JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014 - 35

carbon-skinned fin box for the A310,
which saved 20% in weight over metal.
Other early carbon prepreg applications
were the fenestron (rear tail boom) of
the Dauphin 2 helicopter, the main and
tail rotor spars of the Sikorsky S-76 and
the 5-m blade skins for the Westland 30
helicopter.
In 1988, the pioneering carbon prepreg
outer wingbox for the ATR 72 made this
the first commercial aircraft with a fully
carbon composite wing - saving 500 kg
per aircraft.

For the A350 XWB, Hexcel supplies
HexPly® carbon fibre prepreg for all
of the primary composite structures
including entire fuselage panels, most
of the fuselage frames, keel beam, wing
covers, spars, centre wing-box and entire
empennage. The A350 XWB lower wing
covers are the biggest single civil aviation parts ever made from carbon fibre,
measuring 32 metres long by 6 metres
wide.

times, greater responsiveness, reduced
transportation of materials, point of
use delivery, less packaging, reduced
inventory and less requirement for cold
storage space.

Why composites have surpassed
aluminium in aircraft structures
Performance and weight savings have
historically been the key drivers behind
the increasing penetration of composites
into aircraft structures at the expense of
aluminium. However, there are many
other major advantages, such as:
- Density: The lower density of carbon
fibre composites makes composite
structures more than 20% lighter than
even the latest aluminium alloys. Weight
savings mean greater fuel efficiency,
reduced emissions and lower operating
costs.

All of the A350 XWB composite primary structures
are made from HexPly® carbon fibre prepreg

The company secured the A350 XWB
contract by developing a complete
composite proposal, combining its experience in intermediate-modulus carbon
fibre with the new HexPly® M21E epoxy
prepreg resin matrix that was developed
by its chemists to ensure that the very
high performance properties in the fibre
are fully optimised in the cured prepreg
laminates.
To produce the vast quantities of
prepreg required for the A350 XWB,
Hexcel introduced a new model for the
cost-effective large-scale production
of prepreg, producing resin film in a
continuous process to very tight areal
weight tolerances which has improved
the quality, accuracy and consistency of
the resin film. The resin film from the
UK is converted into UD prepreg at the
facilities in France, Spain, Germany and
the USA, from where it is supplied to
nearby Airbus facilities and the Tier 1s
throughout Europe and the USA.
This has resulted in a highly effective
supply chain model for prepreg production, which results in shorter lead

- Durability: Composites are not subject
to corrosion and exhibit excellent
fatigue properties, for a longer service
life. Aluminium fatigues and is subject to
crack propagation. Most metal parts are
subject to ALI (Airworthiness Limitation Items), which means mandatory
inspections in service.
- Design optimisation: The wide choice
of resin systems available enables special
features to be designed into the composite, such as meeting fire, smoke and
toxicity requirements, high temperature
performance or higher impact resistance.
In addition, the fibre reinforcement
can be uniquely tailored to meet the
stiffness/strength design requirements,
by orienting the fibres in a particular
direction to achieve maximum performance where it is most needed, without
any weight penalty.
- Reduced part count: With composites,
several components can be combined
into one single composite part - saving
manufacturing and assembly costs.
- Better buy-to-fly ratio: With aluminium, the finished part may weigh as

No86 January - February 2014 /

Feature Prepreg

Since then, these weight-saving composite materials with exceptional
stiffness and toughness have been used
increasingly on each successive Airbus
programme. Applications extended from
A320 fin box structures and horizontal
stabilizers, to the giant carbon fibre keel
beam for the A340-500/600. Yet composites accounted for less than 15% of the
structure of these aircraft.
The A380 was a game-changer with a
structure that is 25% composites by
weight. The wing box alone, built with
Hexcel's HexPly® M21 carbon fibre
prepreg, saves up to 1.5 tonnes of weight
per aircraft. This giant airliner also
marked the maturity of automated composite manufacturing techniques.
The A380 composite tailcone is built
with HexPly® 8552/AS4 12K prepreg in
the form of finely slit tape - with widths
as narrow as 3.2 mm or 6.4 mm. This
labour- and scrap-saving form of prepreg
allows parts to be manufactured by automated fibre placement (AFP), a computerised process providing tight tolerance
control and exact part reproduction.
The A380 pushed back the boundaries
for composites in aircraft, showing the
scale of carbon fibre composite structures that could be produced - and
automating the manufacturing process
for greater efficiency. This paved the way
for the next big jump in the penetration
of composites into aircraft structures
with the Boeing 787 Dreamliner and
A350 XWB twin-aisle aircraft, both
having more than 50% composites in
their structure.

A350 XWB:
53% composite structure

jec composites magazine 35

JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #86 - January/February 2014