Saturday, July 18, 2020

Varnishing the Lower Left Wing

I'm using Oil Based Polyurethane Spar Varnish to have a finish which is flexible.  The idea being that as the wood expands and contracts over time the varnish doesn't crack allowing moisture in.

 I started by varnishing the big areas first, wing walk, spars, etc.  A 1 1/2" tapered brush is about perfect for these areas.
 With the big areas done the problem was how to varnish in the corners of the ribs where the gussets are attached.  I was at the hardware store and saw these 1" wide by 1/2" thick foam brushes for $0.79.  They are pointed, like a paint brush along the tip, so I took the scissors and added a point on the flat side to fit the corners better.

 That worked well.  It was a little big for the small areas, but I was able to get varnish in them.

 It only lasted a few minutes before the foam fell off.  Bummer, but I like the idea.
 I decided to make my own.  I had some similar open cell foam, unfortunately a little dirty but good enough to try it.  I also had 3 sizes of craft sticks, wide tongue depressors, Popsicle sticks, and skinny coffee stirring sticks.  I also used the foam from a couple of the ones I bought.

Split the foam open and glue it together with Contact Cement.  It just has to dry for about 15 minutes before closing it together.

The skinny ones worked best but didn't last long.  We need more of them.

 I had some softer foam, which didn't last as long in use, but I have plenty of it.  I sliced off some pieces 3/8" thick, the same width as the rib sticks, from a 2" thick piece of foam.

Then I cut them to width.  I tried some more 1" wide and the rest 3/4" wide, they worked best.

 Just take a 30 degree breakaway knife, stab it in to the edge about 3/8" from the end.

Then cut a split to the other end.  It works.

 Fold one side back and apply Contact Cement to the other side.  Fold them back together and gently press.  Glue ends up on both sides.  Then peal it back open.

Put glue on the stick. Push the end of the stick in the fold to help hold the foam open while the glue dries, 15 minutes.  When it's dry gently squeeze it shut and let it dry overnight.

 Point the ends with a pair of scissors and you're ready to swab some varnish.
 The wider, 1", ones were nice in the big nose rib gussets but you need the flexibility of the coffee stirrer stick.

In the end the only ones that worked well were the 3/4" wide ones for all inside surfaces.  You can feel it slide easier as you get the wood coated with varnish.  It doesn't take much varnish to do the deed.  That little piece of foam will hold a lot more varnish than you need.

 This would be a fools mission without the rotating stand.  I varnished from one side of the wing on a couple ribs, then walked around and did it from the other side.  Then I rotated the wing 180 degrees and did from each side again.  It's slow but you miss a lot of little spots from any one position.  It takes about 2 - 3 hours per coat per wing and uses 1 1/2 to 2 quarts per coat per wing.

I got 2 - 4 ribs per swab before they started falling apart, so I made a bunch of them.

 I borrowed my wife's Handy Paint Pail.  It has a clear plastic liner, a strap to hold it on your hand, and a magnet to hold the brush while using a swab or rotating the wing.  Much easier than holding a quart can, which I kept tipping and pouring varnish on the ground.  At $45 per gallon you do not want in poured on the ground.

Along with the swabs I'm using a 1" brush for everything not needing the swab.

 By the end of the first coat I was getting pretty good at this.

 I decided I needed a can for cleaning the brush.  There are a lot of solids which settle to the bottom.  They make a mess when you stir them up cleaning the brush.  I made a grid from 1/2" hardware cloth with the edges folded down so there is about 2" for yuck to accumulate.  The paint thinner is an inch or so above the grid.  It works great.

 Finally a wing with 2 coats of varnish.  I still need to put 2 coats of epoxy varnish where ever the fabric will touch.  It's about $90 per quart so it only goes where fabric will touch.  The solvents in Dope or Poly-Brush will lift regular varnish if it's not protected with the epoxy varnish.  It needs to dry for a week or so before putting on the fabric so no rush this minute.  I only put 1 coat of spar varnish on areas getting the epoxy varnish.

After taking the pictures of the wing I went inside to work on our big printer which we use for printing banners and tee shirt transfers.  There were these nice foam swabs I'd forgotten all about.  They work great in the small areas and the 3/4" homemade ones work great in the nose ribs.  We buy them in packs of 50 from our distributor, but I've seen packs of 200 for $18 on line.

