SM-25 Service Module: What for?

[klesh]

On 6/13/2019 at 11:19 AM, lajoswinkler said:

I can't get this thing to crossfeed fuel. My "Resource transfer obeys crossfeed rules" option is turned OFF and it still doesn't work. No matter what fuel arrangement I use inside, nothing. Sometimes fuel path shows in VAB as normal, sometimes it doesn't, but during flight engine on its bottom just doesn't work. No propellant.

I tried central node for tanks, two lateral nodes, lateral pouring into central by fuel pipes... nothing. It's been like this since "Making history" came out.

 

I had a few designs where it was working as intended, but now I can't seem to get any fuel placed inside to work. The deltaV calculator in the VAB is giving me some extremely low numbers (based on what I know it should have), but when I launch even the most simple test with a probe core, the sm-25 and a single fuel tank, it will flame out.  The part is effectively useless now.

Edited October 17, 2019 by klesh

[lajoswinkler]

On 10/17/2019 at 9:17 PM, klesh said:

 

I had a few designs where it was working as intended, but now I can't seem to get any fuel placed inside to work. The deltaV calculator in the VAB is giving me some extremely low numbers (based on what I know it should have), but when I launch even the most simple test with a probe core, the sm-25 and a single fuel tank, it will flame out.  The part is effectively useless now.

 

Oh, in the meantime I found a solution. Connect the fuel tank directly to the service module using the fuel pipe, as if it's another fuel tank. That worked for me.

[klesh]

Thats a good idea, I hadn't tried that.  I'll give it a go and see if it works.  Alternatively, I was thinking you could put a fuel tank on the bottom of the SM-25, an engine below that, and translate them both upwards with the move tool until they're in the right spot.

[lajoswinkler]

10 hours ago, klesh said:

Thats a good idea, I hadn't tried that.  I'll give it a go and see if it works.  Alternatively, I was thinking you could put a fuel tank on the bottom of the SM-25, an engine below that, and translate them both upwards with the move tool until they're in the right spot.

That doesn't work since translation doesn't shift actual "what comes first" thing. It's still in the order in which it has been joined.

Solution with the pipe is so simple, but many people, me included, never thought about it.

[klesh]

58 minutes ago, lajoswinkler said:

That doesn't work since translation doesn't shift actual "what comes first" thing. It's still in the order in which it has been joined.

 

I just had a go, it definitely works. Here is some photos, maybe they explain it better?

 

Confirming that putting a tank and engine below the SM-25 works.

 

 

Translating the tank and engine up inside the SM-25 in the VAB.  Yes, the game will think its outside the SM-25, but that shouldn't matter in a vacuum.

 

 

The translated tank & engine working fine in flight mode:

 

 

 

 

Although, rather than redoing any SM-25 related craft, I agree the fuel duct is a very simple and elegant solution.  Ever since the fuel flow priority additions to the game, I have not used the fuel duct part at all, so it had never occurred to me.

 

Here is my existing Command and Service module which up until 1.8 seemed to work just fine and the way you would expect.  I've placed the fuel duct on the 3 x 1.25m tanks which are connected to the interior center node of the SM-25:

 

 

 

And here is that elegant solution working like a charm in flight mode with cutaway enabled for proof:

Edited October 19, 2019 by klesh

[lajoswinkler]

Oh, that. Yes, that will work, but gamewise, that tank is not inside the service module. I thought you put the tank inside, and then pulled it outside, my bad.