The strongest sign of the current uplift in the aerospace composites' fortunes is their being accepted for major primary structures on both Boeing's new 7E7 ‘Dreamliner’ and the world's largest airliner, the Airbus A380, now in build. Passenger aircraft present the severest test for composites since they have to justify their existence on performance and economic grounds equally. In contrast, procurers of combat aircraft can regard composites as a ‘must have’ for their strength-to-weight advantage, and pay a premium for out-and-out performance.
Boeing's recent decision to proceed with the 7E7 twin-aisle passenger jet followed its dropping of plans for a Sonic Cruiser. Any negative impression left by its abrupt change of direction was, however, countered by the daring decision to produce most of the primary structure, including the wings and fuselage, in fibre reinforced plastics (FRP). Having half of its structural weight in composite eclipses anything yet seen from Airbus Industries, previously regarded as the leader in terms of civil airliner composites exploitation.
Boeing's choice was not, however, a foregone conclusion and metals fought back strongly. According to Mike Bair, senior vice president of Boeing Commercial Airplanes' 7E7 programme, the aluminium industry offered new alloys that are ‘about as light as composite materials.’ Had it not been for the fact that the composite companies had made progress on cost, the decision might have gone aluminium's way. Composites do, Bair concedes, also provide advantages of durability, reduced maintenance, parts consolidation, increased development potential and the possibility of self-monitoring through the inclusion of ‘smart’ fibres and embedded sensors.
In adopting the most modern materials technology at the beginning of the second century of flight, Boeing underlines its message that its new 210-250-seater will be ‘super-efficient,’ using an estimated 17% less fuel than comparable current-generation widebodies. Before its large-scale adoption of reinforced plastics, the airframer canvassed the views of potential US customer airlines, which said they would be comfortable with a composite airframe.
Each 7E7, the first predominantly composite airliner since airframe ‘composites’ meant wood and fabric, will require some 25 tonnes of toughened carbon fibre/epoxy laminate and sandwich material. If, as Boeing predicts, it sells 3000 7E7s over 20 years, the reinforced plastics industry can look forward to supplying a healthy 75 000 tonnes of high-performance composites. Boeing is also reported to have been in discussion with UK research agency Qinetiq over the possibility of incorporating metal matrix composite content.
The first flight of the 7E7 is scheduled for 2007 and the model could be in service five years from now.
Global suppliers are clamouring to partner Boeing in developing and building the 7E7. The airframer, which plans to assemble each aircraft rapidly by mating major sub-assemblies provided ‘just in time’ by risk-sharing partners, quickly opened discussions with five selected structures partners – Alenia Aeronautica of Italy, Vought Industries of the USA and Japan Aircraft Industries members Fuji, Kawasaki and Misubishi Heavy Industries. Vought and Alenia will produce centre and aft fuselage sections and horizontal stabiliser assemblies, accounting for 26% of the structure's content. Fuji expects to produce the centre wing box, Mitsubishi the composite wing box, and Kawasaki a forward fuselage section and wing items, within a Japanese workshare expected to reach 35% of the total, equalling Boeing's own share.
Boeing will manufacture the vertical tailplane, the fixed and movable wing leading edges, part of the forward fuselage, the wing-body fairing and the movable trailing edges at facilities in the USA, Canada and Australia. Finished assemblies will be shipped by air to the final assembly facility at Everett, Washington.
Among those seeking to become aerostructural sub-contractors are France's Latecoere, which joined the 7E7 airframe technology team in November and has hopes of building fuselage sections and doors; Composite Technology Research Malaysia, bidding for parts of the rear pressure bulkhead; and a number of Chinese companies including Boeing/Hexcel/AVIC joint venture BHA Aero Composite Parts.
A roomy and attractively styled interior will be attached directly to the Dreamliner's monocoque fuselage shell with minimal use of the secondary structures that normally support ceilings, stowage bins and panels. This will permit the use of higher ceilings and expansive sculpted composite arches. Larger windows will add to the impression of light and space.
A380
While Boeing threatens to overtake Airbus in the use of composites, the European airframer is taking a radical new path by adopting a novel material that combines the advantages of metals and composites while mitigating the disadvantages of both. The roll-out next year of the new 555-passenger (initially) A380 will not only mark the debut of glass reinforced aluminium (Glare) in primary aerostructure, it should also delight the Delft University of Technology in the Netherlands, which started its quest to provide a synergistic metal/composite hybrid a quarter of a century ago. Use of Glare for over 400 m2 of the A380's fuselage crown will not only secure a 25% weight saving over a conventional structure, it could also start a major new trend in aerospace material application. Glare will be less susceptible to fatigue than aluminium and less expensive than pure composite. Moreover, the alternate aluminium/glass prepreg layered laminate can be manufactured into structures using near-conventional manufacturing techniques. Fokker Aerostructures is supplying, from its new factory at Papendrecht, A380 fuselage panels fabricated in their final curvatures and with stringers in place.
