Fuel Return line question

[dweyant]

I'm working on my tanks for my 9A (just about done, yeah!).

I'm hoping to build my plane so that I can run MOGAS, so I'd like to put in a fuel return line.

It was suggested that I put a fuel sump fitting into the inboard rib. Does it matter where I put the fitting? I.e. about the only place I have to put it is fairly low on the rib, that will have the fuel return going fairly close to the pickup. Does that matter? Am I overthinking this?

Thanks,

-Dan

[N427EF]

Good Plan Dan.
You can install it anywhere where it does not interfere with anything else such as linkages to the ailerons or wing attach brackets etc.
Your concern about dumping fuel back into the tank near the pick up is
hardly an issue. <20> Gallons of cool gas will be mixing constantly while you are flying and will not warm up your pick up fuel.
Backflow is more of a concern where you must have a means to shut your return fuel off in case of an engine fire for example.
My return goes through a selector valve, the one Van supplies as the main fuel selector, I use an Andair for the main.
Other solutions would be a check valve in the return line or the very expensive 4 way Main valve from Andair. Your choice, simple is better.

I have burned nearly 1000 Gallons of mogas E10 over the last year and never experienced any vapor lock or other issues.

[airguy]

I put my return lines into the tank with a line extending just past the first interior rib, not because I was worried about hot fuel recirculating but because I was concerned about possible foaming or splashing and catching air bubbles in the fuel pickup. This way the return fuel has a chance to settle for a few seconds and flow back through the bottom flow holes in the rib to the first (most inboard) bay of the tank where the fuel pickup resides. Yes, this method will keep perhaps a pint of fuel as "unusable" because it's always in transit from the first bay to the wingroot - but we're talking about maybe a pint of fuel - if I'm that low on the tank, then it means I'm oblivious to the amount of fuel in there anyway and I'm going to run it dry by accident one way or the other because my head is up and locked. That pint won't help...