February Program

February Meeting Program

Fiberglassing

This was the second part in our continuing project to get club members up to speed on building a High Power Rocket. If you missed the meeting here is the basic outline of what was discussed. Don't miss next month - Booster Construction.

Cloth selection
There are many types of fiberglass cloth. The ones most commonly used in HPR for laminating tubes are:
- 6-oz to 8-oz (weight per sq yd)
- Satin weave (easier to finish)
This cloth is ideal for laminating body tubes. It is heavy enough to keep its’ shape while laminating and easy to fill.
Other specialty cloths exist for other situations:
- Lighter weight for laminating complex shapes and curves
- Extremely light weight ("veil") for top covering and finishing
- Heavier, coarse weave for maximum strength when finish is not an issue
- Hybrid cloth with carbon in one direction, fiberglass in the other direction for directional strength
- Carbon or Kevlar cloth for maximum strength, extreme projects
Epoxy Selection
Recommended epoxy is West Systems marine epoxy. This epoxy is specifically designed for fiberglass:
- Long cure times = long work times
- Very strong
- Easy to use pump system
Other brands designed for fiberglass would also work well
- EZ-Lam epoxy from ACP
- Aeropoxy from Shadow Composites
Bob Smith 5-minute, 15-minute, etc. not suited for fiberglass
- Sets up too quick
- Difficult to get the fabric completely "wetted out" (soaked) before cure sets up
- 30-minute "Finishing Epoxy" can be used for small jobs
Work Area, Tools and Fixtures
In general, you’re going to make a mess. Cover as much of the work area as possible with newspapers, plastic sheeting or large trash bags.
You will need the following items:
- Spindle for supporting and rotating tubes while laminating
  - Sawhorses or large cardboard boxes for support
  - Dowel rods or PVC pipes for spindles
- A large flat worktable
  - Very useful for measuring and cutting glass cloth
  - Measuring and mixing epoxy
- Disposable items
  - Latex or vinyl gloves
  - Small ("chip") paintbrushes
  - Epoxy mixing sticks or plastic spoons
  - Epoxy mixing trays (milk jugs)
  - Newspaper
  - Paper towels
  - Masking tape
  - Rubbing alcohol for cleanup
- Tools
  - Scissors and/or (sharp) hobby knife
  - Metal straight edge
  - Calculator
  - Yardstick or measuring tape
  - Pencil or pen
Cloth measurement

Two complete wraps of the airframe tube are required for maximum strength
How much cloth is required for a 4-inch airframe tube?
Typical "yard" of cloth is 36 inches long by 50-52 inches wide
Typical airframe tube is 34 inches long
Circumference of a 4-inch tube:
= 4.0 * pi
= 4.0 * 3.14159
= 12.56
For two complete wraps:
= 12.56 * 2
= 25.13 inches
Typical 50-in by 36-in yard of glass, cut in half, will produce two pieces 25-in long by 36-in wide.
A typical yard of fiberglass is sufficient for laminating two 4-inch diameter airframe tubes
Cloth Prep

Lay cloth on flat surface and unfold completely
Trim extreme edges using metal straight edge and hobby knife to minimize fraying
Measure desired length
Cut to length using metal straight edge and hobby knife
Airframe Prep
Sand the entire surface of the tube with 100-grit sandpaper
- Allows epoxy to get a better grip on the tube
Friction fit two centering rings into the ends of the airframe tube
- Use masking tape to secure the rings
- Center hole must be large enough to accommodate spindle
Draw a straight line along the airframe tube from end to end
- Metal angle-iron very useful here
Mount airframe and spindle across support stands
Mix epoxy and "paint" approximately ½ of the circumference of the tube with epoxy
Cloth application
Position cloth under tube so it is held straight by gravity
Carefully line up end of cloth with straight line on tube
- Edges of cloth should extend beyond ends of tube by at least ½ inch
Adhere first 2-3 inches of cloth onto tube along straight line
- Press cloth into epoxy using gloved hands
- Smooth out any wrinkles or bubbles
- Make sure cloth adheres to tube completely to the ends of the tube
- Brush on additional epoxy to cover dry spots if necessary
When first few inches of cloth are completely transparent ("wetted out"), rotate airframe (away from you) a few inches
- Press a few more inches of dry cloth onto tube and work with gloved hands until transparent
As dry portion of tube is reached
- Roll dry cloth onto tube
- Brush epoxy onto the cloth from the top
- Work with gloved hands until wetted out
Continue until entire piece of cloth has been wrapped onto the airframe tube
Problem minimization
After completing cloth lamination, continue to rotate tube looking for dry spots or wet spots
- Brush a little more epoxy onto dry spots and work into cloth
- Use a paper towel to lightly dab wet spots and remove excess epoxy
- Turn towel frequently to avoid lifting glass from tube and creating a "bubble"
Resist the temptation to "pull" loose fibers from the cloth
- Good way to create bubbles and other problems
- Much easier to sand them off when everything is dry
Make sure edges are completely adhering to the ends of the tube
- Optionally, you can wrap ends of the tube with masking tape to ensure a good bond
After 30 minutes or so, you’re done. Quit and set the tube aside to dry
- "Green cure" (no longer tacky) in 4 hours
- Complete cure in 24 hours
If masking tape was used on ends of tube
- Remove tape at green cure stage
- Trim glass flush with ends of tube using hobby knife
Otherwise, trim edges after full cure

A follow up with a hands-on session was held the following Sunday at the Phoenix build location.

Fiberglass Resources

Impulse Aerospace/Joe Grasso: 8-oz glass cloth, carbon cloth; http://www.homestead.com/impulseaerospace/
West Marine: 4315 S. Sheridan, Tulsa, OK; West System epoxy, pumps, fiberglass and supplies
Shadow Aero: Cloth, (Aeropoxy) epoxy, supplies, composite rocket kits; http://www.shadowaero.com/
Aerospace Composite Products: Cloth, (EZ-Lam) epoxy, supplies; http://www.acp-composites.com/
Mr. Fiberglass.com: Cloth, (West) epoxy, supplies; http://www.mrfiberglass.com
Wicks Aircraft supply: Cloth, epoxy, supplies; http://www.wicksaircraft.com/

Hands on Session

Click on a picture to get a better view.


We had several airframes that were 'glassed.		You should sand the tube (paper or phenolic) so the epoxy soaks in better.	Trim the fringe after removing any uneven strands.	Use a metal straightedge to get an even cut

		Mix the epoxy throughly.	Start by applying the epoxy around about a third to a half of the tube.	Carefully lay the glass sheet on the airframe even with the pencil line.

Start pressing the glass into the epoxy and brushing on extra as needed.		Don't be afraid to use your hands as you go to smooth the glass into the epoxy and remove air.		After applying the glass around the tube, you can wrap the ends with masking tape to help assure the ends adhere to the tube.

If you have attached the fins, it's not too late. Just wrap ahead of the fins first. Then go back and glass over the fin across the tube and up the next fin.	As you're wrapping, be sure you are applying the glass on straight or it will start to go over the fins.	The process is the same for phenolic tube as well as cardboard.

	A jig will help with glassing.	Getting started on the transition is similar to a normal airframe. It is a little trickier on foam.	The same procedure works for transitions, you just have to cut the glass accordingly.	Glassing the transition.

Photo Credits: Randy Luhman, Hal Ellis, and Vince Moore

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