Tip Ribs

The rib at the wing tip bow is a smaller rib made of 3/8" sq. spruce cap strips with 1/16" plywood gussets. The are no internal sticks. A new rib jig was needed. A piece of 1/2" plywood 24" x 48" from Lowes and a drawing of the rib and we're ready to build the jig. I only need 1/2 of the sheet so the rest of the plywood was used to make some 2" strips of wood to stiffen the jig. I know you can just use a piece of plywood, but I just can't use a warped jig to build ribs. Also the space under the jig board allows screws to stick through without worry of the length of the screws.

The drawing was glued and taped to the top of the board and then waxed with carnuba wax to keep glue from sticking. The drawing took longer than all this building work. The factory drawings show the same rib as the TEN but that is not exactly correct. The aileron arrangement is different on the TEN. As a result the ribs for the lower wings are longer and the upper are shorter than on the TEN. I decided to make them all long and trim them to fit for the upper wings. They did design the taper at the end of the spars so the same basic rib fits both upper and lower. The ends if the sticks have no gussets and get trimmed and positioned to fit on the wing.

The 3/8" sticks need to be steamed and bent at the forward spars. I could have made form blocks like I did for the main ribs but we are just making 4 ribs total. Therefore I made the form blocks part of the jig. The sticks are left in the jig 24 hours to dry the wood before adding the gussets. I over bent the top stick slightly to help with spring back. To make the block I used a sheet of overhead transfer plastic and drew the block shape on it with a permanent marker. It doesn't have to be perfect because I'll belt sand the block to fit. Cut out the pattern and trace it on the block. I use these projector sheets rubbed onto my computer screen to freehand draw complex curves with washable markers and then draw with the CAD system.

Holding blocks for the sticks are cut from 1-1/4" dowel. I use a piece of tape as a guide to cut the length. You can't use the fence because the block will get stuck next to the blade until the saw flings it out.

I drill the off center holes in the blocks with a vee block on the drill press because it make it easier to hold them. The paint bucket is my parts catcher, better than the floor.

I countersink the holes because I use flat head drywall screws and the countersink keeps the block from splitting when the screw is tightened.
The blocks are laid out on the board to make sure I have enough.

.

.

.

.

.

.

.

.

The final position of the blocks varied a little because I bent a stick as I installed them to make sure where they were needed to hold the sticks to the lines.

After steaming the forward ends of the sticks were quickly bent using the top of one of the form blocks before installing in the jig. The holding block at the front of this rib is removed to do this.

.

.

.

.

.

.

.

.

While the bent stick is still hot it is quickly installed in the jig.

.

.

.

.

.

.

.

.

The end of the lower stick on this rib had to be cut to length so I could bend the last stick on the top of the block.

.

.

.

.

Once the last stick was bent the holding block at the front end of the rib had to be quickly reinstalled.

Adjust block to hold stick tight and in the correct position.

.

.

.

.

.

.

.

.

Sticks in the jig and drying before adding gussets.