Model aircraft covering materials

Perhaps experienced people will turn their noses up at the upcoming lines, as they do not bring any groundbreaking information and work procedures, but only comprehensive information about the most common covering materials and working with them. It is necessary to realize that many years have passed since the last articles devoted to basic work procedures, and with the known absence of modeling circles, today's beginners are dependent only on the advice of more experienced people or on searching for instructions in older editions of Modelar, if they have both available. Therefore, several articles, which we will gradually print, should give them a helping hand. The first one is about covering. Intentionally, because a bad cover will devalue an otherwise nicely built model, and on the other hand, a good cover can hide some of the skeleton's flaws and is actually the first thing everyone notices.

Before we begin to focus on the individual covering procedures, we will describe the different types of covering materials and adhesives for gluing them. Covering materials can be divided into papers, fabrics and plastic films. We will take a closer look at the papers, as they are the most used in the first models. Commonly available are: Modelspan, Japan and Mikalenta. Other types of paper are also used, for example capacitor paper, but this is already a certain specialty and is beyond the scope of this article.

Modelspan is sold in three thicknesses and thus different weights (thin, medium and thick) in several color shades. We choose the thickness of the paper according to the size of the model. In general, we will use thin Modelspan for small models and surfaces with a rigid coating, medium for the wings of A1 glider-sized models, and thick for larger models. Usually, however, the paper used is listed in the construction description with the plan, or it is included in the kit. Modelspan has both sides equally smooth. The fibers of the paper are parallel to the longer side of the sheet. Its biggest advantage is that it can be turned off with water and it can be worked well even in a wet state, as it hardly loses its strength.

Japan is a paper with similar properties to Modelspan. However, the fibers are arranged chaotically, and in addition, one side is smooth, the other rougher, which can be easily recognized by touch (we always place it with the smooth side on top). It is also sold in three weights and several colors. It can also be turned off with water, but it is difficult to work with it in a wet state, as it loses strength.

Mikalenta is sold only in one thickness and in white.
We can easily recognize the direction of the paper fibers. Working with Mikalenta is more difficult, as it cannot be turned off with water, but only with varnish. Disintegrates in water. Two layers are used to reinforce the covering of larger models, usually with fibers across.

We need to prepare the skeleton of the model for covering. First, we carefully sand all the places where the cover will be glued to a smooth surface. We use sandpaper with a grain size of 320 to 400, glued to a flat pad. In order not to squeeze holes in the already sanded part of the frame with dirt on the work table, we place the sanded part on a thin foam pad or other soft pad. We also remove excess glue from the frame. After sanding the frame, we paint it with a clear nit-roller (not tensioning) and after it dries perfectly, we sand it again. Because by varnishing, some years will emerge from the wood, which will be smoothed out by subsequent sanding. If we stick the cover on an unpainted surface, these summers would come out under the cover, which would then not be smooth.

There are many opinions on the adhesives with which we glue the coated paper to the frame. Almost every modeler uses their "true and guaranteed" glue, which they cannot tolerate. However, in general, Modelspan and Japan stick best with water based adhesives. They can be glued very well with the office's White adhesive paste, which we dilute with water so that it can be spread with a brush. Adhesives for wallpaper, for example Lovosa, Apeko, are also suitable. We can also use slightly diluted Hercules. On surfaces with a rigid coating or on solid balsa parts, it is best to paint the covering with a clear adhesive nitro varnish, which can of course also be used to paint the paper to the frame.

For gluing Mikalenta, nitro lacquer is the most suitable adhesive. Some modelers achieve good results with the aforementioned water-based glues, however, for beginners nitrolacquer will be better. When gluing with any glue, do not apply an unnecessarily large amount, as the joint will not be stronger, but only more substantial and less attractive.

Before covering, cut the paper into strips that will exceed the coated part by 10 to 20 mm. We choose the addition according to the size of the coated part. For papers with recognizable fibers (Modelspan, Mikalenta), we orient the longer side of the strip parallel to the fibers. If we are gluing paper without an addition, for example in the folds of the wing or in the interfaces of different colored papers, we cut the edge of the strip with a razor according to the ruler so that it is straight.

If we have all the parts of the cover ready, we proceed to the actual coating.

For flat surfaces (wings and tail surfaces), first coat the lower side and then the upper side (Img. 1). If the wing has folds, we cover them in parts (Img. 2). If the wing has a profile with a bent lower side, it is necessary to glue the paper well to the lower part of the ribs so that it does not come off after switching off. The rounded end arches can be covered at the same time as the wing, if we cut the paper in the area of the arch several times in a fan shape and gradually glue it (Img. 3). However, it is simpler to cover the rounded end with a separate strip of paper with oppositely oriented fibers, the protruding ends of which are cut and gradually glued (Img. 4).

