Does fuel flow across hydraulic decouplers these days?

[Brainlord Mesomorph]

Working on my “spaceplane sandwich†strategy: (imagine the shuttle on top of the 747, with another 747 on top of that) anyway, it seems to be working, except for a really crazy fuel flow problem I just noticed.

I have a payload (fuel tank) sandwiched between two spaceplanes, hydraulic decouplers on both sides, and some struts are the only connections. (no fuel lines or docking ports). I’m strangely losing control of the vehicle at 30 km.

I go and look: the top plane is empty of fuel, the bottom plane that is full of fuel, and half of the payload fuel has been consumed. What gives?!

There should be no fuel exchange between these components! The whole idea of this is to have each plane consume its own fuel and NOT that of the payload!

I get that the new model is supposed to draw fuel evenly, but across a hydraulic decoupler?

Edited September 5, 2015 by Brainlord Mesomorph

[Reactordrone]

Air breathing engines have fuel flow rules similar to monopropellant now so that you don't need fuel ducts everywhere. Unfortunately that does cause some issues in some designs.

[Brainlord Mesomorph]

Well *&^%^!

How do I stop that?!!

This totally screws my entire idea AND GIVES ME BACK THE PROBLEM that was this designed to FIX !!!

Edited September 5, 2015 by Brainlord Mesomorph

[sal_vager]

Right click the payload tank and disable the flow

[Brainlord Mesomorph]

Right click the payload tank and disable the flow

That would stop consuming payload fuel. But it wont stop the problem of the top plane emptying to the bottom plane ,will it?

I'll try, I'll have to climb back up to 30 km to know.

BRB

[tbarcello]

Well *&^%^!

How do I stop that?!!

This totally screws my entire idea AND GIVES ME BACK THE PROBLEM that was this designed to FIX !!!

My sight is 20/20.

Topic with solution is right down there.

http://imgur.com/F1GfQfK

[Brainlord Mesomorph]

OK! I HATE THIS GAME NOW!

(edit: even after turning off the payload tank, the bottom plane still burns the fuel of the top plane!)

I figured out a thing that would actually work in physics. That would work in the beta! That solves a major problem (getting 80 ton payloads to orbits on spaceplanes)!

And because they "updated" this game to make it easier for noobs to play, it CANNOT work. (contrary to the laws of physics, and anythng I try to design)

They have ruined KSP.

wow.

(add that to the ever growing list of software I used to love that has been ruined!)

They think that magically teleporting fuel all over the airplane (or across two airplanes) without any ability of the DESIGNER to control it, is an improvement??? AND why TOP to BOTTOM??! and not back to front? or both ends to the middle?

If the whole idea was to burn fuel EVENLY, why top to bottom? THAT"S NOT EVENLY!

Seriously, I just rage quit out of the game, and I won't even be in this forum for a while.

See you guys later.

- - - Updated - - -

My sight is 20/20.

Topic with solution is right down there.

http://imgur.com/F1GfQfK

http://imgur.com/F1GfQfK

WHAT?

Edited September 5, 2015 by Brainlord Mesomorph

[cantab]

KSP has always had oddities in its fuel flow. Here's the new secret of the jets - they draw evenly from all tanks in what KSP thinks is the lowest stage, the first one to be dropped. That is generally a sensible thing to do, but as you found it can give unexpected results. Consider fiddling with your staging.

[Clipperride]

A bit of "blue sky" thinking. Would adding a probe core to the middle, payload section there using Control From Here command help? Which part is currently the root part?

[Padishar]

The fuel flow for air-breathing engines should take fuel evenly from all tanks that are separated from the root part by the same number of decouplers, with the furthest ones being used first. Your root part is currently in the bottom plane so the top plane is 2 decouplers away and is drained first, then the payload is 1 decoupler away and is drained next. You should be able to set a part on the payload as the root and then the two planes will drain evenly as they are both 1 decoupler away and then the payload will drain (so make sure that you transfer some fuel back over to the planes before decoupling them if they use all their fuel).

[Red Iron Crown]

Airbreathers, RAPIERs in rocket mode, monoprop thrusters and engines, and ion engines all use the same fuel flow rules:

1. Determine stage for each tank, by counting the number of decouplers between tank and root part (not by looking at the staging list).

