The Return of the TigerKitten (8)

That white stuff in indeed "fiberglass"...woven glass fiber cloth. There are more categories and variations of fiberglass cloth than I can keep track of, so I manage by knowing what I need to know about the varieties that I use to build airplanes. What I'm using here is, I believe, referred to as "E" weave cloth (if somebody out there can correct me, let me know and I'll post the info) This is the stuff you'll most often find packaged for model airplane use...it's suitable for both laminating (building up molded parts) and surface coating, which is what we are doing here. This is "two ounce" cloth, which means that it weighs two ounces per sq. yard, and is just about the ideal weight for reinforcing wings and fuselages of medium sized models like this one. One of the important characteristics of E cloth is that it is really LIMP, which means that it will drape and form easily around compound curvatures even more severe than the ones formed by this wing center section structure. To get to this point I have used REALLY SHARP scissors or shears to cut the cloth enough oversize that I have plenty of margin past the edges I want to cover. You'll see why this is important. DON'T try to cut glass cloth using dull scissors or razor blade cutters... you'll end up with a frayed mess and waste a lot of good material.

For years the term "fiberglass resin" meant polyester resin, that you catalyzed with methyl ethel ketone peroxide (MEKP, which is nasty stuff) and which can be really fussy about whether it wants to cure or not over various substrates such as wood with any sort of finishing product already on it. We used it because it was (and is) very easy to sand. Until recently epoxy resins, which are far more tolerant of whatever might be underneath them beside glass cloth and balsa wood, were nasty to sand...they'd gum up, clog sandpaper, and generally frustrate you. That time is past. Choosing a good surfacing epoxy like Z-POXY Finishing Resin, which I get from Frank Tiano Enterprises ( http://www.franktiano.com/ZapFrameset-3.htm) gives you trouble free curing with easy sanding. For surface glassing jobs like this I mix the Z-POXY per the instructions and thin the mixture with 25% denatured alcohol by volume...this makes it easy to fill the weave of the cloth without tugging and slipping. Right here is where it's necessary to strike a balance... you must FILL THE WEAVE so that the cloth becomes translucent as you see here. That indicates that the glass fibers are thoroughly wetted with resin and will provide full intended strength. Any extra resin pooled on top becomes extra weight. There are various techniques around for wiping or blotting any such pooled resin away before it cures, but I've had the best luck with thinned resin brushed out carefully and left to cure.

We have to make the glass cloth lie smoothly around whatever sticks out, protrudes, or otherwise can't be temporarily removed. In this case the previously installed aileron horns are in the way. The fix is easy...cut a couple of short slits in the cloth so it will lie neatly around the horn extensions. It isn't necessary to make the edge of the cloth fit perfectly around the openings in the balsa sheet...close and neat is OK here. Do this with plenty of extra loose cloth to work with BEFORE you get any epoxy up close to what you want to work on.

The glass cloth we are using is limp enough to lie easily around compound curves,. but it is not going to fold around a sharp edge without a little help . What's happening here is that I have applied epoxy to the cloth over most of the upper center section sheet with only the aileron horn area and the aileron cutout edges left to do. You can see how I have cut the cloth right up to the edge I'll be asking it to stick to so there won 't be any folds, tucks or puckers to keep it from lying nice and flat against the balsa structure.

The next step is to stick the cloth in place along the aileron well trailing edge with a nice wet coat of my thinned epoxy mixture. Pull any overhang well past the structure you want it to cover and leave it alone until the epoxy has cured...don't fuss with edges like this while the cloth can still slip and slide and end up where you don't want it to be.

Here's the top surface of the wing center section with the glass cloth in place, stuck down, and saturated with my thinned ZAP finishing epoxy everywhere I want it to become part of the finished airplane structure. When it's cured I'll trim those overhangs away and we'll move on to the bottom surface.

On an inside edge like this the best way to trim the overhang is with a new/sharp blade, and it will work best if you use a slicing motion rather than trying to push the blade through the glass cloth. I'll trim the outside edges after finishing this cut.

Once the epoxy has cured on the top surface and all the overhanging edges of epoxy-saturated glass cloth have been trimmed, it's time to do the other side. Here I'm using the same wet brushing technique to be sure the epoxy fills the weave of the cloth. In the case of this airplane the upper surface of the wing presents the most complex part of the job... getting this bottom section covered is just a matter of getting the glass cloth smoothed out and thoroughly wetted.

Remember, you can't force the glass cloth to fit around or into tight corners without puckering or wrinkling. Where the bottom covering wraps around the leading edge and up toward the top of the wing, the leading edge attachment dowels are in the way. I cut slots to permit the cloth to lie flat around them...the excess will get trimmed away after the epoxy cures.

The TigerKitten design calls for two aileron servo cutouts in the top center section. I chose to make these after the structure was already glassed. Here you can see how I have laid masking tape over the area to be cut out and used that as a surface that is easy to mark with a pencil to lay out cut lines. I'm cutting aileron mounting rails that will slip into those "T" openings from a piece of 1/4" x 3/8" spruce, which you can see at the top. One insert has already been cut.

There is another way to attach glass cloth to the airplane structure. In this case I wanted to reinforce the aileron servo cutout area after fitting the servos, so I cut a small piece of that same 2 ounce cloth just big enough to cover the area I was concerned about. For this little extra section of "glassing" I did not want to mix up more epoxy, so I used a simpler method that works fine for small jobs.

Thin (fast) ZAP will wick into a piece of fiberglass that is placed smoothly against a surface like this one and bond the cloth into place almost instantly. The drawback to using this method is that the cyanoacrylate adhesive does not provide much of a sanding base for getting a smooth finish on the glass weave, and using ZAP in this way except for small, quick tasks would be a very expensive way to employ it.

You can see where the thin ZAP has wicked past the edges of the structure out into the weave of the glass cloth. It happens that this makes the glass easy to trim, just as it would have been if I had used epoxy. I'll clean up these servo mounts with my No. 11 blade and then set this part of the job aside until it's time to do some covering.