Another Fuel Leak - Left Tank This Time

[Andre]

I have another fuel leak - left tank this time.  It is underneath the front leading edge of the wing at 80.5" from the fuselage (20" outboard of the fuel filler cap).  I need to know if the fuel tank extends that far into the wing to ascertain if it a local fuel tank leak or a leak in the fuel tank somewhere else that shows up at that location.  I put a borescope to take a look and it seems like the fuel tank does not extends that far but I want to make sure.

Thanks

Andre

[Tom Baker]

The fuel tank extends to just beyond where the filler cap is. You can see the end of the tank from the filler opening. The CTLS has some vent lines at the outer end of the tank, but a CTSW does not.

[Andre]

Thanks, that is what I thought.  So my fuel leak is indirect i.e. the leak is somewhere else and it is getting out at that location - probably because I have a small crack in the paint at that location.  This is not obvious because of the wing dihedral i.e. the leaking fuel should pool towards the fuselage, not outboard of the tank.  This leak is many inches outboard from where the tank ends.   I must say that I am more than a bit confused.  Any ideas of what could be happening?

[Tom Baker]

For the fuel to be outboard of the tank, I suspect the leak is in the outboard rib.

[Andre]

I used my borescope once again and I do not see anything obvious on the outboard rib.  There is a small area that is "discolored" yellow on the rib but that is not the only such place in the tank so I do not know if it is normal.  I did find a spot where the paint is peeling in the tank but that is about 6" inboard of the filler cap on the back-bottom of the tank.   Pictures of these two potential issues here.  I have no baseline to determine if these are problems so I will appreciate any help from somebody who has dealt with a fuel leak and knows better.

[GrassStripFlyBoy]

Sorry I don't have any suggestions for you, but am collecting data points on those who encounter these situations - wondering what fuel type you typically use?

[Anticept]

You should take the aircraft to Airtime Aviation or other specialized shop.

Fuel leaks are no jokes, they can destroy your wing's sandwich structure and you shouldn't play around with them.

[Andre]

Fuel is 93 with Ethanol because there is no Ethanol-free fuel at the correct octane rating around here.  I am beginning to suspect that the Ethanol is the culprit but I have no evidence of that.

 

[Anticept]

I'm 4000 hours in and fine.

I know of another CT that is 6000 hours in on ethanol fuel.

There's another that was only 4000 in and had to have the tanks sanded out for recoating. It and another came from new mexico with the same problems.

There are other additives that can be added to gas, ethanol isn't the culprit.

[Towner]

22 minutes ago, Anticept said:

I'm 4000 hours in and fine.

I know of another CT that is 6000 hours in on ethanol fuel.

There's another that was only 4000 in and had to have the tanks sanded out for recoating. It and another came from new mexico.

There are other additives that can be added to gas, ethanol isn't the culprit.

That’s really good to hear. In California, it’s 100LL or 10% ethanol. Not really any other options and I am always wondering what the long term effects of ethanol might be.

[GrassStripFlyBoy]

I'm still operating with limited data, the few I've noted have common connection of using ethanol fuels.  These wing tank issues are the primary reason I'm avoiding it, having options to avoid it make it an easier decision.  Are there any reports of those not using ethanol fuels having a wing leak?

[Roger Lee]

If the Kreem Weiss coating was applied correctly any ethanol fuel will not hurt it. It's only where the coating was applied too thin and flaked up or broke away.

[Anticept]

4 hours ago, Towner said:

That’s really good to hear. In California, it’s 100LL or 10% ethanol. Not really any other options and I am always wondering what the long term effects of ethanol might be.

To add to it, these are all 2008-2011 models.

N566FD (4000 hrs, had to do touchups from people slamming the nozzle into the liner)

N178CT (6000 hrs)

N503NM (4000 hrs, had to recoat, whatever was in these tanks would bubble and react to the kreme weiss coating and this was years after the fact. Came out of NM when purchased and one other CT had the same problem. Recoating done at airtime aviation).

N26KJ (2000 hrs)

As said it's definitely not ethanol, BUT the ethanol + a tiny bit of water + gasoline makes it POTENT against the airex foam in the wings. It is important to inspect the inside of the tanks periodically and treat any discontinuity URGENTLY. It's no joke and several CTs have had significant wing damage!

[Towner]

Corey, thanks for all info. Luckily, I haven’t had to deal with fuel leaks yet, but it is a concern when I read one of these.

Just out of curiosity, does not keeping the tanks full cause any problems with delamination? I’m guessing most of us don’t keep full tanks, so I wouldn’t think it would be an issue.

[Anticept]

Never had issues with keeping the tanks full. While they hold a good bit of gasoline, it's only a few inches high, meaning the weight per square inch is next to nothing.

The general wisdom is tanks full or tanks dry if you're going to store it. Further wisdom relies on what kind of tank it is, how long between flights, and what kind of fuel. Rubber bladders should be kept full. With ethanol fuel, due to its hygroscopic properties, all tanks should be bone dry for long periods. With non-ethanol fuel, keep tanks full for storage.

For a couple month stint of not flying, this isn't really important.

[Jim Meade]

Why would the fuel level have any effect on delamination?  Is there any science to cite on it?  And what kind of fuel - 100LL?  91 octane w/ethanol? 93 octane with no ethanol?...etc etc.

