FEATURE
Wing worker
for the world
GKN Aerospace is heavily involved in the manufacture of the composite
wings for the new Airbus A350 aircraft. George Marsh visited the
company’s Filton, UK, site to see the composites technologies involved.
B
oeing has established a new level of
composites penetration in civil airliners
with its 50% reinforced plastic B787
Dreamliner. However, Europe’s Airbus Industrie
looks set to trump even this, albeit by a
narrow margin, since its new A350 XWB (extra
wide body), now in gestation, is advertised
as being some 53% plastic. Practically all of
the A350’s visible airframe – wings, fuselage,
empennage, nacelles and control surfaces, will
be very largely of carbon composite.
This is good news for the aerospace
composites supply chain and good news
for UK industry which, as long-time
builder of Airbus wings, is to construct the
extensively composite wings for all three
variants of the A350, the -800, -900 and
-1000. A major player in the wing build
programme is GKN Aerospace (GKNA),
now installed on the site at Filton, near
Bristol, that it acquired from Airbus in
January 2009, with the aim of making it an
acknowledged global centre for designing
and building advanced wings for newgeneration passenger jets. Airbus was
already building primarily metal wings for
the full range of Airbus commercial aircraft
in the UK. With the acquisition of the
Airbus manufacturing operation at Filton,
GKNA has inherited this work for the lives
of the aircraft programmes concerned, and
is adding the ability to produce composite
wing assemblies.
A350 demonstrator rear spar recently completed by GKN Aerospace.
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FEATURE
Wing ambitions
GKNA needed new Europe-based facilities in order to achieve its wing ambitions. The chance to co-locate itself with
Airbus UK (which retains the rest of the
site) in a refurbished facility at Filton
not only offered the space needed to
assemble large A350 wing sections in
parallel production streams able to turn
out anything up to 14 aircraft sets per
month, but also fitted in with its wider aim
to produce wings for other new aircraft
as well. In line with the expected high
composite content of those new-generation wings, the company is commissioning
about now (early Spring), a new advanced
composites production facility at Weston
Approach, close to its major Filton site. This
features the latest in production automation to meet airframer requirements for a
continuous stream of wings that meet ever
more stringent standards for aerodynamic
efficiency, low weight and affordability.
Together, these two sites, along with its
original facility at Cowes, Isle of Wight,
underpin GKNA’s drive to become an
‘advanced wing maker for the world,’ as
Frank Bamford, senior vice president business development and strategy, puts it.
Bamford explains that the company is
investing some $280 million over five years
in its risk sharing partnership with Airbus
to design and build the fixed trailing
edge (FTE) section of the A350 wing. This
comprises the fixed internal wing structure
aft of the main wing box, but excluding the
carbon wing skins, for which Airbus plants
in Germany and Spain are responsible. The
most significant part of the GKNA contribution is the rear spar, the crucial longitudinal
strength member that forms the after edge
of the central wing box and supports all the
fixed sub-structures that carry the movable
surfaces and, in the inboard portion, landing
gear fixtures. The spar is subject to high
loadings and stresses, a situation that
favours composites with their high strength/
low weight characteristics, tailorability and
high fatigue tolerance.
Thorough material characterisation and
painstaking design are pre-requisites for an
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M. Torres lay-up machine at GKN Aerospace.
optimum structure, of course, and GKNA
can call on its extensive experience in
engineering a wide range of composite
items for aircraft including nacelles, flight
control surfaces, cowls, ducts, engine
fan blades and containment casings. It
produces the primary composite wing
spar for the Airbus A400M military airlifter
and wing trailing edge sections for the
world’s largest airliner, the Airbus A380.
Not that its wing work is entirely Airbus
focussed; it also produces the wing leading
edge ice protection system for the B787,
recently won a contract to build performance-enhancing composite winglets for
Bombardier’s new C-Series airliner and also
produces winglet structures for Aviation
Partners-Boeing. Its sites in the USA manufacture wing spars for the Lockheed F22
fighter, airframe structures for unmanned
air vehicles and parts for various business
and light jets. All these components have
substantial or majority composite content.
A350 wing
The Airbus-designed wing for the A350
wing is a largely composite assembly,
though with ribs, internal frames and
certain other sub-structures of metal.
The wing’s beam strength derives from a
central wing box in which two full-span
spars form the forward and rear faces of
the box. The spars have to be of carbon
composite, both for weight saving and so
that their coefficient of thermal expansion matches that of the wing’s carbon
composite outer envelope.
GKNA is responsible for the rear spar and
assembling it to all the fixed structure that
attaches to it, these together comprising
the fixed trailing edge (FTE). The composite
spar, along with its attached structures, is
produced in three 10 m sections that are
joined for final checks before the full FTE
is disassembled again for transportation
to Airbus UK’s wing final assembly facility
at Broughton, North Wales, where the
complete wing is integrated.
