Airbus takes on Boeing with composite A350 XWB

When Airbus recently launched its A350 XWB (extra widebody) competitor to Boeing's B787 Dreamliner, it indicated that the airframe will be 52% reinforced plastic composite – similar to the B787's 50%. The new airliner will be produced in three sizes, the largest of which can compete with the Boeing B777 twin-aisle widebody. George Marsh reports.

The A350 XWB will have a carbon composite wing and, most notably, takes Airbus into the reinforced plastic fuselage territory now being occupied by Boeing with the B787 Dreamliner.
The A350 XWB will have a carbon composite wing and, most notably, takes Airbus into the reinforced plastic fuselage territory now being occupied by Boeing with the B787 Dreamliner.

The A350 XWB will have a new carbon composite wing and, most notably, take Airbus into the reinforced plastic fuselage territory now being occupied by Boeing with the B787 Dreamliner.

The European company's adoption of a predominantly composite fuselage (as well as wings and empennage) was partly in response to Boeing's earlier decision to have a carbon fibre fuselage wound in several barrel sections that are subsequently joined. Boeing's programme partners produce the sections by laying composite tape onto rotatable mandrels. Fears that an all-composite fuselage would prove a step too far for potential customers proved unfounded and Dreamliner has been a rapid seller. Airbus found itself wrong-footed by Boeing's bold escalation in composites usage and its original A350 design, largely a derivative of its successful A330 twin-aisle aircraft, cut little ice with an air transport community beguiled by the B787's innovative airframe structure along with its promised low weight and running costs. The largely A330-based design would have had a metal fuselage.

Faced with a lukewarm market response, Airbus was obliged to re-think and come up with a new design – hence the A350 XWB.

Before the American airframer trumped its European competitor in the composite stakes, Airbus had been reluctant to go down the all-plastic fuselage route, citing concerns over costs and maintainability. Even now, Airbus is less revolutionary than Boeing, favouring a more conservative approach to the fabrication of an airliner's critical pressurised fuselage. Instead of following Boeing's radical lead in producing fully integral barrel sections, it has opted for the more conventional technique of placing skin panels over frames – albeit both these entities will be of carbon composite. A previously-proposed solution involving carbon skins over metallic frames was rejected because of a perceived corrosion risk at the interface of the two materials and higher maintenance inspection requirements.

In a break with Airbus tradition, the fuselage will be ovoid in shape rather than round. Tall, flattish sidewalls will facilitate the use of large cabin windows and the provision of an area over the main cabin where flight attendants can rest.

Metal may be retained for the fuselage cross beams, though Airbus is said to be conducting trade-off studies to evaluate a possible switch to composite. Aluminium strips will be included in the frames to ensure electrical continuity and dissipate lightning strikes.

John Leahy, chief commercial officer, customers, says that although official freezing of the A350 XWB design is not due until October 2008, the fuselage design is virtually finalised and Airbus will not be following Boeing down the all-composite barrel route. The ‘parallel’ fuselage (all except the nose and tapering rear sections) will be made in three parts – forward, centre and aft – each of which will have long skin panels for the top, bottom and two sides. On the mid-sized -900 model, these sections will be 13 m, 18 m and 16 m long (from forward). The skin panels will be attached to the frames with fasteners.

Airbus believes that this more traditional arrangement offers positive advantages of reduced weight, because each panel can be optimised in thickness and weight according to its position on the fuselage, and simpler repair procedures. It claims that the four-shell concept provides a 2% lower empty weight per seat for the A350 XWB than for the B787 and suggests that, because no barrel-size autoclaves are needed to cure fuselage elements, production costs are reduced. Lap joints between the panels will be installed with the aid of automation.

According to Gordon McConnell, chief engineer for the A350 XWB, the nose section is likely to be aluminium-lithium, though Airbus is considering an alternative carbon composite structure that could be made substantially in one piece. Airbus believes that, despite the advantages of composite for a complex-curvature structure, aluminium could still be cost-competitive given a need to strengthen a composite solution with titanium reinforcement so as to withstand high-velocity impacts from birds. According to media reports, if a composite nose does nevertheless become the preferred option, the airframer could decide to produce the structure itself, most likely using a tape laying machine developed by machine tool manufacturer Forest-Line. Similar machines supplied by the French company laminate upper and lower single-curvature wing panels for the competing B787 at rates up to 60 m a minute, from tape of widths up to 300 mm.

The rear fuselage section will be an integrated carbon fibre structure and will draw on technology already familiar to Airbus. The horizontal stabiliser and fin/rudder assembly will be of carbon fibre too, maintaining Airbus' composite empennage tradition.

Carbon wing

Airbus is moving to an all-new carbon fibre wing for the A350 XWB. The wing, to be manufactured in the UK, will be common to all three variants. It will have a span of 64 m and incorporate advanced high-lift devices and winglets. The aerodynamically efficient 33° swept wing will enable the A350 XWB to fly at Mach 0.85, about the same speed as the B787.

