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military applications. There may be two
reasons for this. Firstly, prepreg materials
offer the highest mass specific stiffness and
strength compared to other composite
technologies (such as liquid moulded textile
preforms). They therefore provide the
highest weight saving potential. Secondly,
fighter aircraft programs normally run for
more than thirty years from the definition
phase to the start of series production, and
the number of such projects within a given
company at any time is very limited
(normally only one). Therefore, it is not
possible to use the strategy followed by
Airbus (for example) of implementing new
technologies in a stepwise fashion across a
whole family of planes.
1 Forward Fuselage
2 Cowling 3 EFA Center Fuselage 4 Tornado Fin
5 Finbox
6 Tornado
Lid
for RAT
7 Tornado
Undercarriage Lid
9 Fuselage Center Part 8 X31 Wing
with Integrated Tank
9
Helicopters
Helicopters have employed composite
materials in the rotor blades for about 40
years. Compared to aluminium blades, the
adoption of glass fibre reinforced plastic
blades increased the service life by a factor
of up to 200. Nowadays, all helicopters use
composite blades because of their superior
fatigue properties and their potential for
multifunctional design. The rotor blades and
the rotor blade head are typical examples in
which composites are used not only for their
high specific stiffness and strength, but also
for their additional functionality. Tuned
anisotropy and integrated hinges are just
two examples of how composites can be
used to improve both performance and cost.
In Figure 12, a conventional rotor blade
head is compared with that of the EC 135, a
highly optimised composite design. The part
reduction and integration of the latter leads
to a significant reduction of the assembly
and maintenance costs, as well as improved
reliability.
The helicopter industry also makes
extensive use of composites as structural
passenger cell materials. Following several
technology projects such as the BK117
“Composite-Cell” (a joint development
between MBB and Kawasaki in the 1970s),
an increasing number of composite parts
have entered series application. Nowadays,
nearly all military and civil helicopters use
composite materials for the passenger cell.
Two examples, the EC 135 and the Tiger,
are shown in Figure 13. Due to the specific
requirement for lightweight structures in
helicopter applications, extensive use is also
made of sandwich structures.
Another specific requirement for helicopters
is the energy absorption capability of the
underfloor. Extensive research has been
conducted into the development of energy
absorbing structures. Due to their high mass
specific energy absorption capability,
composites are also employed for this
purpose. One of the most interesting
concepts is the composite sine wave beam.
Figure 12 – comparison of a conventional and
optimised rotor blade head (source: Eurocopter)
Figure 13 – composite parts of the Eurocopter EC
135 and Tiger (source: Eurocopter)
Conventional Rotor
Sikorski S 58
Bearingless Composite Rotor
Eurocopter ATR-Design
Flexbeam Rotorblade
With Integrated
Control Tube
GFRP
CFRP
CFRP /
Aramid
Sandwich
Metal
Glass
Plexiglass
GFRP
Sandwich
Metal
Secondary Structure
Carbon-Aramid Fibre
Sandwich
Plastics (PMMA)
Primary Structure
Carbon Fibre
Sandwich Monolith
10
Space Applications
The aerospace sector with the highest
interest in lightweight design is of course the
space industry. A kilogram saved can have
a value of more than €10,000. Therefore,
high modulus carbon fibres are the most
important candidates for structural space
materials. In addition to their mechanical
performance, the low coefficient of thermal
expansion of carbon fibre reinforced plastics
is highly relevant for satellite applications.
A typical structure, a sandwich for solar
panels, is shown in Figure 14. The skin
consists of high modulus carbon fibres
produced by a special filament winding
technique. The core is extremely light
aluminium honeycomb.
Another use of composites in space
applications is the carbon/carbon technology
employed, for example, as the heat
shielding material of re-entry structures or
rocket nozzles.
Figure 14 – ultra-lightweight design of a solar
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