Notes

Construction

Thin CA glue; no workbench should be without it. Most paper, and balsa, soaked with thin CA gets much stiffer and stronger. I use it to reinforce centering rings and inside body tube joints, protect balsa fin edges, and stiffen paper couplers.

CAUTION!!! CA (Super) glue will adhere (polymerize) almost instantly when pressed into a thin film, or in the presence of water. But a drop of liquid CA, or piece of CA saturated paper, will stay wet and ready to "grab" anything that touches it for many minutes. NEVER press on, or touch, CA soaked paper with bare fingers unless you are certain it is dry. Acetone (in some nail polish removers) will dissolve the structural polymer and is an effective CA debonder. Thin CA has extremely low surface tension and viscosity and will flow into places you might not think it would.

Paper fins. A double thickness of tagboard (Manilla folder paper) soaked in CA makes a great fin for small or high performance rockets. I lay the fin tip on the folded edge of the folder, trace out the planform, then leave a 1/4" to 1/2" tab at the root edge. When cut out with scissors, it's like a little book. You can fold the tabs slightly apart, then glue the rest of the fin together. The tabs form their own fillets when glued to the body tube. These fins are flexible and will bend instead of breaking. If they do crease, wick some more thin CA into the crease while holding them straight. Voila!

Braided steel fishing leaders make great flame-resistant shock cord mounts. Epoxy one end deep in the body tube or onto the motor mount. Attach the shock cord to the other end with the built-in snap swivel.

Note: A post on the USENET newsgroup rec.models.rockets by long-time rocketeer Bob Kaplow indicated that steel fishing leaders can, indeed, melt from ejection charges. Sure enough, one of my leaders was found to have over half the strands melted through. This particular leader packs up against the forward end of the motor during flight and takes the full heat of a charge. None of the other leaders showed this damage, but examining an installed leader carefully is a problem. Keep an eye on them and replace if necessary.

Fiberglass. My L1 project involves my first attempts at fiberglassing paper body tubes. Definite learning curve involved here! For practice, I tried glassing some models to increase their durability.

Fiberglass cloth has a certain amount of "torsion" within the cloth fibers; it will tend to "unwrap" when rolled around a tube. This is especially evident with small diameter tubing and thin (finish grade) epoxies. Let the epoxy get tacky before wrapping small tubes, or wrap the applied cloth with plastic wrap to hold it down as the epoxy sets up.

My glassing jig is simply a broomstick supported between two shelves. The airframe tubes are friction fit to the jig with pieces of old poly sponges. My first BT-80 wrap turned out okay on a 14" length of tubing using finish grade Zpoxy and SIG 5oz glass. My second attempt on a 28" tube came out terrible; there are bubbles, warps, and ridges everywhere. This happened because I took a "shortcut"; I tacked the cloth down with CA before applying the resin and became overconfident. The cloth bunched up and could not be smoothed flat. It didn't look "bad" while wet, but a coat of primer revealed the problems.

Patience pays off. The third glassed section (fin can) turned out as well as I could have hoped. I simply painted the tube with a thin layer of Z-poxy, let it tack up a little, then carefully applied the cloth with a foam brush being careful to stroke from the center out as I worked around the tube. Dry spots were filled with the brush and wet spots were dabbed off with tissue. It looks good to me and to a couple of experienced glassers. Use long setup time, thin epoxy, foam brushes, and take your time. I trim the tube end overlap with a hobby knife, then sand smooth. Thinned Fill'n'Finish covers the weave and gives a smooth surface after sanding. A strong, light, and easily finished airframe is the result.