Trying to track down a fuel leak.

For the past 6 or 7 months I've noticed blue fuel streaks going across the fuselage coming from the left wing root. I've taken the access panel off several times and everything seems dry, except that the ledge that the access panel is screwed to is soaked in fuel. I've wrapped white rags around every fitting and port that could leak and still can't identify the source. I've also searched around the cockpit area and can't find any leakage coming from there.

It only happens while flying. I almost always keep my plane at least 80% full of fuel and nothing is leaking while sitting in the hangar, it's only after coming back from a flight that I notice this. Apart from that I can't find any other place on the plane that appears to be leaking.

The only thing I can think of is that it's leaking directly from the tank, on the back side that's up against the wing spar. The last time I took it up (yesterday) I deliberately let that tank run to below 50% capacity, figuring the next step was puling the tank, and when I landed there was very little evidence of leakage - which tells me the tank was below the level that it's leaking from.

But it doesn't leak when the plane is static, regardless of how full the tanks are. Do the tanks somehow become pressurized in flight? I'm really hoping I can track down this leak without having to pull that tank, but I'm running out of places to look.

Is your vent clear? Are these quick built tanks?

It could be that the leak is at the rear bulkhead and the air is moving it around during flight. You will likely have to pull the tank to even see the spot it's leaking from. Of course you need to pull the tank to use the Vans repair kit anyway.

-Marc

Fuel pressure return?

I recently repaired a leaking RV-10 tank that dripped from the vent. It was a quick build tank, and I put an access in the I/B bay. The leak was caused by a bad flare (inside of end rib) on the vent line, and it leaked from the vent until that fitting was below the fitting level. I know there is a pressure return line in the same region from the fuel injection HP pump, and it possible your may be leaking from a slightly loose connection or line that doesn't leak under ambient pressure. this would be consistent with occurrence only in flight. You can see in the attached picture the return line fitting is next to the vent line fitting..but if you built it, you already know this. At least its a place to start..and that would pressurize your tank if the vent is plugged also.

These are quick build tanks, both of which have been previously pulled and sent back to Van's due to vent B-nut leakage issues.

fixnflyguy said:

I recently repaired a leaking RV-10 tank that dripped from the vent. It was a quick build tank, and I put an access in the I/B bay. The leak was caused by a bad flare (inside of end rib) on the vent line, and it leaked from the vent until that fitting was below the fitting level. I know there is a pressure return line in the same region from the fuel injection HP pump, and it possible your may be leaking from a slightly loose connection or line that doesn't leak under ambient pressure. this would be consistent with occurrence only in flight. You can see in the attached picture the return line fitting is next to the vent line fitting..but if you built it, you already know this. At least its a place to start..and that would pressurize your tank if the vent is plugged also.

Click to expand...

FWIW, that EFI return isn't stock on the -10 (it is on the -14 however). It's either the EFII screw-on model or someone used the stock Van's NPT flange and installed it backwards.

A safe method to pressurize

You can fill your tanks and use a balloon filled with air secured to your vent to apply a safe steady pressure to see if you can simulate the slight overpressure demonstrated inflight.

Very similar leak on my 7 tank, my first blue evidence was a smidge bit of blue on the spar under the wind inspection plates. Sometimes it had a smidge of blue on the inboard rib under the fuse fairing. Never more than what would amount to a couple drops. I was able to get a small WIFI/borescope camera in behind the tank s brackets and find a little blue.
Pulled the tank and could see 2 spots on the lower aft baffle that the fuel was coming from. Pressurized and leak checked the tank via the plans, never could get any sign of a leak. The balloon stayed inflated and stable 3-5 days before I started working on the tank. Re-sealing now….
Side note, the repair kits show out of stock on vans webstore but the individual parts should be in stock. I called and the kit Plate&rivets haven’t been bundled yet