Want to Damage Your Windscreen? Treat It Like Glass
Caring for Plexiglas Windscreens
Plexiglas: we call it “glass,” and this lightweight, shatter-resistant material is widely used for helicopter windscreens.
But we know it isn’t glass, and therein lies the problem — we treat the transparent acrylic as if it were. Glass is hard, scratch-resistant, and generally impermeable; it holds its shape well at both high and low temperatures and is resistant to all sorts of chemicals. Acrylic doesn’t share those qualities.
Whether it’s called Plexiglas, Perspex, or just plain ’glas, all brands are made of acrylic, which is soft and easy to scratch. Almost anything solid can damage it, from bugs to dirt to a “clean” shop rag. Even paper towels are abrasive enough to do damage. What cleans glass may not be safe on acrylic.
While glass is resistant to most household and shop chemicals, acrylic is more susceptible, whether in direct contact with them or even as vapor. This includes glue, MEK, acetone, petroleum-based solvents, and even ammonia (common in many glass cleaners).
Glass can withstand temperatures from very cold to very hot. Acrylic, not so much. Cold weather makes acrylics brittle. A hot day can cause crazing and fogging. Heat can strain poorly fitted windows, setting up future damage.
Knowing all that brings up the question of care and cleaning of your acrylic windscreen — what can we do?
Cleaning Best Practices
Avoid using heat, abrasives, and volatiles to clean your acrylic windscreen. Don’t put hot water on cold acrylic, or vice versa. Use a mild soap in a climate-controlled hangar (or at least in the shade on a pleasant day) and clean, warm water in a new bucket, with a new microfiber cloth. Rinse thoroughly and dry with another new microfiber cloth. Then you may want to apply a recommended protectant.
You may think But what do I do if there’s a huge bug splat to clean, I have to fly in 10 minutes, it’s 100°F, and there isn’t any shade. Answer: soak the offending parts off with water and the cleanest cloth you can find. Alternatively, look around that splat or postpone the flight. Next time, clean bug splats off when they’re fresh.
Grady Aldorondo, customer and tech support for Tech-Tool Plastics, an acrylic window manufacturer, gets a lot of questions about Plexiglas care. “I’ve been asked if it’s okay to use a window cleaner mixed with sand,” she laughs. “It isn’t. And although ammonia or acid-based chemicals may eat away at the grime a lot faster, that would not be the only thing they’ll eat away.”
People try lots of home remedies, Aldorondo says. “Don’t chip away at stuck-on, sunbaked bugs, bird poop, or dirt, and don’t scratch at the dirt with your nails, especially if you have acrylic nails.”
Floating off the dirt with water is a good idea, but don’t pour hot water over your windscreen if you are in a cold environment, and don’t use cold water if the acrylic is hot.
One specific piece of advice Aldorondo offers: do not use highly acidic products designed to clean aluminum. “A customer called me after applying several coats of this product. The chemical compound in the product apparently was too harsh for the acrylic material. Acrylic is porous. The filmy appearance that would not wash off later may also be evidence that the product may have started breaking down the acrylic.”
It’s Scratched. How Bad is “Bad”?
Minor or light scratches to Plexiglas can be buffed with a soft buffer pad and Butter Wax or Micronol and a cotton ball. Aldorondo also recommends Micro Mesh and 3M kits that help to remove minor scratches but cautions to buy a product for use on acrylic windows.
Lighter scratches, the kind we get from using paper towels, can usually be buffed out. Aldorondo offers advice here as well, based on both best practices and customer stories. First, “Don’t think that all scratches can be buffed out. When you pass your nail lightly over the scratch and you can hear your nail ‘click’ over the scratch, it may be time to buy a new window,” she says. Though you may get rid of the scratch, Aldorondo says that windows that are buffed too hard or too long may get distortion marks.
It’s common sense, but don’t expose the windows to common aircraft lubricating and hydraulic fluids and agricultural sprays. These can damage not only the acrylic, but rubber seals as well. Wash all that off with water, as soon as possible.
How Do I Protect Acrylic?
Tech-Tool Plastics does not recommend any specific aftermarket finishes. Some polishes, waxes, or coatings may be great; there is a whole industry around these. Just be sure they’re formulated and recommended by the manufacturer specifically for your particular use on aviation acrylics.
Aldorondo notes that there are a lot of don’ts and very few dos in acrylic windscreen maintenance. “So knowing what you can do is relatively easy,” she says.
“Clean the windows with mild detergent washes or common soap (without ammonia or lemon) such as Dawn dishwashing detergent. It’s concentrated, so dilute it or you’ll have a soapy residue if you don’t use enough fresh, clean rinsing water,” she says. “A soft cloth baby diaper is great for washing, drying, and buffing the windows.”
If you’re replacing a windscreen, you may encounter one sprayed with Spraylat, the coating used to protect windows during shipping. Aldorondo says to use “warm (not hot) water to soften the Spraylat, or a water-saturated cotton ball. Place it at the edge of the Spraylat coating, let it sit for a minute or two, then rub in a circular motion. The Spraylat should start moving and you can start peeling it back.”
In summary, if you have to rub, pick, scrape, chip, or use solvent on a Plexiglas windscreen — don’t. Nearly everything can — and should — be floated off with clean water, mild liquid detergent, and patience. Doing this at the end of every flight will help ensure that residue and debris do not accumulate and harden.
If you take good care of your acrylic, you will not only increase the lifespan of your windscreen, but you will also have safer flights with a clear field of vision.
Tim Kern is an aviation writer whose work has appeared in more than 50 aviation publications. He is a private pilot and holds an MBA in finance and operations from Northwestern University. He has extensive experience in machining and both motorcycle and auto racing, and was CEO of an airplane engine company in the early 1990s. Tim is the only journalist to complete the ALEA Accident Investigation course or to have earned NBAA’s CAM (Certified Aviation Manager) certification.