Source: 2022 Q1 Beartracks, Jay Townsend
Firstly let me say I am not a “handy DIY” type of guy. I undertook this project as a complete novice.
There are probably easier planes to build, but none had the flying envelope of the Bearhawk, so it was an easy choice for me. I am very lucky to have a mentor who has built both a Rocket and a Carbon Cub along with all his tools. My local airport, Heber City, can easily be called a hot bed for experimental builders so I have a great group of guys to lean on for advice. That being said, the rear windows on the
Companion had us all baffled.
Most things building up to this point (getting ready to cover the fuselage) have been pretty straight forward. Ok, I may have called Mark a time or two! Rear Windows have been confusing. We collectively had a lot of discussions which resulted in a lot of head scratching. In the end both Bill (my building mentor) and I came up with a very similar plan the same evening, which is amazing as this had been analyzed for a good 2 to 3 months. I had sent Bill a text early one morning telling him I had figured it out, he texted back that he was looking forward to hearing the solution as he had an idea too. I was planning on installing and gluing in screws from the
outside of the outer frame, to allow the window and inner frame to be attached after covering. Bill had an odd look in his eye as I explained it. Turns out he had a very similar idea, but with a better solution for attaching the inner to the outer frame.
So here ya go, this is how I solved the problem. To begin with, I really wanted the window frame inside the door former, but this makes a potential window replacement without cutting into covering very difficult. First I drilled out the factory rivets to separate the inner and outer frames. I bought 70 Clickbond studs, #CB5000, but they are round, so I had to grind each one to allow the window to fit into the window channel (photo of the modified stud below).

The flat plate portion of the stud is adhered to the inside of the outer frame with special adhesive, creating threaded studs protruding into the cabin. The inner frame is attached using these studs, forming a sandwich with the window plastic. I used denatured alcohol to clean the frame and the back of the stud for bonding using the proprietary Clickbond adhesive that is super strong and fast-acting. Next I put down cling wrap on the inner frame and pushed the studs through the cling wrap. This protects the inner frame from the adhesive. This was Bill’s idea and a brilliant one to keep things nice and clean (photo below).

I put the Clickbond adhesive on the stud backs. The Clickbond adhesive is amazing and sets up in less than five minutes, so it is not really possible to do all the studs at the same time, so I did 1/3 of them at a time. Then I put the outer frame on very gently so as
not to mess up the orientation of the flat sides of the studs, and used clecos and clamps to allow the inner and outer frames to be perfectly matched (photo below).


I also used Knipex “Pliers Wrench” pliers (part number 86 03 250) to align the inner and outer frames perfectly by squeezing the edges so they align. These pliers are the perfect tool as the jaws move parallel to each other, squeezing evenly rather than on an
angle like conventional pliers. This is crucial in my view as you want the studs to line up when the inner and outer frames are aligned.
I also used JB Weld on the top and bottom of the outer frame to allow it to be riveted to the door former while remaining parallel to the door former. Otherwise the joggle of the outer frame would cause it to be at an angle.

I will attach the outer frame to the tabs on the fuselage with solid rivets. I will have to drill the inner frame to allow for the shop head of the rivets. Next I will cover the interior cargo area and glue the fabric to the inside of the outer frame. Then I will cover the fuselage and wrap the fabric over the outer frame, and glue the exterior fabric to the the inside of the outer framer. This will allow me to install, but more importantly in the future, to replace a rear window all the while having nice clean lines of the window frame inside the door former. I will be using acorn nuts to hold the inner frame in place.
This method also makes sliding the window into the channel a non-issue. There have been multiple threads on the Bearhawk forums about the difficulty of sliding the windows in the window frame channel. This also allows you to determine the thickness of the “glass” rather than the channel dictating the thickness you can use, personally I will definitely use a slightly thinker window than the original
frame channel would have allowed.
I know I spent a LOT of time trying to come up with a plan that was pleasing to my eye, hopefully this will save others time contemplating a plan and make life easy should I need to ever replace a window. I am trying to think of anything down the road that may need to be done and how I can best set up the plane during the build process to allow for the needed maintenance.
Editor’s note– Bob likes to slide the window in from the front, but says folks are always free to innovate!