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Fiberglass 101, Part 1: Preparation

Text and photos by Barry C. Forrest.

The following steps are a guide for understanding the process used to fiberglass Model and HPR rockets. The following procedure is referred to as laminating. The outcome is a high strength, low weight frame that will last longer than most rockets made with cardboard or phenolic alone.
The kit that is used here is a 4" Public Enemy Bull Pup with an added payload section for an altimeter and dual deployment.
The resin used here is Gougeon Bros. "West Systems" brand. I've used this resin (as other rocket builders have) with great results. Any high quality Epoxy (Best type) or Polyester (ok type) resin will work but your results may vary from those below.
First is a list of the supplies you will need (left to right, front row then back row):
  • 301-A mini pump kit for resin 5:1 ratio (for use with 105 resin & 205/206 hardener in Group "A" size - 1qt resin, .44 pnt hardener)
  • Latex or vinyl gloves (latex is not solvent resistant, vinyl is)
  • Mixing stick
  • Squeegee (auto body Bondo spreader)
  • Disposable paint brush (2 are good to have. This is a 2" size.)
  • 105 Resin
  • 206 hardener (fast)
  • 205 hardener (slow) (see West Systems site to pick best usable time for your temp- I used fast here because it was 60-65 degs when I did this-too cold for slow)
  • 406 Colloidal Silica (for thickening resin to make fin filets-best all around thickener for hardware and bulkheads. This will be used later in the building process but is good to have on hand)
  • Wax paper
  • Acetone (for clean up of tools and work bench)
  • Rubbing alcohol (for smoothing fin fillets OR clean up of tools and work bench-cheaper than Acetone)
  • Mixing cup, wax-free (I used small plastic yogurt containers-resin will pull out when dry. A mixing cup that is flat and wide is better than one which is tall and thin.)
  • CA adhesive (thin style)
Here are the two types of fiberglass being used
  • 1.5 oz bi-directional type- normal weave
  • 3.25 oz bi-directional type- "crowfoot weave"
For most applications, a layer of 3-5 oz covered by a layer of 3/4-1.5 oz works best. The light outer layer of glass will leave the surface with very little texture keeping sanding to a minimum.
Here are the airframes as they are supplied in the kit (fin slots were trimmed out).
Seal off the ends of the frames by wicking thin CA into them. (You can also seal about 1/2" inside the frame for a better fit to the coupler.)
Prepare the surface of the frames for laminating

Cut out all fin slots and notches with xacto knife or razor knife.

Roughen up the frames with 80-100 grit sandpaper so that the resin will have a good surface to "bite" into.

Here are the results and what you are trying to achieve. Don't worry about small tears as the resin will soak into them and seal nicely.

The Public Enemy frames had an glossy outer layer that needed to be removed. I remove the glassine from other frames and MMT's by peeling off or sanding. On these frames I used 40 grit paper on my sanding board followed by 80 grit by hand. Wash off the frames with alcohol or acetone to remove all dust and oils from handling.

Make sure to use the mask or respirator so not to inhale the sanding dust!

Here is what I was left with.

Total prep time: 30-40 minutes.

Set up the work area by taping the wax paper down.

Lay out the roll or unfold the sheet of fiberglass. Measure and cut the glass so that is overhangs the frames by 1/2-3/4" on the ends and will overlap about 1/2". At this point, cut all glass pieces for each layer and section. Smooth all the glass pieces out and make them square.

Here is what a first cut piece of glass looks like.

Remove any small frays on the ends and dispose. These frays if not removed will be a nightmare to you later. It is OK to remove a few threads from the ends so that you have all the frays out of your material. Lay each layer aside on newspaper. Make sure to group each layer so that when you laminate you can easily get the next fiberglass section with no errors with regard to what piece goes to what section..

Here is what it should look like once you remove the frays; note the ends.

Continue to Part 2...

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