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TommkII

Bought Viking Dragonfly with leaking fuel sump. Any ideas on how to fix?

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Bought a Dragonfly in rough shape and the sump on the main tank leaks. When attempting to unscrew it for replacement it just spins. It appears the builder glassed in the female threaded part of the sump and I don't know how to disassemble it without causing damage. Any ideas?https://i.imgur.com/2UMu1Hu.jpg

Screenshot_20211006-134533.png

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1 hour ago, TommkII said:

Bought a Dragonfly in rough shape and the sump on the main tank leaks. When attempting to unscrew it for replacement it just spins. It appears the builder glassed in the female threaded part of the sump and I don't know how to disassemble it without causing damage. Any ideas?

I'm not familiar with the specifics of the D-fly installation, but I'm going to make the assumption that it's approximately the same as the VE, LE, COZY, and all other canards with 1/8" NPT fittings for fuel drains. There's probably a 1/4" thick AL plate buried in the composite sandwich, and it's spinning between the layers of glass and chewing up the foam. Maybe it was too small - maybe the threads have just galled or something. Don't know - don't care. It's got to come out.

You'll need to do some surgery:

  1. Drain all the fuel
  2. Using a dremel tool and permagrit grinding bits, remove the outer layer of glass around the AL plate, and remove the foam around the plate
  3. Sand the surrounding area at least 2 - 3" down to the glass - no paint/fill remaining
  4. Pop the plate loose from the internal tank glass layup
  5. Sand the internal glass smooth without damaging it or breaking through into the tank
  6. Fabricate a new plate - at least 1" square, preferably 2" square
  7. Drill and tap it for a 1/8" NPT thread - do NOT tap too deeply - make sure that you can screw in the fuel drain without coming close to bottoming out the threads - this is a guaranteed way to ensure that it'll leak down the road, if it can bottom out
  8. Using WET EZ10-87 epoxy/flox, flox the plate into the bottom of the fuselage so that the hole in the plate lines up with the opening in the inner skin - make sure that you don't get flox into the NPT hole
  9. Fill the area around the plate with wet flox
  10. Layup 2 - 4 plies of BID cloth over the top of the plate, each ply lapping at least 1/2" more onto the surrounding fuselage exterior glass surface (previously sanded) than the previous ply
  11. After cure, sand, fill, prime, paint
  12. Install a NEW fuel drain with appropriate teflon thread sealant

This will take a few hours for the install, and then a few hours for the finishing.

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Marc's advice is spot on.

Was this the Lake Charles Dragonfly?  You should come and party with the Dragonfly group on groups.io too if you haven't already joined.

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