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question re- fiberglass canopy skirts

Desert Rat

Well Known Member
Hey guys- I have a question for Larry Larson or really anybody who's done fiberglass canopy skirts and windshield frame.

If you go this route, how much gap does the sika cause between the fiberglass and the canopy or skin in front of the windshield etc. You have to leave some room for sika expansion right?

The reason I ask is that the RV14 videos show the windscreen fairing being laid up in place and they make a big deal about the fwd edge being feathered into the foredeck, which seems aesthetically pleasing, but then again being able to pop this thing off the airplane for finish sanding then sticking it back on seems pretty appealing as well.
 
Sika

Hey guys- I have a question for Larry Larson or really anybody who's done fiberglass canopy skirts and windshield frame.

If you go this route, how much gap does the sika cause between the fiberglass and the canopy or skin in front of the windshield etc. You have to leave some room for sika expansion right?

The reason I ask is that the RV14 videos show the windscreen fairing being laid up in place and they make a big deal about the fwd edge being feathered into the foredeck, which seems aesthetically pleasing, but then again being able to pop this thing off the airplane for finish sanding then sticking it back on seems pretty appealing as well.

It's really a builder decision although I don't know how to layup with a planned gap for Sika. That's more brain cells than I have left. :D

However, if it helps.
I did fabricate several samples with plexi, metal & fiberglass. All were bonded with Sika Aktivator, Primer and Sika. Basically just a thin fay seal. After curing I failed them. It took all my 200 lbs and strength with a vise and pair of pliers. All the fiberglass samples ripped the layers apart. The Sika was still intact. That said, I didn't put them in sun and freezing cold but my gut tells me it's not letting loose.

My windshield trim is fay sealed. My idea was to bond it like tank parts and seal out the weather. Coating was applied to both surfaces then the parts stuck together. A little oozed out and was formed into a nice fillet. The thickness wasn't enough to change the fit from the dry layup. I would estimate 1/32. I did have tape on everything for the layup so the Sika is probably the same thickness.
Hope that helps.
 
When I did my canopy with Sikaflex, I read all of their product literature. I seem to recall that they wanted ~1/8" of material for thermal expansion for the typical yacht window that was a flat plate of acrylic around 6-8 feet on any side. I can see why they specify that for such a large flat plate of acrylic.

Given that our canopies are much smaller, and curved, you can probably be very safe with just a 1/32" amount of sealant under the plexiglass fairing.
I did 1/32" along the sides of my canopy where the longerons and canopy rails all come together by putting a strand of fishing line under the bond area. The fishing line prevents all of the Sikaflex from squeezing out and assures a consistent and minimum amount under the plexiglass.

After I started flying, I found that my 1/32" gap between the sides of the canopy and the frame has been just fine from temps below zero to 119F. No apparent stresses from thermal expansion along that few feet of distance. My canopy is a tip up and Van's plans say to leave a 1/32" gap between the front window and the rear window. You'll need more like 1/8" there, since on any sort of hot day, the plexiglass will expand quite a bit and will lock the front to rear window gap.

As Larry mentions, I also did some test samples of the Sikaflex bond between the plexiglass to aluminum and that stuff is NOT coming off. I've been flying now for 9+ years and it still looks like new. When I had the airplane painted, the painter used some black silicon sealant along all of the edges to prevent any flaking off of the paint where it butts up against the plexiglass. It looks very nice and I can imagine that the Sikaflex on the skirt would be similar looking.
 
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