Windows Update

Posted On May 29, 2025

(not the annoying kind that requires a reboot!)

The next challenge I decided to tackle was fitting and attaching all the Perspex (acrylic) windows to the canopy. I completed fitting and cutting of the windows in late March / early April, and then attached & sealed the windows in the last week of April going into May.

All of the windows come oversized and must be cut down to fit. I used the same abrasive cutting wheel that I used for the engine cowling. Cutting the windows is a pretty tedious and iterative process: after first marking off for the rough cut, it took many more iterations to get to a final cut. The windows have multiple curves, and the channel that the window sits in has a beveled edge that is not consistent. Each cut makes the window fit a little bit differently causing additional cuts to be needed for a perfect fit.

Once I was satisfied that I had achieved perfect fits on the two rear windows plus the doors, the next step was to mask off the areas to apply Sika cleaner, primers and UV295 sealant. The build manual says to use 80 grit sandpaper to rough up the surfaces to be bonded; I found this to be incredibly laborious to do by hand (since it’s a small area), so I used a detail sander to do the job instead. As per the manual, I used:

• Sika Aktivator 205 for cleaning the bonding surfaces (after sanding them)
• Sika Primer 206 G+P for the fiberglass side of the bond
• Sika Primer 209N for the window side of the bond
• Sika UV295 for the adhesive / sealant

To protect the areas around the bonding surfaces, I used three different sizes of masking tape; the narrower 1/2″ green tape is easier to fit around curves, while the wider 2″ blue tape protects large areas. I 3d-printed a tool to help spread the Sika evenly on the fiberglass surfaces, as recommended by Henry Rise over at Midwest Sky Sports.

The 3D printed tool is just a spreader with little notches in it to spread out the Sika 295 in a ridge pattern, so that the sika will spread evenly over the sealing area.

The windows are simply pressed into place, and then I used straps to apply light pressure to the window to keep it from lifting as the sealant cures. The sealant starts to set in about 2 hours, but I left everything strapped overnight to ensure a good cure. I didn’t want the straps touching the wet sealant, so I used some high density foam blocks (reused from packaging of some gadget I bought) to lift the straps off the surface, but they also helped distribute the pressure over a wider area. In the near picture, you can also see that I filled in the gap all around the window with a bead of sealant and then used a small silicone caulk tool to smooth it down flat.

The process for the doors was similar, but just slightly easier since I could work on these on a bench.

The windshield was a little trickier due to masking being more difficult. You can’t really apply a line to the inside of the window when it’s in place, so it’s necessary to put the window in place, create a line on the outside of the window, then remove the window and transfer the line to the inside. Otherwise the process was the same as the other windows, but it just took longer because of the bigger size. I learned the hard way that you need to be careful about where you apply masking tape so that it is still accessible after the window is bonded.