40 - Flap System

Starting on the flap system, I first trimmed the four Delrin Flap Torque Tube Bushings to the dimensions specified. To make this easier, I first 3D printed a template sized to the required specifications, and clecoed that via the bolt holes to accurately indicate where cuts should be made. 

I found that using a coping saw with a coarse tooth blade (~10-16 tpi) worked well to quickly cut through the Delrin to the approximate shape, and then using coarse files to gradually sand down each block to the final shape. Sanding was then completed using 180 grit sandpaper.

Flap torque tube bushing template

Rough cutting the flap torque tube bushing using a coping saw with a coarse tooth blade

Flap torque tube bushing was held to the 3D printed template via the bolt holes to ensure that the final cut result matched the specifications given in the plans

Four flap torque tube bushings cut and shaped to size

Next I match drilled both Flap Torque Tubes to either side of the Flap Crank, by first match drilling to #30 and then #13, followed by reaming to #12. 

With the Flap Horn then slid onto the end of the assembly, I first measured the required width of 24-7/16" and I was then able to use the W-730 Bellcrank Jig to accurately match drill the remaining holes from the Flap Torque Tube into the Flap Horn, mirroring the left and right sides. These holes were match drilled to #30, then #12, then 0.247" and finally reamed to 1/4".

Match drilling holes from the Flap Crank into the Flap Torque Tube. The trick here was to not push too hard while starting to drill, and then gradually increase pressure to finish drilling through the steel. This helped prevent the drill bit from catching the edge of the steel during the early stages of drilling. Of course, lots of Boelube was used as the drilling progressed.

Both Flap Torque Tubes match drilled to the Flap Crank

Flap assembly clamped to the workbench in order to match drill the Flap Horns using the provided jig

With the initial two holes match drilled and clecoed into the Flap Horns, the remaining holes were match drilled and upsized by clamping the Flap Torque Tube in the vise. This made it easier to rotate and hold the assembly in a suitable position for drilling comfortably and accurately

Both sets of holes match drilled and upsized into the Flap Horn on one side of the Flap System assembly

Dates:    April 21 - April 22 2026