Cover small models with tissue

Model Airplane News, Feb 2001 by Robelen, Dave

A new twist for a classic technique by Dave Robelen

If you've become involved with RC airplanes only in recent years, there's a good chance that the only covering materials you have used have been the iron-on sort. Now, however, with the increasing popularity of slow flyers and park flyers, the tissue-paper covering is a very attractive option. Tissue is very light, definitely economical, reasonably easy to repair and can be very attractive. I'll take you on a "tour" of how I apply colored tissue covering with a clearcoat on a typical lightweight model, and I'll tell you about some of the tools and materials involved. YOU'LL NEED

First, note that there are different types of tissue paper. The sort found in craft and gift shops can be bought in a multitude of colors, but it's too heavy and too difficult to work with as a model covering. True Japanese tissue that is intended to cover model airplanes is available from just a few sources: Peck-Polymers* offers a very nice grade that is available in a variety of colors and is pleasant to work with; the other main choice is Esaki tissue that is normally sold by Campbell's Model Supply*. Esaki tissue is the lightest grade that comes in a choice of colors and is also quite reasonable to work with.

Although modern tissue is the same as it was many years ago, the materials for adhering and coating it have undergone a major change. Formerly, you had to coat a project's framework several times with a model dope and then use more of it to fasten the tissue in place. Still more dope, thinned down, was used as a coating to seal the tissue. This process usually required brushing the dope onto the tissue and was often quite time-consuming. This method still works fine for those so inclined, but the system I describe uses several craft materials that are available from most craft stores.

I have found Elmer's School Gel excellent for bonding the tissue to the framework. The smallest amount is adequate, and the bond becomes permanent within a short time.

COVERING TIPS

Prepare the framework by lightly sanding all over with 220grit sandpaper to remove all glue bumps and irregularities. Starting with the wing, cut the tissue into panels so that you can cover a single segment at one time, e.g., left bottom; right bottom. Do not try to wrap the tissue around to cover a second panel with one sheet; this is the path to warps and wrinkles. Tissue has a "grain": its fibers are aligned in one direction on a sheet. Since the tissue shrinks more across the grain, we want these fibers to run across the wing panel to best preserve the airfoil shape.

Tissue is usually attached only around the edges, but there is an exception with undercambered wings. Here, the tissue must be fastened to all of the exposed structure. Cover the bottom first, initially attaching the tissue only to the center spar. Apply the glue very sparingly to avoid having excess weight. After you've attached the tissue to the spar, cover the bottom front and then the rear of the panel. Repeat until you've covered the bottom of the wing. Cover the top of the wing by attaching the tissue only to the edges. Draw out any slack or wrinkles before the glue hardens to avoid having warping or wrinkles later. After the glue has dried, you can trim the edges with scissors or a sharp blade and smooth them with fine sandpaper.

Rubbing alcohol lightly sprayed on does a fine job of shrinking the tissue just the right amount. Be sure to pin the wing to a flat board (with suitable props) to prevent it from warping as it shrinks. Krylon Crystal Clear spray lacquer does a fine job of clearcoating; two light coats are usually adequate.

Covering the fuselage is pretty much a repeat of the wing: work in sections and don't wrap the tissue around corners. To cover simple compound curves, first moisten the tissue with water to help it stretch into place. For really complex curves, occasionally, you may need to slice the tissue into strips to help it lay down properly. Again, clearcoat with two coats of lacquer. Elmer's white glue will hold clear plastic windows and windshields nicely in place, and it dries clear.

When you apply tissue to sheet balsa, first spray two coats of lacquer onto the balsa, then lay the tissue in place and brush acetone over it. Rub the part smooth with a fingertip, and the tissue will bond nicely.

The delicate tail frames are a special case because they can easily become warped. To deal with this, first bond the tissue onto a sturdy frame, then shrink and coat it on the frame and let it dry for a couple of days. Then cut out pieces of the precoated covering and lightly glue them onto the tail frames.

Because the tissue will continue to shrink for several days-and occasionally longer-you should clamp parts such as slender wings to a board while the glue is curing.

TRIMMING AND REPAIRING

To bond tissue trim to the tissue covering, use acetone to soften the lacquer, then apply the trim pieces and respray. For small trim work, felt-tip pens can be very useful to add a touch of color.