I've a experimental aircraft in need of a windshield due to crazing caused by fuel and cracking caused by stress. It is made of polycarbonate/Lexan and I want to replace it with acrylic because of its susceptibility to fuel and scratching. However, as there are a jillion kinds of acrylics I need recommendations of specific brands and types.

  • 1
    $\begingroup$ Are you sure you don't have that backward? My experience with acrylic is that it scratches easily, cracks if bent just a little too far, and crazes from the slightest exposure to solvents (like gasoline, isopropanol, etc.). Polycarbonate, on the other hand, is used for motorcycler helmets, windhshields, and other high-impact applications as well as being more impervious to solvents. $\endgroup$
    – Zeiss Ikon
    Aug 28 '18 at 13:34
  • $\begingroup$ Have you tried contacting an OEM like LP Aeroplastics lpaero.com and see if they have one for your model of plane already? Or at least browse their online catalog, link on their homepage. $\endgroup$
    – CrossRoads
    Aug 28 '18 at 13:41
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    $\begingroup$ Sorry but requests for product recommendations are off-topic pretty much everywhere on Stack Exchange. $\endgroup$ Aug 28 '18 at 14:58

You need cast acrylic sheet (not extruded). If you are in North America you can get it from Aircraft Spruce https://www.aircraftspruce.com/catalog/mepages/plexiglas.php?clickkey=7342. The cast sheet made for airplanes has UV blockers as well.

Acrylic has roughly the same tensile strength as Lexan (8-9ksi - a 1/8" sheet of acrylic or Lexan has roughly the same strength as a sheet of .032 6061 aluminum) but is more brittle and has to be formed into as close to the final shape as possible, with the minimum possible preload on the sheet and at fastener holes.

On the plus side of being brittle, although it still scratches a lot easier than glass, the surface is way harder and doesn't scratch if you look at with furrowed brow like Lexan does (although it can come with hard coatings - which tends to get removed by polishing), and is immune to fuel to boot.

Lexan is popular because it can take a lot of pre-stress and you can force it into moderate curves and clamp fasteners on it without it cracking. But acrylic is superior for the other characteristics important to airplanes.

If your homebuilt's windshield is made up of flat sheets, it's a no brainer - cast acrylic. If it's a curved wraparound, you'll have to form the acrylic into the curve by heating it in an oven and draping it over a form. If fuel was an unavoidable problem because of a gas cap in front, it's probably worth going to the trouble to form an acrylic windshield if you have an oven big enough to fit the sheet. If the fuel exposure was an unlikely to repeat fluke and you need a curved windshield, it might be easier to just do another polycarbonate one that you can cold bend.


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