Make your own fiberglass parts

Making fiberglass parts for our model airplanes is often considered a difficult task. Several companies

produce engine cowls and wheel pants for popular designs, but if

you scratch-build a new airplane, you'll have to make your own custom parts.

I have offered many aircraft designs that required additional fiberglass parts, but I never had to tell builders how to make them because commercial parts were often available. Let's face it; it is a lot easier to simply order a molded part than to produce one from scratch. Or is it?

My lh-scale Miss San Bernardino (see page 76), can be built by the average modeler, and all its fiberglass parts (the engine cowl, cowl cheeks and wheel pants) were fabricated using this simple method. This technique can be applied to virtually any project for which a custom-made fiberglass part is needed.

Here is what you will need:

* Blue insulation foam.

* Fiberglass resin (epoxy or polyester).

* Fiberglass cloth.

* Fiberglass mat.

* Mixing cups.

* Inexpensive 2-inch paintbrush.

* Mixing sticks.

* Acrylic automotive touch-up putty.

FIBERGLASS AND RESINS

Several sizes of fiberglass cloth are available; it is identified by its weight per square yard (9 square feet). The size of the part you want to make and how durable it needs to be are what determines the cloth's weight. For general model applications, 1/z- to 3/4-ounce cloth is appropriate. Fiberglass mat comes in sheets; it can be used as is, or it can be shredded before use to produce a lighter structure.

Available at hobby shops, most marine-supply outlets and at some automobile-parts stores, fiberglass resin is available in various grades depending on its use. It is best to use a resin that has the viscosity of motor oil. I use Marson-brand resin because it has a thick viscosity, is semi-flexible when it has cured, and it sands easily and sets up quickly. Because it is thick, it won't penetrate into the wood as much as thinner resins do, and that means you'll get a lighter finish over a balsa structure. A lot of commercial companies use epoxy resin, but I like to use polyester resin because it sets up much faster-usually in about 5 minutes. You can vary the setup time by adding more or less catalyst (usually 10 to 12 drops for each ounce of resin). When using polyester resin, be sure the air temperature is above 60 degrees F, or it will take a significantly longer time to cure.

THE PLUG

I use blue household-insulation foam to make the plug for the part I want to mold. Blue foam is cheap, and it is much denser than white expanded-bead foam. Blue foam can easily be glued together and is easy to work with. It can be carved with a sharp knife and sanded almost like balsa. It can be purchased at most home-improvement outlets and comes in large 4x8-foot sheets.

When you determine the size of your part, cut the foam to approximately that size. Slice the foam into layers and laminate them together into a block of the required thickness. I use foamsafe ZAP to laminate the foam, but epoxy or white glue works, too. Draw the part's top outline on the top of the foam block and cut it to shape; then draw and cut the side view and whittle and sand the foam to its final form. When you have a foam plug that looks like the part you want, cover it with iron-on Econokote or another plastic film that has low-temperature qualities so you won't melt the foam with your sealing iron. Once the plug is covered, you can apply a coat of mold release. This isn't necessary, however, if you let the resin cure long enough.

Apply the thick fiberglass mat first. Smooth it around the plug and apply your resin. Using a brush, start at the highest point and work the resin downward. Then add the fiberglass cloth, and when you have the foam form completely covered, use the mixing stick to squeegee out the excess resin, again starting from the highest point and working downward. (Old plastic credit cards make good squeegees.) Remove as much resin as you possibly can. After the first resin coat has hardened, apply a second coat and let everything set up overnight.

The next day, remove the molded part from the plug. Sand the part smooth and fill any imperfections and pinholes with acrylic automotive touch-up putty. Sand it smooth again, wipe it down with a tack cloth, spray on a coat of sandable primer, and you are ready to paint on your final color.

Custom making parts is very easy to do once you learn this technique. A whole new selection of modeling subjects will open up to you when you know how to make molded fiberglass parts.

Copyright Air Age Publishing Sep 2001
Provided by ProQuest Information and Learning Company. All rights Reserved