Correct glue for Lexan windshield

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Eugene

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Hello guys I am looking for help.

In the process of replacing Lexan windshield. Original one was 2 mm and I will be going with 3 mm this time. It was flexing and vibrating in flight and developed some cracks on the sides around the rivets.

First question is about the best technique to install new windshield with the rivets, so it doesn't crack again. Maybe aluminum strip should be used on top of Lexan before riveting?

Second question is about correct glue to use to bond windshield to fabric glass cockpit on top and the bottom. What ever they were used in Czech Republic 20 years ago not available here.

I appreciate any info I can get on this one. Thank you!

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Kyle Boatright

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I would absolutely put something between the lexan and the rivets - flat washers, an aluminum strip, etc. Also, best practice is to oversize the holes in the lexan so thermal expansion doesn't put as much stress on the holes/fasteners.

One adhesive that is widely available is Lexel which is a polycarbonate adhesive/caulk from your local home improvement store. I've used it on plexi and it seems to work well.
 

TFF

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It’s nice if you can use screws and nuts to control the pressure. I have used special rivets that were large area soft aluminum. They are pretty expensive; the ones that plug the shaft are not designed to break the pull, but are supposed to be cut off after you set the rivet. It will pull straight through if you try to use like a regular rivet.

I have made aluminum and plastic doublers but have also had to go straight on. Oversized holes in the plastic is necessary so the plastic can float and not bind on the fasteners.

There is a PRC made for windows. Don’t know the number off the top of my head. Makes good messes too
 

BBerson

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Any pop rivet can be pulled a small amount then just cut the stem with a cut off wheel.
Looks like they may have done that at the factory (rivet in the photo).
 

rv7charlie

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Research 'Sikaflex'. RV-x guys (including me) use it to glue on the entire canopy; no holes in the plexi at all. (Haven't tried it with lexan, so do your research.) Plenty of other adhesives out there, too.
 

Angusnofangus

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Are you sure that it is Lexan? I ask because I can't remember ever seeing Lexan crack like that. Plexiglas, yes, but never Lexan. Mind you, every window or windshield that I've ever worked with was Plexiglas.
 

dog

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Get you some scrap lexan and some pl,polyurethane adhesive,PL will generaly stick
anything to anything else.If it works then think about about what it would be like to have to remove a windshield installed with it.
Also ordinary windhield adhiesive from an auto parts store might be good,might be a softer form
of hardware store PL.
Scrap is your friend.
Edit PL isnt the best for UV exposed places,so whatever you do use must be UV stable,like ordinary windshield adhesive.
 
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Eugene

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Are you sure that it is Lexan? I ask because I can't remember ever seeing Lexan crack like that. Plexiglas, yes, but never Lexan. Mind you, every window or windshield that I've ever worked with was Plexiglas.
It is 100% Lexan 2mm and it was OK for 50 HP-75 MPH ultralight. When they started installing 100 HP engine at 90 MPH windshield is starting to flex. I ordered 3 mm this time.

Another reason is large wing incidence that was intend for large AOA. For higher speeds fuselage should've been bolted on to the wing at much smaller angle.

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I am changing deck angle by 5°
 

Eugene

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Any pop rivet can be pulled a small amount then just cut the stem with a cut off wheel.
Looks like they may have done that at the factory (rivet in the photo).
Yes I was thinking the same thing. I see on picture below alum. strip installed before riveting. I think

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Sniffler

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Zach has developed a great technique that I used on my Sportsman. Silproof is GE’s version of Slkaflex. Make sure silicone does not have an expired date, old product will fail.
 

Doran Jaffas

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Research 'Sikaflex'. RV-x guys (including me) use it to glue on the entire canopy; no holes in the plexi at all. (Haven't tried it with lexan, so do your research.) Plenty of other adhesives out there, too.
I'm glad the subject got brought up. a friend of mine who was nearly done with his new RV8 USED SIKAFLEX AS WELL. I'm going to replace my windshield that is 20 years old or close to it anyway was New 2 mm plexiglass. I will ask him but I'm also asking here,, sikaflex work on plexiglass? If so that will save me a bunch of rivets and something I do not want to do.
 

Richard Roller

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Many years ago when we were doing Bonanza windshield replacements, we would use PS870B2 polysulfate sealant, like we used in sheetmetal repairs. I don't recall the material the aftermarket windshields were made of.
 

rv7charlie

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I'm glad the subject got brought up. a friend of mine who was nearly done with his new RV8 USED SIKAFLEX AS WELL. I'm going to replace my windshield that is 20 years old or close to it anyway was New 2 mm plexiglass. I will ask him but I'm also asking here,, sikaflex work on plexiglass? If so that will save me a bunch of rivets and something I do not want to do.
RV canopies are acrylic (plexiglass). That's why I cautioned to do research if the windshield is really lexan.

While not a universal truth, if the part is 'blown' or molded in a complex shape (beyond flat-wrapped), it's likely acrylic. Lexan (polycarbonate) is tougher to mold with heat.
 

Doran Jaffas

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RV canopies are acrylic (plexiglass). That's why I cautioned to do research if the windshield is really lexan.

While not a universal truth, if the part is 'blown' or molded in a complex shape (beyond flat-wrapped), it's likely acrylic. Lexan (polycarbonate) is tougher to mold with heat.
Been around aviation a long time and I didn't know that. Excellent information.
 

Doran Jaffas

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I did just confirm what I had hoped one was saying about the sikaflex. I'm going to order some and breathe a huge side of relief I will no longer need rivets at the replacement. It will be a much cleaner installation as well.
 

Jerry Lytle

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Zach has developed a great technique that I used on my Sportsman. Silproof is GE’s version of Slkaflex. Make sure silicone does not have an expired date, old product will fail.

Caution, Silproof is not GEs version of Sikaflex. I would hesitate to using any silicone sealant where it will be exposed to view. Look at any older application such as a motorhome, and you will find silicone seaslant loosing it's adherence and collecting dirt. Once silicone has been applied almost nothing adheres to that same surface and that includes paint or polyurethane.
On the otherhand polyurethane is rather permanent. For marine applications it is stated on the tube that it should not be used where removal or replacement is planned. I have seen it pull off jellcoat when changing a stanchion.
 

Map

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My canopy is blown Lexan. I bonded it to the frame with urethane window adhesive from HomeDepot. Works great, strong bond, stays flexible to dampen vibrations and can be painted over (unlike silicone). I painted the outside of the Lexan bonding area white. It is best to avoid holes and fasteners in such thin material, they are stress concentrations where cracks start. You will need a lot of clamps to hold it on while it cures.
 
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