Craft & Technique: Aircraft Plastic Repair

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Craft & Technique IF YOU’VE EVER OWNED AN AIRCRAFT method. There are three with a cracked instrument options: welding, gluing, or panel or taken a chunk out of a using a product like PlastiFix. tail cone with a tow bar, you’ll Welding, the certified repair be happy to know that you can method for ABS, produces a repair many plastics with relastrong and light fix, and if the Tips and techniques for success tive ease and at a reasonable area needs reinforcement, cost. Plastic components on airyou can melt some stainless SCOTT E. BIXLER craft are typically made of ABS steel mesh into the weld for (Acrylonitrile Butadiene extra strength. The disadStyrene) or an FRPM— vantage is that it tends to fiber reinforced polyester warp thin parts and matrix (i.e., fiberglass, carsometimes alignment can bon fiber, or Kevlar)—and be an issue. are more easily repaired Glues like Urethane than you might think. Supply Company’s InstaBecause some structural Weld, a cyanoacrylate components are made of adhesive, work well plastic, you must first deterbecause they are lightmine if the damage has weight, fast drying, compromised the part’s strong, and easy to use. integrity. If there is any Other adhesives like question about its structurepoxy produce an adeal integrity, do not attempt quate bond and can be a repair—have a qualified made thicker and reintechnician perform a thorforced with glass, but ough examination and The shattered plastic instrument panel from a Cessna they are heavier, messier, make the call. With that 206 would make an interesting test for the author’s resmelly, and often difficult said, virtually every non- pair techniques. to sand. structural piece of plastic PlastiFix melts into on your plane is worth fixing—espeMade of 1/16-inch ABS, the panel ABS, producing a bond similar to cially if you’ve checked their replace- cover was brittle from cooking in solvent welding and, it produces a ment costs with the original equip- the Alabama sun for more than 20 thermoplastic when cured. It can ment manufacturer (OEM). years. It had pieces missing, was fill large cracks, create missing To test repair methods for thin cracked like a jigsaw puzzle, and was pieces, and re-thread stripped bolt ABS, Larry Hancock, a local EAA ready for the trash. But in experi- holes in plastic. It is also lightChapter member, lent me the menting with repair techniques and weight and strong, and can be reininstrument panel cover from a materials, the job turned out to be forced with fiberglass for additionfriend’s Cessna 206. It was in pretty much easier than I expected, and al strength. bad shape, which got worse after I the results were spectacular. Bonding With Insta-Weld got it caught in a self-closing door. For this project, I used a combinaAs you can see in the photo, the Establish a Plan of Attack damage was extensive. Even though Begin by rough assembling your tion of Insta-Weld and PlastiFix. I have virtually limitless resources part (or, in my case, what’s left of Insta-Weld was the bonding agent for plastic repair through the com- it) to find out in what order the that would hold the ABS pieces pany I work for, I was having some pieces should go together. Start together while I made the actual serious doubts as to whether or not with the largest pieces and work repair with PlastiFix. For this part of the panel was salvageable. But a your way down in size until you the repair I used aluminum auto body tape, Thin Insta-Weld, Instareplacement panel would have cost run out of pieces. Next determine the best repair Weld activator, and 80-grit abrasive $500, so I got busy.

Aircraft Plastic Repair

Sport Aviation

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Craft & Technique paper. Begin by lightly scuff sanding the area to be bonded. This cleans the surface and promotes adhesion by giving the glue more surface area. Spray the area to be glued with activator and let it flash off. It will remain active for 15 minutes. In this time, you will need to tightly

Insta-Weld initially holds the broken pieces together. join the cosmetic side of the item with aluminum tape to properly align the surfaces. Then apply InstaWeld to the length of the repair and let it wick in for a short time. Let it dry or spray with more activator to instantly cure the Insta-Weld, and you’re done! Because of the small bonding area a butt joint in 1/16-inch ABS offers, I needed to reinforce the joint with additional material to make it more durable. Because PlastiFix has superior adhesion to ABS and I needed to create some missing pieces, I knew PlastiFix would be the best method of repair. FREE 30-DA Y Trial

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Joint Reinforcement With PlastiFix PlastiFix is mixed in place on the repair area so there are no mixing sticks or globs of adhesive to fall on the floor. The supplies needed are similar to the previous step, with the addition of fiberglass cloth and a PlastiFix repair kit. With 80-grit abrasive paper scuff sand the non-cosmetic side of the repair about 5/8-inch to either side of the joint. Using aluminum tape, make a mold for any edges of the crack that may have chipped off or any areas that may need to be dammed up so the PlastiFix will take on a shape close to the original manufactured part. To fill small areas or areas that are in a tight spot, you’ll use the ball drop application method. Fill the dropper bottle with PlastiFix liquid and fill the small mixing cup halfway with PlastiFix powder. Drip one drop of liquid into the powder and immediately impale it with the tip of the needle and remove it from

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mold without curling the bar too far around the edges and trapping the part in the mold. Squash multiple bars together to make a big mold bar if necessary. This was the case for the rectangular cutout on the panel. Once you get a suitable mold, fasten it with aluminum tape to the location where you want to make the part and fill the mold with

The PlastiFix “ball drop” application.

