Wing Ribs

From "Construction Notes" Falco Builders Letter, December 1990

We're in the process of making new jigs for the wing ribs, and as I was laying out the jigs, I found myself rebelling at the thought of making the ribs as originally designed. Certain parts of the ribs seem needlessly complicated and with some very minor changes we can dramatically reduce the parts count of the pieces that go into the ribs, with no decrease in strength and negligible increase in weight.

At this point, I am in-process on the design changes, but I can describe them fairly easily. On ribs 1, 2 and 14, I want to make the trailing edge part of the rib (aft of the aft wing spar) of solid spruce. That's the way the aileron and flap ribs are made, and we can make them very accurately and quickly on our inverted pin router.

On ribs 1, 2, 3 and 4, I want to make the leading edge part of the rib (forward of the forward wing spar) out of solid spruce, probably including a lightening hole large enough so that it would leave about 25mm of 'meat' at the thinnest points. This will eliminate not only a silly number of parts, but also the difficulty of bending the capstrips at the leading edge.

On ribs 1, 2, 3 and 4, on the ribs between the forward wing spar and main wing spar, I'm pondering the idea of eliminating the plywood gussets and instead using a piece of plywood over both inboard and outboard faces. It would be stronger, a tiny bit heavier, and much more sensible from a production standpoint.

Finally, on rib No. 1, I'm thinking about using a single piece of solid spruce for the upper spine of the rib. This would extend from the main wing spar to the aft wing spar, and would be a good part to profile on the inverted pin router. There would also be a minor change in the framing around the opening for the flap torque tube. I'm thinking of using a single vertical brace there and allowing a little more clearance with the flap torque tube, which is presently rather tight.