The most substantial, inboard, FTE spar
section weighs some 500 kg and includes
the tough spar root with composite
laminates up to some 25-30 mm thick. The
mid-section, which has many attachment
points, weighs about 150 kg, while the
outboard section weighs 100 kg. Each spar
section is produced by laying composite
tows onto a large rotating mandrel, the
formed part subsequently being autoclave
cured under slight pressure. The spar
tool is of Inconel metal and the mandrel
for laying up spar sections is of carbon,
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FEATURE
in high modulus grade so that deflection is minimised. The mandrel concept
contrasts with traditional metallic tooling
philosophies, resulting in lighter, more
affordable tooling.
Hexcel’s M21E pre-impregnated carbon/
epoxy composite material, as specified by
Airbus, is used throughout. Comprising
a toughened epoxy resin reinforced with
unidirectional carbon fibres, this system
confers superior mechanical properties, in
particular high impact resistance. Advanced
5-axis automated fibre placement (AFP)
machines, purpose-designed and built by
M. Torres in Spain, each wind 0.25-inchwide tapes from up to 16 bobbins via a
pulley system onto the rotating mandrel.
Machines can be programmed to lay
varying thicknesses of material onto the
mandrels and can, for instance, build up
thickness locally to provide integral pads
for rib attachment points along the spar.
Automated fibre
placement is part of our
drive for a high level of
automation.
“AFP is part of our drive for a high level of
automation so that we can efficiently produce
wing sections to a consistent high quality
while requiring as little manual work as
possible,” Comments chief engineer Chris Gear.
“It will enable us to achieve high production
rates so that we can meet our commitments
as A350 production builds to a possible 14
aircraft a month. We’re also incorporating
robotic drilling and machining and assembly.”
Interestingly, GKNA developed automatic
tape laying (ATL) technology for its previous
similar project, the spar for the A400M.
(This is claimed to be the first major
primary structure to be produced in carbon
composite for the wing of a large transport
aircraft). ATL machinery at Cowes can lay
up composite tapes 150 mm or 300 mm
wide at the rate of about 18 kg (40 lb) of
material per hour compared to hand lay-up
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Hot drape forming machine.
rates of just 1-3 lb/hr for a similar item. For
the A400M spar, the resulting flat laminate is
then formed to the required ’C’ section spar
shape over a heated tool, using a doublediaphragm press forming technique. The part
is then put into an autoclave for final cure.
The method also enables the company to
achieve void content as little as 1-1.5%,
compared with 4% considered a more
normal value for hand lay-up. AFP results in
similar dimensional precision and laminate
quality, while being potentially faster.
For the A350, however, automated fibre
placement (AFP) is the preferred lay-up
method. This is partly because the toughened resin used in the Hexcel M21E prepreg
flows less readily than that in Cytec’s
977-2 used for the A400M spar, and partly
because of the ability of AFP to produce
more complex shapes. The A350 wing
has significant curvature, particularly in
the inboard sections where the profile is
distinctly gull-winged. While ATL is viewed
as excellent at producing large, reasonably flat structures, it can cause composite
fibre buckling in more highly shaped
components. AFP, on the other hand, while
no better at laying up large flat surfaces,
is accurate over more extreme curves
and changes in direction because it uses
narrower, independently controlled separate
tapes to make up varying laminate thicknesses, including three-dimensional features.
Essentially, each A350 spar section is layed
on the mandrel, which is a long four-sided
box, with cross-section, profile and wall
thickness all varying according to location
along the span. The AFP machine can lay
two 10 m spars at one time, these subsequently being removed and placed onto a
metal mould tool for curing in an autoclave.
Both methods enhance quality consistency and accuracy. ATL, for example, can
produce the 14 m (45.9 ft) spars for the
A400M wing to a dimensional tolerance of
0.5 mm. The metallic equivalent usually has
to be adjusted during the build process.
Composite work takes place at the new
Weston Approach facility near Filton in a
5000 m2 clean area. Two M. Torres winding
machines are at one end of this space while
a number of autoclaves plus ultrasonic
testing and finishing facilities occupy the
remainder. As production rate increases,
more machines will be added in the clean
room to cope with the volume.
At te time of a recent visit by Reinforced
Plastics to Filton, GKNA had produced and
evaluated a prototype composite spar for
Airbus’ A350 wing box demonstrator and
was preparing to embark on series production. The prototype milestone was achieved
by a collaborative team comprising
engineers from GKNA sites in Munich in
Germany, Cowes and Filton, and utilised
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FEATURE
expertise gained at Cowes in manufacturing the A400M spars. Completed A350
production spars will be moved from the
composites centre to the Filton assembly
facility where they will be integrated with
other fixed trailing edge components. Each
FTE is assembled on a fixture, the spar
section being placed therein hollow face
up so that it can be drilled and machined
as necessary, and the various ‘A’ frames,
fitments and other structures can be
attached.
