Fire-resistant and lightweight: Aviation textiles

Seat covers, safety belts and carpets used in aircraft must be flame-retardant and lightweight. In the future, high-tech fabrics will fulfill a broader range of applications.

07.2018 | Text: Denis Dilba

Text:
Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.

At almost 1,000 degrees Celsius, yellow-orange flames shoot out of the blow­torch to a length of some 30 centi­meters. For nearly two minutes now, the flames have been relentlessly barbe­cuing the air­craft seat from the left-hand side. Then, after precisely 120 seconds, the torch goes out. Any remaining pockets of embers are immedi­ately extin­guished and a light veil of smoke fills the test cabin. Once it clears, we can see the extent of the damage. How much remains of the seat cushion, backrest and cover will decide whether or not this par­ticular mix of materials will get its wings. As per FAR/CS 25.853, the flamma­bility regulation that applies to Europe and the United States, the fire must not spread more than 43.2 centi­meters from the source. That’s the width of the narrowest aircraft seat.

“All textiles used in aircraft cabins must be flame-retardant,” says Daniela Grunder, Director Brand Communi­cation & Product Manage­ment at Lantal Textiles AG. Based in Langenthal, Switzerland, the company specializes in fabrics for the aviation industry and manu­factures products including seat covers, carpets, curtains and wall coverings. All the major air­craft manu­facturers as well as more than 300 air­lines—including Swiss Air, Lufthansa, Delta and China Airlines—place their trust in the expertise of this company located in the Canton of Bern. This makes Lantal a world leader in its industry.

Video: High-performance textiles for aviation applications Article with video

High-performance textiles for aviation applications

Every tenth of a gram counts: Flame-retardant properties are an absolute must for high-tech textiles in aviation. All major airlines trust the expertise of Lantal, a company headquartered in the Swiss canton of Bern. To the video ...

Every decigram counts

According to Grunder, having flame-retardant properties is just the first require­ment fabrics must fulfill if they are to be used in air­craft cabins. “Aircraft textiles should also be wear-resistant, stain-resistant, non-toxic and—most importantly—as light as possible,” she says. After all, the lighter the air­craft, the lower the airline’s fuel con­sump­tion and, in turn, its CO2 emissions. Extrapolate that to the level of an entire fleet of some 100 air­craft and reductions of even a tenth of a gram per seat cover can quickly result in six-figure savings. Still, more light­weight textiles have their drawbacks; for example, a slimline aircraft carpet is thinner and often less resistant to wear than its heavier counter­parts. Plus, the more lightweight versions tend to get dirtier faster.

Aramid

Five times as strong as steel
Pound for pound, aramid fibers (“aromatic polyamide”) are five times as strong as steel. The material is better known under the brand name Kevlar.

400 °C
is the point at which aramid textiles slowly begin to smolder without flames.

Four layers of aramid
make up the “skin” of the Fly-Bag. This flexible luggage container can withstand the energy of an explosion caused by a device hidden in luggage.

Look and feel

Another key factor for seat upholstery is that it feels good against the skin. Wool does this best, partly because it absorbs moisture and as such doesn’t feel “sweaty,” Grunder explains. But com­pared to artificial fibers like polyamide or poly­ester, fabrics made from natural fibers can be heavier. “Given the many, often varying, require­ments that air­craft textiles must fulfill, there is no one best fabric or carpet for every case,” Grunder says. “The decision as to which material or material blend gets used and where depends on the individual customer’s require­ments.” While one customer might place greater emphasis on comfort, another will be more con­cerned with reducing fuel con­sump­tion—and yet another will want both.

But occasionally it’s simply a matter of taste: when it comes to carpets, European air­lines almost always favor products with a very high wool content, while US air­lines are just as adamant about having the synthetic material polyamide. “A more tech­no­logical look simply goes over better in that market,” Grunder says. A blend of wool and polyamide is the standard for seat covers, with wool fibers ac­counting for 89 to 95 per­cent of the fabric. Grunder says polyester’s use in seat upholstery is dependent on being combined with what are known as fire-blocking materials. This may for instance be Kynol®, a special heat- and flame-resistant fiber used for electrical insulation in high-per­for­mance electronics as well as other applications.

Smart textiles

Up to 5 kg
of weight per aircraft seat can be saved using upholstery manufacturer Lantal’s Pneumatic Comfort System (PCS), which replaces foam cushioning with air cushions.

Each 1 kg weight reduction
in an aircraft seat saves some 80 euros per seat annually.

LOI – limiting Oxygen index
This value expresses the percentage oxygen concentration in the air at which a fiber will start to burn.

Wolle LOI 25
In normal air with an oxygen concentration of 21 percent, wool won’t even smolder.

