Engins running but produce no thrust ....

[Green Baron]

Hello,

am using 0.23.5 with the Kethane Pack. Am flying a Kethane mining ship from Minmus to the mothership in orbit for refueling but i have to fly several times to fully fuel up. Am mining/refining on Minmus surface and then dock with the mothership to exchange the tanks contents. That means for the flight back to Monmus surface i just leave enough fuel in the miners tanks to have it safely touched down.

After 2 succesfull flights in this way (and in principle that worked 2 times before), when i throttle up to deorbit the miner the engines show (slight blueish, LV-T45) exhaust flames but consume no fuel and produce no thrust.

I have checked that the right engines connected to the tanks that still contain fuel are activated, thrusters are not limited, the control is set to the same unit (capsule, the miner is kerbaled) as on the 2 flights before, there is plenty of electricity. But ... no thrust ...

Anyone any ideas ? What i oversee ? Was probably playing too long yesterday ...

Cheers

Klaus

Edited June 6, 2014 by kemde

[Streetwind]

The most common cause for this is that there is something in the path of the exhaust. Engines need a minimum clearance behind them where no other ship part may be in order to produce thrust.

If it's not that, try simply going back to the space center and then to the ship again. With mods I sometimes have odd effects with ships not behaving right when loading them the first time.

[Tortoise]

A screenshot would help

[Green Baron]

Yes ... this is the miner:

http://imgur.com/a/a81MN

For the flight to the mining area only 4 tanks contain fuel, the ones directly over the 4 "working" engines in the second screensshot.

Thanks Streetwind, but going completely out of game and loading new did not work ...

Edit: i added a third image showing that of the 8 engine pylons 4 are completely deactivated and of the remaining 4 only the lower tanks contain fuel. That worked at least tonight ...

Edited June 6, 2014 by kemde
typing mishaps ...

[Green Baron]

When i pump the fuel from the lower to upper tanks (the ones further away from the engines) it works ...

Miracles in space

Klaus

[michaelhester07]

I can tell you why the top tanks need the fuel. It's kinda silly too. Here's your ship with the flow of fuel outlined on it

The fuel flows from the bottom tank through the girder to the kethane tank, up through the top through the kethane converter and out to the top tank. I've done this design thinking of why it works on mine but my secret is I only ever used one tank for the engines. The problem is that fuel can flow through a girder out of a tank so long as the receiving object is not a fuel tank (in this case it's a kethane tank). You won't get a circular flow through this system so the bottom tank drains first causing your engines to flame out.

To fix this: Run the fuel lines from the kethane converter to the bottom tank instead of the top tank on each engine stack.

[eempc]

When i pump the fuel from the lower to upper tanks (the ones further away from the engines) it works ...

Miracles in space

Klaus

I just had a similar phenomenon happen to what you described with my two fuel tanks and an LV-N. The LV-N could only access fuel from the immediately-attached tank and not both even though they are all in a simple, single column. I had to manually pump the fuel round. Weird bug.

[Pecan]

Fuel-flow was my initial suspicion too, but the problem is harder than that, isn't it? The engines ARE receiving fuel and burning, but not producing thrust, I thought?

[cantab]

How are you inferring that there is no thrust?

If it's from the lack of change in orbital velocity when you burn prograde or retrograde, or a lack of change in the delta-V meter at a manoeuvre node, then are you sure you are controlling from the right part? If you're controlling from a part that faces "backwards", or worse sideways, then you won't be thrusting in the direction you think you're thrusting in, and it can be mistaken for no thrust at all. I did exactly this once before.

[Green Baron]

Ok, last question first: yes, i'm pretty sure. For flight purpose the control is set to the kerbaled capsule, for docking purposes to one of the docking ports. I wrote "no thrust" because the velocimeter does not change, the orbital path stays the same and when i deactivate all but one engines the craft doesn't start to turn when thrusting up.

The fuel flow could be interesting, though. Up to now i thought that engines take their fuel from the directly connected tank and if other tanks are attached to that fuel flows from there in the direction towards the engine, from distal to proximal sotosay in respect to one stack of engine and tanks. Fuel lines direct the fuel from one tank to another in a single direction, keeping the receiving tank proximal and making the connected tank distal. At least that were my assumptions.

It was not clear to me that fuel passes through girders. The contents of the tanks (Kethane tank is empty after delivery to the mothership) did not change during the effectless burning. The fuel lines that connect the upper tank to the kethane converter run from tank to converter because the kethane pack tells to do so. Maybe i forgot to shut down the converter functions and that was the difference to the previous flights, but i can't test that anymore right now.

The next miner will have a different design, just for mining purposes, no science/lander/capsule stuff, shorter, broader and more sturdy to land in rugged areas and with single LF-tanks as proposed by michaelhester07.

Be it as it may, i know about the problem (thanks everyone), the design can't be changed anymore. The party is on it's way to the outer kerbolar system to save Jeb who, when they arrive, will not have had any snacks since threeandahalf years ...

Cheers :-)

Klaus

Edited June 7, 2014 by kemde