Covering Techniques

Written by Jerry Smith Tips and tricks for using iron-on covering How-to As seen in the February 2014 issue of Model Aviation.

After you have built your airplane, it’s time to cover it. Some builders prefer to stick to cloth and paint it. That is a lot of work and takes a different skill. The modern, iron-on covering material I am going to discuss takes only one skill: to properly apply it. Color and finish are included! To some, covering an airplane is a daunting task, although others enjoy it.  The completed job, depending on your level of perfection, differs between builders. The covering we have available today is a marvelous technology, requiring less work to achieve a beautiful model. Covering materials have different features with which to become acquainted. MonoKote is a Mylar-based material, glossy in finish, and it shrinks during heating. UltraCote, a polyester-based material, is less glossy and better resembles a painted finish. It shrinks as heat is applied and is more flexible. Lighter films such as Solite for smaller models are thinner, weigh less, and take less heat with different handling techniques. There are plenty of covering materials from which to choose, but all have different application characteristics.
Tools of the trade.

After you choose your covering material, if you are new to covering, read the instructions that come with the material. You will find some helpful information on its use including the temperatures to set your iron for sealing and shrinking. If you are using an iron sock on your covering iron as I always do, it will be necessary to elevate the temperature to improve heat transfer to the covering. It will also keep you from scratching and marring the finish. Before covering the airframe, I spend time shaping, filling cracks, and sanding. I actually spend more time doing this than building. I use 150-grit sandpaper for shaping, 220 grit for general sanding, and I finish sanding with 400-grit paper. This pays off when I apply the covering and the results will show in how nice it looks. It’s time well spent! I also vacuum the work surface and dust the part to be covered with a brush to remove any loose dirt and dust particles before covering.
After shaping and sanding the airframe, dust it off using a vacuum with a brush. Make sure your work area is clean. Lay the part on the backside of the covering, trace around it with a magic marker, then cut it out leaving a 1-inch margin for gripping and arranging.

Covering materials are not cheap, so spend some time planning the use of your covering. I lay the part to be covered on the back side of the covering and draw around it with a marker. I trim it out, leaving a 1-inch margin for gripping and arranging during application. When doing this, keep in mind that the surface of the airframe that comes in contact with the material is the side of that part you are covering. If you get mixed up, the glue on the covering will be on the wrong side.
Lay the part to be covered on the covering and center it. Note that the glue side of the covering is against the airframe.

Spend time figuring out how to get the most out of your roll of material with the parts you are covering. Before covering my model, I choose a flat, easy-to-cover part such as a rudder or fin. This gives me a chance to get up to speed on what is involved and how to go about it.
Tack the covering to the airframe according to the number of steps shown. Pull the covering taunt in the direction of each number as you go. This will arrange the covering with the fewest wrinkles.

With your iron set at the sealing temperature, lay the material on the airframe and tack it in place on one corner, pulling it flat and then diagonally to the other corner and tacking it. Do the same for the other two corners and then in the middle on both sides. Then start from the center and seal the film to the edges. When it is sealed, trim off the excess material. Now seal the trimmed edges with a rolling action, ironing it down and around the edges. Make sure it is sealed well before you shrink the covering.
After the flat part is trimmed and sealed around the edges, weigh it down on a flat surface to keep it from warping. Use a heat gun blowing the air over the surface, not into it. To control the heat, tip the gun at a downward angle for more heat and up for less heat.

Before shrinking, I cover both sides of the part. I lay the part on a flat surface and weigh it down to keep it from warping during shrinking. Using a heat gun, I direct the heated air over the surface of the film, not directly into it. By tipping the gun down and up I can control the heat applied. Down is for more heat and up is for less heat. After the covering is tight and smooth, I turn my covering iron up to shrinking temperature.
Lay the part on a flat surface and weigh it down. Turn the heat on your iron up to shrinking temperature. Now iron the covering to the airframe, guiding the iron in a circular motion over the covering. Seal and trim the edges, shrink it with a heat gun, then iron it down again using the same circular motion.

Leaving the part weighed down on the flat surface, I go over the covering, sticking it down to the airframe. This is where that good sanding job will show up. Do the same on sheeted surfaces. The benefit will be a surface that is less likely to wrinkle in the sun. Sometimes I set the covered model out in the sun and leave it for a while. If any wrinkles occur, I iron them out.
Right: When covering a sharp corner, iron the flange of covering from both directions leaving a tab at the corner. Trim off the tab flush with the corner with scissors. Then iron it down in both directions.

Compound curves present a problem. You will often run into this on wingtips. The easier route is to cover the tips separately. If you do this and make the seam on the end rib neat, it will be difficult to see from 5 feet away. Other compound curves, such as around the nose of the model, can be handled by laying the covering on in sections and not doing it all at once and consider painting it another color.
When you encounter a moderate radius corner, place the part on the workbench with the end hanging over. Weigh it down and use a heat gun to pull the covering around the corner. Use a glove to protect your fingers from the heat.

Putting covering over covering presents a problem if the iron is too hot. The adhesive will begin to emit gas and cause bubbles. Do not try to do this in large areas.
After shrinking the covering with a heat gun, it looks great, but you are not through. Note how nice the round corner looks.

The graphics I put on my models are uncomplicated. I tend to stick to simple ones and not get carried away. I lay out the pattern on the back side of the covering and cut it out with a razor. I clean off the area where I am going to place the graphic with alcohol, and then spray on some Windex. I lay the trim in the Windex, sliding it around until it is aligned. I call this floating on the trim.
Here is my recently finished Top Flight Contender. I covered it with UltraCote and panel lines in 1/16-inch black tape. Although it is a 1970 design, it is still one of my favorite flying airplanes.

When I’m satisfied with its position, I squeegee off the excess Windex under the trim with a credit card, soaking it up with a paper towel as I go, getting rid of the air bubbles. I do this several times, removing all of the moisture, letting it set for a while, and then I seal it with a low-temperature iron—approximately 200°. I have had the best luck with this method of adding trim. Covering your model takes time. Don’t be impatient. I hope I have imparted some information on this subject that will stick with you and help you achieve a better covering on your next model. Happy covering! —Jerry Smith [email protected]


Top Flite MonoKote (800) 637-7660 Hangar 9 UltraCote (800) 338-4639 Solite

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I appreciate you article! Covering is definitely an art all by itself! I find using a trim iron set to hot and a heat-gun with an F.E.T. rheostat to control the temperature works best for me. The trim iron seals it down, the heat gun shrinks up. Of course, as you mentioned, over planked surfaces can wrinkle in the sun. That is where I use the Iron to shrink it to the wood. I would like to know how manufacturer's of ARF's manage to cut the trim pieces in such nice curves! Next level of expertise it must be! Thank you! -DEREK GERRY-

Looks like good information

"Lay the part on the backside of the covering, trace around it with a magic marker, then cut it out leaving a 1-inch margin for gripping and arranging." Are the magic marker lines permanent marker?? After the covering is cutout, how do you remove the magic marker lines?

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