Chapter 25: Skim Coating the Fuselage Top


 

Skim Coating the Fuselage Top

With the fuselage upright and back on its feet, I proceeded the skim coat the canopy and the upper half of the fuselage. 

 

Canopy

After applying the window treatments to the canopy windows, I taped off the windows and applied 5 coats of raw epoxy to the canopy.  I used a brush instead of a roller to apply the epoxy.  Again, skimcoating is applying a coat of pure epoxy (resin + hardener, no fillers), letting it tack up for a while, then scraping most of the coat off with a squeegee.  All that's left is what is a very thin coat covering scratches and filling pinholes.  Repeat 5 times.  Again, I cheat.  I really don't wait for it to tack up.  I'm slow and meticulous enough that the epoy kicks off enough to start taking a set by the time I'm ready to apply another coat.

 

The canopy is nice and shiny right now.  It won't stay that way as I'll sand 99% of it off.  My plan is to sand off the skim coats with the canopy in place on the airplane.  That way I can ensure I sand the canopy along with the other cured skim coats on the surrounding turtleback, forward deck, and fuselage sides.

 

Upper Fuselage

The next day, I prepared the upper fuselage for its skim coats.  I removed the nose hatch and ballast cover and set them aside.  I taped off the door joggles to keep any excess epoxy from adhering to the door joggles.  You can see the blue masking tape in the picture below.  Alot of pain and suffering went into ensuring the hatch and door sat flush onto their joggles.  Alot of pain and suffering went into getting those perfectly spaced seams around the door edges, too.  You don't want drops of cured epoxy ruining the fit. 

 

I had already skim coated and sanded most of the fuselage sides when the fuselage was upside down.  So I had only the top of the nose and the extreme tops of the fuselage sides left to skim coat.  I masked off the already-done areas so I wouldn't recoat them.  When everything was ready, I began applying the skim coats with a brush.  First the nose, then the sides, then the nose hatch cover, then the ballast door, then the canard cover.  (You can see it sitting off the side near the hangar wall.) 

 

 

I didn't use any cabosil in these skim coats.  Again, the good thing about cabosil is that it thickens up the epoxy and keeps it from running on vertical surfaces.  The bad thing about cabosil is it makes the cure epoxy very hard and makes it very hard to sand off.  So I chose not to use cabo.  Be aware that the raw epoxy WILL RUN off the nose and down the sides of the fuselage.  Hence one of the reason the masking tape is there -- to catch the runs.  But it doesn't run off very fast.  So what I would do is coat the nose, then squeegee the nose.  Then I'd coat a side, then squeegee a side.  Repeat on the other side. I'd coat the canard cover, squeegee the canard cover.  (The hatch and door were laid flat, so the epoxy didn't run on those pieces.)  I'd do this for every round of coats. 

 

After the 5th coat was applied, I stayed at the hangar for about an hour until the coats had kicked off.  I would check for runs every 10 minutes or so.  When I certain the epoxy was congealing (kicking off), I peeled off the masking tape.  You don't want to leave the masking tape on during cure.  It will not release and you'll be sanding masking tape in addition to epoxy!
 

The next steps are to treat the windows on the turtleback, do a little bit of prefilling the drip rails, then skim-coat the turtleback.  Once that's done, I'll install the canopy, forward deck, canard, nose hatch cover, and the ballast door.  I'll sand off all of the skim coats at the same time.  I'm really looking forward to having the entire fuselage in final primer!  Yahoo!

 


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