On to the next wing.

Friday, July 17, 2020

Upper Right Wing Ready For Varnish

 Before I shaped the tip bow I added a small scrap of the lamination at the joint between the leading edge and the tip bow.  The idea was to be able to shape it to a slightly better transition.  I tapered the end so it would fit in the joint better.  I think it was worth the trouble.

 I followed the same process as the last wing for shaping the leading edge, plane, file, sand. 

The tip bow came out great using the disc sander for most of the wood removal.  I did it outside so I wouldn't make such a mess in the workshop, much better.

This wing is ready for varnish.

Now I need the remaining spars from Aircraft Spruce, help guys.

Friday, July 10, 2020

Upper Right Wing - Tip Rib and Tip Bow Braces

 Building the tip rib went about the same as the last wing.  I fit the end of the rib capstrips an glued the rib in place.  The vertical sticks were glued to the spar. 
 Once the glue was set the corner gussets, at the spars, were added.  The bracing sticks and their gussets were cut to fit, and glued in place.

The lower rib stringer and the filler blocks along the bottom of the rear spar were finished.

I still need to add the upper rib stringer and a couple filler blocks on the top of the rear spar, and carve the tip bow to shape.  I think I'll move the wing to the driveway to do that.  I made a sawdust mess in the shop last time.

Monday, July 6, 2020

Last Lamination on Upper Right Wing

Yesterday I went back to the airport and figured out the Fly Baby won't start because neither magneto is firing.  That was quick, so I went home and glued the last lamination on the tip bow.

The next task will be to install the tip rib and figure out what happened to the magnetos.

Sunday, July 5, 2020

Leading Edge On Upper Right Wing, Varnishing Lower Left Wing

 It's been a busy day.  I worked on the Fly Baby first thing this morning while it was coolish at the airport.  Then I came home and glued the leading edge to the Upper Right wing.
 We mover the Lower Left wing to the tent in the driveway.  I have to push the C-140 out the other end to be able to rotate the wing all the way around.
 I started varnishing.  I did all the areas I could do with a 2" brush, wing walk, spars, etc.  I have an idea for getting into the gussets.  I need to run to the hardware store.

I'm using just over 1 quart per coat per wing.  I expect I'll be well over 2 gallons when I'm done with all for wings.  I've got about 2 hours doing the easy bits.

Back to the airport to work on the Fly Baby this evening.  It will be flying again soon.

Upper Right Wing - Next 2 Tip Bow Laminations Added

The next 2 laminations are glued in place.  The leading edge strip and last lamination will get added after the glue sets up.

Saturday, July 4, 2020

Upper Right Wing - First Tip Bow Lamination Glued in Place

 I decided to do this bow slightly differently then the one on the lower wing.  Now that I have an idea how it all fits I've put the glue blocks on the ribs and spars first, then glued on the lamination.  The risk is if I over grind a block, trying to get a good fit, there's no putting the wood back on.

 The blocks on the nose ribs are easy, they just have to be positioned carefully.  The pin nailer helps keep them from sliding under the clamps.

For the spars I used the old bow to draw some guide lines then added blocks to give a good sized surface for the lamination to glue to.

I only did the forward block on the front spar since it was easy and this bow doesn't get the ground handling like the lower wings.

On the upper wings the tip bow ends at the rear spar because of the elephant ear ailerons so there can only be the block on the front side.

 A rough cut was made on the blocks and the first lamination clamped in place.  The square was used again to get the correct wide point in the bow.  The little clamp is my guide.

 With the lamination in place, pencil cut marks were made. 
I then ground of a little and did a fit check until It fit snug to the block.

An inspection mirror was handy to see the gap better.

 Once the grinding was done, so the lamination fit, the extra wood was ground off the top and bottom, and the corners chamfered.

 The process was repeated for the rear spar.

The band file worked well to remove excess wood at the corner, right into the trash bin.

 The lamination was glued in place, nailed to prevent sliding under the clamps, and clamped snug.

Once the glue is set I'll add the next 2 laminations.