2004 8KCAB Super D - Wing Tank Fuel Leak?

[SwiftWing]

My 2004 8KCAB Super Decathlon is currently in annual, and my mechanic suspects the left fuel tank may be leaking. I'm hoping to get some advice on what to check, and also recommendations for a good shop in case the tank needs to come out for repair or replacement.

Over the last year I've occasionally noticed dried blue fuel dye on the underside of the left wing, seeping through small cracks in the paint and leaving a pattern as if it has been blown by the wind toward the tail. I think it tends to appear after I accidentally overfill the tank, and possibly after aerobatics (including inverted flight). I don't see any logbook mention of the fuel cap or gasket being replaced, so I'm also wondering if this could just be fuel sloshing around, getting through a worn fuel cap gasket rather than a leak in the tank itself.

A few years ago, the left tank was removed and repaired (not replaced) by a prior owner, then reinstalled. I've only flown the airplane for about a year. I've never seen active dripping while the plane is parked (no puddles in the hangar), but the dried blue dye under the left wing has shown up a few times over the year.

Any thoughts on likely causes or common trouble spots? And if replacement ends up being the best option, I'd really appreciate recommendations for a reliable shop that can handle the tank work, recovering, and painting.

Thanks in advance!

 

[Bob Turner]

As I recall, tanks welded around 2003 were prone to failure. I have heard of repairing in situ, but I was involved in a removal and replacement. You strip all the fabric off, top and bottom, around the tank, struggle to get it out, weld the seams, struggle to get it back in, recover a third of the wing! In retrospect it might have been better to pull the wing off.

We just replaced both tanks in a 2003 - I was ready to help, but it got sent to a specialist. You don't wanna know what that cost.

Sure hope it is just careless refueling!

 

[Skylarktc]

When I was researching buying a DECATHLON, I emailed Chad at ACA and asked about tank cracks. The 2004 model was the last model year that was prone to cracks. The 2005 models and on have redesigned tanks. So unfortunately, you may be looking at a crack somewhere.

 

[Bartman]

Hello @SwiftWing ..... I saw your post to the acro exploder and was going to invite you to join us here, glad you found us.

The issue with the tanks is usually related to aerobatics with heavier fuel loads sloshing around and causing the tabs of the tank baffles to crack where they are welded through the surface. Imagine a rectangular opening in the tank shell and a matching bent tab on the interior baffle that is welded into place from the outside. They redesigned the tanks to have more weld tabs, not sure what the other improvements were but later tanks are less prone to cracking.

It could be overfueling, leaking cap gaskets, hoses in the wing root that are old or need to be tightened, a leaking fitting at a tank connection......it isn't necessarily a leak but that is a possibility. How many hours on the airframe and how was it used before you got it? Ever used for aerobatic instruction? That might point towards a crack but hard to say from where I'm sitting.

Good luck with it. If you're going to do all of the work to remove the tank, better to invest in a current version tank than on repairing the old one.