RV-8a Wing Tank Leak

[Majorpayne317641]

I recently started smelling fuel in the cockpit and went over every fuel line I could find but could never really figure it out, never could find any fuel on the ground in the hangar nor any blue stains on the floor. Finally I went out flying and after coming back I noticed blue fuel stains on the bottom of the wing. After pulling off the wing root fairing it does not look like it’s leaking from any of the fuel sensor cover plates or the fuel lines. I also find it strange that it leaks only when flying and that there is so much on the spar/tank area of the wing.

I think I need to take it off to really see what’s going on.

How best do you accomplish this? I see the front wing root bracket has an L shape that is bolted to the tank but in a way that it probably won’t slide forward without me removing the L bracket, is that correct?

Once it is off, is there a way to pressurize the tank with water? Or do you fill it up and let it sit?

Aircraft has 1300 hrs on it and is 12 years old. I am not the builder, it looks like the builder used pro seal on everything to include the fuel level sensor.

 

[PaulvS]

It would be worth getting the plans for your aircraft from Van's so you can understand how the tanks are attached. It was only $10 for the USB stick. There's a bunch of Z brackets that need to be un-bolted.

The leak is highly likely in the rear baffle and the blue dye will confirm it. The tank should not be pressured above about 1 psi (balloon pressure) otherwise it will be damaged. Soapy water on the outside will show the bubbles where it is leaking.

There are lots of posts on VAF for how to repair; essentially it involves cutting access holes in the rear baffle and cleaning and re-sealing the seams.

 

[D Weisgerber]

Like Paul said get the plans, you can get them on a USB memory stick. I agree that is probably is the rear baffle.

 

[Majorpayne317641]

Thanks I have the plans. Asking advice from someone who has done this already. Looking at plans and actually doing the work can sometimes be two different things. I’m aware of the 21 bolts on the spar in addition to the 200 Phillips screws. Should I leave the aileron pushrod in or should I unbolt it from one end to get to the spar bolts easier?

 

[PaulvS]

Here's another thread that may be helpful:
https://vansairforce.net/community/showthread.php?t=212912

 

[Majorpayne317641]

Here's another thread that may be helpful:
https://vansairforce.net/community/showthread.php?t=212912

I didn’t see this one thanks, it’s the best thread I’ve seen and it looks like my case.

 

[D Weisgerber]

I got a 3/8 drive cordless ratchet, it made it much easier to take out the 21 bolts from the Z brackets.

 

[Richard Connell]

Thanks I have the plans. Asking advice from someone who has done this already. Looking at plans and actually doing the work can sometimes be two different things. I’m aware of the 21 bolts on the spar in addition to the 200 Phillips screws. Should I leave the aileron pushrod in or should I unbolt it from one end to get to the spar bolts easier?

It can be done with the pushrod in place, but it is easier with it removed.
It may depend on the size of your hands and forearms.
The challenging bit is getting it off once all the fasteners are removed.
There’s a moderate amount of resistance at the outboard splice plate.
A block of timber against the rear skin edge and gentle tapping with a rubber mallet has worked well for me in the past.

 

[Majorpayne317641]

It can be done with the pushrod in place, but it is easier with it removed.
It may depend on the size of your hands and forearms.
The challenging bit is getting it off once all the fasteners are removed.
There’s a moderate amount of resistance at the outboard splice plate.
A block of timber against the rear skin edge and gentle tapping with a rubber mallet has worked well for me in the past.

Thank you great advice

 

[Majorpayne317641]

Does the front spar attachment angle need to come off to remove the tank?

 

[lr172]

Once it is off, is there a way to pressurize the tank with water? Or do you fill it up and let it sit?

Make a home made manometer and and adapters/covers, then pressurize (with air) to about 1 or 1.5 PSI then spray liberally with soapy water. Leak source should become obvious. A leak that shows up down the road from initial build points to issues that may warrant a complete reseal.

 

[Majorpayne317641]

This is what I have. It seems like where you see blue dye on the back side of the baffle, the pro seal is soft and squishy. Everywhere else the proseal is firm. I think the inboard stains may be from pooling while the main leak is near the center rear bottom of the tank.


For those that are wondering in the future, yes the wing root bracket must come off to get the tank off without scratching any paint. You can dive down into the cockpit and reach it with a 3/8 socket 12in extension and a helper holding the other side with a box wrench at the wing root.

 

[gear1]

Fuel tank leak

Chris,

I had exactly the same leak in my right tank a year ago. The 1.5 psi inflation and soap bubbles confirmed the source of the leak, right at the junction of the inboard tank rib, baffle and lower skin. Using a wooden Popsicle stick, I dug out the Proseal at the junction, including a small area "hole" at the junction of the rib, baffle and lower skin. I than sanded the area with 600 grit sanding paper and acetone. I cleaned the area forward past the first nut plate, also. Using the Aircraft Spruce sealant Part# 09-38510 (the small tip and a caulking gun helps to inject the sealant into the small hole), I resealed the tank from the ourside. It has been nearly a year and 200 flight hours and no leak.
I cannot claim that this is the best way, but it certainly was simpler than making additional holes in the baffle, or removing in inner panel and fighting the flop tube. I hope you are successful in fixing your leak.

 

[D Weisgerber]

Does the front spar attachment angle need to come off to remove the tank?

I think you're talking about the L bracket on the inboard tank rib, it overlaps with an L bracket on the fuselage. You should only have to remove the bolt that connects them, one of them should have a slot cut in it.

 

[fixnflyguy]

Baffle reseal likely needed

By the looks of the stains and lack of squeezout on the baffle flanges, I'd say you need more than a single spot fix. I've done a few. Sent you a PM a couple days ago.

 

[Majorpayne317641]

By the looks of the stains and lack of squeezout on the baffle flanges, I'd say you need more than a single spot fix. I've done a few. Sent you a PM a couple days ago.

I agree, I ordered the kit and will reseal the entire baffle. I’m getting 5 sets of plates from vans and their pro seal. I bought a HF 5 inch hole saw. Before I do any cutting I want to verify the diameter of the plates vans sells. The best I could tell is it’s good for a 5 inch hole is that accurate?

I plan to use polygone to clean it up, scuff the aluminum clean everything out and reseal the baffle in one phase. Then seal up the access holes in a second phase to verify the fillets are good before closing up the tank.

 

[Majorpayne317641]

I verified with Vans it’s a 5in diameter hole

 

[Majorpayne317641]

It looks like the builder of this tank didn’t put much proseal on the baffle and that’s why it failed. Lots of aluminum shavings to clean!

 

[PaulvS]

I ended up removing the baffle completely to clean out the softened sealant. Hopefully you don't need to do that. With the better access it is possible to properly finish the seam of sealant. This cannot be done during the initial build without the access holes.

 

[Majorpayne317641]

I finished match drilling the vans cover plates. I also used polygone for cleaning off the old proseal. It was so bad on the access plate for sending unit that I needed a hammer and chisel to get it started to get it off! Now on to sanding sealant surfaces and washing really well to prep for sealant. I’ve got naphtha for final cleaning.

 

[Majorpayne317641]

Finished sealing up the tank. I guess we will see if it holds soon.

 

[Majorpayne317641]

Leak test was successful!

 

[Majorpayne317641]

I added gas today and flew for an hour still no leaks.