Fuel overflow

When upside down the fuel overflow outlets are in an area of low pressure and so vent out a lot of fuel.

This has been a problem since day one and I've only just got around to a long term workable solution.

My idea was to restrict the size of the outlet hole which as standard is quite excessively large at about 6mm.

For a while I was just using a piece of duct tape over the outlet with a small hole pierced in it but that did not last very long as the fuel soon got to the sticky part of the tape and made it fall off. I needed a more permanent solution to the problem.

So I made up two small discs out of thin ali sheet and drilled them in the middle with the smallest drill bit I had - 1mm.

These were then glued to the outlets using 5 min epoxy.

A recent flight test proved that these to work well - there is still a tiny bit of fuel leaking out during and after inverted maneuvers but it is hardly anything compared to before.

I never fill my tanks till they are overflowing so there is plenty of space in the top for expansion should it sit in the sun - the fuel can still flow out of the outlets at a reasonable rate anyway with the 1mm hole so I don't think expansion is going to be an issue.

Fuel venting out whilst upside down. This is before the fix.

Ali plate restrictor with 1mm hole drilled in it.