Decathlon fuel tanks.

Gotta pull a tank. The factory says remove all the fabric top and bottom, all the way out to the second rib beyond the tank. It also says to drill all the rivets out of the hat sections prior to removing fabric.

Is it really necessary to uncover a third of the wing just to get the tank in and out, or can it be done with less invasive surgery? And can't the top hat sections be removed before drilling out all those pop rivets?

Any "gotchas" here?

Yeah, I tried googling, and the Bellanca Champion club, but this is the only source for truly good advice.

The last one I did I uncovered from the aileron rib inboard because the trailing edge was cracked along with the tank. I uncovered top and bottom. I was working on a Citabria. What is the hat channel for?

Thanks Steve. The "hat" sections are apparently riveted to wing structure fore and aft of the fuel tank, and serve as false ribs to anchor the fabric to. From the outside, they just look like ribs. My plan is to cut them out at their ends, remove the rivets holding them to structure, carry them over to the bench, and then remove the fabric attach rivets. And as of right now, I am thinking that I only need to do that on the top.

The Citabria manual calls them "ribs" and says just remove top fabric. I am wondering if the wings are that different - I realize the airfoils are dramatically different, but am thinking that the general idea must be a lot like a Cub, only with three piece stamped ribs.

I take it this is a "new" metal spar 8KCAB? Are you sure you need to pull the tank? I haven't seen one yet that didn't leak at the tank outlets. 99 percent of the time if your pull the fittings and retap the treads in the tank then reinstall the fitting with some good sealant, the leak is solved. If it is a earlier metal spar check the butt rib real close. The first ones were weak in this area, and are often cracked, and the upper skin is torn loose. If you really do have to pull the tank, cut the fabric inside the butt rib, drill the fabric rivets out through the fabric, and try to peal it back with minimal cutting, then reglue the original fabric back down and rerivet as needed through a new reinforcing tape, and finish tape back over the new rivets. Dealing with the urethane finish and repainting the sunburst really sucks, I'd try every other option I could first.

Mark: that's excellent news. It is a wood spar aircraft, but still, I'll check the threads as you suggest. All Randolph butyrate over Ceconite, and the sunburst is trivial, so I am not scared of new fabric - just didn't want to uncover a third of the wing, and be re-covering the under side while standing under the wing. The service manual is not real clear about what is involved - pretty cryptic about removing the rivets before removing the fabric, which makes sense only if you intend to yank the fabric without cutting first. Even more cryptic about how the false ribs, or hat sections, are attached. But checking the threads may save us a week of work!

The job is not trivial. So far, it is semi-clear that some of the fabric must come off the lower side, if not all of it. The rear brackets appear to require removal, which means drilling rivets out of the rear hat section on the bottom. The factory says it can be done from the top, but getting the diagonal brace tube out is the big headache, requiring that the tank be moved aft prior to lifting.

I still need advice . . .

I got good at removing Taylorcraft wing tanks by removing the compression strut and but rib. The drag/anti-drag wires ran through the tank. Don't know if that helps or not. Sounds different than the Citabria tanks I have pulled out.

Here's the deal: Factory manual says remove all the fabric from butt rib all the way out to the second rib outboard of the tank. That seems to be the only way to really do the job. Factory says remove the brackets from the spar. Ditto. Gotta remove them. That means all hat sections get un-riveted from brackets. This is a really big deal, but doable if you do exactly what the manual says.

The tank itself was interesting. Dated 2004 from the factory; it looked maybe like it was done by a beginner. I cannot begin to tell you how it waved back from every angle we looked at it. Even after repair, it doesn't look real good. It still "oilcans", which means it will fail again unless we force it to one position so it can't flex during inverted maneuvers. ACA ought to get a subcontractor to do these things; they apparently fail with regularity. My opinion.