Evolution
Chris Gear emphasises that the pace
of composite manufacturing evolution
is rapid, with significant changes being
evident between successive generations of
wing manufacture. Resin film infusion was
developed for the Airbus A380 ‘superjumbo’
FTEs, designed by the company at the start
of the millennium and in build from that
time. ATL technology followed and went
into production on the A400M spar in
2004. AFP is making its debut on the A350
FTE production line this year.
The pace of composite
manufacturing evolution
is rapid.
On the assembly side, another sign of
evolution is the difference between the
A380 and A350 programmes over the
basic assembly method. In the A380 shop,
the wing FTE remains fixed in position,
on static jigs, requiring personnel and
machines to move around the structure.
On the more highly automated A350 line,
however, there are no static jigs. Instead,
FTE sections are moved on assembly jigs
through a sequence of workstations where
assembly, drilling, reaming and other
machining operations are carried out
robotically, to extremely tight tolerances.
Flow line movement takes place on automatically guided vehicles (AGV), under
the precise positional control needed
to maintain overall wing geometry.
This change permits the faster assembly
process needed to meet anticipated
high production rates for the A350
wings. As Frank Bamford points out,
both the A380 and A350 are remarkable for their large scale, but in the
A380’s case this is in terms of sheer
structure size, whereas for the A330 the
scale is related to fabrication volume.
A350 XWB update (source: Airbus, April 2010)
The A350 XWB is a new family of midsized wide-body airliners. There are three
passenger versions capable of flying around
15 380 km. In a typical three-class configuration, the A350-800 will offer 270 seats; the
A350-900 and the A350-1000 will offer 314
and 350 seats respectively.
The baseline A350-900 design was frozen
in December 2008 and is on track for entry
into service in 2013. The A350-800 will enter
service in 2014, and the A350-1000 in 2015.
Design
The A350 XWB brings together the latest
in aerodynamics, design and advanced
technologies to provide a 25% step change
in fuel efficiency compared to its current
long-range competitor.
Over 70% per cent of the A350 XWB’s
airframe is made from advanced materials
combining composites (53%), titanium and
advanced aluminium alloys. The aircraft’s
carbon fibre reinforced plastic (CFRP) fuselage
results in lower fuel burn as well as easier
maintenance.
Next generation Rolls-Royce Trent XWB
engines and state-of-the-art aerodynamics
help reduce emissions well below current
and anticipated future regulatory levels.
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Carbon dioxide emissions per passenger
will be up to 25% lower than with current
generation aircraft in this category.
Production
More than 5000 engineers are carrying out
design work on the airframe. The workforce
is expected to increase to around 13 000 at
peak production. Airbus is continuing with
specific design work as well as implementing
the necessary buildings and tooling to ensure
the start of final assembly in 2011.
Structure demonstrators are produced and
tested to confirm composite manufacturing
and assembly techniques, as well as fatigue
and damage tolerance. A second full-scale
carbon fibre fuselage section, 18 m in length,
made-up of three sections and complete
with CFRP door, is undergoing testing, and
an 18 m full-scale wing-box is being used for
testing manufacturing techniques and validating the selected technology. Production
started last December with the successful
first carbon fibre tape lay-up of a centre wing
box panel with a surface area of 36 m2.
Assembly
Aircraft sections, already equipped and
tested, will arrive at the new A350 assembly
facility in Toulouse, France. This will reduce
the amount of systems work required at the
final assembly line.
Before final assembly starts, the galley
and flight crew rest compartments will be
loaded into the three fuselage sections.
The fuselage sections will then be joined
together, giving a complete interior shell that
can be furnished in parallel with ongoing
assembly work. In the next stage, the wings
will be joined to the fuselage, and the
horizontal and vertical tail planes will also
be installed. While this is taking place, the
first stage of cabin installation will start,
much earlier in the aircraft assembly process.
Integration of the landing gear and other
systems will run in parallel with the wing
join-up, and first ‘Power On’ will take place.
The aircraft will then move from the new
A350 XWB facility to the existing A330/340
final assembly line, also in Toulouse, where
it will undergo all other ground testing and
further cabin work. The aircraft will then
follow the current A330/340 assembly and
delivery process.
When production reaches its peak, the
whole process, from start of final assembly to
delivery to customer, will take two and a half
months, representing a 30% lead-time saving.
