Covering with Tissue and Balsaloc

It works great.

While it might not always replace the other tried-and-true methods such as dope, thinned white glue and/or glue sticks in every situation, it has certain advantages and has joined my arsenal of techniques for building nice airplanes. The part I like best is the tissue stays dry for the entire process! This is especially wonderful for those covering jobs that demand the fabulous colors of "domestic" tissue which I find simply can't take being manipulated while wet. And, best of all, it is so much easier to pull the tissue tight and then have it instantly tack down. I covered the nose cone on a canard pusher (sharp compound curve) with this method and it ended up as smooth as silk. Here are some photos of my covering the underside of an highly cambered wing from an R/N models "Two Step" an all balsa Coup D'Hiver model. See my FreeFlight page for a blurb about the airplane itself.

1) Once all of the sanding is done I brushed on a layer of balsaloc. The balsaloc should have the consistency of white glue. I had to thin mine a little with water. Make sure the coat is even and not too thick; it does not take very much to make an effective bond. Because the balsaloc goes on clear it is sometimes hard to know what parts have been covered and which have not. Sometime in the near future I will try mixing up a small batch with a little dye in it (the same color as the covering, of course).
2) Set the iron to 90 - 100 degress C (212 F). A Coverite "intelligent" iron or another iron with the temperature adjusted using a coverite thermometer works as well. I find balsaloc is quite sensitive to the temperature and it's vital that it be accurate.
3) I started by tacking down one end of the tissue on the bottom spar, then the other end and then tapping it down along its length so I don't get any wrinkles from the tissue stretching as I run the iron over it. I went back and forth over this a couple of times to make sure that it is all stuck down.

4) Next I attached the tissue to the ribs by running the iron along the ribs from the spar to the leading edge. I then did the same for the trailing edge.
5) I then ran the iron over the perimeter to glue everything else down. The tissue shrinks a little when heated but it loosens again when it cools and absorbs a little moisture from the air. Just be aware of it as it could mean the tissue pulling away from the edge before the balsaloc hardens.
6) I like to wrap the tissue around the edges a little. A Topflight trim tool does a great job trimming.
7) This is what the edge looks like all nice and trimmed.
8) After it's all ironed down I like to go along the edges with a little thinned weldbond (70% water, 30% glue). Balsaloc is water soluble and can soften when wet (such as during the water shrink). The tissue is ready to shrink within a half hour but I like to leave it for a couple of hours to really let the weldbond cure; it's water resistant when properly cured. Note while the weldbond is very strong it leaves sort of slick looking ridge after the tissue has been doped. You can avoid that by going over the edges with nitrate dope thinned 50/50 instead; it also works well in gluing down the tissue. Don't omit this step, though. I've had tissue come loose when I tried to shrink it with either water or alcohol before properly gluing it down.
9) Finally, it's time to shrink. I use water sprayed from either my air brush or from my window washing spray bottle. Once the tissue is damp, I then weigh down the structure on a large piece of glass with brass weights (steel or iron weights may stain your tissue; see the stain on my Parnal Elf.) I put brass shims under the wing to hold it about 3.2 mm from the glass. I put it aside and let it dry for a couple of hours and work on another airplane (or play some quake.) I always end up with a flat, straight structure with this method. Note that I shrank the tissue before putting the top covering on. This is so I could get at any tissue that may have pulled away during the shrinking (which did not happen).

Last modified: May 19, 1998 - Hey, WIND! Will you PUULLLLEEEAASSSEE die down; I wanna test fly these things!