JEC COMPOSITES MAGAZINE - Issue #79 - March 2013 - 27

Fig. 2: Arm and sail structural box design

mercial aircraft wing. The sail
has a central box section, designed with tapering thickness
skins, two C-spars with ribs and
“omega” shaped hat stringers to
provide resistance to buckling
(Figure 2). The sail central box
components were manufactured from multi-directional
carbon fibre fabrics and epoxy
resin using a vacuum infusion
moulding process. Glass fibrereinforced leading and trailing
edge components are added to
the central box.
Bearing in mind that the scaled
up 10MW wind turbine sails
would be 80 metres long, finding ways to reduce weight in the
overall sail design was critical.
For the prototype, the rotor
sail weight was significantly
reduced by using a structural
adhesive, which had the added
benefit of also providing lower
overall manufacturing costs
compared to a jointed sectional and mechanical assembly
design. The carbon fibre epoxy
ribs, spars and skins of the box
design were bonded together
with Crystic Crestomer. The
leading and trailing edge components, separately fabricated
from glass fibre epoxy resin,
were then bonded onto the
central box of the sail using

Fig. 3: Sail leading edge component bonding

1152PA structural adhesive. All
the bond joints used a simple
joggle design and shim plates
to allow for rapid assembly
with minimum fixtures and
aerodynamically smooth joints
(Figure 3).

Adhesive selection
and bonding
As the adhesive was such a critical factor in both the manufacturing and long-term offshore
performance of the two lightweight rotor sails, the Cranfield
University Composites Centre
carried out their own detailed
study to evaluate a range of
possible adhesives for this very
demanding application.
The design and scale of the
sail rotor structure mean that
there are large bond surface
areas and wide bond lines. The
fully cured structural adhesive
must, therefore, have long- term
performance properties which
meet a number of key requirements. These include gap filling
and providing outstanding peel
resistance, while at the same
time being strong and very
tough, with exceptional flexural strength properties.

mance comparative testing on a
range of bond-line thicknesses
from 30mm down to 2mm.
The test results they obtained
clearly showed that the best
performing adhesive for bonding both carbon fibre and glass
fibre epoxy laminate substrates
was Crystic Crestomer 1152PA
structural adhesive. Their findings are supported by the quality and long-term performance
of Crestomer adhesives having
already been proven for over 30
years in many demanding fibreglass marine applications, such
as deck and hull stringer and
bulkhead bonding, endorsed
by both Lloyds and RINA who
have certified Crestomer adhesives for bonding a variety of
marine composite applications.

out the use of complex assembly jigs. As part of the assembly
process to ensure joint accuracy, after positioning without
adhesive, each part was drilled
and the holes used to either pin
or rivet each part together after
adhesive application. All of the
adhesive joints were post-cured
in a portable taped foam board
oven for 24h at 50°C and joint
gaps were subsequently filled
with a body filler and abraded
smooth using a circular sander
to eliminate evidence of the
component joints. n
More information:
www.scottbader.com
www.cranfield.ac.uk

For the 10 metre sail prototype,
each component and mould
tool was designed with joggled
part fit, scored fitting positions and 1mm adhesive
shims. This provided
accurate final sail
dimensions
with-

Fig. 4: Completed
painted sails with
end plates attached

The Cranfield project team
carried out adhesive perforNo79 March 2013

/ jec composites magazine 27

http://www.scottbader.com http://www.cranfield.ac.uk

JEC COMPOSITES MAGAZINE - Issue #79 - March 2013

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