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FEATURE
To win the A350 FTE work package, GKNA
has had to develop its new fibre placement
manufacturing process for a wing that is
50% greater in span, has the main landing
gear attached to it and is much heavier
than that of the A400M. Meeting production commitments called for high rates of
material deposition onto the rotating spar
mandrel along with further development
of automated machining, spar and trailing
edge tooling, flexible assembly, waterjet
cutting of composites, single-step drilling
and reaming of composites and inspection
techniques. Methods for laying up, forming
and processing the primary M21E composite
material at speed had to be devised and
refined. Modular tooling concepts had to be
engineered so that tooling can adapt to the
different component sizes required for the
three aircraft variants.
Much of this technology has been developed at GKNA’s Composites Research Centre
at Cowes on the Isle of Wight, though not
without external assistance. Evolution has
benefited from collaborative research, often
supported by external funding.
“We are a builder and integrator of aerospace assemblies and have limited resources
for research,” Chris Gear explains. “The R&D
that we carry out is generally part-funded
by GKN with support from the Government and other partners. We have engaged
with a number of projects funded by the
European Union and aimed at enhancing
Europe’s competitive position in aerospace.”
For example, the Advanced Low-Cost
Aircraft Structures (ALCAS) programme,
funded as part of the EU’s sixth framework (FP6) research platform, helped the
company to move on from the ‘black metal’
syndrome, characterised by designers
simply substituting existing metal parts with
carbon copies of the same thing, towards
fully integral composite structures with
much reduced part counts.
“Ideally, one would like to see a large
composite structure infused as a single
integrated whole in one hit,” declares
Gear. “We‘re moving progressively towards
this ideal.”
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ALCAS, which resulted in a full-scale
partial wing and some representative
spars, itself built on the earlier FP5
Technology Application to the Near term
business Goals and Objectives (TANGO)
programme, which helped pave the way
for more integrated airframe structures
to be built in reinforced plastic materials.
ALCAS supported development of
technology underpinning the design and
build of the complex composite spar for
the A350.
The company has also taken part in
the EU’s Aircraft Wing with Advanced
Technology Operation (AWIATOR) research
and is active on the Next-Generation
Composite Wing (NGCW) programme,
a £103 million UK initiative designed to
keep Britain at the cutting edge of wing
innovation and development. GKNA
brings its composites manufacturing and
ice protection capabilities to this latter
programme, which is targeting high
manufacturing rates and standards for
future composite wings. Extending over
three years from 2008, NGCW has helped
the company optimise its factory layout for
high-volume production and investigate
new tooling developments.
Technology drive
As A350 production gets into its stride and
progresses through the variants, GKNA will
further refine its methods and processes.
While it looks forward to a long continuation of its close partnership with Airbus,
GKNA sees Filton as key also to opening
doors into other future wing projects. In
particular, it is targeting a share of the
glittering prizes associated with nextgeneration single aisle (NGSA) aircraft,
especially the yet-to-be designed types
which, sometime late in this or early in
the next decade, will start to replace the
thousands of Boeing B737 and Airbus 320
jets that are the backbone of air transport
today. GKNA aims to be airframer agnostic
and hopes that its technology will appeal
to both the established giants as well as
regional aircraft builders like Bombardier
and Embraer, plus up and coming aspirants
like China’s Comarc.
To do this, it knows it will have to maintain the intensity of its technology drive,
developing wings that improve still further
on the state of the art represented by the
A350 wing, itself the most efficient ever
designed by Airbus. Wing design is likely, for
instance, to benefit from laminar flow, an
extremely smooth flow of air closely over
the wing surface promoting maximum aerodynamic efficiency and lift. This will require
the engineering of ultra-smooth composite
wing skins, a fresh challenge for composite
engineers. Future wings may evolve more
towards a closed-cell, fully composite type
of structure.
Efforts are on-going to achieve shorter
composite manufacturing cycle times and
cost reduction. One focus already yielding
promising results is the use of microwave
curing, with a view to reducing reliance
on expensive and wasteful autoclaving
methods. Such methods can also help
bring about increased melding of parts by
co-curing, so reducing part counts substantially. Further robotisation of machining and
assembly operations should bring down the
costs of volume production. Other developments will centre on effective integration
of metals with composites since trends
suggest that reinforced plastics will never
entirely supersede metals and that the
future lies in a creative partnership between
the two.
Inclusion of sensing elements within
composite laminates could assist the
development of the ‘all-electric wing’,
in which control surfaces are moved
electrically rather than hydraulically. For
example, sensors able to detect the
formation of ice on leading edges could
trigger de-ice heater mats.
GKNA is intimately involved with these and
many other developments in its strategy,
greatly facilitated by the Filton acquisition
and the A350 FTE partnership, to be a very
special Tier 1 supplier, a wing worker for
the world in fact. ■
Further information
GKN Aerospace; www.gknaerospace.com
www.reinforcedplastics.com