Dealing with Fuel Tank Leaks

[RVbySDI]

I hope this post may be of use to those out there struggling like I am with a leaky fuel tank. I have a few pics and videos to show concerning my process along with a question concerning something I found in my fuel tank that I would like to understand.

I have been fighting fumes in the cockpit pretty much since my first flight. I have approximately 150 hours on my 9A now. I have always had a distinct smell of fuel whenever I would initially open the canopy prior to flight. The fumes have always dissipated on the ground once the engine was started. I attributed this to the air movement through the cockpit once the prop was spinning. I have never smelled fuel at any time during flight, only on the ground prior to engine start. Up until just a couple of months ago I had never seen any visual indications of a fuel leak, only a smell of fuel when I initially opened the canopy. However, back in November after fueling up one day I knelt down to take a look underneath the wing to see if there was any indication of fuel anywhere. There it was. There was a line of blue dye along the trailing edge of the fuel tank running from the fuselage outboard to the first inspection plate.

Well that was it. I grounded the plane in December. Over the Christmas/New Year holidays I pulled the left fuel tank off to see if I could fix the leak. I will not go through the process involved in pulling the fuel tank except to say that even though it does take a couple of hours of physical contortion to get back into the back side of the wing spar to remove 21 bolts and, every time I do this, the process does take some skin off of my hand, wrist and forearm, overall the process is doable.

At any rate, to shorten this post, I removed the tank in December and did the typical soapy water bubble test only to find . . . NOTHING! I pressurized the tank for days with a balloon that pretty much held its pressure. I was never able to see any bubbles form with the soapy water. I did see where there were some blue dye stains so I took some ProSeal to that section of the tank along the rear baffle seam and along one of the Z-brackets. I let it cure for a week and pressurized it again. It appeared there were no leaks. So, I put the tank back on.

I am sure you know what happened next. After 3 or 4 flights I looked again underneath the wing. Yep! There was the blue dye again. Only this time it was worse! So, this weekend, off came the tank again. Again, I put the balloon on the tank, sealed it up and pressurized it. Only this time around the soapy water revealed multiple pin hole leaks along the bottom rear baffle seam. I took some pictures along with a couple of videos of my process.

Click on the picture below to see the first video of the leaks along the bottom rear baffle seam:



After some deliberations I decided I could take the end plate off of the tank and with a long screwdriver reach through one of the rib baffle holes and get to the inside of the seam with some ProSeal. In the video above you also saw a leak in the far outboard corner of the rear baffle. I was able to reach down through the fuel filler opening to get to the inside of that seam.

Click on this picture to see the other video showing the inside of the tank after the access plate was removed.



So, if you watched the video you noticed the question I had. I noticed some fine powdery type residue on the inside of the fuel tank. The pictures do not really show all of the inside of the tank but it did look like the residue was mostly on the floor of the tank. From what I could tell, especially when I look closely at this picture it looks like this residue is from the ProSeal:


You can clearly see where the ProSeal on the reinforcing stringer on the floor of the tank is flowing outward from that seam.
[ed. 2/23/12, just in case you may not read all the way to the end of this thread I have discovered this residue is rust from my steal fuel storage tank I use for my 100LL fuel source. RVbySDI]

So the questions I have for everyone: Has anyone seen this before? Should I be concerned with it affecting the fuel as it flows into the engine? I would guess the filter(s) will catch most of it. Any thoughts at all would be appreciated.

I have the fuel tank sitting in my living room floor now in front of the fireplace. It will take several days for the ProSeal to cure. After that I will seal the access plate up and pressurize the tank again. We will see if my patch worked or if I missed. I was having to go more by feel than sight especially when I had to reach through the small baffle hole in the first rib. It is completely possible I could have missed sealing that section of the rear baffle seam. Once it cures and I can test it again I will have a better feel for whether I will have to reach into any of these areas from the inside again or not. Time will tell.

Click on https://picasaweb.google.com/1140831...CILc6YSAxIOlMA to see all of the videos and pics I took while working on this repair.

[Carr]

Steve

Did you build the tanks?

What type of fuel are using? Any auto fuel?

I've never seen residue like that when using 100LL.
Better find out what it is before flying again.

Carr

[RVbySDI]

Originally Posted by Carr

Steve

Did you build the tanks?

What type of fuel are using? Any auto fuel?

I've never seen residue like that when using 100LL.
Better find out what it is before flying again.

Carr

Yes, I built the tanks. I have never used anything except 100LL.

[Walt]

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

[ccsmith51]

Originally Posted by Walt

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

A couple of months ago I purchased a quart of B-2 Flamemaster from Van's. There was a slip with the tank sealant that says that it will take 3 - 7 days to cure, and will remain soft for up to 30 days.

Even after a week of curing and extra heat, it was still somewhat soft. Not tacky, but certainly not solid. I used a 1g resolution scale so the ratio was exact. My sealant also has a brown tint to it. Maybe that is a characteristc of Flamemaster over Proseal??

[RVbySDI]

Originally Posted by Walt

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

The sealant does have a brownish tint to it. I used Flamemaster B2 from Vans. I built these tanks in 2008-2009. Those tanks cured for about 4 weeks or longer before I ever sealed up the rear baffle. They spent another 2+ years sealed and empty before I ever put fuel in them while I built the rest of the airplane.

I know there are bound to be a lot of opinions about this and I welcome all comments. Never the less, I would greatly appreciate anyone who may have any first hand experience with this. Better yet, is there anyone out there that can do a chemical analysis of this material to find out for sure what it is? If it is the Flamemaster B2 sealant I would like to know what is causing it to break down into this powder like substance.

[RVbySDI]

I just thought of something while looking at the video again. I think this potentially could be rust. In fact my thoughts are that it if it is indeed rust then I know the source. I have a 300 gallon steel fuel tank that I use to fuel my plane. It has a filter on it that is designed to keep this type of contamination out of the fuel but my guess is that rust from the steel tank is making it through the filter and into the fuel tank. It definitely has a reddish-brown tint to it that reminds me very much of rust.

I think I am going to pull the filter off of my fuel tank and see if it has the same substance in it. I will post when I can get out to check it.

[Walt]

I've never used the Flamemaster, I've always used PRC Desoto "ProSeal" and have used the AC Tech for repairs with no issues (it is also dark gray). For building tanks I personally would only use PRC (this is what I've used/seen used my whole career) with good results (very rare to get a bad batch). We would seal a tank and put fuel on it 8 hours later with no problem. Using B-1/2 we would put fuel on it after just a few hours if we were in a rush.

[Wayne Gillispie]

The military uses it for a reason. I thought I would try a little Flamemaster from Van's. It cured slower and it had a different smell. I used it on everything but my tanks. Scothbrite all mating surfaces and 1/2" beyond. Clean with MEK. Spend the extra money on PRC proseal and don't be stingy...it only adds a lb or two more. Go over all accessible proseal with PR-1005-L from ACS(red Buna-N). It bonds great to proseal and bare, scuffed aluminum. Pressure test to 1 psi using homemade or electronic manometer. By all means build your own tanks.

Note in one pic above...I notice many are not putting proseal on both sides of ribs and also not covering all rivet shop heads. The proseal adds a bunch of strength to those joints to prevent loose rivets/weeping rivets down the road.

[Tharpo]

Is there a brand name for the red sealant mentiioned here..haven't found it at ACS( assuming that means Aircraft Spruce..right? )
Thanks
Tharpo