Care and Repair of Acrylic Aircraft Windows
Story and Photography By Ron Kilber
WHEN MY AIRPARK NEIGHBOR returned from an FAA-sponsored maintenance seminar (where the instructor claimed he hadn't yet run across acrylic that couldn't be repaired), I just had to find out more about that. Wow! If that's true, I realized that I might avoid replacing the hazed windows on my own Cessna 150. More than once, when landing at dusk, I had to go around and land downwind just to keep the sun's glare off the hazed windshield.
So began a repair odyssey that started with anticipation and excitement, then deteriorated to discouragement and disappointment after I couldn't achieve optical clarity not much better than when I began. Then, like Superman arriving out of nowhere, an expert showed up at my hangar to set me on the right path. Now I've got an airplane that I can see from -- together with a wide smile with a lot of saved money still in my pocket.
Neither an expert of acrylic nor its repair, I really didn't even know the real truth about aircraft window care and maintenance -- let alone restoration -- until I got this story assignment. Much of what we learn as pilots comes from other aviators who've shown us the ropes over the years. For example, more than one experienced pilot has advised me to use car wax to fill scratches on acrylic. Even my Owner's Manual recommends wax to hide minor scratches, though no mention about the type of wax. Any pilot or owner could assume anything from bee's wax to petroleum-based wax, never realizing that damage could be taking place that wouldn't be visible until years later. Now I know better -- and why. And there'll be old bloats with lots of egg on their faces after learning what I've discovered from the experts.
It should be inspire you to know that even an acrylic neophyte like me actually managed to not only repair his Cessna 150 windows but, more importantly, I also learned a lot about acrylic care and maintenance. Even if you never tackle a window restoration project on your own, you'll at least find out what I did, not to mention the real truth about how to take care of your aircraft windows.
After calling the FAA in Scottsdale, Arizona, I managed to chase down the seminar instructor, an employee of Bombardier Incorporated in Tucson. From there I learned of other industry experts, as well as companies, in the acrylic-repair business. While there are many products and kits out there to serve this market, the experience I gained for this project is limited to the Micro-Mesh and 3M systems. In fairness to all, more than one expert told me that virtually any acrylic repair system works, market share, customer service and technical support driving one's preference.
To get started, I ordered the Heavy-Damage Removal Kit from Micro-Surface Finishing Products, Inc., in Wilton, Iowa. This company has been in business for years, serving many military units around the world, as well as corporations such as Lockheed Martin and Boeing.
Selling for $68.75, the kit is one of six offered that removes everything from sub-surface crazing and gouges to scratches, halos and haze. For tackling less damage, there's a smaller kit priced as low as $21.50.
Especially useful for me was the technical information manual shipped with my kit. I learned, for example, that Plexiglas is a trade name for acrylic, as is Acrylite, Lucite, Shinkolite, etc. As far as I knew prior, each was a different plastic, not one and the same cloaked with different trade names. I also learned from my tech manual that other plastics, such as Lexan and Tuffak, are polycarbonates (of bullet-proof fame), which are tougher to attain the clarity as with acrylic (caution advised when restoring these). Finally, I learned that my repair kit works for fiberglass, painted surfaces and some resinous materials too.
EQUIPMENT AND TOOLS REQUIRED
While it's entirely possible to fix acrylic windows without power tools, after the job is all done, the old elbow might need fixing next. Otherwise, all that's required (besides the kit) is a random orbital sander, angle polisher and a high-volume air compressor capable of maintaining 120 psi continuously. A spray water bottle and a few all-cotton towels or rags round out the list.
Being a little nervous about using power tools on my trusty little Cessna 150 windows, I decided to take my neighbor's offer to practice on his motorcycle windscreen, which was severely gouged and damaged. Beginning with 1200-grit paper and working through all the prescribed steps, I managed (with beginner's luck) to put a big smile on my neighbor's face. As far as he was concerned, I had traded in his old windscreen for a brand new one. And he regretted giving away another windshield he believed was worthless and loaded with scratches.
With my new confidence and experience gained from the motorcycle, I began work on my Cessna 150. For window hazing problems, the directions say to begin with 1500 or 2400 Micro-Mesh disc. Wanting to be conservative, I started with 2400.
Using a pneumatic sander, I worked away on the rear left window, being careful to use enough water to prevent scratching and a pattern to remove plastic evenly. The water spray I used gradually turned to a milky-white substance. At first I thought I was removing 27 years of surface-contamination build-up. Each time I stopped and wiped away the white stuff, more always appeared as I worked on.
Eventually, the window surface became translucent, convincing me that the white stuff was actually released acrylic, made opaque from all the sanding. The whole process of using 2400-grit paper took me less than five minutes, including clean-up of the window for the following step.
Next the directions called for a 3600 Micro-Mesh disc, which I used until I could see symmetry throughout the plastic using a bright light from an angle. Once I was satisfied that this process removed all the 2400 scratches, I cleaned the window again. No more than five minutes here too.
Use of the Tuf-Buf polishing pad was next. Using a helping of Micro-Gloss for several minutes magically began to transform the window from a dull appearance to one of approaching optical clarity.
Micro Gloss is a one-micron, water-based compound specially designed for removing fine scratches, haze and swirl marks created by improper cleaning methods. It's a cleaner too, and can be applied by hand or power tools. The compound is even approved for F-16 aircraft canopies.
The last step involved more Micro-Gloss, only this time using a white foam sponge pad instead. Even more optical clarity was achieved.
To clean the pads between applications, I got rid of the water the same way dogs do. I spun the lambs-wool disc at a high rpm rate until it was bone dry. Be careful to avoid what happened to me. Don't run the pneumatic tool at full tilt to shed all the water. My pad came apart and launched into the air with the lambs wool still on it. Good old RTV (room-temperature volcanizing rubber) solved the repair problem, but I had to quit early so the mend could dry over night. The next day the pad was stronger and better than new.
Being a perfectionist, I wasn't exactly satisfied with the clarity of my rear window. It was certainly in better shape than before I started, but there are many airplanes at this airpark with much clearer windows. Wanting something approaching the same thing, I repeated all the steps again.
Still, in the end I made no improvement. Things were still the same. I even tried a third time using elbow grease alone (i.e., no power tools), but still I had no better luck. Now what?
At this stage I was discouraged and disappointed by the thought of my acrylic being too far gone for restoration purposes. I began to resign myself to the fact that I'd have to eventually replace all my windows.
Until, that is, I finally was able to speak to someone from the 3M company,. I had been playing phone-tag with them for more than a week. Luckily the representative lived only 90 miles down the road from me. Even better, he said he could stop by my hangar on his way to another appointment the following morning.
Dennis Brenna from 3M arrived the next day, complete with enough tools and material to fix the windows of all the F-16s at Luke Airforce Base. All that was needed was to turn on my air compresso