This tip was sent by Michael Harfst.
An extra note for anyone considering a stiffener for the elevator end rib. I have the fiberglass tips but wanted to add a doubler for the counterweight rib anyway. I had the elevator all finished and sealed up but the nutplates and fairings were not installed. To avoid drilling out rivets, or getting rivet and drilling remains inside the elevator, I made a carbon fiber rib. I just laid up a three laminate fiber rib inside the end of the already installed elevator counterweight rib. I waxed the aluminum rib first so the laid up rib comes out. The lay-up goes over all the rivet heads and matches the rib flange perfectly. I trimmed the carbon fiber flanges about 1/4″ wider than the aluminum ribs.
When I drilled the bolt and screw holes I drilled through the aluminum and carbon fiber rib together. Pull out the fiber rib and install the nutplates on the inside of the laid up rib instead of the aluminum rib. The ribs weigh 2 ounces each (pre-balancing) so this is traded off against the weight, the elevator does not gain any weight. The carbon fiber rib is a bit stiffer than the aluminum rib so the stresses induced by the counterweight load will be carried disproportionately by the carbon fiber rib. Now that I’m done the assembly is rock solid and very stiff.
Here are some pictures of the carbon fiber ribs I laid up. They extend into the elevator so that the stress gets distributed well back into the stronger part of the elevator. The three larger bolt holes are to clear the dimpled areas for the screws. I taped over the rivet heads before I laid up the carbon fiber and it conforms very well to the flutes in the flange. It pops right in and out easily. The rib is three layers of material and I used the vinyl-ester resin that SHAI supplied, which works well with carbon fiber. I, on the other hand don’t like working with carbon-fiber, I keep getting a rash from the slivers. There is not too much else I can say, the pictures are pretty clear. Good luck if you try it. It is not difficult.
