Preparing to Put a New Covering on a Model Airplane

Originally by Jon Putnam for Model Aviation (February 2009). An extended version was posted on Sport Aviator.

Recovering a model doesn’t always involve a crash. Wear, tear and time can be stimulations for recovering an airplane. The sharp metal molding on a car or the wooden corner of a work table can produce a dent here or a puncture there. That, plus the normal wear and handling from flying can necessitate a recovering job. Another reason for recovering a model is less about the flying qualities and more about not wanting your airplane to look like all the other ARFs at the field. Re-covering can let you express your individuality, resulting in a compliment like “I didn’t know that airplane came in that color scheme.”

A shorter version of this article was originally published in Model Aviation magazine. Model Aviation is the monthly 180-page plus, full-color magazine published by the Academy of Model Aeronautics (AMA) for its members. The knowledge and techniques presented here will help both new and experienced pilots to personalize an ARF airframe, repair a damaged airplane or refurbish an old model.

The photo below makes it look like a lot of tools are required. If you are an experienced modeler, you have these already. If not, even RTF assemblers need most of these items, especially the heat irons and heat gun used to tighten RTF and ARF coverings. Of course, if this is your very first covering project, you might want to try borrowing some of the more expensive items.

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 The structural damage on the Tiger 400 used in this exercise was minimal and repairable, so recovering rather than buying a new ARF was the better choice. Besides, when completed, the Tiger 400 will look different and better than new. Remember, everything must be kept straight and aligned once repaired. If the damage is such that proper alignment is not possible, it is not truly repairable.

Removing the Old Covering

Once the re-covering decision has been made, it’s time to remove all the old covering unless you plan on retaining the same color scheme or just recovering a broken or punctured part, such as a wing.

If you only cover one part, do some research to find out what brand of covering the model originally used. Matching the same brand will facilitate matching the original film color. On the Tiger 400, the kit instructions state clearly that the airplane was originally covered with Cub Yellow and White Oracover film.

To remove the old covering, first warm the old covering with heat gun to loosen the adhesive. Wear cotton gloves to protect your hands; at temperatures of up to 450°F, a heat gun can burn an uncovered hand. As you pull off the covering, go slowly and pull at an angle to minimize residual glue problems. A covering iron can also be used to loosen the adhesive if you do not own a heat gun.

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Once you have the covering off, remove any residual adhesive or stuck bits of covering with Acetone or a covering thinner like Coverite Ironex. Acetone and the toluene in Ironex are toxic, flammable, and can be absorbed through the skin so wear rubber gloves and have adequate ventilation.

Working outside on a folding work bench covered in plastic is a safer way to use these chemicals. A spot remover like K2R (if you can find it) can be used to remove and absorb fuel stains on a glow model. (Note: Since K2R is extremely hard to find today, there is an even better way to remove oil from wood. That heat gun works wonders on oil-soaked wood. Keep the gloves on, hit the wood with full heat; close up. The oil will bubble out of the wood. Wipe away the oil that surfaces with a paper towel. Repeat the process until the wood is dry enough to cover.)

Preparing the Surface

As in painting or wall-covering, good surface preparation and surface damage repair makes the final covering appear professional: Now that the covering is gone, re-inspect the model for cracked ribs, broken spars, cracked sheet surfaces, loose engine and landing gear mountings. If the airplane needs repairs or additional re-gluing, now is the time to do it.

Once the repairs are made, fill nicks and dings using light or vinyl spackle and a palette knife. Lightly sand the surface with 240-320 grit sandpaper. When you are done sanding, wipe it off with a tack rag, running your finger over the surface and holding it up to a light at an angle to a light to check for imperfections. If you can feel or see any imperfections now, you’ll see them later when it’s covered. Covering does not hide poor workmanship under it.

Checking the Assembly

Careful pre-assembly saves time later: Pre-assembling the model, before recovering, ensures all surfaces fit together and all hardware is in place. During the trial assembly, be sure to check the following items if they are on your model:

