Adhesives

ADHESIVES - by Roger Layton [from Rock Valley RC Flyers, Rockford, IL.]

Cyanoacrylate adhesives: The history that abounds relative development of CA is this. It was developed as an alternative to sutures and bandages for treating open battlefield wounds during the Vietnam War. This seems to make sense in light of its ability to instantly weld the fingers together of any careless modeler. That little bottle of instant repairs that you buy is actually a chemical called cyanoacrylate monomer which, except for an inhibitor, would instantly form a single plastic blob of polymer with accompanying heat and fury that would resemble the China Syndrome. CA was on the market for a number of years before it came to the construction hobbies. The adhesive was so fluid that it could only be used to mend nonporous materials like ceramic, plastic, and glass. It certainly did not work on balsa, which merely soaked it up like a sponge. Later, when viscosity modifiers were added, it became generally useful and ended up "in our hands" (pun intended). The advantages of CA are speed and hold. The disadvantages are cost, vapor, and brittleness. Please be your own judge but I will not use it for whole plane construction. It has a place and is excellent in certain applications. For many butt joints and T-joints, CA is too brittle, especially in large airplanes. Aliphatic glue is a much better choice. CA is specified as the adhesive of choice for wing skins. In this application, it is too hard and makes sanding to an invisible butt joint very difficult. Animal glue like Sigment is the quintessential choice since it is the sole truly sandable adhesive. Cyanoacrylates are excellent for tacking parts into place to speed up construction followed by regluing with an aliphatic adhesive. CA is unequalled for making repairs and piecing a crashed beauty back together. When you use CA, be careful not to draw debris such as sawdust or baking soda (incidentally a good inexpensive accelerant) into the bottle. It may cause the entire contents to harden.

Aliphatic glue: The parent for this type of glue is doubtlessly Borden's white glue. Borden's is a very strong glue which penetrates wood well. A second generation of such glues contains fillers which render them somewhat "sandable." Regardless of the claims, none are truly sandable since their binder is rubbery. In my mind, more expensive is not better. The hobby store brands like Pica's "Gluit" and others are expensive and not very sandable. Borden's yellow woodworkers glue is strong, inexpensive, and as sandable as any I have found. On large built up fuses and wings, I recommend using Borden's woodworkers glue for most of the "inside" construction including attachment of the skin. But I glue the skins together and other places to be subsequently sanded with Sigment. Firewalls, landing gear blocks, and hard points are attached with epoxy.

Silicon caulk or RTV: This is an excellent adhesive which does not harden. This provides considerable shock absorption. This material is particularly good for attaching parts inside fiberglass fuselages. There must be ample gluing surface. Fiberglass flexes in a finished airplane during flight will cause brittle joints made with CA epoxy or other adhesives to fail. Many servo trays have broken loose during a hard landing. Certainly, you have noticed the vinegar-like smell of silicon adhesive when it cures. Do not use this adhesive around electrical components. Connect cells in a battery with hot melt adhesive. Rubber cement: The next time you want to make little protective foam boxes for your receivers or batteries use rubber cement. It maintains its flexibility and will never let go once it is dry.

3M Spray Adhesive: Formula 77 is excellent for attaching paper rib and bulkhead patterns to balsa or plywood during scratch building. If you want to remove the pattern from the wood after cutting, allow the adhesive to dry on the paper for more than a minute before applying. The paper will not stick quite so tightly and the adhesive will not transfer to the wood. 3M can also be used to hold 6oz. fiberglass in position on the wing center while epoxy or polyester resin is applied. It is great to hold plans flat on building board.