I've seen it recommended each way. Lexan lasts longer. Plexiglass can be kicked out if you get stuck in the plane but it breaks in shards. What do you guys recommend?

I have a large skylight, seaplane doors and some windows that I need to get material for.

Also, what about tint? I'm think really dark tint for the skylight but I'm not sure about the doors and windows.

Acrylic = plexiglass
Polycarbonate = lexan.

Polycarb - low shatter. Scratches Easy.

Acrylic - Shatters easier, scratch resistant, you can glue it easier with solvent.

Go with acrylic. Smoke Grey.

http://www.delviesplastics.com/

Thanks BP. I used trade names for the masses; not everyone knows what acrylic and polycarbonate are.

I have scratch resistant/uv stabilized polycarbonate for the windshield on the boat. It's good stuff and what I'd use on the plane if I used poly.

Why would I be concerned about being able to glue it?

I've been planning to use acrylic mostly so that I'd be able to break it out.

I've heard that Lexan doesn't handle fuel exposure so well, at least with auto gas. That's one reason to go Plexi in the skylight and side windows at least.

Working with Plexi will make you want to toss the whole thing over the fence into the neighbor's yard after shooting it with your 12 gauge. It's super easy to crack and all holes drilled have to be drilled with a gentle hand. Special plastic drills are recommended to reduce stresses.

I don't think Lexan can be polished if scratched but it's also not so bad to replace. I don't see being able to kick it out as that important because for something like the skylight, the tubing is like a jail cell anyway. Windshield is a done deal in plexi from LP Aero, I'm not sure they even make those in Lexan.

I'm curious whether one could run slightly thinner Lexan because of its ductility, versus having to run thicker Plexi. Could it be considered a weight issue?

Makrolon AR2 is what I used on my boat. It is rated as chemical resistant and from the data sheet, "MAKROLON AR polycarbonate sheet also performs well for view windows and machine guards in harsh chemical environments." I'll see if I can find some of my scrap pieces and see what fuel does to it. That Makrolon stuff is spendy though; think it cost just over one AMU for the two sheets it took to make my boat windshield.

Untreated lexan will supposedly discolour with exposure to sunlight as well. I recently cut all new side windows from plexi and didn't find it that difficult to work with, just make sure you take your time.

I don't know how much this means, but I bought a little piece of Lexan at Home Depot to make a divider for my Yeti cooler, fortunately about twice what I needed. I didn't care about fading or yellowing, just wanted something strong, light, and waterproof. I cut it to shape with my compound miter saw using a fine tooth plywood blade. The first effort, though, the saw shattered it instead of cutting it. The second was more successful, as I very slowly lowered the saw onto the Lexan.

Since Lexan is supposedly softer and easier to work with than Plexiglas, I don't know what would have happened if I'd tried the same thing with it. Good idea to wear safety glasses, though, right?

Cary

I've always found plexiglass easy to work with, with the caveat that you are careful. To cut it, tape both sides, and back it with scrap lumber. Use a good, clean step drill to drill holes, and drill them oversize. Pretty simple, really.

In my experience, Lexan scratches really easy, and I'd never consider using it on windows that I'll regularly be cleaning. Now, there may be different grades/flavors of the stuff that don't scratch as easy......

But, plexi has been around a long time, and I suspect that's what's used in most if not all current production airplanes.

MTV

Many whitewater boats use polycarbonate windshields and they all run wipers and with proper care they last a long time. The scratch resistant polycarbonate is exactly that, scratch resistant. The only scratch I've put in my windshield is from where I accidentally smacked it with my 50lb anchor.

Lousy pic of my boat with the polycarb windshield.


Maybe worth noting; I thought the acrylic windows and windshield in my Luscombe scratched pretty easy and the side windows we installed crazed pretty fast. Maybe we used the wrong stuff.

I've worked with both acrylic and polycarbonate and I didn't think either were all that bad to work with.

Acrylic in smoke grey sounds good with maybe a really dark tint skylight.

Thanks guys.

I prefer lexan because it doesn't crack as easily. You can make a perfect window out of plexi and put it in the plane and come winter or summer when the plastic shrinks or expands it'll crack if you didn't oversize your wholes enough. I used both in my plane and my kids are always touching the windows and I haven't had an issue with scratches on either type, all my windows are .080". I have also gotten gas on both plexi and lexan and haven't had an issue, maybe if you have a constant drip or leave a puddle of gas on it you might have problems.