Last year, Robert Lafontan, Airbus senior vice president, engineering of the A380 programme, announced that weight-saving Glare will also be used for the leading edge ‘D nose’ sections of the vertical and horizontal stabilisers. The decision, which followed earlier tests showing the material to be sufficiently resistant to bird strike impacts, will shave 20% from the weight of the original design for the 14 m tall tail fin.
Meanwhile, Boeing is not abstaining entirely from fibre-metal laminates, since it is reported to be specifying a titanium/composite hybrid for certain wing components.
The A380 also uses ‘conventional’ composite structure. For instance, use of carbon fibre reinforced plastic (CFRP) for 40% of the wing box saves 1.5 tonnes, cutting the weight of the fully equipped structure to 11.6 tonnes. Most of the tail section, including the empennage and fin, is of carbon composite, following the precedent set by earlier Airbus airliners. The unpressurised aft fuselage is constructed from carbon fibre skin panels attached to a combination of composite and alloy frames. Altogether, composites will account for some 16% by weight of the A380 airframe, saving about 15 tonnes over the weight of an equivalent all-metal structure (total empty aircraft weight will be around 170 tonnes).
International partners and sub-contractors include EADS-Casa Aerospace in Spain, responsible for the horizontal stabiliser; Composite Technology Research Malaysia, producing leading-edge wing panels; and Japan's JAMCO, producing carbon upper deck floor crossbeams, plus stiffeners and stringers for the fin centre box.
Cost reduction
Impressive though these top-level aerostructural ‘wins’ are, composites interests must work hard to consolidate their position. The battle with metals over the 7E7 resulted in a close call that left leading aluminium supplier Alcoa pursuing a cost and weight reduction programme to improve its own competitive position against composites. William Christopher, Alcoa's president, automotive and commercial transportation, says that forging technology can help aluminium meet the parts count reduction challenge, while high performance alloys and more intelligently designed structures will compete on the weight savings front.
At Airbus, A380 programme executive vice president Charles Champion has said that improved aluminium products could buy their way back onto the structure, for example replacing composite wing ribs in future, heavier, versions of the aircraft. Composites could have secured a greater presence on the aircraft than the present 16%, had costs been lower.
Well aware of these pressures, aero-space composites departments everywhere are targeting the area of their greatest perceived vulnerability – cost – by seeking alternatives to expensive prepreg/autoclave techniques.
One route, suitable for long components of fixed cross section, is pultrusion. Airbus will, for example, use pultruded floor beams up to 7 m long and 0.25 m thick in the A380 cabin. Another drive is to automate fabrication and assembly processes that have traditionally been manual. Thus, the A380's high-integrity 8 m by 7 m by 2.4 m CFRP centre-wing box is being assembled largely automatically.
The ‘super jumbo’ is also accelerating the trend towards the use of reinforced thermoplastics. Composites that can be thermoformed and also recycled at the end of first-use life have considerable appeal and are to be used for the entire wing leading edge, along with other wing items such as ribs and brackets.
Another current focus is resin film infusion (RFI), used in conjunction with new resins that can be cured at reduced temperatures without undue sacrifice to properties. Airbus is utilising infusion processes to produce wing panels, vertical stabiliser ribs, rear pressure bulkheads and other primary structure. Use of RFI and other techniques to reduce manpower costs was a strong feature of the Civil Aircraft Structural Composites Application Development and Exploitation (CASCADE) programme, led by Airbus UK, which is responsible for the wings on all Airbus aircraft. Partners on this programme included Qinetiq, Advanced Composites Group, INBIS and W&J Tod.
According to GKN Aerospace Services (GKNAS), a sub-contractor which is providing a number of infused carbon wing panels for the A380, RFI is a user-friendly process that can yield parts of high aerospace quality at reduced cost compared with autoclaved prepregs. GKNAS says it has transferred infusion technology developed at its Cowes, Isle of Wight, UK facility to its Alabama, USA plant so that it can be used to benefit sub-contract production for the F-35 Joint Strike Fighter (JSF), the F/A-22 Raptor, the C-130J Hercules and other military aircraft.
On this side of the Atlantic, the company is working with the Advanced Composites Group and others, under the UK Department of Trade and Industry-sponsored EFICOM programme, to exploit resins able to cure at temperatures down to less than 100°C. Success in this endeavour would, it believes, boost the prospects for RFI, enabling integrated structures to be cured in ovens or on directly heated mould tools. Furthermore, according to a company spokesman, RFI and other autoclave-free technologies are likely to be even more positively regarded by the aerospace community once the report on the European collaborative TANGO key airframe structures research programme, now in its final testing phase, is published. (TANGO denotes Technology Application to the Near-term business Goals and Objectives of the aerospace industry).
On the strength of its technology developments for civil airliners, GKNAS is collaborating with Airbus Germany to produce composite wing spars, ribs and the vertical stabiliser for Europe's intended new military transport, the A400M. Composite main wing box, stabilisers, movable wing surfaces and other components will account for 35-40% of this advanced transport's structural weight, thereby maximising its payload capability.
