Lexan vs Acrylic/Plexiglass - help

[Osprey220]

Hi All,

Getting ready to replace the windshield and doors - and trying to decide between Lexan vs Acrylic/Plexiglass.

I've been reading through the archives here and at Avidfox - and there are good arguments for both.

Seems like most posts have been on use of Lexan, but a few mention Lexan's sensitivity to gas, UV, and crazing around bends and so strongly recommend acrylic.

The price here is almost the same 4'x8'x1/16th" sheet of Lexan ~$62 and $75 for Plexi - so pretty much a wash there.

Downsides on acrylic I've read are propensity to crack when drilled or bent, easier to scratch but much easier to buff.

The plane sits outside with a cover.

So any suggestions? Which way should I go? Do I heat at the plastic for the forward spar bend?

Cheers,

Owen

[jiott]

Acrylic is much LESS easy to scratch. Also I believe it is more optically transparent. You do have to be much more careful when drilling, bending and handling.

[HighWing]

A question. Are you taliking about replacing the Lexan with similar sheets of Plexiglas? I don't think that has ever been done. Most discussions on Plexiglas has been regarding the factory heat formed windshields and bubble doors. I suspect with the two piece doors that Plexiglas could be used because of the gentle curves, but for the windshield with the small radius curves at the wing roots careful heating would be necessary there. Not totally sure that it has never been tried, but no memory of it over the years.

[Guy Buchanan]

I started with the acrylic windshield. When it cracked I switched to Lexan. I'd blown an acrylic bubble door some years earlier and had seen how an impact could turn it into flying shards. (I also "tested" my cracked acrylic windshield. It also turned into shards when hit, and not very hard.) I didn't want that in front of my face. Yes, it's more opaque. Yes it scratches much easier. However it was much easier to fabricate and install, and will supposedly handle a bird/drone strike. (Look at the F-16 bird strike videos. Very impressive. Yes, all military canopies are polycarbonate.)

[Osprey220]

A question. Are you taliking about replacing the Lexan with similar sheets of Plexiglas? I don't think that has ever been done...

Yes - naively I thought the lexan and acrylic almost interchangeable.

So flat sheet 1/16 would not stand up to the bending for a windshield?

Owen

[jiott]

For a windshield the thickness is more important for strength than for bending. To be able to resist say 140 mph Vne a minimum thickness (probably different for Lexan vs. acrylic) is critical to avoid flexing inward in the slipstream.

[Osprey220]

Plane I'm working with is a 582 model II that cruises at ~65 and Vne is 100 or 95. The 1/16 is supposed to be sufficient for this plane.

Supposedly the 1/8th or .93 is needed for the later models with 912's.

[avidflyer]

I've always run .060" lexan on my Avid MK IV with a Jabiru engine. At 100 MPH, you would see the windshield start to buckle into the v tubes just behind it. Didn't seem to hurt anything, but I stayed below that speed. Not hard to do, cause that was right at max speed anyway. Lexan does scratch fairly easy, but when it's time to change it out, clamp the old windshield to a new piece of lexan, drill out all the holes, cut it to the same shape as the old one, bevel the edges where you cut it, and reinstall. 2-4 hrs later, you are good to go. JImChuk

[HighWing]

Agree with Jim. My first IV - 1993 came with .060. The new was "upgraded" to .093 and has lots of craze lines at the wing root. Soon, I will go back to the .060. I guess we have a tendency to "upgrade" over time, but I don't remember of a case of the thinner windshield doing anything more than the oil canning described, but I do remember reports of the thicker windshields cracking top to bottom at the wing root max bend area on at least a couple of occasions - one a close friend on a cross country. His emergency solution drill and stitch using safety wire. As far as caving at 140 mph. Not an issue as it far exceeds max speeds on a IV. This is one of the reasons I wish the IV was still available. The vast majority of current builds are 7s and there are a bunch of differences and many decisions we IV and earlier builders are contemplating are unique to those models. And, truth be told, I am still heavily influenced by an old flying buddy who built several IVs - the lightest weighing 604 lbs empty. It was a screamer as far as off airport flying was concerned. .060 Lexan weighs pounds lighter than the heat formed plexiglass.

[efwd]

not to mention a SS7 acrylic will be a nightmare to replace if its source goes defunct. Wish I had that IV windshield if that's all that there is to it to make a new one.
Eddie