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.
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