Still other promising cost-reducing technologies are automated fibre placement and filament winding. Advantages include speed, reduced labour and material scrap costs, parts consolidation and high part repeatability. These new technologies can also provide the high structural integrity fuselages need to withstand the internal pressurisation required for passenger survival and comfort.
Raytheon has set an impressive example by winding the fuselage for its Beechcraft Premier 1 business jet in just two parts, and in three parts for its larger sister, the Horizon, which is scheduled for certification this year.
Airframers observing Raytheon's developments with interest include Boeing, intrigued by the idea of building the fuselage for a 7E7-sized aircraft from just three or four unitised sections. Composites proponents might note that, while reinforced plastics are now making the grade for fuselages, Raytheon has retreated from the all-composite airframe stance it espoused for its 1980s vintage Starship, having specified metal for the wings of both the Premier and Horizon jets. This demonstrates a trend for designers to select the most appropriate material for each application.
Where substantial production runs are involved, resin transfer moulding (RTM) and advanced RTM can provide reduced cost due to the short cycle time and automation capabilities of the method. Moreover, RTM's use of matched metal moulds generally secures high part quality. GKNAS alone has spent US$40 million on expanding its RTM facilities in St Louis, USA, to produce parts for the Lockheed Martin Joint Strike Fighter (JSF). It has formed a US company, GKN Aerospace Services Structures, to produce a range of components for the F22 Raptor as well as the JSF, using hybrid RTM.
Embracing
Although reinforced plastics are clearly making their mark at the leading edge of commercial aviation, their presence at the next level, that of regional aircraft, is less pronounced. (Except in turboprops where, notably, the ATR 42 was the first airliner to have a carbon wing). As many hundreds of these mid-sized aircraft are needed to serve regional airports, by-passing the major hubs, it is to be hoped that manufacturers like Bombardier and Embraer will raise the composite content of their next product generations. Otherwise, regional jet airframes could be eclipsed structurally not only by aerospace giants Airbus and Boeing, but also by the growing number of smaller aircraft manufacturers who are eagerly embracing these materials.
A prime example is Diamond Aircraft in Austria, which has just inaugurated a factory at Weiner Neustadt capable of turning out composite structures for up to 600 aircraft per year. Diamond opted for all-composite airframes for its DA-40TDI Diamond Star single-engined four-seater; the DA-42 Twin Star powered by twin diesel engines, and most recently its personal five-seat D-Jet, for reasons of structural integrity, low maintenance and aesthetic appeal. Diamond restricts costs by standardising parts, where possible, across its product range and basing new designs on previously produced platforms.
Honda Motor has specified a composite fuselage and metal wings for its Hondajet, a compact twin-engined business jet/air taxi currently under development. Composites have facilitated the shaping of the aircraft's nose to promote laminar (smooth, skin hugging) aerodynamic flow, thus contributing to the aircraft's 420 kt speed capability.
Adam Aircraft Industries, meanwhile, has an all-composite airframe on its A700 light business jet, now undergoing flight testing prior to intended certification late this year. Adam, whose existing A500 model is also composite, hopes that its new, unusually-configured twin-boom aircraft will be first to market in the emerging entry-level jet sector.
Las Vegas start-up Aircraft Investor Resources hopes that its all-carbon fibre Epic, a single-engined turboprop six-seater, will appeal initially to owner/flyers, but also in due course to the air taxi market. The company's owners were clear that appearance is important for aircraft in this category and have used composites to secure an aesthetically pleasing design. Deliveries are expected to commence in 2006.
Composites are also specified for many of the emerging breed of unmanned air vehicles (UAVs) and micro-UAVs, many experimental aircraft and even Burt Rutan's SpaceShipOne, the Scaled Composites-built contender for the X-PRIZE, on offer for the first privately funded and built manned vehicle to ‘fly’ in space. The materials also remain crucial for helicopters, where they have revolutionised rotor design and secured lighter airframes. It is not all ‘win’ however, since the US Department of Defense has just cancelled the advanced Comanche helicopter, which would have been a rotary-wing showpiece for composites.
Coping with demand
Nevertheless, the activity outlined suggests that aerospace composites could, subject to costs and fresh competition from metals, truly be taking off. However, it should also raise a question. With the combined B7E7, A380 and A400 programmes alone likely to require more than 3000 tonnes per year of composite materials, at least 50% up on current civil airliner usage, and similar growth to be expected in parallel aviation markets, will industry be able to cope with the demand? There are fears it could run into the buffers on materials supply, fabrication capacity, engineering skills or finance.
As Bob Griffiths, president of the Society for the Advancement of Material and Process Engineering, Europe has aptly put it: “Given this very large tonnage, I am unable to understand why the industry is neither euphoric nor panic stricken in face of the fact that all this expansion needs to take place by the end of the decade!”
