Can't feed fuel from parallel stacks to single LV-N

[Plusck]

I'm having a devil of a time trying to stack multiple LF-only tanks to fill the 2.5m form factor and put a single LV-N Nerf underneath it.

These are two designs that do NOT work:

Spoiler

In the first design, I used the Tri-Adapter to take 3 stacks down to one 2.5m node. It is impossible to get fuel lines from the tanks to the engine, they just end up attaching to the adapter. I then found that I could still attach mk0 tanks to the 3 nodes, clipping through the adapter. Fuel lines to the LV-N and everything seemed to work fine, only it doesn't: even though they are connected at the same node, th mk0 tanks don't draw fuel from the Mk1 tanks.

Of course, I had to be well into my interplanetary burn by the time I found this out, so that was a huge pain.

In the second design, I thought the Mk2 Bicoupler might work. The LV-N draws fuel fine from the bicoupler, so I just removed the oxide and added Mk1 tanks above. And again, it was only on the interplanetary burn that I found out that the bicoupler will NOT draw/allow the transfer of fuel from the connected mk1 tanks. Again, fun to have to transfer fuel every minute or so on a long burn.

So, has anyone found a way to get this to work? I'm coming to the conclusion that I'll just have to bite the bullet and clip the engine into the parallel stacks of tanks. or clip a cubic thingy into the tanks and attach the engine to that. The downside is obviously the time and effort making sure the thing is actually perfectly central.

[mudkest]

There's GPO fuel pump and TAC fuel balancer mods that can help you with the transfer every minute.

 

nice post on fuel flow rules, dont think much(if anything) has changed since it got posted

[sal_vager]

Hi Plusck, designs like this are always a bit tricky because only one node of the adaper/tricoupler will connect to the tanks above. only one stack of tanks will be accessible to the engine.

If you run fuel lines from the Mk1 tanks to the adapter it'll allow fuel to flow from them to that part and then the LV-N can draw from the adapter, it helps to add struts as well because with only one node actually connected the adapter may twist a bit when the LV-N is running.

Another trick is to put docking ports with fuel crossfeed enabled on the bottom of those tanks and the top of the adapter, this can be done by first adding the adapter, adding the docking ports in symmetry then removing the adapter and using the re-root tool (4) to make one of the docking ports the root.

Or just by adding one docking port, then the adapter, then the other ports singularly.

One node will connect and the others will dock when you launch so you won't need fuel lines or struts, the only downside to this is that aero occlusion will only work on the node attached docking port.

But then you will already have ends exposed to the airflow with the strut+fuel line method.

Bonus feature, with the adapter on docking ports you can replace the engine in flight.

Here's what it would look like.

Spoiler

 

[Plusck]

Excellent, thank you for all that info. The docking port suggestion does look a lot better than leaving things hanging, and now I understand vaguely how to use docking ports to game the system.

Still, I'm a touch annoyed that I didn't just try connecting the fuel lines to the Tri-adapter, since that would have solved everything and I'd have saved a lot of time and effort (and weight) trying other ways of doing things...

 

[Snark]

My solution is just to hack together a few lines of ModuleManager config to clone various LFO tanks to LF-only versions.  That way there's no mucking about with tricouplers and struts and fuel lines etc. 

IMHO, it's a major hole in KSP that they don't have a reasonable selection of LF-only fuel tanks that are friendly to rocket (not spaceplane) form factors.  As soon as they changed the LV-N to be LF-only, that became a pressing need.  It's really annoying that they haven't closed the hole.  Yes, I can mod my way out of it, but I shouldn't have to.

[Red Iron Crown]

Even using the multi-docking node method the fuel still won't flow, multicouplers only allow crossfeed in the one-to-many direction, not the many-to-one direction.

Better off to use one big LF tank (the smallest of the Mk3 tanks, maybe), or mount a stack of 1.25m tanks centrally with the LV-N at the bottom and radially attach additional tanks to the center stack.

[cantab]

I think this is what I would try

screenshot288 by cantab314, on Flickr

The I beam provides a structural spine, and the 1.25 tanks can be attached as you choose - I put them on the small nose cones that are attached to the command pod. No messing around with the multi-way adapters. In a "real" ship I would arrange and gizmo it all to look tidier. I-beams are late in the tech tree, earlier on you can use girders and let them clip into the tanks.

The main drawback to this approach is possibly increased drag in stock aerodynamics. The tailcones on the fuel tanks will help reduce it. In FAR if you make it all look smooth you should be good.

[Wanderfound]

I'd be avoiding the tri-adaptors and 1.25m tanks entirely.

2.5m pod : 2.5m -> Mk3 adaptor : Mk3 LF tank : Mk3 -> 2.5m adaptor : 2.5m ->1.25m adaptor : LV-N. Omit the lower two adaptors if you don't care about engine-side aerodynamics.