The new wing will have carbon fibre stringers and skins and will benefit from experience gained by Airbus in building its first carbon wing, for the A400M military airlifter. The material for the ribs has yet to be chosen. A £57 million investment being undertaken at Broughton, Cheshire, will augment composites capability at the Airbus UK site in preparation for final assembly of the A350 XWB wing. Staff will be deployed as necessary and many will be retrained in relevant composite techniques, some through secondments to other Airbus composite centres of excellence, for example the Spanish centre involved in the production of the A400M wing

Airframe manufacture will be divided up into about ten work packages to be undertaken by Airbus and outside suppliers. Under the company's Power8 restructuring programme, Airbus intends to place more work with Tier 1 suppliers, a number of which are in the running to take control of sites that are currently Airbus-owned and operated. A short list of those who could become partners in the A350 XWB programme in this way includes GKN Aerospace, Latecoere, MT Aerospace, Spirit Aerosystems and Voith Aerospace. GKN is interested in the Filton site of Airbus UK, while Spirit has expressed interest in French and German locations. This partnership model would bring both investment and expertise to the Airbus camp in return for a share of the revenue from the airliner programme.

No surprise

As a result of its having taken a wrong turn on the road to offering an acceptable alternative to the B787, Airbus will not be able to introduce its A350 XWB into service before 2013-2014, several years after the B787's service entry. In mitigation, Airbus asserts that its airliner will be larger and more technically advanced than the Boeing product, and is therefore likely to be more economical and ‘greener’. In any case, Boeing is experiencing difficulties with its B787 development programme and recently announced that the first Dreamliner deliveries will not now take place until the end of 2008, six months later than intended. First flight is now likely, the company says, during the second quarter of 2008.

The A350 XWB

The A350 XWB (Xtra Wide-Body) is Airbus' response to market demand for a medium capacity long range wide-body family. Designed with airlines' priorities in mind, the A350 XWB confronts the challenges of high fuel prices, rising passenger expectations and increasing environmental concerns.

Available from 2013, it has an entirely new design with a wider and taller fuselage for extra space and passenger comfort. Three basic passenger versions are being offered. With a range of up to 8300 nm/15 380 km they include the A350-800 for 270 passengers in a three-class configuration; the A350-900 for 314 passengers; and the A350-1000 seating 350 passengers. An ultra long-range version, the A350-900R, will fly even further, and there will also be a freighter version, the A350-900F.

Airbus says that the A350 XWB is able to offer 20% lower cash operating costs per seat than competing aircraft in this size category and fuel efficiency improvements of up to 25% per seat.

Airbus forecasts that the requirement for twin-aisle aircraft will continue to grow strongly across a wide range of market applications. The demand over the next 20 years is for some 5700 new twin-aisle passenger and freighter aircraft, representing 41% in terms of value for all new aircraft delivered above 100 seats.

With a cabin cross-section of 220 inches/5.58 m from armrest to armrest, the A350 XWB is designed to provide wider aisles and the widest seats in the industry.

Few industry observers are surprised by Boeing's difficulties, given the radical nature of its new aircraft. Indeed many say that the company is still being over-optimistic and argue that flight test and certification of a novel aircraft based on a new composite airframe still cannot be achieved in the time allowed. Further delays therefore seem likely. Explaining why some elements of the Dreamliner programme have become less of a dream than a nightmare at present, Boeing cites issues within its extensive supply chain and, in particular, problems with fasteners and flight system software.

The fastener issue is particularly relevant from the composites point of view. Even though the adoption of a half plastic airframe has greatly reduced the fastener count compared with a conventional metal aircraft, thousands of fasteners are still needed to hold the various structural parts together. Many of these are aluminium-based and Boeing selected a leading aluminium supplier, Alcoa, to provide most of the fasteners needed. These products must comply with stringent aerospace quality standards and are significant engineered items.

Commentators have pointed out that Alcoa shed 40% of its fastener workforce during the aviation slump that followed 9/11 and has taken time to rebuild it to the levels now required. Alcoa says it is working hard to catch up and can successfully retrieve the situation.

A result of the fastener shortage is that Boeing's manufacturing partners have delivered fabricated items that are held together with temporary fasteners acquired from various everyday sources – even, reportedly, hardware outlets. Although these have generally been painted red, the task of locating, removing and replacing them with the approved items once the fabricated assemblies have reached Boeing's Everett final assembly plant, has proved challenging. Leaving just one unapproved, sub-standard fastener in position could potentially have serious structural consequences. Boeing insiders have unofficially suggested that documentation hastily prepared in different formats by the various contractors has not always identified the locations of the temporary fasteners clearly and consistently.

The situation has echoes of the configuration control problem experienced by Airbus with its A380, the world's largest passenger aircraft, though in that case wiring was the area affected.

Wholesale fastener replacement is not ideal from the structural point of view. Composites, especially, can be sensitive to clamping pressure and installation force and subjecting them to repeat fasten/unfasten cycles may raise quality issues.

Despite the apparent confidence of suppliers that they can catch up, one wonders whether material issues like the fastener shortage will go away, given Boeing's stated intention to build its B787 production rate up to 14 aircraft a month. Moreover, any residual material shortages could be exacerbated when A350 XWB manufacture starts. Pressure, for example, on carbon supply may once again find suppliers severely stretched to meet demand.

Overall, however, plastic airliners should be good news for both aviation and the environment. Currently, the industry burns 160 million tonnes of fuel per year (according to Airbus). The world's two leading airframe contenders hope that their new light, fuel efficient composite airliners, together with likely plastic successors to their ubiquitous A320 and B737 narrowbody workhorses, will help limit further rises in this figure.