Seals are crucial to aircraft performance, and are used in countless applications where they have to withstand the most challenging conditions. Nicolas Poussineau, global marketing leader, Aerospace – Saint-Gobain Performance Plastics, looks into the demands, the applications, and how to source the right solution

Despite being just one small part of modern aircraft, seals are crucial to their operation – if they fail, they can compromise the entire plane’s performance. Seals, in fact, are used in countless applications throughout a plane – from exterior flaps to cockpit windshields.

As a result, seals are called upon to perform in some of the most challenging conditions known to commercial applications. Some are expected to repeatedly withstand extreme weather, endure high air-flow pressures, and face huge variations in temperature; others must resist constant degradation from aviation fuels and other chemicals used in aircraft manufacturing and operation.

Take, for example, the seals used on flap support fairings, which protect and streamline the flap operating mechanisms on commercial airliners. These must support high pressures and, temperatures from -58 to 176°F while simultaneously withstanding the corrosive effects of de-icing liquids, fuel, and atmospheric agents. Although expected to form strong bonds with metal substrates to avoid separation, these must also retain excellent flexibility.

As a result of such stringent requirements, aircraft sealing technology is not a ‘one size fits all’ industry. When developing a seal, aircraft manufacturers need to evaluate each application to determine the type and composition of materials they should employ. Often – especially for complex seal requirements like those on flaps – the best options available are engineered solutions that include fabric reinforcement or a compound of several materials with different properties.

Engineered Solutions

For the applications with the highest demands in the aeronautics industry, a seal solution often has to be specifically engineered in order to meet the necessary performance levels. Consequently, considerable R&D needs to go into the development of seals made of composite materials or those materials that include reinforcement with different fabrics in order to improve seal performance.

Composites: The introduction of polymeric compounds, which can be customised for a broad spectrum of applications, has proven to be a game-changer. Composite seals can be made of silicone or metals such as stainless steel, aluminum or plastic parts to provide specific characteristics. These compounds have proven especially effective on aircraft exteriors, such as flaps, rudders, and door seals – which have extremely complex technical demands and require materials that can be tailored precisely for those applications.

Wing seals, for example, need to be resistant to corrosion, so coatings or protective materials can be added to the composite that safeguard the seals. Other layers may be added to provide extra protection against wear and abrasion from airflow.

Reinforcement: Reinforcement with other materials, such as special proprietary fabrics, is another way to tailor seals for a specific application.

Certain seals, for example, must meet stringent smoke toxicity standards, which can be addressed through the use of composite materials reinforced with fabrics specifically designed to be flame-resistant. Where damage from friction is a concern, special fabrics are incorporated that reinforce the seal and reduce this threat. For those applications that require extreme temperature-resistance and the ability to operate consistently in conditions ranging from -40 up to 1,000°F – such as aircraft flaps – a mix of silicone, fabrics and metal parts, with an aluminum top, is used.

Meeting requirements

For an OEM, it’s critical to choose the right partner for seals for this industry. In terms of capabilities, a seal/materials supplier should meet three clear requirements.

Firstly, a global presence is needed: and compounds need to be developed that meet global aerospace standards.

Secondly, prospective partners must have strong R&D capabilities in order to meet the need for customised solutions that fulfill a myriad of technical requirements. As the global aviation industry faces increasing pressures to create more fuel-efficient, ‘green’ designs, suppliers must innovate constantly, researching the right materials that will best meet a specific design application.

Finally, given the scale of aviation projects, it is necessary to identify a partner with considerable financial resources. Specifying seals for an aviation project can take up to five years between an initial sales enquiry to final production. Such ventures require a risk-sharing partnership between the manufacturer and vendor.

Saint-Gobain Performance Plastics