Thermoplastic Hatch Covers For Quest Kodiak Floats

Thermoplastic composite parts made by Plasticomp are replacing traditional aluminium materials in a non-structural application for Wipaire, an aircraft float manufacturer. 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 USD1.1m (GBP730,000), single-engine-turboprop, 10-seat, 750hp, backcountry utility aircraft manufactured in Sand Point, Idaho.

The float-equipped Kodiak is scheduled to be certified for service in spring 2010. The long, glass-reinforced, thermoplastic hatch covers were a joint development: Plasticomp provided technical guidance on materials and processes plus the actual part moulding, while Wipaire designed the part and made the mould in its in-house machine shop. The project took just less than 120 days to complete. This Quest Kodiak, equipped with Wipline 7000 floats manufactured by Wipaire, is shown in flight testing prior to the installation of new compression-moulded composite hatch covers made by Plasticomp.

The floats add approximately USD250,000 to the aircraft's base cost. The hatch cover measures approximately 14 x 16in (36 x 41cm). 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 moulded in a self-coloured, black-pigmented, ultraviolet-stabilised, long, glass-fibre-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 the right, the underside of the part shows its reinforced structural and attachment design features.

The new hatch cover replaces earlier machined aluminium versions. Dan Garrett, Wipaire's research-and-development engineer in charge of the project, said: 'The aluminium parts were too heavy, while these new ones weigh less than 2lb [907g]. '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. 'The composite hatch covers have good corrosion resistance and have the advantage of being easily replaced, which was another benefit we were looking for,' he added.

Garrett said that he also considered a thermoset sheet moulding compound (SMC) with long fibres, but the high material and development costs for that approach made Plasticomp a more logical choice. According to Steve Bowen, president of Plasticomp, its proprietary Pushtrusion technology, which has been installed in its Technical Development Center in Winona, allows it 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 moulding was limited to injection moulding with Pushtrusion Direct In-line Compounding, but it is now also offered with Pushtrusion D-GMT for compression moulding - the technology that produced the hatch covers for Wipaire. The Pushtrusion D-GMT system produces hot charges of customised, precisely metered, long, fibre-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 moulding. Pushtrusion units are custom sized to the job and can be used with a variety of polymers (PP, PA, TPU and PBT) and fibres (E-glass, S-glass and carbon).

Bowen said: 'The Pushtrusion process gives processors the flexibility to customise their specific formula by fibre loading, polymer type and colour. 'They are not limited to standard GMT sheet offerings,' he added. Customers for D-GMT parts, once the material has been selected, have several options: the part can be purchased directly from Plasticomp; a part-sized pre-form can be purchased for moulding; or a Pushtrusion system can be used to mould parts in their own facilities.

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