ALCAS: lightening the load for civil aircraft

A £100 million project to develop a cutting-edge range of carbon composites is helping the European civil aviation industry meet its 2020 Vision commitments – and keep its aircraft manufacturers competitive in a multi-billion dollar market. Project Co-ordinator Allan Kaye, at Airbus’s UK research centre in Bristol, is confident the giant consortium behind the Advanced Low Cost Aircraft Structure (ALCAS) can deliver..

Aircraft are heavy. And heavy means more fuel. Which is more expensive and worse for the environment. Which is an issue when the European Commission has an ambitious plan to cut emissions by 20% by the year 2020. It’s an even bigger issue when you know your main rivals are developing new technology of their own – and that new developing countries will inevitably join the table in a few years.

ALCAS began in 2005, as an attempt to meet these challenges, and follows on from the successful Framework 5 projects TANGO and FUBACOMP. Both these projects looked at the application of composites to Aircraft structure of the outer parts of the wings and fusel. Now ALCAS aims to build upon that acquired knowledge and looks to achieve similar savings on the more complex highly loaded regions of the Airliner and business jet aircraft. The aim is to make significant weight and cost savings, against the traditional metallic versions, across four areas:

* Airliner wing: 20% weight reduction in the inner wing and centrebox with zero increase in recurring cost

* Airliner fuselage: 20% weight reduction of the fuselage structure, with zero increase in recurring cost

* Business jet wing: 10% weight reduction of the overall wing box structure, with a 20% reduction in recurring cost

* Business jet fuselage: 10% weight reduction of the fuselage structure, with a 30% reduction in recurring cost

This seems like a big ask. The key to achieving it lies in the development of carbon fibre composites – lighter than their traditional metallic counterparts – together with assembly and bonding methods that reduce the need for metal fastenings to hold the structure together. To do this, a consortium of 60 European partners, across 16 countries, has each been tasked with contributing a particular specialism to the development of composite manufacture and assembly.

“Composites are not new – they’ve been used in the various industries for quite a few years and indeed we have bench marked those industries to see what we can learn from them,” says Allan, who has been the ALCAS co-ordinator for the last two years.

“But because of the far greater physical extremes an aircraft experiences, the challenge for the consortium has been to develop high-end composites that are sufficiently light to achieve the weight savings, sufficiently strong to take the load-bearing stresses and temperature extremes in flight, sufficiently durable not to fatigue like metal, quick and easy to repair so a damaged aircraft is not grounded for too long – and quick to put together, to reduce assembly costs.”

That’s quite a wishlist but Allan is confident that all four project areas are achieving their goals. “If we take the airliner wing, for example, we have already delivered the weight benefits and are now at the testing stage with a full size structure of the inner wing. These tests will validate the design and verify our weight saving. We are confident of achieving a weight saving which exceeds our target.

The inner sections that ALCAS is concerned with have proved an even greater challenge than the outer sections of its TANGO predecessor. “If we take the example of the inner wing again, says Allan, “this is essentially a large box, consisting of a top and bottom cover, supported internally by a series of ribs and two spars running down between each edge of the covers. It contains the highly loaded regions of a wing, where the landing gear and engines are attached and where the wing joins on to the body, so it is much more complex than the outer parts of the wing. The lateral wingbox accounts for approximately 70% of the overall wing weight. Thin composites are enough of a challenge, but it is even harder to develop a thick composite that is still lighter than its metallic equivalent.”

The business jet wing and the two fuselage projects face similar challenges but all are progressing well, with developments in composite technologies, assembly techniques and easily repairable sections key to their success.

Indeed, the progress towards pre-fabricated, easily assembled parts is seen as another key part of aircraft design, to remain competitive in the future. “At the moment, composite sections of a wing or fuselage – like those on the Airbus A400M which is already flying in fact – are largely bolted together with several metallic fastenings, which adds to the weight, is more costly to transport to the assembly line and takes longer to assemble when it gets there,’ explains Allan.

“If we can further integrate the structure we then have weight and assembly cost savings combined. This was shown in the Business jet wing platform where a box with integrated spars and stiffeners was produced significantly reducing the wing assembly time due to a dramatic reduction of fasteners’’

This ‘less is more’ approach to aircraft construction requires some clever reverse engineering to work out what kind of composite section you need to start with on the assembly line, by working back from the finished product. It’s a bit like seeing a cardboard box for the first time and working out how you would design that from a flat piece of cardboard. It also presents challenges in terms of manufacturing processes to make them.”

“Even when you’ve decided what new part you want to make, that design may never have been manufactured before so you need to understand the materials and processes a tool to then make the part,” says Allan. “But if there’s one rule of manufacturing it’s that thankfully the second one of anything you make is invariably easier – and better – than the first.”

Thanks to the ALCAS project, which has been 50% funded by the European Commission and the remainder by the partners themselves, Europe has developed a range of cutting-edge design and manufacturing skills in one of its major industries. “Like any consortium you get a range of skill levels and we all learn as we go along,” says Allan. “We had partners on the TANGO project who had never worked with composites, so they were able to develop their knowledge during the project and increase their capability for the future which, in a relatively new field like aircraft composites, is invaluable. Partners that learnt on the TANGO project, for example, went on to help create the Airbus A400M which is now flying. That’s the big change I’ve seen with the ALCAS project as it’s unfolded – people’s knowledge of composites and their skill in making the parts is greater.”

That ability to adapt skills and learn new ones will be crucial in the unforgiving white heat of the aircraft industry. “You may have mastered a composite technique for an existing aircraft design – only to find aircraft design itself has moved on and you need to develop new skills to meet those designs,” says Allan. “For example; developing a civilian airliner with a blended wing, [similar to the stealth bomber] which is a revolutionary design for such an aircraft. And who knows what developing countries will bring to the table in a future years?”

Allan is extremely proud that such a large European consortium has collaborated so well and developed the vital new skills that will ultimately achieve a very demanding set of deliverables.”

But as ever he still has one eye on the future. “I think we can make even greater weight savings in the future as our understanding of the new materials improve,” he says. “To remain successful you’ve got to keep innovating, you’ve got to keep ahead of the game.”

Published: Wednesday, 26th October 2011