GKN develops processes for integrated composite wings

The company is also evolving its plans for drag-efficient natural laminar flow wings as part of the recently extended Clean Sky 2 EU research consortium.

Both wing concepts should be ready for test flights in either 2014 or 2015 according to the company, which plans to be ‘a major wing component supplier’ for the next generation of aircraft.

‘Up to now aircraft such as the [Airbus] A350, A400M and [Boeing] 787 have been largely based around a traditional “metallic” design philosophy, but using composite materials,’ Rich Oldfield, technical director at GKN Aerospace, told The Engineer. ‘We’re now moving towards a philosophy optimised for high-rate composite production.’

The company is aiming to achieve weight savings of five per cent relative to existing composite wings, while reducing overall cost by 25 per cent and maintaining a production rate of around 50 wings per month, or two per working day.

‘At the moment you’ve got automated technologies producing single-piece components that are then fabricated, bolted and assembled together; what we’re looking at for the next generation is to integrate those composite products and create them in a highly automated, very high-rate fashion,’ said Oldfield.

Some aspects of the wing are, however, likely to remain metallic for the foreseeable future, such as the ribs. For this GKN is looking at more efficient manufacturing techniques such as linear friction welding and additive layer manufacturing to create ‘near net-shaped raw materials’.

‘In aircraft there’s a big cost in the equipping phase — you build a structure and you’ve got to equip it with all of the fuel, hydraulic, pneumatic and electric systems,’ said John Cornforth, head of technology at GKN Aerospace. ‘If there’s a way of doing that more easily and quickly there’s some big benefits to be gained, which needs a different kind of architecture.’

Alongside this work GKN will continue to explore the concept of natural laminar flow wings. Here the wing is designed in such a way that the air over the foil surface mostly flows in a smooth ‘laminar’ fashion, with any turbulent flow pushed backwards. This reduces drag achieving overall fuel savings of around 3–4 per cent.

‘The concept isn’t new, but the issue is: can you come up with a full-scale working wing that you can produce at a rate of 50 a month, accurately, at reasonable cost that can be operated in service?’ said Oldfield. ‘This is the first time we’ll be changing the architecture of a large commercial aircraft for well over a generation, and if you want to do that it’s an enormous undertaking to cover all the aspects. It’s a big leap of faith — you need enormous confidence.’

GKN has now settled around a design with a slender metallic leading edge and composite cover sweep. It is currently being tested on the ground and in wind tunnels.

The flight demonstrator platform, which is due around 2015, will be an A340 with the outer third of the wing replaced with natural laminar flow wing sections. However, there are challenges to be solved as Cornforth explained.

‘You’ve got keep the leading edge clean during take-off and landing — even bugs sticking to the surface will impair natural laminar flow — so there’s a mechanism by which the slats become extended in a different way to conventional slats.’

If through the extensive testing phase the laminar flow wing proves to be a viable and cost-effective concept, GKN expects it to be on commercial aircraft by the mid-to-late 2020s.