I am currently building an RV-7 rudder, and I am considering changing the plan to make rudder top tip removable.
I have already drilled and dimpled the last three holes on the trailing edge on both of the skins (as per plans, since the space is "tight" there, they suggest you to dimple it before the skins are riveted).
Now the problem is that dimples are for the CS4-4 rivet, which uses -4 dimples. The #4 screw would fit the dimple, but the hole is too big for it. #6 screw requires a slightly deeper dimple, but the hole size is about right for it.
Also, the edge distance from the hole is 1/4", which is both defined by the tip rib (because of its flanges facing up) and also it is the minimum edge distance on the fiberglass as per plans (however, this distance is given assuming the CS4-4 rivet).
Here is what I am thinking:
1. Go with #6 screw as the three trailing holes are almost dimpled for #6 already.
2. Unrelated, but trim the fairing so it sits deeper (see the first attachment, currently it hits the tip rib flanges too early so there is a big gap). Or should I just epoxy that gap, as per Section 5.18 (currently the gap is ~1/8").
3. Epoxy a backing plate of aluminum (can I use T-88 epoxy here, since I have it already?) to the fiberglass rudder tip so it adds a bit of the strength. I don't think this is strictly necessary, but aluminum backing strip should remove any concerns about the edge distance. Right?
4. Install K1000-06 nutplates on the fiberglass / aluminum backing plate, countersink fiberglass as necessary to take #6 dimple.
5. See how well it would fit, attaching it to via the three (six) existing holes (without re-dimpling them for #6 yet). In the worst case, I would reorder R-909 and go with the original plan to use CS4-4
6. If everything goes well, re-dimple the holes to #6 (any concerns with that? like metal fatigue on the skin?), drill the remaining holes and dimple them for #6. For re-dimpling I would make female dimple for #6 on a steel plate and drive the male #6 dimple with the rivet gun.
Does that sound like a reasonable plan? Never worked with fiberglass before.
I have already drilled and dimpled the last three holes on the trailing edge on both of the skins (as per plans, since the space is "tight" there, they suggest you to dimple it before the skins are riveted).
Now the problem is that dimples are for the CS4-4 rivet, which uses -4 dimples. The #4 screw would fit the dimple, but the hole is too big for it. #6 screw requires a slightly deeper dimple, but the hole size is about right for it.
Also, the edge distance from the hole is 1/4", which is both defined by the tip rib (because of its flanges facing up) and also it is the minimum edge distance on the fiberglass as per plans (however, this distance is given assuming the CS4-4 rivet).
Here is what I am thinking:
1. Go with #6 screw as the three trailing holes are almost dimpled for #6 already.
2. Unrelated, but trim the fairing so it sits deeper (see the first attachment, currently it hits the tip rib flanges too early so there is a big gap). Or should I just epoxy that gap, as per Section 5.18 (currently the gap is ~1/8").
3. Epoxy a backing plate of aluminum (can I use T-88 epoxy here, since I have it already?) to the fiberglass rudder tip so it adds a bit of the strength. I don't think this is strictly necessary, but aluminum backing strip should remove any concerns about the edge distance. Right?
4. Install K1000-06 nutplates on the fiberglass / aluminum backing plate, countersink fiberglass as necessary to take #6 dimple.
5. See how well it would fit, attaching it to via the three (six) existing holes (without re-dimpling them for #6 yet). In the worst case, I would reorder R-909 and go with the original plan to use CS4-4
6. If everything goes well, re-dimple the holes to #6 (any concerns with that? like metal fatigue on the skin?), drill the remaining holes and dimple them for #6. For re-dimpling I would make female dimple for #6 on a steel plate and drive the male #6 dimple with the rivet gun.
Does that sound like a reasonable plan? Never worked with fiberglass before.
Attachments
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