Brief Description: De-rivet spar caps inboard & install web doubler
As noted on 5/27, I accidentally dented the spar cap web while driving the 3/16" solid rivets. Per discussions with Caleb at Zenair, I am installing a 0.040 spar web doubler to reinforce the dent area. I'm placing the doubler on the front of the spar because it would be difficult to flex the new extruded angle around the doubler..
1. Cut the doubler 212x100mm so that it would engage 3 spar cap rivets with adequate edge distance, and not obstruct the attachment of nose rib 3. I beveled the outboard edges of the doubler at ~30-45° for 39mm on top and bottom to make it easier to slip the doubler under the spar caps.
2. I removed all the spar cap rivets to one rivet past the outboard rivet that would engage the doubler.
3. One rivet stuck in the spar cap, and I could not drive it out with the 3/16" rivet gun punch. I postulate 3 causes for the failure:
- The two jigs supporting the spar were too far apart, allowing the spar to flex under the impact of the rivet gun.
- The clamp holding the spar cap-web assembly tightly together was a bit (~0.25") too far from the rivet being drive out, and thus allowed the assembly to separate when the gun impacted the rivet.
- The rivet was extra tight.
I believe that a combination of the 1st two causes were the likely cause of the problem.
4. I drilled a 3/32" hole through the rivet, in an attempt to reduce the friction between the rivet and the spar caps. Then I cleaned up the end of the rivet with the 3/16" pin punch. Finally, I used the rivet gun and 3/16" punch to drive out the rivet. A small amount of rivet material was left along the edges of the hole. I removed that material with small pick.
5. I slipped the doubler behind the the spar cap doubler. It was tight fit, but I was able to drive it into position using a block of wood and a small hammer. See Figs. 1 & 2.
GOOD IDEA: I clamped a couple of angles to the spar cap angles at the spar-spar tip joint to minimize bending of that joint while handling the spar for the upgrade. See Fig. 3
Doubler in place between spar web and spar cap doubler
Edge view of doubler.
Angles to eliminate bending of spar-spar tip joint
