black pyjamas and sneaks around.

Posting in threads with nary a sound.

He's the ninja Red Iron Crown.

Edited May 6, 2015 by sal_vager

[Vareo]

I think you don't see the problem. I know that it is intended for the fuel to be drained equally from all tanks, but you can't stop that from happening with decouplers. I've tried. As you see in the picture it the side tanks are only connected by structural pylons and struts which have no fuel crossfeed. I don't think it is intended for fuel to pass through parts that have the line "no fuel crossfeed" in their description.

[Red Iron Crown]

Fuel crossfeed doesn't apply to air-breathers, that is only for rocket engines (including the LF-only LV-N). Left unchecked an air-breather will drain all LF in a vessel, no matter where it is. The only way to prevent it is to disable the tank in the right-click menu.

You can, however, prioritize which tanks get drained first, those with more decouplers between tank and root part will drain first.

Edited May 6, 2015 by Red Iron Crown
Fixed an error.

[Vareo]

Ok, now I see what you guys meant with the use of decouplers. Sorry to be a bit slow on the uptake there and thanks for enlightening me.

Even though I really dont like that feature then, but thats my personal opinion and nothing that needs discoussing here. So I guess it was intended after all

[Vorg]

Need to find a better way then loading down with decouplers you don't need.

[Giggleplex777]

Fuel crossfeed doesn't apply to air-breathers, that is only for rocket engines (including the LF-only LV-N and the RAPIER in rocket mode). Left unchecked an air-breather will drain all LF in a vessel, no matter where it is. The only way to prevent it is to disable the tank in the right-click menu.

You can, however, prioritize which tanks get drained first, those with more decouplers between tank and root part will drain first.

I feel like this decision was a slight oversight because it can really screw with spaceplanes. Perhaps an option to set the jet engine's fuel fuel-draining behavior could be the solution.

[Red Iron Crown]

I feel like this decision was a slight oversight because it can really screw with spaceplanes. Perhaps an option to set the jet engine's fuel fuel-draining behavior could be the solution.

As I understand it this behavior for air breathers was implemented to make spaceplanes easier. Because they will drain all tanks in a stage at the same rate instead of draining one tank after another, the CoM shifts less as fuel drains under the new system.

It is like any system, though, in that not knowing how it works can create situations that bite you; knowing how it works allows you to take advantage of that behavior.

[JoCRaM]

It makes simple designs easier, but it makes it much harder to be creative.

I recognise it is probably an overall improvement, however I have the following suggestions:

As an interim fix make enable/disable/toggle fuel flow from a tank an action group item.

Docking ports and launch clamps should (but don't currently) count as decouplers for the calculation.

If you're going to allow "no fuel crossfeed" parts to cross feed fuel, make them count as a decoupler.

- alternately add radial and stack parts that count as a decoupler for the calculation.

Most importantly, In the old system you could compensate with fuel lines, in the current system you can't. Please add jet fuel line logic. Possibly add a new "jet fuel line" part. At a rough guess the logic should be:

- any part fed by a fuel line is treated as a decoupler for the stage calculation, but is considered to be "after" the decoupler.

- any part feeding a fuel line is considered to be in the stage the fuel line is connected to iff that stage is "before" the current stage

here the root node is "after" everything else, and in most cases the engines are before everything else

[Vorg]

For my craft it screwed it up by not following the cross flow laws. They drain from the rocket tanks, but the rockets can't drain from the jets. That is wrong. I am not far enough along in the tech tree from fuel lines (though they really should be much sooner), so the craft got screwed up. putting all the fuel tanks in line makes the craft too long and because the rockets still pull from the farthest end, it still has massive balance problems. In fact it makes it worse, not better.

Call it a bug in the design, but it is still a bug. changing the subject doesn't change that fact.

[Brotoro]

How does one do drop tanks under this new system? Say you have a plane with a bunch of tanks all over, but you want to use up the fuel in your wing-mounted drop tanks first (so, like, they can be dropped).

[Supernovy]

How does one do drop tanks under this new system?

STAGE_PRIORITY_FLOW should drain from those droptanks first, before other tanks, due to the decoupler. If it does not, that's a bug.

[Red Iron Crown]

How does one do drop tanks under this new system? Say you have a plane with a bunch of tanks all over, but you want to use up the fuel in your wing-mounted drop tanks first (so, like, they can be dropped).

More explicitly:

- Make sure the root part is in the main body of the aircraft (this is usually so but worth mentioning because it is required)

- Mount drop tanks on decouplers, those tanks will drain before the aircraft body

- If you have another set of drop tanks meant to drain before the others, they need to mount to the first drop tanks with decouplers or mount to the aircraft body with two stacked decouplers.

Edited May 7, 2015 by Red Iron Crown

[Padishar]

Unfortunately the behaviour of the STAGE_PRIORITY_FLOW mode is only indirectly related to the number of decouplers between the engine and the root, it actually depends on an internal stage number that each part is assigned during the loading of the vessel. Making any changes to the flow mode to treat other parts as decouplers would involve totally changing how it works or else risk various, very hard to diagnose, bugs in the system.

I think the best solution that is even remotely likely to be implemented is to allow the user to change the flow mode that each jet engine uses via a tweakable, then you would be able to set your engines to behave in the old way if it suited your vessel better.

[Brotoro]

More explicitly:

- Make sure the root part is in the main body of the aircraft (this is usually so but worth mentioning because it is required)

- Mount drop tanks on decouplers, those tanks will drain before the aircraft body

- If you have another set of drop tanks meant to drain before the others, they need to mount to the first drop tanks with decouplers or mount to the aircraft body with two stacked decouplers.

Sounds good. Thanks.

[WinkAllKerb'']

I think the best solution that is even remotely likely to be implemented is to allow the user to change the flow mode that each jet engine uses via a tweakable, then you would be able to set your engines to behave in the old way if it suited your vessel better.

+1

current sytem is not really ergonomic and intuitive via the root workaround when building launcher that use jet engines, for exemple, as they tend to suck the top stages first wich is not what you intend usually.

Edited May 8, 2015 by WinkAllKerb''