Is the future composite aircraft?

According to Manchester University, School of Materials, Andrew Walker energy efficiency and the cost of energy are the key economic drivers this millennium, which for airlines means less fuel burn and more profit! With its supercritical wing, Boeing's composite B787 Dreamliner has considerably higher lift-to-drag ratio than equivalent metallic aircraft. Operators have seen up to 25% savings. For future 300-seat sized large airliners, composite wings are favoured over metal. The argument for smaller 150-seat sized airliners, metal versus composite, is more balanced. There's an ongoing debate involving traditional aluminium alloys, advanced aluminium/lithium (Al-Li), and polymer based composites. The corrosion resistance, fatigue and strength properties of Al–Li have significantly improved since the 1980s. Alcoa claims weight parity between its third generation Al–Li alloys and composite materials. Bombardier adopted Al–Li in its new CSeries fuselage; in reality it has seen weight reductions of 12% over traditional aluminium. Composites are fatigue sensitive, especially at high strain. Nevertheless, composite materials offer a significant stepwise advantage, greatly reduced density and significantly higher stiffness/strength. Translating these properties into superior aerodynamics, whilst reducing manufacturing cost, will determine whether composites replace metal. Airbus and Boeing are enhancing their respective A320 neo and B737 MAX metallic single aisle designs. Aerodynamic upgrades and new efficient engines will realise 10–12% savings. Single aisles account for 75% by number of total aircraft built. Airbus has plans to increase production capacity to 60 aircraft per month (‘Rate 60') with a typical selling cost of $80–110 million each. Both aircraft builders have a huge investment in aluminium manufacturing. The cost of either company launching a new small composite plane would exceed $130bn (capital + work in progress + disruption to sales). Aircraft builders in China and Russia, unencumbered by an existing ‘aluminium infrastructure' are already building 150-seat composite airliners. Composites comprise carbon fibre and polymer matrix resin. World production of carbon fibre is 70,000 tonnes/year whereas by contrast, aluminium is closer to 20 million tonnes/year. 150 years ago pure aluminium was a curiosity. In 1903 Alfred Wilm discovered Al–Cu alloys, these alloys still dominate aviation. Although carbon fibre can be traced back to Thomas Edison, it was in the 1960s that Royal Aircraft Establishment scientists developed present day polyacrylonitrile (PAN) based carbon fibre. Commercially available carbon fibre is typically 15% of its theoretical strength. Aircraft designers seek improved composite materials with good compressive strength and improved toughness. A coordinated research initiative to discover a new family of strong fibres is needed, such as alternative precursors to PAN, i.e. lignin, polyparaphenyline and polyefin; hybrid/binary fibres that translate toughness; novel fibre manufacturing techniques; laser spinning/melt spinning. Existing matrix resins are either thermoset or thermoplastic polymers. New resins that infuse easily, but cure in minutes are needed. Autoclave curing is expensive; cycle times are several hours long. Industry seeks a low cost, faster alternative. Australia's Quickstep Technologies has successfully developed a fast curing out-of-autoclave technique aimed at aerospace and automotive. Composite material producers and aircraft manufacturers have developed their own individual materials/manufacturing specification, magnifying cost of entry into market. Standardising on a few international grades of carbon fibre that can be translated across producers would benefit uptake. The National Composites Certification and Evaluation Facility, University of Manchester is compiling a design criteria for composite materials. Lockheed Martin's X-55 ‘Advanced Composite Cargo Aircraft' (ACCA) is an experimental twin-jet transport aircraft, intended to demonstrate the use of advanced composite materials. Based on a Dornier 328JET, it first flew in 2009. It's been estimated that this plane could be built for half the cost of a conventional design. The UK last built a ‘significant' manned flying prototype aircraft in 1982. Perhaps its time for a European X plane? www.materials.manchester.ac.uk