Airframe and Powerplant: Wash me!

Pilots who view the world and its always-changing natural palette of shapes and colors through a spotless, scratch-free windshield are fortunate indeed. Those who aren’t so fortunate are surely handicapped by their lack of forward vision and may have to squint and side-slip to get a glimpse forward, especially when flying into the sun. A clean, scratch-free windshield improves the flying experience and increases safety for both pilot and passengers.

One skill that’s rarely taught in pilot primary training is no-damage aircraft windshield cleaning. Aircraft owners, even the purchasers of new aircraft, are rarely briefed on this subject. No-damage window cleaning is easy and, if practiced, will pay dividends for years to come. Well-cleaned and sheltered light airplane windshields can last up to 30 years. Because of the toughness of light airplane windshields, very few single-engine light aircraft have a published windshield service life. To provide a measure of this toughness, Cessna’s pressurized 210 aircraft windows must be replaced at 13,000 hours according to the aircraft type certificate data sheet. This is because of the long-term effects of pressurization.

Lightweight and tough acrylic plastics are the most common material for light aircraft windshield and side windows. Acrylics—also known by trade names such as Plexiglas, Lucite, and Perspex—are members of the thermoplastic family of resins. These thermoplastics can be softened and shaped by heating, yet after cooling they maintain their shape and exhibit good visual clarity. While acrylics expand and contract at a rate of one-sixteenth of an inch per foot for every 100 degree F change in temperature, they’re stable enough to be used in airplanes operated in climatic conditions ranging from the blazing tropics to the freezing poles. Acrylics also are used because of their high strength-to-weight ratio.

Flat sheets to windshields

Take a sheet of acrylic, heat it up to between 230 and 280 degrees F and it will become as flexible as pasta cooked al dente. Drape this flexible sheet over a form; then push, pull, or suck it into contact with the smooth surface of the form; let it cool slowly; and voilà, you’ve just manufactured a landing light lens or, with a little more effort, a windshield. It’s not quite that easy, but it’s not rocket science. What’s akin to rocket science in windshield construction is reducing distortion to a minimum. This goal is easier to attain in a bubble-shaped window than it is in the more convoluted shapes designed into the windshields of aircraft such as a Cessna 172 or 182. These must be bent and stretched in the upper corners to fit into the wing root cut outs. Some distortion almost always occurs.

Cast acrylic

Jeff Pfister of L.P. Aero Plastics in Jeannette, Pennsylvania, has been working in the light airplane window business for years. “We use different types of cell-cast acrylics for our windshields,” he says. Cell-cast acrylic is used for aircraft windshields because of its optical clarity and surface hardness. Although it’s harder than the acrylics created using other manufacturing methods, it still scratches easily. Even the softest paper towel will cause scratching. Never use a paper towel to clean or polish a windshield.

Replacement windshields and side windows for almost all certified aircraft are readily available from the aircraft manufacturers or from one of the three companies—L.P. Aero Plastics, Great Lakes Aero, Beryl d’Shannon, and Cee Bailey—that manufacture and sell replacements approved for installation by the supplemental type certificate (STC) process.

The most common windshield thicknesses are three-sixteenth inches (0.187”) and one-quarter inch (0.250”). Thicker windows are heavier but do reduce the amount of wind and engine noise in the cabin. The most common side window thicknesses are one-eighth (0.125”) and three-sixteenth inch. Contact the window manufacturers listed for information about STCs for window replacement options on your airplane. In addition to replacement windows, manufacturers also offer windows that improve both visibility and aircraft appearance. The most common of these are one-piece windshields, side windows with removable camera ports, and bubble-style side windows. Proper cleaning procedures will extend the life of all acrylic windows.

Replacement costs

“The labor costs of replacing a windshield are almost always higher than the cost of the windshield,” said Pfister. Cessna’s flat rate manual, which is the company’s guide to warranty labor charges, cites 14 hours for the replacement of a windshield in high-performance, single-engine airplanes such as the Cardinal 177RG, the R/TR 182, and the 210 models. Forty to 45 hours are cited for light twins such as the 310R and 340. Pressurized airplane installations are much more costly with 82 hours cited for the 414A and 421C.

Windshields and side windows come in clear, green, and gray tints. According to Pfister, gray-tinted windows and windshields are the top sellers. An STC replacement windshield for Cessna singles such as the 172, 182, and 210 sell for between $325 and $500 depending on the aircraft model, tint, and thickness. Both L.P. Aero and Great Lakes Aero are now manufacturing a complete line of windows and windshields that have an increased ability to block all ultraviolet B rays and 99 percent of UV A rays. Normal windows are good at blocking UV B rays but can only block approximately 80 percent of the UV A rays. UV radiation increases by 5 percent for each 1,000-foot elevation gain. This means that windows that provide sufficient protection at sea level are woefully inadequate at higher altitudes. These new-style windows also keep cabin temperatures lower by providing 30 percent greater protection against greenhouse heating. The price premium for these products is about 30 percent.