Either way you go, use a die grinder with a cutoff wheel to cut it. Anything else is a form of Russian Roulette! I started using my cutoff wheel about 20 years ago, after the second windshield I'd put a crack in, and have never looked back. I'll second the step drill for the holes. Just nice and slow (a little WD-40 on it will help too) and light pressure. Drill the holes at least one size over, and then I take a dab of silicone in the oversized hole when I put the screw in. Never had one crack since I started that system.
As far as which to use, I'm a fan of both. I don't consider it such a big advantage to be able to break it out....'cause if I'm in a crash I usually have enough addrenalin flowing to kick it out! Another factor is that maybe it would keep something from coming in as well.
JH

Whee, it doesn't take much tint to make a big temperature difference on the skylight. Mines a light smoke tint and it's not an oven in AL summers.


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All my side windows were initially lexan. After 3-years, they were scratched so badly that I was embarised walking up the the plane. Replaced them with Acrylic and I'm much happier with that. They still scratch, but not as much and just look better.

Deet is pretty hard on lexan too when the wife decides to wet-up next to the plane

Even the acrylic scratches enough to bother me, and I am fairly careful about the windows. I cannot imagine how soft and scratchable the Polycarb must be.

I was happy with acrylic. Just don't go too thin (at least 3mm), or the windows will drum like crazy and you'll end up replacing them.

If you use polycarbonate with the hard coating (either AR or MR depending on manufacturer) it will not scratch as easy as plexiglass does. I used it for 10 years in Bushwacker and no scratches. You can not bend it for wing lights but slight radius like I had in my one piece doors was no problem. I have never seen it crack when cut or drilled and I used .080 for all my windows. You will not be able to kick it out is my main concern so I probably will not do it again in the areas that I think I may need to get out in a hurry.

Will the polycarb behave like plexiglas when heated? As in, bubble windows? I've never tried it or messed with it in that capacity.....
John

hardtailjohn wrote:Will the polycarb behave like plexiglas when heated? As in, bubble windows? I've never tried it or messed with it in that capacity.....

I can not answer your question based on any experience but according to the data sheets I've read polycarb can be head formed but it is more sensitive than acrylic, bubbles form easier. Also, I don't think you can form the coated stuff so you'd have to buy the regular poly, form it then send it off to be coated with the uv/abrasion resistant coating. That would probably be pretty spendy.

Mauleguy wrote:If you use polycarbonate with the hard coating (either AR or MR depending on manufacturer) it will not scratch as easy as plexiglass does. I used it for 10 years in Bushwacker and no scratches. You can not bend it for wing lights but slight radius like I had in my one piece doors was no problem. I have never seen it crack when cut or drilled and I used .080 for all my windows. You will not be able to kick it out is my main concern so I probably will not do it again in the areas that I think I may need to get out in a hurry.

I wonder about building a failure mode into the windows. Something like reduce the edge distance of the holes so that if you kick the window the fasteners tear out. Or oversize the holes so if you kick the window the head of the fasteners pulls through the holes.

whee wrote:I wonder about building a failure mode into the windows. Something like reduce the edge distance of the holes so that if you kick the window the fasteners tear out. Or oversize the holes so if you kick the window the head of the fasteners pulls through the holes.

If it's a flat panel or slightly curved surface (like a door) it's pretty simple to make your windows where you can apply enough pressure so the material will bow/bend out enough to slip out of a channel and pop out. This is easy to get it constrained to a single direction of force (ie bird strike wouldn't pop it out, but kicking from inside would), and this method is used commonly in non-aircraft engineering situations. If I'm not making sense, I can elaborate more or draw up a diagram or something.

Also - more of a mechanical fuse, but I've seen enclosures built where a bolt is used with a rubber washer. The hole in the panel is larger than the head of the bolt but smaller than the washer diameter. When enough force is applied, the bolt will slip through the rubber washer, or depending on hole size, the washer could slip through the hole in the panel. But like all mechanical fuses, you're adding a failure mode into the system. Can also be done with grommets rather than rubber washers.

For the record, my experience is not with aircraft but other enclosures, and there are likely issues in an aircraft application that I haven't thought of. Hope I'm not just adding to clutter.

-asa

Edit: Both options above are resettable - a very desirable quality of engineered mechanical fuses, but if you're actually using this feature to save your life after a crash, it's not really important.

windshield, doors and skylight on my Highlander are lexan, and they scratch very easily. The windshield is made of a flat sheet and the sharp bend at the top corners gets many small cracks shortly after it's installed. the good thing about it is that it is cheap and easy to replace. The first effort will take some time, but then you can make a template for future replacements. With the template it takes about three hours to replace my windshield and I can buy enough material for many windshields before I get to the cost of a formed plexi windscreen.

Die grinder works well, I've also used large tin snips to cut lexan. The edges need to be polished carefully. I sand them, but my friend swears that the best method is to gently melt the edge with a propane torch. I'd practice on some scrap before hitting the windshield with a torch.

In addition to the good suggestions already mentioned, make sure the material is very warm when you are cutting and drilling it. I either took it into a well heated shop or waited until outside air temp was > 80 degrees before working with plastic.