For hulls with a simple (square) cross-section, we coat the sides first and then the top and bottom. We start applying the paper to the frame coated with glue from the center of the part (Img. 5). It is more difficult to coat parts with a round or polygonal cross-section. We coat these parts piece by piece. We will prepare a strip of paper, with which we will cover only a few longitudinal bars. We choose the width in such a way that the breaking capacity of the paper is sufficient to eliminate the bulge of the hull (Img. 6).

First, to the process of covering with Modelspan and Japan. Apply glue to the coated part in all places where the covering is to be glued. Usually, these are all the perimeter sides and the slats of the beams. For wings with a curved profile, the underside of the ribs. We take care not to apply the glue to places where the cover should not be glued. We place the prepared strip of paper on the painted frame, flatten it and gradually apply it, while already trying to turn off the cover in the longitudinal and transverse directions (Img. 7). Of course, we pay attention to possible wrinkles that would not match the paper's breaking capacity.

Let the glued cover dry, then cut off the excess edges. Leave an allowance of 2 to 5 mm (depending on the size of the model), apply glue to the edge and smooth it to the skeleton. We continue in the same way. We choose the additions so large that the paper wraps the frame and does not extend too much over itself.

Modelspan works well when wet. We proceed in the same way as in the previous case, but before placing it on the frame, lightly moisten the strip of paper with a fixing agent or a sprayer. Wet paper better copies round places and is therefore suitable for covering indented parts, for example round hulls, in this way.

If we glue paper to hard-coated parts with water-based adhesives, we glue the paper only on the edges. It is more convenient to paint the paper over the entire surface: place a strip of paper on the coated part and paint it with a slightly diluted adhesive nitro varnish with a brush and then, preferably with your fingers, smooth it out. We will again leave an addition on the overhanging ends, which we will also paint.

Mikalenta and I work in similar ways. However, we glue the paper to the skeleton with nitrolac adhesive. Place a strip of paper on the frame and glue (paint) it in the appropriate places. It is advisable to first score the paper in several places and apply the varnish gradually. For the wing, we usually glue the paper first to the main beam and then, while simultaneously tensioning, to the leading and trailing rail. We make sure to turn off the cover as best as possible already during gluing. Mikalenta can also be glued with nitro thinner. However, we have to paint the frame several times with adhesive nitro varnish (2x to 3x), then lay a strip of paper and smooth it with a brush dipped in nitro thinner.

If we have covered all parts of the cover, we proceed to turn it off. We can shut down Modelspan and Japan with water. It is best applied with a fixer or sprayer, in an emergency, carefully with a clean foam sponge or a piece of cotton wool. For the wings and tail surfaces, we first turn off the cover on the underside. To prevent them from curling, we store them in templates that may already have negatives on them. We then moisten the upper side in the template and let it dry completely. Wet the hull cover less often and switch it off more often to avoid deformation. We repeat the entire procedure until the tension is perfect, as well as in the case when insufficiently closed areas appear.

The Mikalenta cover cannot be removed with water, but only with a clear release nitro varnish. For the first coat, we will use undiluted varnish in order to fill the pores of the covering more quickly and the varnish will not penetrate the frame unnecessarily. We then use diluted varnish for further coatings. Three to four coats should be enough to wear off the coating. It is understandable that the next layer is applied only after the previous one has completely dried. Starting with the second layer, we always carefully sand the surface with fine sandpaper. We paint the switched-off cover with zipper or top glossy nitro lacquer.

We must impregnate the water-removed cover from Modelspan or Japan with a clear nitro varnish against moisture. For the first coat, we will again use undiluted varnish. We will use tension nitrolacquer. For smaller models, zip-lock nitrolacquer, which does not have such great switching capabilities, is more suitable. Carefully sand each layer of varnish with fine sandpaper. Three to five layers are usually enough to impregnate the covering. Let the parts dry again in the templates so that they do not twist. Minor defects in geometry can be corrected over a closed heat source, such as an electric stove or hair dryer.

As I already mentioned, the cover of the model is the business card of every modeler, and therefore we always wash our hands before working on the cover and keep all the necessary tools clean. We only use clean thinner to wash the brush. Dirt from hands or utensils likes to stick to the cover and their removal is often impossible.