Rib attachment

Not much work today, mostly experimenting with the rib attachment and leading edge shells. 

I attached only the outermost two ribs and used the method as described in the drawings.  I first pulled the fiberglass tape around dry, situated the fabric, and lightly marked the edges with a thin sharpie.  After removing the dry glass, a quick rough using 220 grit sandpaper within the lines gave some tooth for the epoxy to grab.  When I mentioned sanding aluminum to a colleague, he warned about removing the oxide protective layer and inviting corrosion.  With the epoxy sealing out the surface scratches, hopefully surface corrosion is no longer an issue.  Anyway, a good wipe with alcohol cleaned the surface and prepped for epoxy.  After adding the epoxy and clamping the fiberglass tape to hold it all in place, it cured for a few hours in the warm sun.

Several leading edge shells were added temporarily just to take another look at this process.  The outermost one had to be cut down an inch or so to fit the reduced width spacing, which was easy enough with a new, sharp Exacto blade.  After it was in place, here's a look at a few of the leading edge shells held in place with masking tape.

I'm considering to put a layer of fiberglass on the back of the foam prior to bonding it in place.  If I also add a layer on the front (after sanding), that will stiffen the foam tremendously, providing some ding resistance and hopefully keeping the foam from getting cracked from any poor handling.  Sandlin calls out for a layer of epoxy seal coat for the foam. The Stewart Systems process I'm using to cover does not eat foam like Polyfiber adhesives, but it is a good idea anyway.  I have a bunch of 2.75oz/yd2 cloth that is probably a bit light.  4oz unidirectional fiber seems about right.

Remaining covering is the right aileron, the cabanes, the nose, and then the wings!  I'll be stopping for a load test prior to beginning the wing covering.

Tail covering

The vertical tail took quite literally all day.  I cut separate left/right pieces.

The first half went reasonably well.  It wasn't hard, just a lot of bolts to go around near the trailing edge in particular.  The cutout for the control linkage was a particularly challenging area.  I ended up making a grommet using a piece of thin metal roof flashing.

The flashing was bonded onto the skin and then a larger patch put on top.  Perhaps the slit could have been shorter, which I'll know after a full reassembly.  With the long slit cut, the grommet deformed a bit relieving the tension in the aft portion of the covering.  Meh, it'll be okay.

 After an evening of covering the second side, I got to the point of match drilling the new tail bracket to fit the tail on.  It's now fixed in place and fully remounted.  The controls have been re-rigged as well, and they work fine.  It's weird having the skins attached.  Just different.

To another day...

A little more covering

I knocked out covering of the two flaps.  They were quick, being rectangular.  Took just one evening each, and that was just enough time between getting home from work and needing to head to bed.  I forgot how the covering task wasn't hard, just takes some time.  Here's a mid-process shot.

The ailerons are now on the bench awaiting covering. Those should take a couple evenings since they're just a bit larger and also have the nice long curve near the tips.  But I'll get to those later.

The tail needed some cleanup work before covering.  It was dusty from sitting in the garage and was easy enough to wipe clean.  I took off the flying wires, control cables, and brackets in preparation for installing the covering.  Then I took a closer look at the foam spacers during this cleanup and just wasn't happy with them.  The epoxy was cracking off the aluminum in places and just wasn't carefully applied back in May 2010.  Instead of covering over this, it made more sense to take care of replacing it now.

After a punching out the foam and a bunch of scraping to remove the flaking epoxy, and some additional clean-up with isopropyl, the tail section looks much, much cleaner, and almost ready for covering.

This part needs to be replaced.  It might be fine, but there is no reason to stick with a part I'm not satisfied risking my life on.  I built this bracket to the specifications in the drawings, but apparently the hole in the horizontal stabilizer didn't align perfectly.  Adding a shim washer made the fit work, but, yuck.  I'll order some more aluminum channel and match drill the holes next time to not need the washers.

That's all for today.

Some simple covering

I took a long break from working on Goat to do other things.  Life.  The EC Goat guys beginning to cover helped encourage how far behind I have gotten.

One elevator half was prepped for covering a long while ago.  Unfortunately, I put the adhesive onto the surface and didn't do the covering.  After months of sitting, it seemed prudent to remove it and start over.  It took a LOT of rubbing with my fingers and some scraping to remove it all. Hours of work.  Don't leave work half completed...  Interestingly, the adhesive is like a very sticky goo.  You can get it off the surface of aluminum one little bit at a time.  It appears the adhesive works by being in shear and having ample overlapping surface area.

After clearing the old adhesive yesterday afternoon, I started anew this morning.  Put cloth tape over the sharp corners of rivets, tube edges, and bolts.  Add adhesive around the perimeter and let dry.  Place the fabric down gently into the dry adhesive on the first side and smooth out all wrinkles.  Iron down (~225F) around the edges, working out wrinkles.  This is the stage of the first photo.  Add adhesive around the edges again, letting dry.

 

Come back and trim the excess, then iron it down inside the perimeter.  Flip to the second side.  Add adhesive about 1" around the perimeter of the first side, let dry.  This is the second photo

Once that perimeter is dry, pull the fabric around and start working carefully to remove all wrinkles, using the iron to help shrink the edges.  Come back with pinked shears and trim to that same 1" overlap.  Iron down, and definitely remove all wrinkles.  Finally, add another layer of adhesive and wipe off while still aggressively wet.  Let dry, then do a final ironing over the overlap to set the adhesive, and do a final shrinking over the whole thing.

I also added reinforcements over the hinge eyebolt penetrations through the covering.  These were a circle traced onto fabric, cut out with pinking shears, and a small slit to slide over the eyebolt.  First slid this into position and traced the outline, then added adhesive to the skin fabric, then pushed the patch down into the wet fabric, wiping up excess.  After that dried, ironed down the patch into the adhesive, then add adhesive and wipe away excess.

This now completes the horizontal tail to include both the fixed and moving portions.  These need to be painted and they'll be ready to go.

Next up is probably the flaps.  Those should be easy, since they're just large rectangles.  Next is probably the ailerons, again because they're mostly just large rectangles.  No formal plans beyond that, lest I get ahead of myself!