I honestly don't know how I'm gonna fix the spar on my Chrysalis... It is completly missing (both top and bottom) between rib F and G. I guess I could try to splice a small section in and extend some carbon a ways beyond. The ribs missing or damaged are D, E, F, and G. LE and TE match perfectly.

From : Don Stackhouse

The old-fashioned way: with a slightly tricky bit of surgery called a "scarf joint".

Clamp/pin the two haves back together on the building board on top of some waxed paper, flat side down, with the broken leading and trailing edges fitted perfectly back together. C/A the broken leading and trailing edges back together. Now, lay a piece of spar stock on top of the upper spar cap, long enough to reach from a couple inches inboard to a couple inches outboard of the damaged area, and clamp or tape it in place.

Use your razor saw to cut a diagonal 2" long taper in one end of the piece of spar stock, and continue the cut downward through the damaged spar underneath. Make a careful note of exactly how wide the saw kerf is as you're cutting. Avoid cutting into any ribs underneath the damaged spar cap, but cut all the way through the damaged spar.

When you're done, that end of the splice will have a taper that exactly matches the taper you just cut in that end of the damaged spar cap.

Now, you're going to do the same thing with the other end of the splice. However, you need to allow for the saw kerf at both ends of the splice, so when you slip it into position it will fit perfectly between the cut tapers in the original spar cap, with no gaps. Slide the splice piece toward the cut you just finished by twice the saw kerf. The cut end of the splice should now overlap the cut end of the spar by a distance equal to the saw kerf. Clamp/tape the spar splice in this new position, and cut the taper in the other end of the splice and into the damaged end of the old spar below.

Remove and set aside the splice piece, and carefully remove the broken bits of the old spar. Now, test-fit the spar splice. It should fit perfectly, with no gaps between it and both ends of the old spar. If it's too long, you can remove a little more from the ends using the razor saw or a knife. Sandpaper works too, but it tends to clog the pores in the wood, making it difficult to get a good glue joint.

Use epoxy or white glue to glue the spar splice in place. Pre-cementing is a good idea here; rub some glue into both surfaces of the joints at both ends of the splice, then add a thin film of glue on top of that, slip the spar splice into position and clamp it in place. Wipe off any excess glue that squeezes out.

Let dry completely. Remove the wing from the building board, flip it over and clamp it down on the building board so you can splice the underside (you'll probably have to lay the wing diagonally across one corner of the building board so that the panels of the wing on either side of this one don't get in the way). Shim the trailing edge in the area of the break so that the upper spar cap lays flat on the board. Make sure everything is held down square and solid.

Now, repeat the process to splice the lower spar cap.

Once the spar caps are repaired, use some fiberglass tape to reinforce the two scarf joints in each spar cap. One layer should be sufficient. Do not use carbon fiber, its much greater stiffness is likely to cause stress concentrations that will actually weaken the wing at the ends of the carbon. Some glass tape at the break in the leading edge is probably a good idea as well, Tape at the trailing edge is probably not necessary if you have a clean break and a good fit.

Next, repair/replace the shear webs in the damaged area. Once everything is dry, sand the repairs lightly to remove any bumps ( be careful not to cut the fibers in the fiberglass tape over the scarf joints with too much sanding there!), repair the covering over the damaged part of the wing, reset the washout, and you're done.

The scarf joints need to be fit precisely for maximum strength, but other than that it's not that hard to do, looks elegant and smooth when you're done, and gives nearly full strength to the wing, with minimal weight gain.

A 2" taper. Thats pretty shallow of an angle. I suspect one can't simply use a zona saw on this bit of repair. What do you guys suggest using? An exacto blade/saw?

Any ordinary razor saw, Zona, X-acto, whatever, will do. The important thing is to have it as long as practical, and to have the mating surfaces match well.

Don Stackhouse
DJ Aerotech