unusual fuel leak

[colin_eyres]

Hi,

I'm looking for some first hand experience and advice from you guys. has anyone encountered a fuel leak coming through the leading edge of the carbon fibre around the stall edging. I'm in a syndicate aircraft and recently we needed to fill in some paint damage with some two pack filler, after a few weeks it was noted that the 2 pack had not hardened and was turning a straw colour and there was a small tail about a inch long of this colour directly underneath it. some members of the group are convinced its a fuel leak and I agree the colouring is similar, but what I cant get my head around is that the tail is not increasing in size or feel damp which would  normally be the case. we have been quoted £1700 by a pro to sort it but I would be upset if the job was done and found not to be a leak after all. any thoughts on proving /disproving that its a leak?

[Tom Baker]

There have been occasions of a fuel leak through the skin, but I have a couple questions. Did the filler that was not used on the wing harden? Why was some filler needed?

[colin_eyres]

we had the wings off about 18 month ago and replaced the hoses and everything was ok, but a few months later one of our syndicate members has just reminded me  there was a very small amount of staining found on our annual inspection and he removed it and refilled the area with 2pac and that seamed to take a long time to harden.could you tell me are there are tanks in the wings or is the whole wing is the tank? and does the wing have to come off to apply a sealing compound. would you think if the whole wing is the tank and there is a leak do you think that it will affect the carbon fibre and spread further?

[NC Bill]

There is a tank in each wing. They are known to leak - likely due to the sealant failing. Adrian at FDUSA told me he estimates 5-10% of the fleet have developed such leaks.

The solution is to remove the wings and reseal the tanks. Fortunately a local shop was able to do that with FDUSA advising for $2500.

[colin_eyres]

Do you know wether sealing the tanks is a 100% effective fix or are there a percentage of failures resulting in a wing becoming unfixable/scrap.

[Tom Baker]

I am not aware of any wings becoming un-fixable due to a fuel leak.

[colin_eyres]

Many thanks for the information guys. Keep up the good work 

[Anticept]

On 6/25/2021 at 10:59 PM, Tom Baker said:

I am not aware o any wings becoming un-fixable due to a fuel leak.

There was one, and it was posted here and later removed.

The leak was next to the spar, delaminated the area, bubbled a pretty big portion of the underside of the wing, the wing was unfixable. I believe flight design stepped in to make that one right though (I think Tom told me what ultimately was done but that was so many years ago).

Other than that, there have been many accidents, some fatal, in aviation in general when it comes to leaky tanks in composites, but the point to make is they were a result of ignoring the problem for a long time, or deviating from plans for homebuilts. In the latter case, someone installed tanks in a styrofoam core wing without consideration to material incompatiblity. It leaked, turned the wing into an eggshell, and it broke off in flight.

[Tom Baker]

9 hours ago, Anticept said:

There was one, and it was posted here and later removed.

The leak was next to the spar, delaminated the area, bubbled a pretty big portion of the underside of the wing, the wing was unfixable. I believe flight design stepped in to make that one right though (I think Tom told me what ultimately was done but that was so many years ago).

Other than that, there have been many accidents, some fatal, in aviation in general when it comes to leaky tanks in composites, but the point to make is they were a result of ignoring the problem for a long time, or deviating from plans for homebuilts. In the latter case, someone installed tanks in a styrofoam core wing without consideration to material incompatiblity. It leaked, turned the wing into an eggshell, and it broke off in flight.

Of course I was speaking of Flight Design Specifically. I was unaware of the one you mentioned, or at least I had forgotten about it.

[Anticept]

It is because flight design stepped in and made it right that I don't go spreading info on that one too much. It was a pretty rare occurrence. Those 2 year internal tank checks are important!

Even though the wings use rohacell (fuselage uses airex), prolonged exposure to ethanol still does nasty things. Mainly to the epoxy.

[Runtoeat]

My CTSW was repaired for a wing fuel leak at the FD main headquarters.  My leak looked to be the same color as your wing but my leak (actually a series of small bubbles) was on the bottom of the wing our from the fuselage and towards the leading edge.  There have been quite a few CT's needing this.  There is an oval shaped access port which is about 12" X 10"  in the wing's lower skin, about 3 to 4 feet out from the fueslage.  This port can be seen when there is heavy moisture in the air and it has a different condensation pattern than the rest of the wing.  This port is removed to access the integral "wet wing" fuel tank for repair.  Access can also be done thru the small inspection port in the wing roott.  The defective portion of the wing that is leaking is removed, new composite is patched in, and the fuel tank is "sloshed" with Creme Weiss" which is a two-part liquid that hardens and is impervious to alcohol fuel.  The CT fuel tanks were sloshed with this material during the factory build of my 2006 CTSW but I do not know if this procedure is still used.