Glues!
by John D. Clark
by John D. Clark
As I find out about new glues, and new uses for old glues, I will add them here. Check back occasionally!
This is the greatest glue that has come along for modeling. It is available in several thicknesses--most simply thin and thick. Thin CA glue is best used where you can position the pieces together, and then just wick the glue into the seam. The doublers in my first trainer were glued this way. Thin CA is also used for glueing "Easy Hinges", where you deflect the flying surface (hopefully in its final position), and wick the thin glue into the weave of the hinge. I've never lost a flying surface with proper use of thin glue on the hinges.
Thick glue is used by spreading it on one part and then pressing the parts together. Make sure that the pieces are positioned correctly, because you don't get much opportunity to re-position them. I also use thick CA glue to re-inforce glue joints made with thin CA. Many of my light-airplane wings were made this way--position the ribs on the spars and touch with a drop of thin CA. Once all of the major parts are in place, go back with thick CA and re-inforce all the joints.
Epoxy is a two-part glue. One part is the resin monomer, and one part is the resin catalyst. It comes in a variety of setting times, and I use 5 minute, 12 or 15 minute, and 30 minute glue. Generally, the longer it takes to cure, the stronger and less brittle the glue becomes. Epoxy glue is best used for high vibration and strength areas like gluing on the firewall, and the landing gear mount.
The primary problem with Epoxy resin is that it is quite toxic, and a cumulative poison. That means that each exposure to epoxy adds up in your system, and some people eventually develop an allergy to it. Whenever I use epoxy, I use vinyl rubber gloves (I have heard that latex gloves are not impermiable to epoxy, so don't use latex gloves) so that my skin never contacts the glue, and when I'm done, I wash my hands thoroughly with soap and water.
Epoxy is used by mixing the two parts, usually in equal amounts. In large quantities, epoxy can heat up quite a bit while curing, so be careful of the un-used glue. You'll find that the glue on your parts takes longer to cure than the excess glue because, generally, the glue is spread thinner on the parts and the heat generated during the curing process is more diffuse. The internal heat generated by the polymerization process accelerates curing in the "pot".
Yellow carpenter's glue has many uses for R/C airplanes. For my 35% Carden Extra 300S, I used more of this glue than anything else on this airplane. The primary benefit is that you have time to position the parts for absolute accuracy. The second most important benefit to this glue is that it is sandable.
It can be used to glue together sheeting. Tape the sheeting together with masking tape the entire length of the joint. Turn the sheeting over, and open the joint slightly by folding the masking tape. Run a bead of glue into the joint (I used a 5 cc syringe), then flatten out the sheeting. Wipe off the excess glue, then sand the joint. Tape the joint perpendicularly with masking tape. When the glue is cured in a couple hours, remove the tape and sand the joint.
This particular glue is urethane based, and has the unique properly of foaming up while it cures. This allows it to fill voids in the glue joint. I have heard of people using it to glue sheeting on foam, but you must make sure to hold the sheeting in place with weight or in a vacuum bag so that the expanding glue doesn't push the sheeting away from the foam.
I have used it to glue dowell hardpoints into styrofoam surfaces. I find that drilling out the hole takes out the styrofoam beads and doesn't leave a nice clean hole. This glue expands to fill those voids.
The procedure for using this glue is to moisten the surfaces before applying the glue. Presumably the water helps to catalyze the glue. It takes about four hours for the glue to set.
Elmer's makes a contact cement that is a green, thin water-based glue. I've heard that some people are using it to glue sheeting, although most people do not use it on wings or stabs, only on non-weight bearing parts such as turle decks and hatches. I have not used this glue, myself.
You brush it on both parts.