FTX-2 External fuel duct not working

[KerbalDad]

Hello,

My son is using KSP 1.10.1. 

He says that the FTX-2 external fuel duct is not working in self-built models. Apparently the ducts are pointing in the correct direction. (Of course there might be other factors he hasn't considered).

Can anyone confirm whether they experience this issue, or whether they can successfully use the FTX-2 external fuel ducts in self-built models?  

Thanks,

KD

 

[Corona688]

A picture of the craft, at least, is necessary to tell you why it's not working.

Fuel ducts work fine but are picky in the way that you use them.

[Geonovast]

If they're spanning across decouplers that have crossfeed enabled, you could easily run into some issues with fuel flow priority.

With the crossfeed function in the decouplers, the only real reason to use fuel ducts anymore is if you're bypassing a part that doesn't allow fuel flow.

[jimmymcgoochie]

Do you mean that fuel isn’t being drained from the tanks correctly or not at all?

Check the decouplers aren’t set to enable crossfeed as this can really mess with the fuel flow when fuel ducts are also present. Fuel ducts are useful to use LF side boosters and feed their fuel to the core stage as well so that when the side tanks run dry their engines stop and can be dropped, but with crossfeed enabled all the engines can drain from all the tanks and everything will use all the fuel until it all runs out.

Fuel priority also makes a difference, the tanks that the duct is going from need to have a higher priority than the tanks the duct is going to as fuel tanks get drained from highest priority to lowest.

Pictures would help here, either in the VAB editor or in flight.

[KerbalDad]

Sorry for late reply to this. Thank you to everyone who offered advice. My son seems to have improved his fuel situation, particularly by following your advice about crossfeed.