Fighting fire with physics

What sets this high-performance textile apart is its high limiting oxygen index, or LOI for short. Expressed as a per­centage, this describes the oxygen concen­tration in the air at which the fibers start to burn. Kynol® has an LOI of 30. Oxygen generally makes up 21 per­cent of the air we breathe; at that con­cen­tration, this special fiber won’t even smolder. Wool has an LOI of 25. This is why poly­amide and poly­ester—with their LOI of 20—are blended with a very high pro­portion of wool; it’s the natural material that makes this fabric flame-retardant. “How well textiles burn can, however, be influenced by the tech­no­logy used to make them,” says Wilko Reinck, Chief Aviation Engineer at safety belt manu­facturer Schroth, based in Neheim, Germany. “Tightly woven fabrics allow very little oxygen to reach the surface of the fibers, which keeps fire from spreading.” In addition, tech­nical weaves can be given a flame-retardant coating. This is just one method Schroth employs to make its polyester safety belts fire-retardant as well as extremely mech­anically robust: its belts can withstand loads of at least 2.2 metric tons.

Safety and security thanks to the Fly-Bag

If worst comes to worst, even higher demands are placed on the four-layer aramid fibers used in the Fly-Bag. Made from the same fiber used in the better-known DuPont brand Kevlar®, this flexible luggage container is designed to provide pro­tection from explosions. The basic idea is that items of luggage or suspicious objects are placed inside the Fly-Bag. Should a hidden explosive device detonate, the high-tensile layers of heat-resistant aramid make sure the blast waves, heat and shrapnel remain inside the bag. “What the Fly-Bag does is dissi­pate the energy of the explosion, which in turn prevents the air­craft from sustaining major damage such a hole in its fuselage—the very thing that caused the Lockerbie air disaster in 1988,” says Heike Illing-Günther, Research Director at the Sächsisches Textil­forschungs­institut (STFI), Chemnitz University’s institute of textile research. Illing-Günther, who played a major role in the develop­ment of the Fly-Bag, believes that a compact version for use in the air­craft cabin could enjoy success on the market.

(strich:Look and feel) Seat covers for aircraft can be made of a wide range of materials, from blended fabrics containing wool, rayon and synthetic fibers to leather. Hover over the image for a bigger view

Look and feel Seat covers for aircraft can be made of a wide range of materials, from blended fabrics containing wool, rayon and synthetic fibers to leather.

aeroreport_griff-look

Look and feel Seat covers for aircraft can be made of a wide range of materials, from blended fabrics containing wool, rayon and synthetic fibers to leather.

(strich:High-tech straps) Seat belts in aircraft must of course have high tensile strength, but they must also be resistant to light and acids, have flame-retardant properties and keep their shape. Hover over the image for a bigger view

High-tech straps Seat belts in aircraft must of course have high tensile strength, but they must also be resistant to light and acids, have flame-retardant properties and keep their shape.

aeroreport_high-tech-band

High-tech straps Seat belts in aircraft must of course have high tensile strength, but they must also be resistant to light and acids, have flame-retardant properties and keep their shape.

(strich:Durable and elegant) Real leather has a high-quality look, and with ultrathin coatings it is still a popular material for aircraft seat covers. Hover over the image for a bigger view

Durable and elegant Real leather has a high-quality look, and with ultrathin coatings it is still a popular material for aircraft seat covers.

aeroreport_robust-edel

Durable and elegant Real leather has a high-quality look, and with ultrathin coatings it is still a popular material for aircraft seat covers.

(strich:Safety first) One property of all textiles on board aircraft is non-negotiable: they must be flame-retardant in air with a normal concentration of oxygen. Hover over the image for a bigger view

Safety first One property of all textiles on board aircraft is non-negotiable: they must be flame-retardant in air with a normal concentration of oxygen.

aeroreport_sicherheit

Safety first One property of all textiles on board aircraft is non-negotiable: they must be flame-retardant in air with a normal concentration of oxygen.

“In addition to being lighter than the large versions, the main advantage of a small Fly-Bag is that it wouldn’t affect loading procedures,” she says. The larger safety bags designed for the hold add at least one step to the process: the cargo has to be put into the bag, which must then be sealed. This costs time, which is enough for the airlines to reject the idea. A small Fly-Bag wouldn’t have to be loaded, making it simply another way to increase safety. “If an unclaimed object—say a mobile phone—is found in the cabin after takeoff, current safety protocol is for the aircraft to land imme­diately,” says Illing-Günther. But if the crew could put the suspicious object in a small Fly-Bag, the airline would have the option of allowing the flight to proceed as planned.

Smart textiles

Regardless of whether the Fly-Bag makes it on board, Thomas Stegmaier, Research Director for technical textiles at the German Institutes of Textile and Fiber Research Denkendorf, says we can all expect a great deal from the devel­opment of textiles for aircraft applications. “What’s going to be really interesting are smart textiles with additional functions,” says Stegmaier. Take the work currently being done on self-illu­minating textiles, which incorporate metal fibers that emit light when electrified. “Upholstering the aircraft cabin ceiling with this kind of fabric would mark a signi­ficant reduction in weight,” says Stegmaier. “Ulti­mately, that’s what all devel­opments in textile tech­no­logy are trying to achieve.”

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