[Anticept]

Generally accepted practice. The only way I could see fuel level being a direct factor is if fuel level weren't the only issue (flaking sealant higher in the tank for example).

I know before you mentioned that the amount of breathing would have to be astronomical for any effect, but there's already some water in ethanol fuels so it doesn't need a whole lot more. I've also seen this happen first hand with fuel being ruined from a 6 month sit in a hangar. Full tanks means no condensation can collect, empty tanks for long term storage so you don't have to deal with bad fuel (you aren't inspecting it regularly either so if a problem does develop, it can progress much further before you finally catch it). In addition, when you have only partial tanks, you're already letting in a bunch of air with moisture; the lower the tank level the higher the ratio of moisture you have to potentially contaminate the fuel.

Mainly the issue with ethanol fuel is that even a fractional amount of fuel + ethanol + water turns it into an extremely potent solvent.

Cars mainly don't deal with this issue anymore due to a side effect of having an evaporative emission system.

Anyways, if you want formal research on the subject to narrow down the exact parameters that cause all of these issues (since it seems to highly vary by time of year and location, plus rule out things like leaky caps or storage on ramps), you'll have to commission it. Until such research comes out to prove otherwise, following generally accepted practice is a relatively minor inconvenience for hedging against some considerably expensive mistakes if you find out the hard way that the generally accepted practice has merit!

[Andre]

From my understanding, most (if not all) CTSW with fuel leak issues were earlier (pre-mid 2007) aircraft.   I think the factory started to use epoxy sealant in the tanks at some point in mid 2007?.  I am thinking that maybe Ethanol is an issue with tanks that were not epoxy sealed at the factory so it would not apply to the 2008 model.

My CTSW is a 2006 and both tanks have now leaked.  The first leak was the right tank and a previous owner remedied the issue by doing the epoxy treatment .  Except that the tank started to leak again a couple of years ago.  I just disconnected it from the fuel system and flew with the left tank only for the last two years.  My left tank started to leak last April and that one was never epoxy treated.  I parked my plane all summer with the tanks dry.   I am now back and now have to deal with the problem as I am out of fuel tanks.  Unfortunately, there is no Caswell epoxy tank sealant to be found in North America at this time.  That is what FD USA recommend that we use.

Here is a picture of my right tank.  Maybe somebody can recognize the sealant that was use by the color or the flow patter.  That would be useful.   Clearly, the application did not cover the whole tank.  Incidentally, the small red "wart" is exactly where the new leak is.  If anybody has seen something like this before, please let me know as I will want to talk to you - at your convenience of course.

On an aside, I carefully checked the aircraft log before I bought the aircraft.  There was a one-liner entry about a fuel leak on the left tank that was corrected.  There was no details whatsoever about cause, location or work done so I just assumed that it was a gasket or poorly connected fuel line.  It is only after the tank started to leak again that I realized that it was a lot more serious because I found the epoxy in the tank while troubleshooting.  I have no idea what epoxy was used for the repair.

 

[Tom Baker]

Call and talk to Airtime Aviation. They have dealt with tank leaks before. It is my understanding that the have found a new sealer that can be used. 

[Towner]

First, mine is a 2006. I’ve read a couple of times that older models like the 2006 are the ones that have the biggest problems. Though I haven’t had any leaks, I’m just trying to prepare for it in case it happens.

Mine gets flown at least every 2 weeks and is never stored for a long period. It is also kept in a hanger. 

The fuel is almost always 91 octane with up to 10% ethanol. It’s the best I can get unless I fly 100LL.

My question about partially full tanks is because mine are almost never full. I usually have no reason to fill it, so it almost always has between 10-25 gallons in it. I didn’t know if leaving it 10 gallons or more below full could cause any problems with the top of the tanks being dry most of the time.

[Tom Baker]

Bladder tanks need to be kept full of fuel to keep the rubber from drying out. metal tanks are normally kept full to prevent condensation. With the composite tanks condensation is not a problem, and I don't think the coating is required to be kept wet. In my opinion you are fine leaving the fuel level down. That is how I always kept my CT. The only times it was topped off was when I was going on a long trip.

[Anticept]

Tom: I have to ask what makes you believe composite tanks don't have condensation issues. Lower heat transfer and fuel keeping the tank relatively consistent temperature? Agree with everything else.

Usually these issues only present themselves with long term storage (many months) and relatively low filled tanks.

[Tom Baker]

10 hours ago, Anticept said:

Tom: I have to ask what makes you believe composite tanks don't have condensation issues. Lower heat transfer and fuel keeping the tank relatively consistent temperature? Agree with everything else.

Usually these issues only present themselves with long term storage (many months) and relatively low filled tanks.

You know how a glass or can with a cold drink will have condensation if there is enough moisture? Have you ever seen condensation on a Yeti cup? Our tank are kind of like a Yeti Cup. The aircraft skin makes a nice insulator.

[FlyingMonkey]

I have not had any fuel leaks I am aware of, but I guess it's time to scope the tanks on my next annual and make sure.

[Anticept]

6 hours ago, Tom Baker said:

You know how a glass or can with a cold drink will have condensation if there is enough moisture? Have you ever seen condensation on a Yeti cup? Our tank are kind of like a Yeti Cup. The aircraft skin makes a nice insulator.

i will look into the tank next time we have one of those really dewey nights here in ohio!