Hello all,
Looking to engage the VAF brain trust on this one. I'm currently replacing the canopy on my RV-8 due to multiple (7) cracks in the plexiglas. I've been using the procedures outlined by Danny King and Paul Dye https://vansairforce.net/community/showthread.php?t=87210 in a thread from 2012. So far, I have successfully removed the old transparency with minimal damage, and have cleaned up the frame.
The problem I've discovered is that the original canopy was attached with #6 screws threaded into riv-nuts in the tube steel frame. As seen in this photo, the rib-nuts have a flange that I am concerned will induce a stress riser on the new plexiglas canopy, and cause another crack.
I've brainstormed 3 different courses of action going forward, but wanted to pick the VAF braintrust. Below are the options I've thought of, but I'd like to hear everyone's thoughts, even if (especially if) they're different than the options I've considered below.
Courses of Action:
1. Sika-Flex. I've been leaning against this option, just because I like the idea of mechanical attachment, and I know that historically Vans hasn't endorsed the Sika-Flex method. If that has changed, and Vans endorses the Sika method, I'd be open to giving it a shot. Also, I have wondered about the long term durability of the Sika given UV exposure. Not intending to start a Sika-Flex vs Rivets debate, but this is why I haven't already glued the canopy on and moved on with my life.
2. Oversize holes and screws. I've considered drilling the holes in the plexiglas up to 3/8" ( to ensure that they clear the .330 flanges on the Riv-Nuts), then using silicone tubing of 3/8" OD and 1/8" ID to serve as a bushing. Cut the bushings slightly proud of the plexiglas, and secure the canopy with screws. The hope is that the bushings would squish, securing the canopy, as well as keeping the plexiglas from interfacing with the Riv-Nut flanges given that it will flex with temperature changes.
3. Oversize holes and rivets. The other option is to remove the canopy skirt, and punch the Riv-Nuts out of the canopy frame. I'm not sure what size hole this would leave in the steel tube, but I'd likely need to drill the canopy for the same size 3/8" oversized hole, then use a soft aluminum pull-rivet into the holes in the canopy frame (which are oversized due to the Riv-Nuts). This gets rid of the flange interaction problem completely, but I don't know if I can find aluminum rivets that are large enough to work in the holes in the canopy frame.
So, the questions I have are;
1. Which of the 3 options (or other options I haven't considered) do you think would be best.
2. Does Vans endorse Sika-Flex as a canopy attachment method?
3. Is edge distance a concern with the 3/8" holes in the plexiglas? If so, I'd need 9/16" of edge distance, which seems like a lot of extra plexiglas. Not sure if I'll have that much available.
4. For Option 2: Is there a good source of silicon tubing with a 3/8" OD and 1/8" ID that is pliable enough for this application? Is a durometer of 50A appropriate for this application?
Thanks!
Looking to engage the VAF brain trust on this one. I'm currently replacing the canopy on my RV-8 due to multiple (7) cracks in the plexiglas. I've been using the procedures outlined by Danny King and Paul Dye https://vansairforce.net/community/showthread.php?t=87210 in a thread from 2012. So far, I have successfully removed the old transparency with minimal damage, and have cleaned up the frame.
The problem I've discovered is that the original canopy was attached with #6 screws threaded into riv-nuts in the tube steel frame. As seen in this photo, the rib-nuts have a flange that I am concerned will induce a stress riser on the new plexiglas canopy, and cause another crack.
I've brainstormed 3 different courses of action going forward, but wanted to pick the VAF braintrust. Below are the options I've thought of, but I'd like to hear everyone's thoughts, even if (especially if) they're different than the options I've considered below.
Courses of Action:
1. Sika-Flex. I've been leaning against this option, just because I like the idea of mechanical attachment, and I know that historically Vans hasn't endorsed the Sika-Flex method. If that has changed, and Vans endorses the Sika method, I'd be open to giving it a shot. Also, I have wondered about the long term durability of the Sika given UV exposure. Not intending to start a Sika-Flex vs Rivets debate, but this is why I haven't already glued the canopy on and moved on with my life.
2. Oversize holes and screws. I've considered drilling the holes in the plexiglas up to 3/8" ( to ensure that they clear the .330 flanges on the Riv-Nuts), then using silicone tubing of 3/8" OD and 1/8" ID to serve as a bushing. Cut the bushings slightly proud of the plexiglas, and secure the canopy with screws. The hope is that the bushings would squish, securing the canopy, as well as keeping the plexiglas from interfacing with the Riv-Nut flanges given that it will flex with temperature changes.
3. Oversize holes and rivets. The other option is to remove the canopy skirt, and punch the Riv-Nuts out of the canopy frame. I'm not sure what size hole this would leave in the steel tube, but I'd likely need to drill the canopy for the same size 3/8" oversized hole, then use a soft aluminum pull-rivet into the holes in the canopy frame (which are oversized due to the Riv-Nuts). This gets rid of the flange interaction problem completely, but I don't know if I can find aluminum rivets that are large enough to work in the holes in the canopy frame.
So, the questions I have are;
1. Which of the 3 options (or other options I haven't considered) do you think would be best.
2. Does Vans endorse Sika-Flex as a canopy attachment method?
3. Is edge distance a concern with the 3/8" holes in the plexiglas? If so, I'd need 9/16" of edge distance, which seems like a lot of extra plexiglas. Not sure if I'll have that much available.
4. For Option 2: Is there a good source of silicon tubing with a 3/8" OD and 1/8" ID that is pliable enough for this application? Is a durometer of 50A appropriate for this application?
Thanks!