Covering Techniques 2014/02

After you have spent time building 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 apply it properly. 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 today (once you decide which one to use) is a marvelous technology, requiring less work to achieve a beautiful model.
All covering materials have different personalities with which to become acquainted. MonoKote is a Mylar-based material, glossy in finish, and shrinks during heating.
UltraCote, a polyester based material is less glossy and better resembles a painted finish. It shrinks as the heat is applied and is more flexible. The 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 to choose from, but all have different application characteristics.
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 much 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 show in how well it will look. 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.
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 magic 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.
Spend some time figuring out how to get the most out of your roll of covering 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.
With your iron set at the sealing temperature, lay the material on the airframe and tack it in place on one corner, pull it flat and then diagonally to the other corner and tack 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. Once 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.
Before shrinking, I cover both sides of the part. I lay the part on a flat surface and weight 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, more heat and up less heat. After the covering is tight and smooth, I turn my covering iron up to shrinking temperature.
Leaving the part weighted 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.
Compound curves present a problem. You will often run into this on wingtips. The easier route is to cover the tips separately. If you make the seam on the end rib neat, it will be hard to tell 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 do it all at once. You might consider painting it another color.
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.
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 sharp razor. I clean off with alcohol the area where I am going to place it the graphic, and then spray on some Windex. I lay the trim in the Windex, sliding it around until it is aligned. I call this floating it on.
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, let 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 to get it done.
I hope I have imparted some information on this subject that will stick with you and help you achieve a better covering job on your next model. That is my aim. Happy covering!