5.18 FIBERGLASS
Fiberglass Reinforced Plastic (FRP), or "Fiberglass" as it is more commonly known, is used in numerous places in RVs for non-
structural parts. These include the cowl, spinner, and other fairings. The typical part consists of several layers of bidirectional
fiberglass cloth and resin.
Fiberglass parts supplied with RVs come in two resin types, polyester and epoxy. Polyester parts can easily be identified by their
white or gray gel-coat surface. The "wet layup" epoxy parts are translucent green. Some parts (typically large parts such as
cowlings) are manufactured from epoxy pre-preg cloth which requires baking in an oven to cure. These parts can be gray exterior,
opaque green or pink. They are easily identified by the honeycomb pattern visible on the inside surface of the part. Polyester resin
is not compatible with epoxy and can only be used on polyester parts. However epoxy resin is OK to use on either epoxy or
polyester parts. Many builders have had good results with West Systems epoxy resin.
Molded fiberglass can be cut, filed, and drilled with any tools used for metal working. Though it is softer than steel or aluminum,
glass fiber is very abrasive and will quickly dull tools. Set aside some drill bits for use exclusively with fiberglass. Use sanding
blocks and sandpaper rather than files.
Like welding, fiberglass molding is a specialty skill. Fiberglass parts lend themselves more to production methods than do most
other parts. Thus, VAN'S AIRCRAFT offers most fiberglass parts pre-molded. To make the parts that are not supplied in the kit any
fiberglass cloth of medium weight will do. Flocked cotton fiber and micro balloons are mixed with resin for building up and filling.
Using Peel Ply will result in a very smooth finish that is also ready for glass to glass bonding without sanding. Most supplies can be
obtained from a local marine/boat store or from one of the mail order supply houses like Aircraft Spruce.
NOTE: When setting solid rivets in fiberglass composites, use soft rivets or do not fully set normal rivets (shop head
height approximately 1.2 X the hole diameter).
PREPPING THE COWLING FOR PAINT
Fit the cowling to the fuselage with all the hinges, retaining screw holes, and nut plates installed, but leave the oil door installation
for later.
Van's recommends use of a Poly Fiber product called Smooth Prime. We follow the manufacturer's instructions EXCEPT that we
apply the first coat straight-out-of-the-can and un-reduced, using a Bondo squeegee rather than a roller or spray gun. Using a
squeegee to apply the first coat forces the filler into surface voids.
TIPS FOR FIBERGLASS FAIRINGS
When installing fiberglass tip fairings (especially wingtips), ensure that the trailing edge extension is aligned with the control
surface trailing edge. On wingtips, this can lead to inconsistent gaps between the skins and the joggled edges formed into the parts
at the factory. For instance, there may be a smaller gap on the bottom than on the top, differing along the length from leading to
trailing edge. Once the part has been positioned to where the trailing edges align well and the part has been match drilled and
clecoed into position, make sure the metal edges are not riding up onto a fiberglass edge radius as shown in Figure 1.
After the part is prepped for final installation, either with screws and nutplates or rivets, the gap can be filled using the following
steps:
Step 1: Clean the part around the perimeter with solvent to remove any residual release agent.
Step 2: Scuff deeply with coarse sandpaper the recessed area that falls between the normal finished surface and the edge of the
metal (through the gel coat will ensure the best possible bond). After scuffing, clean thoroughly.
Step 3: Wrap electrical tape or equivalent around the inside surface of the metal part. See Figure 2. Insert and secure the fiberglass
tip with either screws or clecos as appropriate, then finish wrapping the tape snugly around the edge of the metal. The tape will act
as a release agent for the next step.
Mix up a small batch of epoxy resin and add flox until it reaches the consistency of peanut butter. Fill in the groove between the
tape and fiberglass with this mixture. Ensure that the thickened flox fills in the entire gap. The flox should come up to the level of the
tape or slightly beyond so there is room to sand it back down after it has cured.
When the resin has hardened overnight, lightly sand off any mixture that overlaps the tape as shown in Figure 3. Remove the tip
and the tape. Complete installation of the tip per kit instructions. The interface can be sanded to leave a perfectly co-planar surface
with a consistent gap.
FIGURE 1: FIBERGLASS GAP
INSUFFICIENT GAP
1/8-1/16 VARIABLE GAP, OPTIMUM
ALUMINUM PART
FIBERGLASS PART
SCUFF THIS AREA
TAPE
RESIN/FLOX MIXTURE
FIGURE 2: RESIN APPLICATION
ALUMINUM PART
FIBERGLASS PART
FIGURE 3: SANDING
PAGE
REVISION:
DATE:
VAN'S AIRCRAFT, INC.
PAGE
REVISION:
DATE:
04/15/13
05-16 RV-ALL
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