Just found this most interesting blog post on this subject: http://www.coloradoplastics.com/blog-0/bid/42625/Polycarbonate-Lexa...

WT

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I went from acrylic to polycarbonate on my Harley a few years ago. I'll never go back. The windshield I got is from F4Customs. I think the brand name is Speedglass. It has a coating that makes it considerably more scratch resistant. It actually came with a sample that was coated on one side and a small piece of 0000 steel wool. When the plain side was rubbed with the steel wool it of course scratched but the coated side did not. I was/am happy with the windshield. I was sort of disappointed the kit came with acrylic after seeing the poly but hey if I am so disappointed maybe I should see about getting one made. Funny the windows on the 750 are poly and the windshield is acrylic.Realize I am not an expert nor do I have stock in any company mentioned here. Just my experience. Maybesome others with experience with both types will chime in. Cool read.

I'd like to know more about that coating and whether or not it can be applied to the plexi on a finished plane. I also wonder why Zenith went with acrylic. Cost? Scratch resistance? Both? Getting one made is an option I'd like to explore too, as I imagine many others might.

W

Thanks for the input, Lane. I'm thinking about scratches and bird strikes.

W

I think the main reason acrylic is more common in windshields is that it's a lot easier (less expensive) to form to shape. One item missing from the article is that chemical resistance of the two plastics is very different. Many solvents will attack both plastics, making them hazy or crazed. Polycarbonate has a particular problem with some of the chemicals that may be present in gasoline, thread locking compounds and cleaning solvents. Just a small amount of some halogenated compounds like freon will make polycarbonate brittle in a few minutes.

That's interesting and good to know when deciding on proper application. Thanks for the reply.

Seems sensible. Thanks for the info; I didn't know that.

But, as design is compromise and progress is achieved by questioning, I can't help but wonder which of the drawbacks of polycarbonate actually govern--money, difficulty in forming and shaping (specifics?), chemicals, or money.

And hmmm, would a polycarbonate windscreen blow the minute my Halon fire extinguisher goes off?

Perhaps some brilliant chemist could make a fortune resolving such issues? It appears that the problem of scratch-resistance has been "solved?"

Money, I think, and then money. Acrylic works, is cheap, and lasts. Polycarbonate has some advantages and is stronger (also money: can make it thinner when you can use flat sheets.)

I don't think there is a compatibility issue with Halon and PC. Dupont has good info on this, and they use Lexan windows in their fire test chambers. Look up the data sheet for the particular Halon you have.

I guess the question of the marginal cost difference and the marginal value or effectiveness elements would/should come into play. How much more scratch-resistant is polycarbonate than acrylic? It appears that acrylic might not be resistant to a bird strike and polycarbonate might. Has anyone shot a turkey at a 750 windscreen at, say 100+ mph? Should be unfrozen, I suspect.

There may be other factors to consider . . .

W

Acrylic, for all its negatives, has one redeeming virtue ... it is fairly easy to polish-out scratches and haze. Years ago, I used a "Micro-mesh" kit to restore a canopy on a glider ... looked like new when I got through!

Lexan/polycarbonate will polish-out, too. I've found that "headlight cover restoration kits" work very well to polish-out Lexan. I have an '84 Honda Nighthawk motorcycle with a polycarbonate windscreen that was so badly blemished the previous owner had covered up the "bikini" windscreen/fairing with black tape! Used a "headlight cover restoration kit" and it looks brand new!

John

N750A

John,

Like you, I have a 750. I forgot what we have at the various spots on the plane. Could you post here, where we have Acrylic, and where we have Lexan ? I have a few spots I could work on when it gets a little warmer. I'm not familiar with Micro-mesh kits, so I just did a quick search and it appears to be just different grit pads. It says they can be used wet or dry. Since you said your canopy came out like new, what steps did you take, and did you do it wet or dry ??

Also, for the headlight restoration kit, do you have any suggestions other than the instructions included in a kit ? 

Thanks,

             Jim

On my Ed. 2 fuselage, only the windshield and the bubble doors are acrylic/"Plexiglass".  The 4 side windows in the baggage area and the top window are polycarbonate/"Lexan."

You're correct that the Micro-mesh kit is a graduated series of very fine abrasives sheets that are used to progressively remove scratches and haze. As I recall, a polish is also provided for the final finish. Also as I recall, I used it primarily wet to keep the abrasive from clogging. It is intended for hand use and doesn't require any expensive polishers, but it takes some time! The effort was definitely worth it!

There's nothing magic about any of the headlight restoration kits for polycarbonate - they all come with some sort of foam polishing head to chuck in a drill and an abrasive liquid compound. Polycarbonate, unlike acrylic, is pretty tough, so you can apply more pressure than with acrylic. Don't be stingy with the compound and starting with the foam head moist helps keep it from absorbing so much compound. I like the "Mother's Powerball 4Plastic" kit best as it provides the most generous amount of polishing compound.

John

Thanks John. That's everything I need to know to fix a few spots at various points.

On my side windows, I made the outside edges hazy or foggy when I used an incorrect cleaner to remove caulk I had installed around all the windows. The guy that painted my plane buffed out most of it, but I'd like to get it better. I don't know if he used any polishing compound while buffing or not.

Jim

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