Fuel Tank Vent Leak

[azcloudflyer]

At about 28 hrs into Phase I flight testing, I noticed that I was dripping fuel from the right wing fuel tank vent. It was too consistent of a drip to be anything but a leak. The leak was coming directly out of the vent, not around it. The RV-10 vent system runs the vent pipe from the high side of the tank, through the fuel, to a bulkhead fitting at the lower inboard end of the tank. This fitting is submerged in fuel whenever the tank has 22 gallons or more of fuel. Within the wing root, 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 riveted 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 first photo. 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 second photo below. Then with another engineer's expert help, 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 back enough to pick up another flat of the nut. I was able to practice placing the tool on the nut using the mock up.

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. It has slowed but the vent was still wet to the touch at the output end.

I decided to give it another try, so I flew off the fuel, transferred remaining 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. There is almost 2" of room between the outboard end of the tank and the next wing rib to add a bulkhead 90 degree fitting and vent tube there.

So my reason for posting this, besides relating my tale of woe, was to offer the use of this tool to anyone else that may discover the same problem with their quick build wing. But from my research in the archive this doesn't appear to be a common problem.

Back to flight testing.......


View of fuel tank rib


Mock up of rib


The right Tool for the job


Internal fuel tank view of tool in use

[N427EF]

That is quite an impressive accomplishment.
Hope I won't need to do that, all my fittings inside the wingtank are sealed in proseal.

[TS Flightlines]

the nut wasnt secured enough originally. Maybe we should rethink the fuel tank vent system?
Tom

[RV10Rob]

Very cool!!

I saw the similar symptoms with my QB tank, so I figured I had a leak. As a hail-mary before attempting a repair, I blew some compressed air into the vent (with the fuel cap off, of course). The leak stopped and hasn't returned since.

-Rob

[chaskuss]

Mike
Very impressive engineering. "If" that leak returns, you can try adding a copper SECO sealing washer between the flare and the fitting. They are designed for just this sort of problem. Very handy. You can get them from a lot of different sources. Aircraft Spruce carries them, but they are hard to find using the search feature. I've provided several links for this product. See

http://www.pegasusautoracing.com/pro...p?Product=3202

FYI, Pegasus is owned by Chris Heitman, who built an RV-9A

http://lastminutemall.com/secoseals/...per_Seals.html

http://www.flaretite.com/flaretite.php

For Aircraft Spruce, do a search for:

04-05004 DEL FITTING SEAL 1/4" OD

Charlie Kuss

[azcloudflyer]

I think those crush washers are a handy thing to have around. Especially when you have a steel-to-steel fitting that won't seal.

There could be a flaw in the vent flared pipe to fitting interface that the DEL Fitting would help with. To insert it, I would have to remove the nut and then manipulate the DEL fitting into place.

At first I wanted to inspect the flare with a bore scope. So I tried removing the nut on the mock up to practice. I was able to remove the nut with the tool but could not get the nut restarted on the fitting. The nut needs to be pressed onto the fitting at the same time it is turned and then not disturbed when you reposition the wrench. So after practicing on the mock up I was not confident I could get the nut back on if I took it completely off.

Maybe if I knew a basketball player that could start the nut with one finger for me via the fuel sender hole and then I could finish tightening with the wrench.

Mike

[gasman]

Originally Posted by N427EF

That is quite an impressive accomplishment.
Hope I won't need to do that, all my fittings inside the wingtank are sealed in proseal.

It sure looks like you could figure a way to swab it with proseal next. And the above should be standard during construction.

[SRC]

We recently purchased an RV10 (0ct 2012). We have exactly the problem that you discussed, only the left wing fuel vent. We had decided that the problem must be as you concluded, and were at a loss on how to tighten the nut in the fuel tank. It has been awhile since your posting. Do you still have the tool? Would we need the mirror image of the tool to use on the left wing? At any rate, your description and pictures should help. Thanks.

[longranger]

Originally Posted by azcloudflyer

... 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. There is almost 2" of room between the outboard end of the tank and the next wing rib to add a bulkhead 90 degree fitting and vent tube there. ...

I know this is an older post, but in case anyone is currently considering this, think carefully before relocating the vent to the outboard end. One of the reasons the vent is routed to the inboard end is to minimize the possibility of running fuel overboard in the event the aircraft is parked on a slope with a wingtip down.

[myrv6180]

The RV 6 tank vents have never leaked on my plane. Why was the -10 designed the way it was?