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Old 02-04-2017, 04:23 PM
Mad City Flyers Mad City Flyers is offline
Intermediate Rocketeer
Join Date: Jan 2015
Location: Madison
Posts: 70
Default Build Progress 4

Hi All,

So the double fin set was not a perfect fit even for the Gorilla Guillotine fin jig, but we made it work.

After setting all of the forward fins it was time for external fillets.

I must say that the fin jig was amazing and the alignment of the tail cone and booster fins appears perfect. I guess will find out when we launch it!

For this bird we went back to our prior method of making external fillets:

We use some heavy grit sandpaper (80-100) to roughen up the airframe and fin areas then use 3M painters tape to mask off the fillet.
  • Great Planes 30 minute epoxy
  • West systems fiberglass
  • Phenolic microballons
  • Formula that seems to work for us is 7.5ml resin, 7.5ml hardner, 1 teaspoon fiberglass, 1 teaspoon micro ballons

Epoxy mixture is poured into the fillet area and then smoothed using a piece of 1" PVC soaked in rubbing alcohol. We only allow it to set about 5-10 minutes before pulling off the tape and then smoothing the epoxy with a gloved finger soaked in rubbing alcohol.

Using this technique we were able to get 4 fillets done in about 30 minutes and all 12 cast in 3 days.

The next step is obviously the dreaded sanding. We like to use the 3M flexible 150 and 320 grit sand paper. After fairly aggressive sanding to smooth down the edges we apply a generous amount of Elmers color changing wood filler. The wood filler helps to fill in those gaps and imperfections and is easy to work with. After letting the wood filler set overnight it was lots more sanding to take the filler down to almost nothing.

Cleaned up the booster/tail cone section with a wipe down using rubbing alcohol soaked paper towels and then set it aside to wait for painting weather.........

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