Drilling Main Ribs for Electrical Conduit

The next task for the wing ribs is to drill some extra holes in the main ribs to provide a passage for a flexible conduit to be installed to carry wires for the full length of the wings. Wiring is needed for things like wingtip lighting in both wings; pitot-heat and stall warning in the left wing; and the autopilot roll servo in the right wing.

Vans provides a supplemental document to show how to add these extra holes:

I am now drilling the 3/4 inch hole indicated by the Sharpie pen.

I started out by picking a rib with left-facing flanges and locating and drilling a #30 hole as a guide.

With this hole placed, I back-drilled a piece of wood to be used as a drilling guide for the other left-flange ribs.

I used this guide to drill identically placed holes in all of the left-flange ribs. Instead of making a jig for the right-flanged ribs, I used a matching left-flange rib as a drill guide for the right-flange ribs. Using a pair of clecos to align the two ribs, I match drilled the guide holes.

With the #30 guide holes all drilled, I then used the step bit on the drill press to open the holes out to 3/4 inch.

The new holes were then deburred for a smooth finish.

The next step will be to drill the access holes for the pitot and angle-of-attack air lines in the left wing.

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