Fuel Tank Vent Leak
This is the biggest problem I have had since starting to fly the airplane. It is complements of the quick build wing builders. I noticed
that I was dripping fuel from the right wing fuel tank vent. The leak is coming directly out of the vent, not around it. The Vans vent system
runs the vent pipe from the high side of the tank, through the fuel, to a bulkhead fitting at the lower end of the tank. This fitting is submerged
in fuel whenever the tank has 22 gallons or more of fuel. Externally, there is
just a pipe that you add to exit to the bottom of the wing and complete the vent system. I've concluded that the leak is at the flared tube to
bulkhead fitting inside the tank. This fitting is not accessible once the tank is completely rivited together.
There is a 1.5" diameter hole for the fuel sender located about 3.7" away from the vent bulkhead fitting which is shown in the top
left photo below. You can just barely
touch the internal nut with your middle finger from this hole. My first step in developing a tool to go in the hole and turn the nut was to make
a mock up of the fuel sender hole and vent position. The mock up is in the top right photo below. Then with expert help from work, we developed a tool
that could go in the hole and swing far enough past the hole in each direction to turn the nut. You have to be able to swing the wrench far
enough so that it can be repositioned enough to pick up another flat of the nut.
I flew off the right fuel tank as far as I could in flight. Then on the ground I transferred the remaining fuel from the right
to left tank. I was able to go in and tighten the nut at least one and a half flats of the nut. It seemed pretty tight to me so I reinstalled the
fuel float sensor, buttoned everything up and filled the tank with fuel. I wish the story ended here but the fitting continued to leak.
I decided to give it another try, so I flew off the fuel, removed all the cover panels and the fuel float sensor and tightened the
fitting as much as I could using the tool. It seems really tight to me now and I don't think going any tighter could possibly be productive. Well
it looks like that did the trick. It has stopped leaking. yeah! If this doesn't hold up I plan on removing the tank, capping the existing vent,
and installing a new always dry vent at the outboard end of the tank.
View of fuel tank rib
Mock up of rib
Internal tank view of tool