Building the butt ribs for the upper wing - 5

Once everything was cured I pre nailed the entire butt rib profile so I wouldn't have to deal with this while spreading the epoxy.

I did not let the nails poke through anywhere on the rib plate.......yet!

Once the nails were all started I very carefully positioned the nose tip / cap strip pre-glued assembly on 1/8" bobbed butt plate making sure it was aligned perfectly. I then set it on the table and tapped on 4 nails on the back side of where the nose block goes. This helps in assembly once the epoxy is on. The nails self alight with the divots.

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Building the butt ribs for the upper wing - 4

Once I was sure the bobbed reinforcing block was sized correctly I glued it and nailed it.

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Building the butt ribs for the upper wing - 3

The trailing edge, which is the bobbed profile, has a reinforcing block glued and nailed to it. The block is 1/4" plywood.

Instead of trying to make the actual part I made a pattern from 1/8" plywood to see how well it would fit. It was an unnecessary step but it did work well. Once the pattern was made I just traced it to some 1/4" plywood and made 2 of them, one for each wing (right & left).

NOTE: I made the upper and lower surface of the 1/4" reinforcing plate a little fat so when it's glued it sticks past the actual butt rib pattern that was made earlier. I did this so once the entire butt rib was made I could could sand it to match the butt rib on the 12" sander making a perfect surface edge profile.

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Building the butt ribs for the upper wing - 2

With the bobbed profile complete the next step is similar to the way I did the other ribs. Remember how I pre-glued the capstrips to the other nose rib blocks? Well, this method of using the jig is similar except the cap strips get notched to mate up with the nose rib. The photos do a better job of explaining it than typing.

What's really important here is to make sure the cap strips are glued flat, or parallel, with the nose block.

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Building the butt ribs for the upper wing - 1

With the 14 normal ribs for the upper wing complete the next task is to build the butt ribs. The butt ribs for the upper wing are made from pieces of 1/8" mahogany plywood reinforced with a 1/4" nose and tail block. For the cap strips the plans call for 1/4" x 3/4".

I made the special cap strips by cutting them out of an old piece of spar material.

The profile of the 1/8" plywood butt rib was made by holding a normal with rib on top and tracing it with a fine pen. To make it accurate I decided to leave the gussets off the normal wing rib so the surface would lay flat and make tracing easier.

Once traced, I profiled it on my 12" disk sander and fine tuned it with a mill bastard file.

The profile of the butt rib is unique because the trailing edge has a bobbed profile. This helps make the half circle cut out in the middle of the wing that sits centered with the cockpit. I pulled measurements for the bobbed profile to give me a length but I drew the curves free hand with a pencil and gently ground it using the disk sander.

Below are the photos, click on the photos to enlarge.