New Float Plane Parts Replace Aluminum with Compression Molded Composite Thermoplastic – An Aviation Industry First
Thermoplastic composite parts made by PlastiComp, Inc. are replacing traditional aluminum materials in a non-structural application for Wipaire, Inc., the largest aircraft float manufacturer in the world.
The parts, inspection hatch covers, provide access to water-tight compartments in seaplane floats for Wipaire’s Wipline 7000 floats as installed on the amphibious version of the Quest Kodiak, a single-engine turboprop, ten-seat, backcountry utility aircraft manufactured in Sand Point, Idaho. The float-equipped Kodiak is scheduled to be certified for service in the spring of 2010. 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; Wipaire designed the part and made the mold in their in-house machine shop. The project took just under 120 days to complete.
This Quest Kodiak, equipped with Wipline 7000 floats manufactured by Wipaire, Inc., is shown in flight testing prior to installation of new compression molded composite hatch covers made by PlastiComp, Inc. The Kodiak is a $1.1M, 10-seat, 750 horsepower turboprop, backcountry utility aircraft. The floats add approx. $250,000 to the aircraft’s base cost.
“Our people saw this project with Wipaire as a particularly good partnership with a well-established aviation manufacturer”, said Steve Bowen, president of PlastiComp. He added, “It spotlights our ability to help develop a custom-designed metal replacement part, which, despite its low-volume, still represents an important breakthrough in the aviation field for our Pushtrusion® D-GMT™ (Direct Glass Mat Thermoplastic) process.”
The hatch cover is approximately 14″x16″. The exposed, upper, surface is largely smooth, with a channel for a sealing gasket and thicker sections at the perimeter for threaded fasteners as well as a perimeter wall with ribs radiating to it from a central boss where a standard, snap-in-place, inspection port is installed. The hatch itself is molded in a self-colored, black pigmented, UV stabilized, long glass fiber reinforced thermoplastic composite material which 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.
On the left, the hatch cover is shown directly above its final position on the float. At right, the underside of the part shows its reinforced structural and attachment design features.
The new hatch cover replaces earlier machined aluminum versions. Dan Garrett, the Wipaire R&D engineer in charge of the project, said, “The aluminum parts were too heavy while these new ones weigh less than two pounds. Also, they were subject to dents and bending, and they cost too much – approximately five times the cost of the composite parts provided by PlastiComp.” He added, “The composite hatch covers have good corrosion resistance and have the advantage of being easily replaced, which was another benefit we were looking for.” In addition, Garrett said he considered a thermoset sheet molding compound (SMC) with long fibers but the high material and development costs for that approach made PlastiComp a more logical choice. “The big reason we went to work with PlastiComp is that they were really interested in making this application work,” said Garrett.
Steve Bowen explained PlastiComp’s interest: “I have a background that includes aircraft design and modification, so naturally I was attracted to this application, but, more importantly, it seemed like the perfect fit for PlastiComp. It was an opportunity to demonstrate our part molding capabilities, an area of our business that we are expanding.” He went on to explain how PlastiComp’s proprietary Pushtrusion technology, which they have installed in their Technical Development Center in Winona, allows them to operate small volume production, preproduction or prototype manufacturing for selected customers. Since 2006 PlastiComp has been producing parts for customers who do not want — or need — full-scale, in-house, Pushtrusion technology but do want the benefits of parts produced with the advanced technology. Initially this contract molding was limited to injection molding with Pushtrusion Direct In-line Compounding but it is now offered with Pushtrusion D-GMT for compression molding as well, the technology that produced the hatch covers for Wipaire.
The Pushtrusion D-GMT system produces hot charges of customized, precisely metered, long fiber reinforced compound that are transferred to a compression press and immediately pressed into finished parts, eliminating the typical glass mat technology (GMT) sheet used for compression molding. Pushtrusion units are custom-sized to the job and can be used with a wide variety of polymers (PP, PA, TPU, PBT, etc.) and fibers (E-glass, S-glass, and carbon).
“The Pushtrusion process gives processors the flexibility to customize their specific formula by fiber loading, polymer type, and color,” Bowen explained. “They are not limited to standard GMT sheet offerings. Our customers see this as a big plus.”
Customers for D-GMT parts, once the material has been selected, have several options: the part can be purchased directly from PlastiComp, or a part-sized preform can be purchased for molding, or a Pushtrusion system can be used to mold parts in their own facility. In the case of the Wipaire hatch covers, Bowen said, “From the start we worked with Wipaire as partners and we are very pleased with the results and the potential for the future. You might say the sky is not the limit; it’s just the beginning.” Wipaire background:
Since 1960, Wipaire has developed a full line of aircraft floats for all sizes of aircraft from the Piper Cub to the de Havilland Twin Otter as well as over 100 Supplemental Type Certificates for a variety of useful aircraft modifications. In addition, Wipaire is a service leader in other areas, including aircraft maintenance, avionics installation and repair, custom interior design and installation, and exterior refinishing. Wipaire is privately held and is headquartered in Minnesota at South St. Paul Municipal Airport (SGS).
PlastiComp, Inc. focuses on developing and providing long fiber reinforced thermoplastic composite technologies to partners worldwide. These include ready-to-process reinforced long fiber thermoplastic (LFT) pelletized compounds, along with process development and manufacturing equipment licensing for LFT pultrusion, in-line direct long fiber thermoplastic (D-LFT) Pushtrusion®, and in-line direct glass mat thermoplastic (D-GMT®) technologies. PlastiComp’s injection moldable Complēt® LFT composite compounds are available as standard and custom formulations that combine long glass, carbon, and other specialty fiber reinforcement with thermoplastic polymers from polypropylene to PEEK.