composite class_ developing the airbus a350-xwb _ in-depth _ the engineer

8/10/2019 Composite Class_ Developing the Airbus A350-XWB _ in-Depth _ the Engineer

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25.11.2014 Composite class: developing the Airbus A350-XWB | In-depth | The Engineer

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Composite class: developing the Airbus A350-XWB

20 June 2011 | By Stuart Nathan

Europes answer to the Dreamliner, the Airbus A350 XWB is beginning to take shape

The future is plastics, as the young Dustin Hoffman was memorably told in the 1960s classic film TheGraduate. For the aerospace industry, it was certainly some distance into the future. Its only now, morethan 40 years later, that polymers are starting to make serious inroads in the construction of aircraft butthe era of the plastic plane is well and truly with us. Boeings 787, the first major airliner to bepredominantly made from composites, is expected to be certified later this year. Meanwhile, the AirbusA350 XWB, which also makes heavy use of the lightweight material, is currently in the final stages ofpreparation before a planned first flight in 2013.

The XWB in the designation stands for extra-wide body, and the A350s cabin will seat nine abreast instandard class and eight in premium class the company claims that each seat will be 1.3cm wider than theequivalent configuration of the aircrafts chief competitor, the Boeing 787 Dreamliner. In fact, the entireconcept of the aircraft was originally conceived as a response to the Boeing 787. Initially proposing anupdated version of its previous wide-body jet, the A330, the company responded to criticism of a lack ofambition by launching a programme to design a lighter-weight, more aerodynamic airliner that couldmatch the Dreamliners claimed 25 per cent reduction in fuel consumption compared with its predecessor.

In fact, the company has ended up designing an aircraft that will compete more with the Boeing 777 thanthe Dreamliner, as its a slightly larger aircraft the A350 family will seat 270-440 people, to the 787s210-330. There are three aircraft in the A350 family, with the basic model actually being the middle one,designated the A350 XWB-900, with a 65m-long fuselage and a maximum take-off weight of 268 tonnesthe smaller -800 is a shortened-fuselage variant, while the larger -1000 is stretched.

Most parts of the aircraft are a mixture of composite and alloy

The A350 also has a slightly higher proportion of composites in its construction than the Dreamliner 53 percent, as opposed to 50 per cent. The remaining 47 per cent is composed of titanium and aluminium-lithium alloy. Most parts of the aircraft are a mixture of composite and alloy in the wings, the main metalcomponents are inter-spar ribs (the spars being the supporting structures running along the wing from tipto root, and the ribs running across the width of the structure). In the fuselage, the outer skin panels arecarbon fibre, as is the frame, although the frame includes aluminium strips to ensure that lightning strikescan be dissipated. The supporting cross beams are metallic.

As this is the first composite fuselage Airbus has manufactured, testing is under way, with a compositepanel replacing an aluminium one on an A340 testbed, providing information on the acoustic performanceof the material. Composite is neither worse nor better [in terms of acoustics] its just different, saidDidier Evrard, A350 XWB programme manager. We thought we needed to get information on adjusting theacoustic dampeners.

Airbus has built two fuselage demonstrators at its Hamburg facility, including a full-scale demonstratorthat it is using to test installation and systems an approach it adopted after problems with the wiringsystems of the A380, which were designed in digital mock-ups. Difficulties with translating this onto thereal aircraft led to delays in the delivery of the super-jumbo. We are training our pre-final assembly linepeople and testing the system installation process on the physical mock-up at Hamburg, said Evrard. Theteams train on installing the harnesses, pipes, tubes and wires before we move to the aircraft for real. Ithas been really useful, with the technicians and designers informing each other on changes andimprovements.

The wing of the A350 XWB is an integral part of the overall design for fuel economy, and may be the mostdistinctive part of the aircraft, with its thin cross section and upwards-curving tips. It is the secondcomposite wing that Airbus has tackled, but the first for a commercial airliner the first was for the A400Mmilitary transport aircraft.

The way the wings will be constructed does, however, represent a first for the company: they will be builtin a horizontal configuration, instead of vertically, like previous wings. This is to allow access to thecentral wing box area and to make the holes for the components installed underneath the wings easier toget to.

The wings will be assembled at Airbuss facility in Broughton, near Manchester, using parts from all over
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the world: front spar from Spirit Aerosystems in the US rear spar from GKN in Filton, near Bristolleading edge also from Spirit, but this time from Prestwick in Scotland upper cover from Germany andlower cover from Spain.

