Composites on the wing

The aerospace industry is embracing composites in a big way. Lou Reade reports on some of the latest innovations

Some of the statistics regarding the use of composites within the aerospace industry are staggering. The Airbus A380 uses an estimated 25% of composites by weight, while the Boeing 7E7 Dreamliner uses around 50%.
The reason is simple: lightweighting. Just as cars must reduce chassis weight in order to accommodate components such as safety systems, so aeroplanes are trying to fly further and take bigger payloads.
And this comes from its position as the leading user of composites. Only the automotive industry – at the cutting edge of Formula 1 – comes close.
A leading example of a composites breakthrough is GKN Aerospace’s integrated wing project, led by a team at its Composites Research Centre in Cowes. It is reaching the end of a three-year programme looking at new manufacturing processes for composite aircraft wings.
“Our team is developing new manufacturing methodologies designed specifically for composite assemblies, rather than adapting traditional processes developed for metallic structures,” says Frank Bamford, vice president of business development at GKN Aerospace.
By the end of this year, the company expects to have produced a demonstrator of a full ‘closed cell box’. These sections are found in structures such as wings, flaps, ailerons and rudders – and can comprise up to 30% of an aircraft’s weight.
This will rely on innovative processes such as automated laying of carbon fibre tape – which can deliver a time saving of around 75% compared with traditional manual methods.
Some of the other techniques that will help composites parts play an even larger role in aeroplane construction include: microwave curing of parts, offering the prospect of performing this task without an autoclave; self-heating tooling; and composite fasteners – which are being tested to compare their weight, lightning strike compatibility and cost with traditional metal fasteners.
And as one project finishes, another begins: back in May, GKN – in partnership with the Ice Protection Facility in Luton – began work on the Next Generation Composite Wing programme.
The main focus will be to ensure that these composites technologies are good enough to make parts quickly enough to meet market demand.
“Our challenge is to develop these processes and apply them to produce more efficient structural components – reducing cost and weight and progressing towards the 2020 emissions reduction targets,” says Bamford.

Riveting stuff
GKN may be looking to replace metal rivets with composite rivets, but the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (Ifam) in Bremen is looking to cut the number of rivets used in an aeroplane.
“Rivet holes are a problem – particularly in carbon fibre composite structures,” says Oliver Klapp of Ifam. “They disturb the flow of forces and reduce the load-bearing capacity of the material.”
Ifam’s answer is to combine riveting with a ‘special’ adhesive bonding process to create a new hybrid technique. Klapp says that it will reduce weight – by using fewer rivets – and retain more load-bearing capacity.
While Ifam has high hopes for the technique, Klapp admits that bonding will not be replacing rivets in the near future.
“It’s true that riveting will not be eliminated from aircraft construction in the next few years,” he says. “The aviation industry is not yet ready to rely exclusively on bonded components and assemblies.”
Elsewhere within the Fraunhofer family, Darmstadt-based Fraunhofer LBF is a leading light in the new EU’s Clean Sky research programme, which will look at new ways of reducing pollution from air traffic – using everything from more efficient engines to lighter aircraft structures. Fraunhofer’s researchers will develop environmentally friendly methods and materials for the design and operation of the aircraft, led by Professor Holga Hanselka.

Net profits
Composites and plastics are most commonly used to apply weight-saving solutions to the aircraft chassis. But sometimes, weight saving emerges in some surprising places.
Capewell, a US-owned supplier of ‘aerial delivery systems’ – basically pallets and nets – switched to a new material to improve the performance and reduce the weight of its products.
The company claims that a military carrier could save up to one tonne in payload weight, simply by switching to these new nets.
There are two main factors at work: the Dyneema net is already around half the weight of a conventional pallet net; and it absorbs very little moisture.
A typical polyester net will gain nearly 30% in weight when wet; a similar Dyneema net will take on a maximum of around 16% by weight. Capewell calculates that for a C-5 Galaxy – one of the largest aircraft carriers – the total dry netting weight will be almost 3,000lbs for a polyester net and 1500lbs for a Dyneema net. Allowing for water ingress, the difference in weights between the two nets would be more than 2,000lbs – almost one metric tonne.
Lawrie Wilson, business manager of airlift cargo systems at Capewell, says: “We achieved a record-breaking weight reduction while enhancing strength and durability for our new pallet and net system. This will help the military meet its strategic objectives for improving the performance of their supply chains.”

Seal of approval
At the recent Farnborough Airshow, a number of suppliers showed how plastics had been used in the development of new thermal sealing technologies.
Beldam Crossley’s new method for thermally insulating solid pipes involves overbraiding – which uses wire and polypropylene – across the entire surface of the component. It is ideal for protecting critical and sensitive components such as wiring harnesses and pneumatic hoses.
Trelleborg Sealing Solutions has developed an advanced format in fire seals, which provide low surface friction and electrical conductivity. They can be used within the Trent, EFA, Nimrod and other aircraft platforms. The new range includes a patented ‘split seal’ option to allow retro-fitting.
Also in fire seals, Simrit has developed a portfolio of fireproof materials that offer protection at 1094ºC for up to 15 minutes. They can be vulcanised to a minimum thickness of 0.25” (6.35mm). For applications that require lower weight solutions, there is a range of materials that work at just 0.81mm thickness.
In a recent project, Simrit worked with a North American light jet provider to develop a fire barrier silicone material – which led to cost savings of around £70,000 per year.

Tom Shelley

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