FITS Air thermoplastic sandwich panels enable durable, lightweight and low cost aircraft interiors

Examples of products using FITS Air thermoplastic panels are shown above, from AC seat tables to box construction. Photo credit, all images: FITS Technologies.

Over the past 50 years, there has been a significant change in the materials – such as the switch from aluminum to composites – used for aircraft exterior structures, a change that follows global trends in light weight, low cost and recyclability. However, when it comes to aircraft interiors, the manufacturing methods of the parts have often remained unchanged; Nomex honeycomb with fiber reinforced phenolic coatings, potting compound and aluminum extrusions, for example, are still the materials of choice and have been for many years.

An obvious alternative to phasing out these outdated techniques would be technology that offers part integration and thermoforming capabilities, which in turn could ease the transition to an Industry 4.0 mindset — an option, says the inventor and CEO of FITS Technology (Driebergen, The Netherlands), Martin de Groot, offered by the company’s Foamed In-situ Thermoformable Sandwich (FITS Air) technology.

FITS Air is produced in sheet form by foaming a foaming thermoplastic polyetherimide (PEI) film (physical blowing agent) in situ between two fiber reinforced PEI liners (supplied by SABIC, Riyadh, Saudi Arabia) via a press. The patented process creates a vertically oriented thermoplastic foam and bonds the fiber-reinforced thermoplastic liner to the foam in a single step (see “Thermoformable Composite Panels Part II”).

According to the company, the absence of an adhesive layer, a foam with vertically oriented cells, a high resistance to compression and a structural orientation without L or W direction guarantee superior properties compared to current Nomex panels (see the table below). below for comparison). Additionally, the use of PEI as the sole thermoplastic material in the core and facing meets all flammability and smoke-toxicity requirements.

Panel t = 10 mm*

FITS Air panel**

Nomex/phenol

PEI/phenol foam

density core

90kg/m3

48kg/m3

80kg/m3

Compressive strength/mod

2.7/120MPa

1.9/145MPa

1.2/70MPa

Shear strength/mod

1.2/19MPa

1.1/32(L direction)MPa

1/19MPa

Climbing Drum Peel Strength

90

45

60

Tensile strength/mod

4MPa

2MPa

1.7MPa

Adhesive weight

150 gsm2

150 gsm2

Panel weight

2440 gsm2

2390 gsm2

2680 gsm2

Jg

210°C

105°C

105°C

Retention at 80°C

85%

65%

75%

* Facings: 2/2 US style 7781 glass fabric + 33% resin

** t = 8mm, same stiffness/flexural strength as Nomex 10mm in L direction

Notably, the fiber-reinforced thermoplastic liners and vertically oriented PEI foam core make FITS Air panels thermoformable, saving weight and cost. Further research has shown that the liners themselves can be made in-house as part of the manufacturing process, which further reduces the cost of producing FITS Air panels. The product is also fully recyclable.

FITS Air is currently being developed to Technology Readiness Level (TRL) 6, with panels manufactured to a size of 1.28 meters x 1.48 meters with optimized mechanical properties.

FITS Technology provides examples of products using this technology, including box constructions, floor panels, aircraft seat table, PSU panels, and oxygen system covers.

Box builds using FITS Air panels would result in thinner parts with no added edge weight. Processing time using a dedicated thermoforming machine is two minutes/panel. Areas of application include OSC, kitchens, floor panels, toilet doors, etc. Weight savings of 200 to 500 kilograms/AC are expected depending on the type of AC, at a lower cost of 10 to 50%.

A rough calculation indicates that all luggage bins (including the support structure) of Airbus (Toulouse, France) or Boeing (Chicago, Illinois, USA) aircraft could be manufactured with approximately 10 machines of thermoforming, inserting and dedicated automated welding machines with a manufacturing time of 90 minutes/bin. This, the company says, can be achieved with minimal manual labor and no curing time; Cost reduction up to 50% is possible.

The seamless properties of FITS Air also make floor panels a potential avenue. Tests have shown that impact levels only show visual damage, with a dent in the top layer of the impacted fiber reinforced liner and crushed in-situ foam just below the dent. Under the impacted facings, the foam is still perfectly intact. Additional peeling of the coating – which, according to FITS technology, sometimes occurs with Nomex floor panels – is not possible with the in-situ foam core.

FITS Air is currently being developed to Technology Readiness Level (TRL) 6, with panels manufactured to a size of 1.28 meters x 1.48 meters with optimized mechanical properties. Although FITS Air is also patented, according to the company, the business itself is still ripe for development and awaits proper adoption and commitment from the civil aerospace sector.

FITS basis

Alternatively, FITS Base is a batch or continuous manufactured FITS sandwich panel based on polypropylene (PP), nylon, polyamide (PA) or other low cost polymers, which is foamed in situ with chemical blowing agents . According to FITS Technology, thermoformable sandwich panels are available for other markets, but without some of the physical features required for aerospace, such as battery boxes for battery electric vehicles (BEVs), motor homes and coatings for houses.

FITS Base panels can be continuously manufactured via thermoplastic films, fibers, fabrics and foamable films (films extruded with a chemical blowing agent), resulting in a panel with fiber reinforced consolidated facings and a foam core in situ with vertically oriented foam cells. This makes it possible to continuously consolidate the fiber-reinforced thermoplastic facings, to foam the vertical cells and to create a complete bond between core and facing in a single step. FITS Base would be well suited for mass production of parts at low cost. Crush energy absorption tests with FITS Air panels reportedly showed 50% better crush energy absorption than round cell foam.

FITS Base is currently at TRL 3 and still requires low-cost fundamental research before moving to batch and/or continuous manufacturing. Like FITS Air, this product is patented worldwide.

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