Once shipped to Broughton, the spars will be attached to the aluminium-lithium ribs, and the covers willbe fixed temporarily into place for drilling. The covers are a single piece, rather than multiple parts as onthe much larger A380 wing and, again in contrast to the A380, the skins for the wings are bonded ratherthan bolted into place, so far fewer holes are needed only 5,000 per cover, rather than the quarter of amillion for an A380 cover. Once drilled, the covers are removed for deburring and sealing, and thenreplaced for fastening onto the structure. The internal structures fuel tanks and some of the hydraulics areinstalled, before the wing is sent for painting and then flown over to another Airbus plant, in Bremen,

where the electrics, pneumatics, control surfaces and remaining hydraulics are put into place. When thatis done, its off to the final assembly in Toulouse.

The shift to composite parts rather than metallic puts a different emphasis on the manufacturing process.Metallic parts are generally produced near net that is, close to the specifications needed but not spot-on,with machining providing the final touches to get within the engineering tolerances. But composite partsare made the right size from the start, so the most precise engineering has to go into making the tools toproduce the parts, rather than into making the parts themselves.

The A350 has a slightly higher proportion of composites in its construction than the Dreamlineraircraft

Electronic systems for the aircraft come from Thales, which is providing both the cockpit and the in-flightentertainment systems. The cockpit will have a similar feel to other Airbus models which is part of thecompanys policy to ensure pilots can make the transition to the new aircraft easily and Thales has

customised its head-up display (HUD) system, used on the A380, for the A350 family.

The cockpit design, currently being tested in Toulouse, has six displays, with the HUD and the on-boardairport navigation system integrated into the display system, which will host the software directly. Thishas allowed Thales to dispense with a separate processing unit for these systems, which is said to free upcockpit space while reducing weight by about 15kg and cutting electricity consumption by 150W.

HUD is a relative newcomer to commercial airline cockpits, although it has been used by military pilotsfor years. However, Airbus began using it in 2009, and had it on its wishlist for the A350 series from thestart, said Michel Soler of Thales Avionics. Thaless HUD was part of the initial design of the A350 and willget certification when the aircraft enters into service, meaning quicker delivery for customers, he said.HUD on commercial airliners is now a real trend. Our goal is for this type of product to become standardon all Airbus aircraft in the near term.

In another similarity to the A380, the A350 will have its own engine, developed by Rolls-Royce. The latestversion of the Trent range of turbofan engines, the Trent XWB, underwent its first test last June. TheTrent XWB has the lowest carbon emissions of any wide-body engine, and will be the most fuel-efficientengine on the market, said Ian Crawford, director of Airbus programmes at Rolls-Royce.

Our goal is for the head-up display to become standard on all Airbus aircraft

Michel Soler, Thales Avionics

The Trent XWB, as its name implies, is a development, rather than a step-change, in engine design. It is athree-shaft turbofan, lighter than previous members of the Trent family owing to the use of bladed discs(blisks) in its compressor stages, rather than turbine discs where the blades are attached to the centralsection the first stage of the eight-fan intermediate pressure compressor is a blisk, as are the first threeof the six fans of the high-pressure compressor. The main fan of the engine is huge 3m across, wider thanthe entire fuselage of a Concorde, and sized to keep the engine operating quietly when it has to handle

heavier loads.

Other innovations include improved heat-resistant materials, which enhance efficiency, and largerbearings able to handle greater load.

One issue that remains to be resolved is whether the same engine will serve all models of the A350 XWBfleet. This was the initial plan, but airlines have expressed concern that the engine as currently designedwill not deliver enough power for the largest version of the aircraft, the A350-1000. There is speculationthat Rolls-Royce will develop a more powerful variant of the Trent XWB for the A350-1000, with newsagency Reuters quoting a major A350 customer, the chief executive of Air Lease Corporation, saying thecurrent configuration wasnt sufficient for payload, range and runway performance on the larger aircraftand that Rolls-Royce had agreed to look again at a new design. An announcement is expected at the ParisAir Show, after this issue of The Engineer has gone to press.

Second nature

Concept Cabin is supported by a bionic structure that is said to mimic the structure of bird bone

Airbuss future designs department has looked into the future to present an idea of how flying might lookin 2050, with a Concept Cabin design that it claims is inspired by nature. Some of the details providesome tantalising glimpses of the engineering developments the company has in mind for future


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generations of aircraft.

For example, the most striking feature of the Concept Cabin is that it can become near-transparent, withan intelligent cabin wall membrane controlling air temperature that can transform the cabin into an all-around view. This membrane is supported by a bionic structure, which, the company said, mimics thestructure of bird bone and is optimised to provide strength where it is needed.

Engineers will recognise this description as being characteristic of additive layer manufacturing (ALM),where structural optimisation software is used to design a complex shape to bear the forces experiencedby the structure, which is then built layer by layer by melting fine powder with a laser.