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the cup. Place the ball on the area where you want the PlastiFix to be and squeeze out enough liquid to get the ball to flow off the end of the needle and into the area you want to fill. Repeat as many times as you need, or if you have a lot of area to cover, try the sprinkle method. For larger, flat areas and for reinforcing joints with fiberglass, scuff sand around the joint and then sprinkle the powder up to 1/16-inch deep over the area to be reinforced. Once covered, rapidly drip liquid on the powder starting at one end and working your way down to the other, saturating it as you go. Repeat this process until you reach a depth where you feel secure with the strength of your repair. If your plan to reinforce the joint with fiberglass, press the glass into an uncured second layer of PlastiFix. Then apply a third layer of PlastiFix on top of the glass to smooth the surface and reinforce the repair.

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Reproducing Missing Parts If you have a missing piece, PlastiFix can make a new one that’s stronger than the original. It always helps to have something to make a mold from, although with a little ingenuity and patience, you can build molds from scratch using aluminum tape. First, you’ll need to use the molding bar(s) from the repair kit. Simply heat the bars in near-boiling water for three minutes and press the softened bar onto the part you need to make a mold of until the bar has cooled. (Hold it in cold water to speed cooling.) Be careful to get the original details in the For more information, visit SPORT AVIATION on the Web at www.eaa.org

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Craft & Technique PlastiFix using the sprinkle method. You can also add some fiberglass for extra strength if you need to. After the PlastiFix has set up for at least 30 minutes, carefully peel off the mold, and voilà, a new part! Making the mounting pins for the back of the instrument panel cover was completed in a similar fashion. It was difficult to get the right ratio of powder to liquid, and I had some major voids in some of the pins. A few tries and a couple of bad pins later, I succeeded. Another problem I experienced in making the pins was difficulty removing the pins from the mold. But by heating the mold slightly to make it more flexible, the pins were easier to extract. If you heat it too far, however, the part will become soft and deform, so be careful. The missing corner of the panel offered a series of challenges. I

Using the PlastiFix “sprinkle method” to create missing parts.

began by making a mold of the curve of one of the other instrument cutouts to complete the missing piece of the circle. Then I extended the raised lip from the top down to the edge of where I thought the end of the panel should be by making a “mold” from aluminum body tape and molding bars. After sanding and a little shaping with a file, you would never

know the piece wasn’t original. Keep in mind that all of the repairs of the panel were done to the back side, so there was less to fill on the front when it came time to finish.

Cosmetic Touches Finishing ABS parts is pretty straightforward. Begin by sanding off any PlastiFix that went beyond the mold, any high spots, or any

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Use a high-speed rotary tool with a teardropshaped bit to cut V-grooves into the fixed cracks.

other abnormality that may impede mounting the finished piece. This would be a good time to re-drill any mounting holes that were filled and to test fit the part on the aircraft. Sand the entire exposed surface with coarse abrasive paper to promote adhesion of the filler and make any low spots stand out. I circled the low spots with a permanent marker before finishing sanding so I would know where to fill later on. Use PlastiFix to fill any structural voids or areas that will experience wear. Be careful not to overfill because PlastiFix isn’t the easiest thing to sand down. V-groove all the joints you just repaired with a teardrop-shaped Dremel bit. Go about one-third of the way through the joint, then round the edges of the groove with coarse abrasive paper. This seems contrary to the repair you just made, but it’s necessary for the filler to get a good bond and to allow it to feather nicely with the surrounding areas. Fill all the hollows and V-grooves with 2020 Hardset Filler (available from Urethane Supply Co.). Follow the product instructions. 2020 Hardset Filler sets up quickly and is ready to sand in about 15 minutes. Sand down any high spots with 80-grit paper, fill any missed low spots, and then sand again. You should now be ready to apply a texture coating to simulate the original finish. If you want a smooth finish, you will use 400-grit abrasive paper or finer to remove any scratch marks from the surface, spray with a primer-surfacer, and re-sand with 400-grit paper. For a texture similar to that of the original panel, you can use a product like Urethane Supply Company’s FlexTex. Flex-Tex is a flexible texture material that can have differing amounts of texture based on the pressure and flow you set on the gun; the higher the pressure, the finer the texture. Other types of texturing materials are available in aerosol cans, but the appearance cannot be varied as easily. When spraying Flex-Tex, be sure to use a 2.0 nozzle on your spray gun so it won’t clog. Set the air pressure between 30 and 40 psi and adjust the flow until you get the desired texture. Spray the part and inspect it for any Sport Aviation

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Craft & Technique defects. Remove any fuzz or loose texture by lightly going over the surface with a 3M scuff pad. For the finished surface, I chose Urethane Supply Company’s Bumper & Cladding Coat (available in assorted shades of gray) for several reasons. First, it was formulated for use on demanding plastics, so it has no problem bonding to ABS. It also has a satiny OEM-looking sheen when dry, requires no thinning, is forgiving to spray, and is dry in 15 minutes. Once painted, the only remaining thing to do is bond the mounting pins to the back of the panel and install it on the aircraft. The finished instrument panel hasn’t been installed on the aircraft yet, but it has been returned to its happy owner. Larry was amazed with the outcome of the project and couldn’t believe it was possible to

The finished panel looks like new—for a lot less cash. get the results I achieved. His jaw dropped when I told him about “the door,” and he anxiously awaits the “before” pictures. Once installed on the plane, I doubt anyone would be able to tell it wasn’t new.

If you would like any additional information on the processes or the products used, feel free to contact me at [email protected], and I will do my best to answer any questions.

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