Lower Left Wing - Outboard Solid Spruce Compression Rib

 The 2nd, light, and 3rd, heavy, compression ribs use the same concept for the upper and lower wings.  The 4th compression rib, outboard end of bay 3, is done differently.  Apparently the loads are higher at this rib in the lower wing because the rib is made from solid 1/4" spruce with 1/4" x 3/4" spruce cap strips.  Maybe they were concerned about ground handling when someone is pushing the plane holding the wing tip.  This rib also has the trailing edge wire and wing tip bow attached to it as well as being a compression rib.

 I'm getting better at not assembling too much in one day.  Put some pieces on, let the glue set then add some more parts the next day.  The first day I just did the center rib web and it's corner blocks.

The rubber pads on the trigger clamps make it easy to just hook them against each other to cross clamp the corner blocks.

 The aft portion of this rib is 1" shorter then a normal rib.  I suspect they did it to make the tip bow laminations some convenient length.  We'll see when I make the tip bows.  I had missed this when I made the rib pieces so I had to shorten the rib.  Fortunately I hadn't glued it in place.

The next day the aft and nose portions were glued on.

 The drawings I use for most of this were made in the summer of 1930.  That's 4 years after my plane was built and 3 years after the last NINE was built.  As a result there are inconsistencies, some of which can only be called mistakes.  This older drawing  isn't dated but based on the other related drawings it was drawn in December of 1926 by Paul Walton.  At the time they were working on the stress analysis, etc. to apply for the Type Certificate, issued in 1927.  Paul had started with WACO as a rib builder and at this time, and when my plane was built, was the supervisor of the wing assembly department.  This drawing has very little detail.  They weren't using it to build planes.  It was needed for the Type Certificate and I believe, since Paul made it, it is an accurate layout of how they were building wings in 1926.

The nose rib in this position on the upper wing is a shorter rib because the wing tip bow starts bending in to give a nice curve.  That's what this drawing shows for the for the lower wing.  The newer drawing shows the full length nose rib with the tip starting to bend after this rib, but also shows the part number for the shorter rib.  Go figure.  I assume it is a mistake. 

 I went with Paul and the shorter rib.  I can't imagine any reason the shape of the tips would be different between the upper and lower wings.

 The portion of the cap strips from the aft spar to the trailing edge is widened from 3/4" to 1 1/2".  The factory made these from 1 1/2" wide stock and cut the forward portion down to 3/4".  I've chosen to glue another piece of 3/4" spruce to the wider area.

 I tapered the trailing edge of the lower capstrip to the upper curve of the rib, but left a little for a final trim to fit.  When the glue is set I'll trim it and glue on the upper cap strip.  I'm sure the factory made these as a finished rib and installed it.  For me it was easier to build this rib on the wing to be sure it all fits tight.

The capstrips were steam formed like the other ribs but I needed the angled clamp at the nose to hold it tight.  I thought a nail there would have just split the rib web.

Lower Left - Heavy Compression Nose Rib

 I decided trying to get everything fitted and clamped around the strut fittings in one shot was more trouble than it was worth.

I glued on the nose rib and the outboard plywood blocks.  Now that the glue is set I'll add the little support blocks and do the inboard blocks.

 This made it much easier to get the blocks in position, clamped, and nailed.

Lower Left Wing - Aft Portion of Heavy Compression Rib

I'm Back working on the lower left wing.

 There is no aileron on the lower wing so the ribs all continue to the trailing edge.  The heavy compression rib has the aft portion of a light rib to complete it.

 The ends of of the cap strips continue forward of the aft spar and are clued to the side of the heavy compression rib.

Those cheap clamps are so handy.

 The strut fittings get all the blocking like on the forward spar of the upper wing.

 I like the little support blocks for all the free ends of the blocks.  Forward outboard corner of the aft spar.

 Aft outboard corner of the aft spar.


Aft inboard corner of the aft spar.

