Direct long-fiber composite parts are replacing machined aluminum
for hatch covers on the amphibious version
of the Quest Kodiak, a single-engine turboprop, backcountry utility aircraft
manufactured in Sand Point, ID.
"The aluminum parts were too heavy while these new ones
weigh less than two pounds," says Dan Garrett, the Wipaire R&D engineer in
charge of the project. "Also, they were subject to dents and bending, and they
cost too much - approximately five times the cost of the composite parts." Corrosion
resistance and ease of replacement were also issues in moving from aluminum to
thermoplastic composite.
The 14 x16 inch hatch covers are made with a new technology
called Pushtrusion D-GMT. Hot charges of metered, long fiber-reinforced
polypropylene compound are transferred to a compression press and immediately
pressed into finished parts, eliminating glass mat technology (GMT) sheet
typically used in compression molding.
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"The Pushtrusion process gives processors the flexibility to
customize their specific formula by fiber loading, polymer type and color,"
says Steve Bowen, president of PlastiComp, the system developer. "They are not
limited to standard GMT sheet offerings." Other thermoplastics that can be used
in the system include polyamide, thermoplastic polyurethane and PBT-type
polyester. Available fiber systems include E-glass, S-glass and carbon.
Garrett says he considered a thermoset sheet molding
compound (SMC) with long fibers but was concerned with high material and
development costs. Thermosets require curing cycles and are labor-intensive.
The hatch is molded in a precolored, black pigmented, UV-stabilized
material and is then painted with a black non-skid coating on its exposed
surface to match the upper, walked-upon deck surface of the float. Foot traffic
dictated sufficient load bearing stiffness as a primary criterion in the
design.
The exposed upper surface of the hatch cover is mostly
smooth, with a channel for a sealing gasket. There are thicker sections at the
perimeter for threaded fasteners as well as a perimeter wall. Ribs radiate to
the wall from a central boss where a standard, snap-in-place inspection port is
installed.
Fast Development
The new long glass-reinforced thermoplastic hatch covers
were a joint development.
PlastiComp
provided technical guidance on materials and processes plus the actual part molding
while
Wipaire designed the part
and made the mold in its in-house machine shop. The project was completed in
less than four months.
The floats add approximately $250,000 to the 10-seat
aircraft's base cost of $1.1 million.
The hatch covers are the second application for the Pushtrusion
process, which previously has been used to make covers and lids for
water-treatment units.
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