One of the first projects a new Skybolt builder usually undertakes is construction of the wing ribs. It can be started with minimal investment in materials and equipment and proves to be a pretty satisfying, if tedious start. The choice needs to be made between the plans-type truss ribs, or plywood routed ribs. The ply ribs are much faster to make, and also heavier and a little weaker. The truss ribs are constructed of 1/4" square spruce stock with mahogany plywood gussets. They are amazingly strong and light, but the manhours required to cut, glue and finish each rib is astounding. There are 4 different jigs required for the Skybolt ribs, with some ribs requiring variations so a lot of attention must be paid to the plans.
I made my jigs out of 3/4" MDF and layed out the ribs right on the board, following the plans dimensions. Some people glue the plans down, and build right on top of them, but I found a lot of variation in the dimensions occured when that was done. Small blocks were glued at strategic locations to hold the truss members in place. I bought the plywood nose pieces already cut from Steen Aerolab–although a router with a bushing could easily be used to mass produce the pieces. I started out mitering all the joints until I was told it wasn't necessary. Each spruce piece only needing a 90º joint makes the cutting and fitting progress faster. After cutting the pieces, a layer of plastic wrap is layed over the jig and the pieces bonded with T-88 epoxy. Steel weights placed on the gussetts are sufficient weights and eliminate the need and weight of staples. After the epoxy cures, a router with a straight cutting bit and a bearing is used to trim the gussetts flush, and the other side gussetts can be glued into place. At this pace, it takes a day to produce 2 ribs. Not very efficient. The new Steen Aerolab is selling a jig to do both sides of the rib at once, and selling pre-cut rib stock. Shown at right is an upper wing aileron rib during construction.