 In the forward inboard corner there is also the aileron cable pulley support bracket.  There is another bracket that mounts in this and holds the pulleys.  The lower bolt is actually in the little block below the spar.

 I used a piece of scrap from the tip of the spar to make the block.  The bolt hole is at the edge of the block so I drilled it before cutting the block to thickness.  The idea was that the hole was less likely to wander out the side if I drilled it in the middle of the block.  It also gave me a wider area to set flat on the table of the drill press.  I still used a square behind the block to help keep the hole square.

You can see, by sawing it after drilling, that the hole is right at the edge and pretty straight.

 I could have made a clean cut for the angled sides using the table saw but I'm sure it would have cost me a finger doing the second side of the triangle.  Instead I used the band saw to make a rough cut and sanded it on the belt sander with a square push block behind it.  A blood free operation and a nice smooth radius at the top.

 The block is glued and clamped to the lower face of the spar.  The position is controlled by the bracket. 

The only down side to what I did was the bracket, backing plate and lower bolt are all glued in position.  I should have nailed the block to the spar, after clamping, to assure it wouldn't move, and then removed the bolt and parts.  There is no reason to remove them but I don't like them glued in place.  Hopefully I'll remember on the next wing.  I did discover another error on the wing drawing.  There is some wood needed to create an opening for the aileron pulleys, and to attach the cover.

Rib Lacing Stick and Leading Edge Plan

Typically we use twill tape laced in a zig zag between ribs to hold them from twisting between the spars.  The tape is place half way between the spars.  You start at the root end of the wing and go from the bottom of the root to the top of the next rib then back to the bottom of the next rib, etc., wrapping around the capstrip of each rib as you go.  When you get to the wing tip you wrap around it and then keep going back to the top of the root rib, forming an "X" between each rib.

 WACO did this by glueing a stick of the 1/4" x 3/8" capstrip wood, the length of the wing, on the inside of the rib capstrips.  The drawing shows the stick 16 7/8" from the center of the rear spar to the center of the stick. 

So far I've only done the piece on the bottom of the ribs out to the secondary strut.  I need to complete the wing tip bow to finish this to the wing tip.  I also need to figure out how to assure the saw horses don't break the strip along the upper cap strip.  When the wing is setting upside down, and top of the spars are resting on the saw horses, the top stick would get broken.  I need to modify my Cessna 140 wing stands to use with these wings.  They hold the ends of the wing so you can rotate the wing to work on it.

My plan for the leading edge wood strip is to cut it from a piece of spruce 1 1/16" wide by 1/2" tall.  I think I can get it to near net shape with 3 saw cuts.  Then I'll glue it to the ribs and finish shaping it by hand on the wing.

Before I do that I'm going to get the lower wing, I started, up to this same point, then do the leading edge and wing tip for both wings at the same time.

Blocking Around Strut Fittings

WACO put blocks of wood around the wing strut fittings to provide a place to attach the fabric.  They tacked the fabric to the blocks.  Today, using synthetic fabrics, we would glue the fabric to the blocks.  For a lot of planes you just make slits in the fabric for the fittings to stick through and then put reinforcing tapes or patches around the fittings.  Using the blocks makes a more finished job, you still put tapes or a patch.

 On the outboard side of the strut fitting, 2 pieces of 1/4" plywood are used to make it level with the wing rib.

I put a small block of spruce under each unsupported end of the plywood.

 The diagonal, flying wire, end of the fittings has a piece of 1/4" spruce between them. 

The blocks on the sides of the spar are 5/8" square spruce.  A saw kerf along one side of the block provides clearance for the fitting.

 The fitting prevents gluing most of the block to the spar so I've added a support block, glued to the rib.

 The joy of having enough clamps when you need them.

 Because of the aileron cut out, the rear spar is a little simpler.  There is just the block between the fittings and another piece of the 5/8" spruce on the inboard side.

I notched and glued the end of the stick to the rib stick and put a small block under it just to be sure it was supported.