The first step was to cut the tapered wing tip ends of the spars. I had lots of ideas for how to cut these in ways which better control the cuts. In the end I took the 7 1/14" circular saw and cut them by hand. I kept the cut just outside the line and cleaned them up with a plane. Spruce is so nice to work by hand.
My next task was to varnish all the areas where fittings will be bolted on. All my reading says Oil Based Polyurethane Spar Varnish is the most flexible and longest lasting. two coats were applied being careful not to varnish areas where glue joints will be made. The factory did not varnish anything. This plane was very much based on practices Bruckner and Junkin learned during WWI. All that work needed to varnish the bits of wood in a wing didn't make much sense if the plane wasn't planned to be in service very long.
The funny thing is that they used a coat of Clear Valspar Varnish as a final finish on the fabric covering. I assume it gave a nice shine. Dope tends to be a dull finish.
Routing the spars reduces the their weigh, but it also reduces the wood to attach the wing ribs. To solve this a piece of spruce gets glued to the spar web to bring the surface back to the level of the flanges. The blocks get glued and nailed to the spar and the rib glued to the blocks and the flanges. The small nails are used to hold things in place while the glue dries.
The front spars are routed 1/4" deep, so sticks of the the same 1/4" x 3/8" spruce used to make the ribs works for these blocks.
For the rear spars blocks made form 3/8" x 3/8" spruce are needed. The flat space between the corner fillets is 7/8" wide. Such short blocks easily split when driving a nail through them, so I made them 1 3/8" long to help. This meant I needed to chamfer the the ends to clear the corner fillets. I figured out I needed the chamfer to end 1/4" from the ends and to slope up 1/8".
I drew a guide line on the table of the belt sander at that 2:1 angle and marked a stop line to control the size of the chamfer. It just takes a couple seconds against an 80 grit belt. I do the grind on the fuzzy edge so I get rid of the burr while doing the chamfer.
The grinding leaves a little burr which is easily removed with the sander. Trust me the factory did not worry about such things as fuzzy burrs.
Most of the line locating the ribs got removed with routing so I made a guide from a piece of 1/2" x 1/16" aluminum angle. You line it up with the lines still on the flanges and the block sits next to the guide for nailing.
That was a clever idea but in practice I needed a couple more hands. I found these little spring loaded clamps were perfect to hold the guide in place. I normally use these when I'm working with aluminum because the rubber ends don't leave scratches.
The one closest to me has the latch handle pointing down because I found you can grip it kid of like a pistol, position it, and squeeze the handle to lock it in place. The one in the back was easy to lock with my thumb. This was easy enough, and worked well enough that it was worth the little time it took.
I'm a Resorcinol Glue guy, but I didn't work the webs down 'till they were perfectly smooth so T-88 seemed a better choice for this.
I mix small amounts by drawing 2 circles. Some of you may still have an old circle template from drafting class. Circles 1 1/8" diameter worked to last about 45 minutes.
The box makes a nice holder so the glue stays at the outlet end.
Post-it notes make a nice, throw away, work surface for mixing the glue. I started with this 3" one and switched to a 4", much better.
The popsicle stick works well for mixing and, in this case, for applying the glue. Get a big box of them.
I put a line of glue on the block and split it with the stick so it would flow out both sides more evenly, to assure a good joint.
The only way to nail these, or most parts, is with this handy, slightly modified,
Great Neck Magnetic Brad and Nail Driver. Really, take the link and go read my old post. I love this thing.
I found 2 nails (3/8") and about 3/4" from the ends worked perfect.
All the front spars with rib blocks installed.
Once the glue dried for a day I used a metal straight edge to check for blocks that were a little high and ones with a nail sticking up above the flanges. You find them real easy with a metal straight edge, just slide it along the spar.
For the few blocks which were too tall, I pulled the nails and carefully used the block plane to shave them down. You just have to hold it firmly and stop it before you get to the flange.
Tall nails are easy to tap down with the nailer, or my cool tack hammer from 7th grade shop class.
When I made the guide I put a notch in the middle of it so it would work with both the front and rear spars. The clamps just worked with the 1 1/4" rear spars.
Even with the longer blocks for the rear spars I still split about 10% of them. I used one 5/8" nail in the middle of the block for these.
I also have the 2 existing rear spars done. The longer Upper spar has the aileron attached to it so most of the aft side doesn't get sticks. The ribs in that area end at the spar.
Lookin' Good.
I hope I remember all this when the other 2 spars arrive.
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