Airbus is developing ALM techniques at EADS Innovation Works in Bristol, and has developed parts such asducting for air management inside the A380 wing and trials for components in landing gear. The companyhas an overall plan to be able to print an entire wing within 25 years.

The Concept aircraft also includes design features such as engines semi-integrated with the fuselage,positioned above a U-shaped tail to help reduce the noise of the aircraft, and wings shaped to provide thelaminar flow of air over the aerodynamic and control surfaces, removing turbulence from the airflow,which increases the power needed to push the aircraft through the air. Thinner wings reduce the spaceavailable for fuel storage, but this is a trade-off with the improved efficiency of the design.

Other engineering features include fully recyclable materials within the cabin space the use of self-cleaning materials to reduce maintenance and systems to recover passenger body heat to power thecabin features.

Readers' comments (12)

brian m | 20 Jun 2011 1:16 pm

Also worth looking at the world of model aeronautics to see how plastic technology is beingembraced. Commercially made models are often made of EPO foam and end up being lighter, lowercost and more amazingly, stronger than traditionally built models (in terms of crash resistance).

The use of carbon fibre strengthening has increased the size of these model aircraft to wingspans of

1.5 m and more (probably limited by the size of a car boot!). Electric power is normally used in thistype of model, with high performance Li-Po batteries flight times similar to conventionally ICpowered models.

Living close to a park where they are flown they are also mercifully silent compared to their ICpowered brethren!

David Holman | 20 Jun 2011 1:23 pm

Our [Goodrich Actuation Systems, Wolverhampton] electric thrust reverser actuation system forA350 XWB is rather fine. What other novel and new developments has the Engineer overlooked?

Editor's comments | 20 Jun 2011 1:23 pm

Several, doubtless, but we have limited space for features so had to choose which systems todiscuss!

David Lawton | 22 Jun 2011 1:21 pm

10/10 for the article but 0/10 for geography - 'Broughton near Manchester'?? It's 5 miles fromCHESTER, 25 from Liverpool and 45 from Manchester!!

Edward | 24 Jun 2011 6:58 pm

Am I right in thinking that by composite fuselage they mean a sandwich of aluminium sheets withpolymer between i.e. a laminate or is it a true composite?

Dutch | 26 Jun 2011 11:25 am

The caption for the first image reads, "A350 XWB has a 64.8m wingspan and a 64m cockpit".

11Like Share Share 9


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A 64 m cockpit? Wow. That's a big plane.

Shouldn't it read "64 m fuselage"?

Editor's comments | 26 Jun 2011 11:25 am

It should. Thank you.

Robert Taylor | 14 Jul 2011 9:29 am

Are aircraft manufacturers still treating carbon fibre as 'black metal'?I had a job interview a couple of years back for a Materials Scientist role where the interviewingengineers complained bitterly that aircraft manufacturers were still treating carbon fibre likealuminium alloy where individual plates were rivetted together rather than moulding largeassemblies which the material lends itself to.

Anonymous | 19 Jul 2011 11:25 am

What about the crash test for the Composite fuselage? Is airbus planning the test duringcertification?

AB | 20 Jul 2011 4:04 pm

@Edward - No, it is a fuselage with solid monolithic CFC skins and separate bolted on frames andstringers. Skin varies hugely in thickness up to nearly 100 plies in high load areas.@Robert - Yes and no Boeing 787 has a one piece fuselage skin, A350-900 has a skin made of largepanels. The Airbus approach is bbetter for in service repairs like being hit by a truck. Due to scaleit's not possible to make some of these structures like wings out of one piece.

Anonymous | 7 Jan 2013 8:09 am

What could be expected as thickness tolerance range for CFC T 800wing skins say 5mm to 16mm when made by hand lay up of prepregs or by ATL with compaction? Does +/- 2% look feasible? If

not what could be best?

mike blamey | 17 Jun 2013 4:21 pm

Fascinating article and commentaries: just as the computer industry 'took' our textile industrypatterning systems (developed by Jacquard et al) and used them for their advances, so the aircraftindustry has done the same. This time, taking our 'fabric' forming techniques and applying them totheir needs. Do we get a royalty?

I look forward to reading more, particularly about braiding of complete parts -indeed with a braiderlarge enough, it would be possible to create a complete fuselage in one go!

I do recall giving a lecture at Boeing in 1973 to aerospace Engineers which allowed me to guide

them away from that concept of composites/fabrics NOT being v thin flexible metal(s) butdesignable structures in their own right!

Best wishesMike B

Editor's comments | 17 Jun 2013 4:21 pm

Braiding is certainly making its way into spacecraft design. A braided aircraft fuselage is a veryinteresting idea. You'd need a big autoclave, though!
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