•  Dowels: Remove these before covering if possible. Fit them, unglued, during the pre-assembly. If the dowels, usually rubber band hold-downs or forward wing mounts for bolt-on wings, can not be removed, it is easy to cover around them. Do not damage the airframe just to remove dowels.
•  Hinge slots: Cut slots and fit hinges in the wing, stabilizer, and control surfaces prior to covering. Make sure control surfaces flex easily. If the hinge control surfaces are still attached using Mylar type hinges, just cut the hinges with a sharp hobby razor knife. Remount with new hinges located adjacent to the ones cut.
•  Control Horns: Fit these prior to covering. I sometimes inset ¹/₃₂ or ¹/₁₆ plywood behind a nylon control horn on a sheeted surface to keep the control horn from flexing or worse, the screws pulling out. (Note: a neat trick is to slice a centered hinge groove under the control horn and insert a Mylar hinge all the way inside. Use thin CAA to lock it in place. This strengthens the control horn mount as much as do plywood inserts but is faster.)
• Pushrods and pushrod exit covers: Fit these before covering, making sure the pushrods line up with the control horns.
•  Structural improvements: On an ARF, check to make sure there are enough internal braces for the control push rods in the rear of the fuselage to keep the cable from flexing and causing control inconsistencies. If you want to change from a wing held in place using rubber bands, now is the time.
•  Air vents: On open surfaces, like wings and some stabs, drill small air vent holes in the ribs if there are none. This allows the heated air under the heat gun to escape to a cooler area so the covering over the heated area can “lay down” properly.

When you are done with the pre-assembly, disassemble the model for covering.

Creating a Covering Plan

Designing is the key to covering success. Before you begin covering, create a covering plan to make the covering job a lot easier and to produce better-looking results. Here’s a simple way to put one together.

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A covering plan starts with a photo of the model from a box top or off the Web. Blow it up to fit an 8½ x 11 sheet of paper using a copier or image editing software of your choice. Make some copies of it. Then make a line drawing of the major components of the airplane minus any surface decoration by tracing over the top of the photo. Make copies of the line drawing and then sketch your covering design on the copies until you are pleased with the results.

You could make multiple sketches of different wing and fuselage patterns until you have something you like. During this process you might often look in books or on the Web for design inspiration. When done, again make copies of your covering design and then shade the drawing with pencil to create a light and dark value drawing. It’s the contrasting light and dark pattern along with good color choices that make an airplane readable at a distance. On complex designs, it may be best to make full-size paper patterns of the design. Last, choose colors that appeal to you and that work with your design.

Selecting a Covering Material

Your choice of a covering material determines not only what your airplane will look like, but may affect how it performs. This is especially true of smaller electric-powered aircraft. Choosing a covering means making the right choice for your model. Before you can decide on the colors, you’ll want to decide if your model will be covered with opaque or transparent film – or some combination of them, and which brands of covering come in the colors you want to use. To choose a type and brand of covering you need to understand the differences between coverings.

Iron-on coverings come in four types; high heat, low heat, fabric, and light films. Fabric coverings are mainly used on heavier scale models of airplanes that were originally fabric covered and I’m skipping them because the Tiger 400 is a lightweight, non-scale airplane. The table below describes the differences between iron-on plastic film coverings:

Table: Comparisons of Iron-on Plastic Film Coverings

Weights and heats shown are an approximate range. For exact weights refer to the web site for a specific covering. For the exact heat ranges to affix the covering to wood or to shrink it, refer to the directions that come with your covering.

For the Tiger 400, we decided to use Coverite 21st Century MicroLite film; a light, iron-on plastic covering suited to models under 50-inches in wingspan. Because the Tiger 400 is a light weight electric, it does not need a heavier covering with fuel proof qualities. And, because the Tiger 400 is lightly built, it does not have structures to resist the force and pull heavier coverings create when they shrink that can lead to warping or breakage.

This table shows the specifications for MicroLite, the film we selected. No matter what film you choose you should be aware of the size roll it comes in, weight, temperature rating, and color selection.

Table: Coverite 21st Century MicroLite Specifications

Making a Cutting Plan

If you can carefully estimate materials with a cutting plan, that saves time and money later: Now that we’ve chosen the covering and colors, you’ll need to estimate the number of rolls of covering required. Again, a little planning now may save you a long drive to the hobby shop later. Here is how to plan your covering materials and make a cutting plan:

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To create a cutting plan, make a scale drawing of each 27¾ x 72-inch roll of Microlite covering on a piece of graph paper. Label each one for color. Each ¼-inch square represents 1½ inches of covering in the example, but you can use whatever scale is convenient. Measure each and every panel of your airplane and sketch them out on the graph paper, making sure to add dimensions and label them. When measuring a panel, add at least 1-inch on all sides of a panel and 3 inches at a wingtip for handling and stretching the film. If the covering needs a great deal of stretching as on a rounded nose, add even more than 3 inches for handholds.

Our cutting plan indicated that we needed one roll of transparent yellow Microlite and one roll of opaque white as our primary colors. We also used a small amount of opaque red for trim. If your airplane is large, remember that most films come on a 6-foot long roll but several brands also sell 15- or 25-foot rolls, ensuring color consistency for larger modeling jobs. Some brands also sell smaller “trim” rolls that can be used for trim colors such as the red used here.

That’s it! You’re ready to begin applying the new covering.

Next step: Covering a model airplane