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Calling the Sika experts.

Desert Rat

Well Known Member
I'm going the Sika route on my RV7 Slider and will hopefully be at that point in a couple of days. I'm also going to likely take the easy(er) way out and do fiberglass canopy skirts.

I've read a ton of threads and build logs, including Larry Larson's excellent Kitplanes article.

I'm planning to rivet the C-759 Inner Canopy Skirt to the frame with every other hole, then use the open holes to eventually attach the yet-to-be-fabricated fiberglass skirts in position in addition to gluing them on with either Sika or epoxy. So far, I'm just copying what lots of other folks seem to have done.

What's not clear to me is how to Sika the plexi to the Inner Canopy Skirt. Sika claims to need 1/8" gap which is pretty easy to achieve everywhere else, but when you get to the skirts, there is essentially zero gap there.

What do people do here?
 
I'm going the Sika route on my RV7 Slider and will hopefully be at that point in a couple of days. I'm also going to likely take the easy(er) way out and do fiberglass canopy skirts.

I've read a ton of threads and build logs, including Larry Larson's excellent Kitplanes article.

I'm planning to rivet the C-759 Inner Canopy Skirt to the frame with every other hole, then use the open holes to eventually attach the yet-to-be-fabricated fiberglass skirts in position in addition to gluing them on with either Sika or epoxy. So far, I'm just copying what lots of other folks seem to have done.

What's not clear to me is how to Sika the plexi to the Inner Canopy Skirt. Sika claims to need 1/8" gap which is pretty easy to achieve everywhere else, but when you get to the skirts, there is essentially zero gap there.

What do people do here?

Look at post #377 here on my build log. I too had a tough time deciding on this area. Opted for no metal skirt and sikad it to the frame. Works great!

8th picture down in that post
 
Inner canopy frame

...

What's not clear to me is how to Sika the plexi to the Inner Canopy Skirt. Sika claims to need 1/8" gap which is pretty easy to achieve everywhere else, but when you get to the skirts, there is essentially zero gap there.

What do people do here?

There is a bead along the side holding the canopy to the frame. I used the inner piece. Long piece of board will hold it till the Sika cures. Some leave it off and use a large bead of Sika to hold it to the frame.
 
well, I've got to say; it never even occurred to me to just skip the inner canopy skirt and bond directly to the canopy side rail. Since I've already got the lower edges of the plexi trimmed above the level of the side rails, I think I'm locked in to staying with the side pieces at this point.

Larry- are you saying that you just glued the plexi to the inner skirt with no gap? Just a bead of sika and clamp it together to squish it out?

Also, while I'm at it, has anybody used less than 1/8" gap at the bows and spine? I see a lot of talk about using garden hose segments for spacers, and the ones I've got laying around are all 1/16" wall thickness. I suspect that's pretty standard...
 
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well, I've got to say; it never even occurred to me to just skip the inner canopy skirt and bond directly to the canopy side rail. Since I've already got the lower edges of the plexi trimmed above the level of the side rails, I think I'm locked in to staying with the side pieces at this point.

Larry- are you saying that you just glued the plexi to the inner skirt with no gap? Just a bead of sika and clamp it together to squish it out?

Also, while I'm at it, has anybody used less than 1/8" gap at the bows and spine? I see a lot of talk about using garden hose segments for spacers, and the ones I've got laying around are all 1/16" wall thickness. I suspect that's pretty standard...

Honestly I'm betting 1/16" thickness hose would work just fine because keep in mind after you apply the fillet there are areas that are well thicker than 1/8" towards the outside while necking down to 1/16" at the middle. In fact, there are a couple of areas on my windscreen that I needed everything I could get to get it flush with the canopy and there is very little gap indeed between the tube and the plexi; although it is made up for by the thickness of the fillet.

All that being said, make a trip down to Ace Hardware or your local supply store and instead of getting garden hose go to the area where they sell an assortment of rubber/plastic hose. You will find many options with 1/8" thickness.

