Jet engine cuts out

[psyper]

So this is a long story, sorry in advance!

I'm playing KSP 64bit with the fine print mod. One of the contracts is to fly to different anomalies drive around in a rover and then fly back (hopefully) to recoup the cost of the craft. So I'm no good at doing planes let alone buggy planes so I take the design of one of my ssto's designs from my old sandbox and rebuild it from scratch as just a air breather. This is it in the VAB:

So we launch, get to about 15,000 ft and get a good speed going - occasionally I would need to adjust its course so taking sas off and taping the pitch or yaw could send it in to a flat spin - very hair trigger at that speed! When that happens I would cut the engines, wait until the spinning slows down, get it pointed back in its right direction, sas on and throttle up the engines while jeb and bill clean themselves up. We get going again no problem. Get about quarter of the way around kerbin, land near the anomaly and undock the rover and complete the mission. We redock back up and launch back to KSP.

About 10 minutes in to the flight we are cruising height and everything is doing well - air intake is about 50% full and all if a-ok but then out of no where the craft pitches down and spins. I havent touched a button and the sas can't cope so I cut the power wait till it stop spinning point the craft in the right direction and spool up the engines again. Almost immediately the craft nose dives again and spins out of control. At this point I notice that the bottom engine closest to the ground is a darker orange than the rest and when I cut the engines its the first to go black before the others join it. I F9 (as I save a lot) and disable the 'faulty' engine and its twin and launch on just the two engines. Get no problems until I'm half way home and the craft spins to the left - one of the other two engines are having the same fault now.

I check fuel and intakes (which at the time was at 99% full as they have half the amount of engines to supply) and all are okay. I had quicksaved mid flight so I f9 back to that point and decide its best to ditch the craft in to the ocean and get the navy to pick them up at a cost - a percentage is better than nothing. So I cut both of the remaining engines. Point the craft skyward and watch as my horizontal velocity decreases and my vertical increase - I then start spooling up the drives to slow the decent down and halfway in the craft spins again - same engine is slowing down.

Why is it doing this and how can I save my poor boys??

tl;dr - the same single jet engine keeps slowing down while the others are operating normally - air intakes and fuel not to blame.

mods:

oblivion cloud pack and city lights stuff with EVE of course

fineprint

goodspeed fuel pump (this was set to move the fuel from inside tanks to the nacelles - checked the fuel balance too and ruled it out)

KAS (no kas objects on the craft)

mechjeb2

navyfish docking dooda

stage recovery mod

TAC Life Support

Kerbal Alarm Clock

edit: been watching the 'faulty' engine stats on the right click context menu and the electrical charge drops for a split second just as it starts to spin - also notice that I can hear a faint pinging noise when it does so as I have my speakers volume up higher this time :/

Edited August 24, 2014 by psyper

[Zephram Kerman]

Is the "faulty' engine the last one you placed? Except for the lack of sparks and sounds, this sounds like the familiar flame-out situation. MJ2 has a 'prevent flame-out' utility that reduces throttle when IntakeAir gets low. Also keep in mind those intakes are all facing up. So if your vessel is moving sideways or downwards, the intakes don't get nearly as much.

If it's not flame-out, try copying the vessel to a clean install with no mods, and see if the problem persists.

Hopefully the MJ2 utility fixes it for you. That's a cool design.

[AlexanderB]

Theres a bit of hassle with the air intakes, see the "fuel flow rules" topic Here

I assume you built the entire thing with 4x symmetry on, the best way to fix it is to grab the whole side-assembly, put it back on 1x symmetry, take it back off, then put it back on on 4x symmetry. That should fix your issues.

[Jean Deaux]

Theres a bit of hassle with the air intakes, see the "fuel flow rules" topic Here

I assume you built the entire thing with 4x symmetry on, the best way to fix it is to grab the whole side-assembly, put it back on 1x symmetry, take it back off, then put it back on on 4x symmetry. That should fix your issues.

I've found doing symmetry in the manner you describe creates a symmetry bug that's been around for some time. It doesn't always bug out, but I can recommend saving a 2nd copy of the ship before doing this, just in case.

Symmetry bug report I made some time back, pictures are gone but descriptions are still relevant.

Edited August 25, 2014 by Jean Deaux

[psyper]

does look like its a problem with symmetry - I'm thinking its having a hard time because they are mounting on to the liquid tanks which are themselves in 4x symmetry too. Might have to play around with the design of the ship a little bit.

Many thanks for the input

[Red Iron Crown]

You should be able to grab the girder connecting the jet propulsion unit to the core and duplicate with symmetry from there. Note that this won't prevent your engines from flaming out asymmetrically, it will just cause it to do so at a much higher altitude.

The root of the problem is that intakes air is allocated to air-breathing engines based on the order in which the parts were placed. Ideally, placing intakes should be interleaved with placing engines; the other alternative suggested here is to build a single engine propulsion unit with its share of intakes and duplicate it with symmetry.

[psyper]

its not a flame out issue but thanks for the input

[Red Iron Crown]

its not a flame out issue but thanks for the input

Before the engines actually flame out they start to drop off in thrust which may be causing your issue. Try Alt-right clicking on your jet engines to see their thrust readouts, that will likely reveal thrust asymmetry even if no engine flames out. This behavior caught me out in my fledgling dual jet engine spaceplane designs.

[psyper]

I was able to reach twice the height in the atmosphere before I even had a slight chance of a flame-out. Its only at 15k from the surface and it has a large number of intakes. The intake air bar is only at 50% with over 1.xx units of air in it and I've had a lot lot less (about 0.12 units) before it actually flames out. When the reduction of power occurred there was no sparks or sputtering noises that you usually get with a flame out and I cut the engines regain control falling to a lower height and then kicking the engines back in and it would be the exact same engine that had this problem. I even landed the craft with the 'chutes and then take off and the exact same engine would start getting a power loss. I've even taken its twin and tweeked its power down to 80% and I was able to fly the vessel back home going above 15k ASL without a flame out.

[Red Iron Crown]

It might also be that the draggy air intakes are above the center of mass. Could you post the craft file? I'd like to poke around with the vessel to see if I can figure out what's going on later tonight.

[psyper]

I think I still have the quicksave file of the vessel - it was landed and I saved before I took off and then a couple of minutes in to flight the engine would bug out so I see if I can upload that if it would be better - otherwise you could end up flying it around for hours on end before the engine started causing problems!

[psyper]

no craft file but I do have the old quicksave for it. I did a copy of the quicksave incase someone asked some questions about it but I rebuilt the vessel over the top of the original but haven't had a chance to use it again (contract hasn't come up for it yet). Heres the quicksave:

https://drive.google.com/folderview?id=0B8S2KVucoU9cdjM3MFZiVWtiS3M&usp=sharing

Heres a screenshot of it when it happens - as you can see plenty of air.

[Red Iron Crown]

I suspect intake air isn't the problem at that altitude.

I'm afraid I might not be able to use that save file, you have some mods I don't use. I'll try it when I get home, though.

[psyper]

I think its happening to a nuke on one of my ships in orbit now :/ Might be time to create a new copy of the game and download all the mods again :/

Edit: looking closely on the stats on the faulty nuke shows that its flicking from normal thrust to 0 along with the electriccharge meter too - its a flicker but enough I suppose to throw it in to a spin. I can't see anything in the f12 logs or f2. Am I looking in the right places?

Edited September 13, 2014 by psyper