Mounting and adjusting the rear side window frames. ![[Rear Windows-20241102201609724.jpg]] Installing the rear window frames is non-trivial. Placement depends on a lot of factors and mounting requires additional parts. It’s a good puzzle if you are into this. After some contemplation the kit parts install very nicely and reflect the solid feel of the Bearhawk. ![[Rear Windows-20241102201624442.jpg]] The kit comes with prefabricated frames. Each frame assembly consists of a planar piece of 5052-H32 .050” (inside) and a formed one (outside). They are riveted together every other hole with -3 sold rivets. The gap between the pieces is intended to hold the clear plastic sheet (typically an 1/8” sheet of clear or tinted acrylic) along with any sealant and the cover fabric (wraps into the gap). ![[Rear Windows-20241102201634165.jpg]] It’s tempting to install smaller windows to save some weight. Many builders have done so. When I built a test frame from carbon fiber it became clear the stock frames solve a couple of objectives very well. Most importantly, they smooth the shape of the fuselage, similar to the stringers. As a matter of fact the stringers are difficult to locate laterally without also considering the windows. Once aligned everything flows very nicely. ![[Rear Windows-20241102201644295.jpg]] With the carbon fiber approach there is difficulty matching the non-planar part of the fuselage. Also the area behind any short windows has a tendency to become concave. ![[Rear Windows-20241102201655986.jpg]] The stock windows solve all these challenges beautifully while also providing good visibility of the horizontal stabilizer and your formation flying friends. The frames come oversized and the mounting and alignment to the fuselage is not easily discernible. Using stringer material works well for the bottom frame but is generally too narrow for the top. For latter I sourced an aluminum angle extrusion, 20x20mm, 2mm strong. The location results from aligning the frame with the stringer and angle extrusion. A bit of further adjustment is necessary to make sure the foremost holes get a good location in the former. ![[Rear Windows-20241102201703626.jpg]] ![[Rear Windows-20241102201714565.jpg]] ![[Rear Windows-20241102201722331.jpg]] ![[Rear Windows-20241102201728113.jpg]] ![[Rear Windows-20241102201745273.jpg]] The transition in the front has many overlapping parts. The outer frame is on top of the door former. This allows for sliding in the acrylic sheet. The inner frame is flush with the former. The support structure is flush with the mounting tabs and touches the former on the inside. ![[Rear Windows-20241102201758022.jpg]] ![[Rear Windows-20241102201807317.jpg]] Finally a word about rivets. The connection to the stringer extrusion calls for blind rivets while the top part of the frame allows for solid aluminum rivets. I had difficulty sourcing -3 blind rivets of sufficient grip length and therefore decided to use -4 rivets for the entire frame.