I'm not sure if you have ever applied Sika but after it cures you will see how insanely strong it is. Before I applied it for the first time I had my doubts and wanted every thing to be absolutely perfect in regard to thickness. Afterwards I saw the light. haha
 
I'm already well acquainted with the Ace Hardware aviation aisle :) I got some bulk tube with 1/8" wall thickness from there the other day for this, but due to variations in the canopy frame that I wasn't able to 100% eliminate, I think 1/16" would make for a nicer finished product. Thanks for the input!
 
Canopy skirt

well, I've got to say; it never even occurred to me to just skip the inner canopy skirt and bond directly to the canopy side rail. Since I've already got the lower edges of the plexi trimmed above the level of the side rails, I think I'm locked in to staying with the side pieces at this point.

Larry- are you saying that you just glued the plexi to the inner skirt with no gap? Just a bead of sika and clamp it together to squish it out?

Also, while I'm at it, has anybody used less than 1/8" gap at the bows and spine? I see a lot of talk about using garden hose segments for spacers, and the ones I've got laying around are all 1/16" wall thickness. I suspect that's pretty standard...

Basically yes. I used the F759 Inside Canopy Skirt as a bonding point. Not sure how thick the Sika was but definately not 1/8". F759 was riveted every other hole leaving the others for clekos to hold the skirt. It gets bonded later creating a very strong sandwitch.
Like Jereme said. Stuff is extremely tenacious when it sets. My personal opinion is don't force the canopy to conform to a uniform spacing. Use the Force! Sorry, watching Star Wars. Find it's happy place with the least amount of stresses. Spacers and clamps force the plexi into localized stresses. Allow it to find it's own shape. It will be pretty close without forcing it. I used a couple clamps along the sides with a chunk of aluminum to hold the sides. A couple more were used center fore and aft. Some places will be almost flush. Others you fill with fillets.
Again, my opinion, I think it's more important to polish edges and eliminate tooling marks.
 
Basically yes. I used the F759 Inside Canopy Skirt as a bonding point. Not sure how thick the Sika was but definately not 1/8". F759 was riveted every other hole leaving the others for clekos to hold the skirt. It gets bonded later creating a very strong sandwitch.
Like Jereme said. Stuff is extremely tenacious when it sets. My personal opinion is don't force the canopy to conform to a uniform spacing. Use the Force! Sorry, watching Star Wars. Find it's happy place with the least amount of stresses. Spacers and clamps force the plexi into localized stresses. Allow it to find it's own shape. It will be pretty close without forcing it. I used a couple clamps along the sides with a chunk of aluminum to hold the sides. A couple more were used center fore and aft. Some places will be almost flush. Others you fill with fillets.
Again, my opinion, I think it's more important to polish edges and eliminate tooling marks.

This is good advice, many people get carried away with clamping. I only clamped mine with F style clamps and just barely enough pressure to keep it in place. Spring clamps which many people use are not the best in my opinion. I used them in the center (where there is good support from the frame and no distortion) but not on the curved sections.

Also, there seems to be some anecdotal evidence that getting primer or cleaner on the edge of the plexiglass has a higher cracking rate. I taped the edges off to avoid this. Not entirely sure I buy the theory yet (not enough data). Like Larry mentioned I think the quality of the edge is really what matters.
 
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What's not clear to me is how to Sika the plexi to the Inner Canopy Skirt. Sika claims to need 1/8" gap which is pretty easy to achieve everywhere else, but when you get to the skirts, there is essentially zero gap there.

What do people do here?

You're slightly ahead of me, and I'm doing a tip-up, but I re-joggled the inner side skirts to allow for an extra 1/8" adhesive thickness:

20210924-05-tn.jpg


...of course, this warped the s*#t outta them, but after much twisting/tweaking, they fit really nicely:

20210926-03-tn.jpg


Hope that helps!
 
If you cut the end of the tube correctly, you pipe a triangular fillet of Sika onto the structure. Due to the high viscosity of the product, you will find that the result is a very uniform 1/8" bed of Sika without the need for spacers that then need filling.

Consider your average windshield replacement fellow - he does pretty much the same and they don't fall out :D

Done 3 now without spacers and I think it gives a much more even and thorough bond.
 
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