2. Drain tanks evenly in a stage, starting with the highest.

Staging list and "control from here" have no effect, the count of decouplers between tank and root part is the only thing that matters.

My guess is your root part is in the bottom plane, so the flow logic thinks your payload is a drop tank (1 decoupler between it and root), and so is the upper plane (2 decouplers between it and root). Reroot the vessel from a part in your payload and it will drain both planes evenly before going after the payload fuel.

Edit: Padishar is a ninja.

Edited September 5, 2015 by Red Iron Crown

[Brainlord Mesomorph]

KSP has always had oddities in its fuel flow. Here's the new secret of the jets - they draw evenly from all tanks in what KSP thinks is the lowest stage, the first one to be dropped. That is generally a sensible thing to do, but as you found it can give unexpected results. Consider fiddling with your staging.

Nope.

- - - Updated - - -

The fuel flow for air-breathing engines should take fuel evenly from all tanks that are separated from the root part by the same number of decouplers, with the furthest ones being used first. Your root part is currently in the bottom plane so the top plane is 2 decouplers away and is drained first, then the payload is 1 decoupler away and is drained next. You should be able to set a part on the payload as the root and then the two planes will drain evenly as they are both 1 decoupler away and then the payload will drain (so make sure that you transfer some fuel back over to the planes before decoupling them if they use all their fuel).

nope too.

- - - Updated - - -

Airbreathers, RAPIERs in rocket mode, monoprop thrusters and engines, and ion engines all use the same fuel flow rules:

1. Determine stage for each tank, by counting the number of decouplers between tank and root part (not by looking at the staging list).

2. Drain tanks evenly in a stage, starting with the highest.

Staging list and "control from here" have no effect, the count of decouplers between tank and root part is the only thing that matters.

My guess is your root part is in the bottom plane, so the flow logic thinks your payload is a drop tank (1 decoupler between it and root), and so is the upper plane (2 decouplers between it and root). Reroot the vessel from a part in your payload and it will drain both planes evenly before going after the payload fuel.

Edit: Padishar is a ninja.

root part is payload.

its only drawing fuel from the top plane.

[Red Iron Crown]

Padishar's solution should work. Can you link the craft file?

[Brainlord Mesomorph]

Padishar's solution should work. Can you link the craft file?

Here

I used the "root" tool in the SPH, but I look at the file and the first part listed is a mk2 fuselage... which is wrong...

you tell me. (buttons 1 and 2 activate engines (3 switch CRAPIERS to LOX) , staging is setup for that other guys idea.

It's a shame, I'm really proud of her. She flies great for a thing with an 81 ton payload.

[Padishar]

The trick is that after re-rooting the vessel you need to detach and reattach all the affected parts. This can be done in one go, e.g. I switched the root to be the nosecone on the payload and tested and the fuel still drained only from the top plane. Then I reverted and detached all but the root part, put it down and then picked it up and attached it again. Now it drains from both planes...

Craft file

Oh, one other thing, the fuel lines on the vessel are doing nothing except slow the overall performance of the game down. This fuel mode ignores them (and fuel crossfeed settings).

[Brainlord Mesomorph]

Thanks!

I was thinking about snapping it back together. (this game is soo still beta)

Yes (now) I realize those fuel line would have to go. (proper "cross-fueling" used to be on of my things!)

Thanks again, I'll try it soon, (wondering what this will mean when I try to swap that out with a REAL payload)

[Padishar]

Well, you should be able to pull the two planes off and save them as sub-assemblies, then just build a new payload however you like and attach the two planes...

[Brainlord Mesomorph]

Well, you should be able to pull the two planes off and save them as sub-assemblies, then just build a new payload however you like and attach the two planes...

I tried that. there are other (root) issues there.

You had a better idea: make the payload nosecone the root, disconnect everything, plug it back on, and voila!

Now fuel flows (somewhat) logically.

But now I lose control of the plane at 45 km! (and its not fuel) LOL,

If I figure this out I'll make a tutorial.

Thanks

Edited September 5, 2015 by Brainlord Mesomorph