fitting Patrol QB rear windows

[Pbruce]

I’m having trouble inserting my rear side windows. The inner and outer window frames are too close to insert the 2.5mm acrylic which was the recommended material to avoid drumming. I have experimented and found that if the edge of the pane is chamfered (tapered for 5/8” where it fits between the frames) it will go in. See pictures. I have not figured out a way to grind that chamfer reliably though. I used a piece of tape as a guide on one, but my grinder cuts right through the tape. Any suggestions, other than separating the frames? I guess 2mm acrylic would help, but prefer not to buy again and still want to avoid drumming.

[Mark Goldberg]

Pat - I would just open up the frames a little so the plexi will fit in. It takes a little time but is not that hard to do. For a time period the opening in those window channels was too narrow. The factory is doing it better now. Mark

[Pbruce]

Ok, I did try that very briefly using a 1” wood chisel but I was making the outside frame irregular and lumpy. So I stopped. What kind of tool and/or technique do you recommend?

[Mark Goldberg]

Perhaps a wider wood chisel. 2"-4" wide. Another possibility is inserting a wedge of wood or aluminum that is wider and tap it around the opening. The wedge would need to be bigger than what you want the opening to be as the material will spring back some.

Builders have successfully opened up the window channels with wide wood chisels without making it lumpy or uneven. Mark

[Pbruce]

Ok. I’ll consider. I have figured out how to chamfer the 5/8” adjacent the perimeter edge using my router table (I think). It may come down to doing both, one, or the other. Thanks for your input Mark. As always, it’s greatly appreciated.

[Bcone1381]

I installed 2mm thick (.080") Plexiglas. My window channels were Circa 2017 and were quite tight. I followed Marks guidance using a 3" putty knife. I opened it a bit at a time so 1/8" material would fit snug. After installing my fabric the 2mm plexiglass went into the slot with little difficulty. I probably should add a finishing tape along this edge.

[Pbruce]

Thanks Brooks. My material is 20% thicker than yours which might explain why I’m having such difficulty. I have been able to chamfer the outer 1/2” of the acrylic panes where they go into the slot so that is helping, but I’m still going to have to stretch the slot in spots.

Did you use any kind of caulking or sealant in the slot, or did you just jam the pane in and let friction do the job? I guess any sealant should be fuel proof, so I’m not sure what would kind work. It seems like it might be tricky to apply evenly as well.

[Mark Goldberg]

You need a sealant at least on the lower side of the window where rain water could pool. Do not use silicon sealant as that can make paint not stick to anything it touches. I have used a 3M stick caulk that Spruce sells. Others have used different sealants. Mark

[Pbruce]

Thanks Mark. I will look for that, and I hear your comments about silicon. Bad, bad, bad around anything which might require paint later. I’m a ways away from actually installing the windows, but I wanted to get at least as far as cutting them to size so I don’t have to store a 4x8 sheet of acrylic. Also to make sure I didn’t have to remove the frames. I seem to be getting close to getting the the panes to fit but still really having a hard time stretching out the gap. I’ll keep at it.

It seems like the appropriate time to install the rear panes is either immediately before painting or immediately after, depending on whether I wish to run the paint onto the acrylic for a quarter inch or so.

I may do this since the front window interior trims stick out visibly beyond the exterior trims in places. I should have anticipated this when constructing the exterior frames. For anyone coming along behind me, I suggest taping the interior trims in place while mocking up the outer. If you don’t have wide enough outer trims to both lap against the door formers and also cover the interior trim, just cut new ones. It takes very little material and only a few minutes, FWIW. Mine are riveted on and I’m not re-doing them for the sake of this minor cosmetic issue.

[Bcone1381]

Did you use any kind of caulking or sealant in the slot, or did you just jam the pane in and let friction do the job? I guess any sealant should be fuel proof, so I’m not sure what would kind work. It seems like it might be tricky to apply evenly as well.

I just finishing installing the fuselage fabric, installed the side windows to check there fit.... nothing more. I will remove them, install a finishing tape around the outer edge of the channel and down into the slot then reinstall the windows before I paint. I don't want multiple sources of coatings to build up in the slot that could tighten up the dimension. Fabric sealant, 3 coats of UV protectant, paint.....that could cause me problems if the slot gets filled. And another builder who is done did it this way. So when they go in next time they stay in.

So, I have not sealed them, but have considered using a sailplane product called Gap Seal Tape. I have some experience flying gliders. Gap seal tape is used to seal things up on a glider. Its like electrical tape....stretchy. I've thought a nice seal could be attained using it, and it comes off without a problem. I'd change the gap seal tape annually. A nice "calking" job would look better. Gap Seal Tape would be easy to install/remove, and keep water out. We'll see. I often change my mind.

https://www.cumulus-soaring.com/store/bowlus-tape-white-1in

[JimParker256]

On RV roofs (campers, not airplanes) they recommend a flexible sealant made by Dicor. It comes in two types: self-leveling and non-sag. For RV roofs, which are a flexible rubber-like membrane, you would use the self-leveling type around every opening (vents, air conditioners, solar panel mounts, etc.). This type remains slightly "soft" and flows to fill any gaps as the components flex with the motion of the RV going down the road.

But for a vertical area like a window, you would definitely want the non-sag type, which does not "run" like the self-leveling type. What's nice about Dicor is that it remains flexible for a long time, and doesn't crack and split even with a lot of heat, vibration, and flexing. And unlike silicone sealants, it does not "contaminate" the surfaces it touches so they won't take paint. However, the Dicor sealant itself is not really a paintable surface, so you would want to select the color that goes best with your paint scheme. It comes in white, black, grey, dove, tan, and ivory.

Caveat: I've only used it to seal windows on RVs (with great success), and have not needed to use it on an airplane (yet). So probably good to test it on some scrap before doing the windows on your plane!

[jaredyates]

I had great results from a product called Lexel. It goes on like a caulk and dries clear.