Fuel line pass-through at sides

[Flying Scotsman]

I'm getting ready to measure and order flexible fuel lines for the runs from the fuel selector to the tanks.

Right side - no worries, Brett at Bonaco has the length for a "standard" Van's fuel pickup.

Left side - flop tube. Need to go selector to side/skin, 90 degree AN fitting, fitting to flop tube.

Trouble is, as I'm sure you're aware, that side skin area has a second, "inner" doubler which is separated from the skin by about 1/8". No way to get in there now to put any kind of washer or filler (should have thought of this back when I was building the fuselage, but I'm here now...).

So...I see three options:
1. Fill the gap with some sort of something (epoxy, fuel tank sealant, some sort of other goop); ick.
2. Drill the doubler to correct size for the fitting, and the skin big enough to take the washer/nut.
3. Same as 2, but drill the skin and open up the doubler.

I think option 2 is best, but am I missing something down the road (when I put the wings on again) which will bite me?

TIA

Steve

[flion]

I think option 3 would be better; the bulkhead nut would seal the hole at the skin and prevent anything from coming inside. With #2 you've opened up a route for things like cold air or anything at the wing root to migrate into the cabin. On the other hand, these airframes are not airtight so it probably doesn't matter that much. I'd say option #1 is right out but you could probably make a shim from aluminum stock to slide in there, which might be the best solution of all.

[Flying Scotsman]

Originally Posted by flion

I think option 3 would be better; the bulkhead nut would seal the hole at the skin and prevent anything from coming inside. With #2 you've opened up a route for things like cold air or anything at the wing root to migrate into the cabin. On the other hand, these airframes are not airtight so it probably doesn't matter that much. I'd say option #1 is right out but you could probably make a shim from aluminum stock to slide in there, which might be the best solution of all.

That's a pretty good thought on sealing the skin...thanks.

No way to slide anything in between them that I can see...sealed on all four sides by bulkheads, stringers, etc.

My only concern with option 3 was that the skin is thinner than the "doubler", and might flex more...but you have a good point.

Thanks...

Steve

[Christopher Murphy]

Why are you using flexible lines from the tank to the fuel selector?

cm

[Flying Scotsman]

Originally Posted by Christopher Murphy

Why are you using flexible lines from the tank to the fuel selector?

cm

Why not?

[rvbuilder2002]

Originally Posted by Flying Scotsman

Why not?

Twenty X's the cost!

Five X's more weight!

Safer? (debatable)

Higher maintenance? (possible, depending on what type hose you use)


But hey, that is what is great about building an experimental airplane.... you can do what you want.

[Flying Scotsman]

So back to the original question...

Any further thoughts on these options?

[Christopher Murphy]

I am not familiar with your situation, but hard lines would be the normal way to plumb this part of your airplane. A couple of grommets would do the job if you cant use a bulk head fitting. Making these lines is not too tough.

Cm

[terrye]

If using hoses on a suction line (which you are) check the specs for the hose to make sure they will not collapse if you draw a vacuum. Some hoses will collapse, others require a spring inside to prevent collapse. Aluminum lines are better for this.

[Flying Scotsman]

5 responses, of which one actually answered the question.

I *know* hard lines are one way to go, I just don't *want* to...I reached my patience limit doing the brake lines, and I just want to finish sometime in this lifetime. I've heard of no reported issues with Bonaco's fuel lines, either.