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.