Safe and sane window cleaning

Chemicals and cleaners that are commonly used during aircraft maintenance should never be allowed to contact, or be left in close proximity to, airplane windshields or windows. Keep glass cleaners and household cleaners containing ammonia such as Windex and 409 and aromatic solvents such as MEK, acetone, lacquer thinner, and paint stripper—and rags that have been dampened with these liquids—a long way from your airplane windows.

Never wipe rags or towels across a dry windshield, and never use a paper towel on a windshield.

One-hundred-percent mineral spirits—also called Stoddard solvent—and kerosene are safe to use for removing tape residue or oils.

Windshield manufacturers are all in agreement on the subject of caring for their products. First, flush loose dirt and dust off the window by flooding the window from the top down with water. Keep the surface wet for a few minutes to soften bug splats. Next, continue to flood the window with water while softly scrubbing and loosening bug debris and stubborn dirt with the palm of your hand. This may sound weird, clumsy, and messy, but nothing works as well as the human hand for this task. Adding a couple of drops of liquid dishwashing detergent to the water aids in softening contaminants during this important initial windshield care step.

It’s also easy and relatively inexpensive—especially compared to the cost of replacing a windshield—to set up a water dispenser or keep a jug of water on the corner of a hangar work bench if water is not available nearby.

After it appears that all the dirt and debris have been flushed off the windshield, do a second flush. This step may be eliminated if the windshield has already been cleaned earlier in the day, but it should be considered mandatory if there was visible dirt on the window prior to the first cleaning. It’s critical to get every speck of dust and bit of grime off the surface before the next step. If all the dirt is not flushed off the windshield during this first step, scratches are inevitable during the second step.

The second step is to clean and polish the windshield with any of the wide variety of commercially available acrylic window cleaner/polishers on the market. Always use linear motions—never circular motions—when wiping on and off cleaner/polishers. The theory here is that “flashes” from sunlight reflecting from the tiny scratches in the windshield will only be seen in vertical and horizontal orientations. Others say that the direction of rubbing doesn’t make any difference if all the dirt has been washed off during the cleaning step.

All of the commercial cleaner/polishers do a good job of cleaning; some contain anti-static coatings and have scratch-filling properties.

Windshield manufacturers and generic parts supply houses all recommend Dupont Sontara AC aircraft windshield cleaning cloths. These towels are manufactured without adhesives or additives. They work great and are relatively inexpensive, especially since they can be washed and reused. One well-known aircraft supply house advertised a box of 125 12-inch by 16-inch wipes for a little more than 27 cents per wipe in its 2008 catalog. Make sure you use only the Sontara AC aircraft window wipes—Sontara wipes made for other applications can scratch acrylic windows.

Chamois skins, cotton flannel cloth from a yardage store, soft cotton terry cloth, cheesecloth, or non-printed T-shirts round out the stable of wipes that won’t damage windows. A recent addition to the OK-to-use wipes list are micro-fiber cleaning towels, which are available at auto parts stores and most big box stores, as well as aviation supply houses. Buy the softest ones you can find and keep all wiping cloths sparkling clean—I seal all my freshly washed windshield wiping towels and rags in Ziploc plastic bags before stowing them in the plastic tub that lives in my airplane baggage compartment. Don’t use liquid or sheet-type fabric softeners when drying these rags.

A number of pilots claim to use nothing but Pledge furniture polish on their windows. I asked Pfister for an opinion. “We don’t have any evidence that it’s harmful to windshields, “said Pfister. “But we do know that an oily residue is left behind.”

Scratch repair

Windshield scratches are inevitable. Fortunately, there is a solution. About 15 years ago Micro-Surface introduced a product called Micro Mesh to the aviation market. Micro Mesh scratch-removal kits contain a series of increasingly finer grits of abrasive paper, a sanding block, some towels, and a tube of crack-filling cream. Micro Mesh is a manual process. Coarse grits of abrasive are first used to sand down through the cracked layer of the window, and then the area is sanded with progressively finer grits until the surface of the window is smooth again. It works but the process is labor intensive, especially when trying to rejuvenate an entire windshield.

Micro Mesh scratch removal kits are great for manually removing scratches from a small area. Three additional kits—for maintenance, light damage removal, and heavy damage removal—are used with power tools. This speeds up the repair process and yields better overall results. The kits retail for about $100 each. Each kit comes with complete directions. The key to success is patience. Going too fast can generate temperatures in excess of 240 degrees F, which spells disaster.

Be a window wizard

Windshields that have been abused or weathered can be restored with a Micro Surface kit. Learning the art of scratch-free acrylic aircraft window cleaning is simple. The process is easy, the tools are relatively inexpensive and the reward—crystal clear vision during today’s flight and for the future—is worth the small time investment.

E-mail the author at [email protected].