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Aeroengine NEWS CFRPs
the outer bypass air past the hot engine core. FACC has produced
more than 1,000 of these for Rolls’ BR700 family of regional and
corporate jet engines since 2001 and also worked with Pratt
& Whitney to develop its first composite bypass duct in 2002,
featuring special sound-attenuation treatment of the inner skin.
FACC worked with Pratt & Whitney Canada (P&WC, Longueuil,
QC, Canada) to develop the CFRP bypass duct for the PurePower
PW800 engines — selected for the Gulfstream G500 and G600
business jets — and began serial production in December 2014.
Composites also could see use in a bladed spinner proposed
as part of Rolls-Royce’s Vision20 (two decades out) strategy.
Currently, spinners do not have blades and might or might not be
made from composites.
As Rolls-Royce refines the CTi fan’s robotic ATL, the GE Global
Research Center in Munich, Germany, is endowing composites
manufacturing robots with mathematical
modeling skills, real-time 3D laser scanning,
computer vision analytics and other sensors.
“Eventually our instruments will be
fully integrated into the brains of these
machines,” explains researcher Stefan
Van Nieuwenhove, referencing the
preform weaving and RTM machines
used to produce LEAP engine blades.
The machines will then know how to
react to changes in the manufacturing
process — what GE calls “adaptable manufacturing.”
Hybrid blades and high-temp BMI ducts
Blades in the GE9X turbofan that will power the Boeing 777X and
enter service in 2020 will be the first to use a hybrid of carbon and
glass fiber in the same resin. Reportedly, 5-10% of the fibers will be
glass, helping GE’s longest and widest chord blades yet meet the
critical bird strike test, thanks to glass fiber’s higher failure strain,
which enables it to flex before it fractures. A new, higher strength
carbon fiber also will be used and a steel alloy will replace titanium
in the leading edges. This new, more swept, 3D aerodynamic
design — the same description used for Rolls-Royce CTi blades —
allows for thinner GE9X blades but also two and six fewer blades,
respectively, than the GEnx and GE90-115B engines. This lower fan
blade count and new blade design enables a faster fan tip speed,
which improves the low-pressure (LP) turbine efficiency so that
blade count can be cut there as well. The GE9X forward fan case
and rear fan frame also will be a composite, designed and built by
Safran using the 3D woven preform technology it has perfected
in LEAP. Although it is GE’s largest fan diameter yet, at 3,400 mm,
using CFRP in the fan case saves almost 160 kg.
According to Nick Kray, a composites consulting engineer for
GE Aviation, these hybrid blades open the door to other combinations
including integrating different CF forms — such as uni
tapes, braids and wovens — into different areas of the same blade.
Kray believes hybrid materials are not limited to the fan section.
He says the engine’s airflow path surfaces, which are not heavily
loaded, could be composite, with future hybrids even replacing
high-temperature metals in certain areas. Kray also sees potential
Future hybrid carbon fiber
composites could replace
high-temperature metals in
certain areas of the engine.
in the 200-425°C compressor section within the engine core,
where a high-temperature composite could increase design flexibility.
However, noting the 25 years of R&D before ceramic matrix
composites (CMCs) replaced metals in high-temperature turbine
shrouds and combustor liners, Kray concedes a similar timeline
might be necessary.
That said, high-temperature composites have indeed moved
beyond the fan, in the GEnx variable bleed valve (VBV) ducts.
Located at the exit of the fan module, 10 of these structures were
developed by EDO Fiber Innovations (Walpole, MA, US) from
carbon fiber-reinforced bismaleimide (BMI). They are able to
withstand internal pressures at high temperatures and resist
oxidation, yet weigh only 3.6 kg per set. The complex-shaped
parts were made with three layers of braid and were matchedmold
RTM’d to ensure accurate, high-quality interior and exterior
finished surfaces. Now manufactured
by Harris (formerly Exelis, Salt Lake
City, UT, US), 11 different VBV ducts
incorporate the company’s most
complex braids and will reach 12
shipsets/month at Boeing 787 full-rate
production. Harris also uses braids to
produce the 1m-diameter by 60-mm-wide
CFRP flow path spacer, located just aft of
the GEnx fan.
Another CF/BMI part is the mixed flow nozzle
(MFN) on the SaM146 engine that powers the Sukhoi Superjet 100
regional jet, which entered service in April 2011. Designed and
produced by Safran subsidiary Herakles (Le Haillan, France), the
large tube is 30% (20 kg) lighter than its metal counterpart and its
inner lining is pierced with 160,000 tiny holes that “trap” sound
waves inside its composite honeycomb structure.
Integrated propulsion system
As engine designers seek every percentage point of greater
efficiency possible, it makes sense that optimization of nacelles
would follow. The LEAP 1-C engine set for the COMAC C919 will
feature a next-generation nacelle designed and built by Nexcelle
(Cincinnati, OH, US), a joint venture between GE Aviation’s
Middle River Aircraft Systems (Middle River, MD, US) and Safran’s
Aircelle (Gonfreville l’Orcher, France). Described by Nexcelle
president Michel Abella as “the first truly integrated propulsion
system,” its structure, he says, was designed concurrently with the
engine’s main structure and part of the engine pylon. This radical
approach cut out excessive conservatism typically built into
nacelle and pylon systems when designed separately. Coupled
with low-mass, integrated composite structures that improve
aerodynamics, IPS’ innovations are projected to cut LEAP 1-C fuel
consumption by an additional 2%.
IPS replaces a conventional thrust reverser’s two-piece “D” doors
with a one-piece, composite O-Duct, which slides aft to reverse
thrust. This eliminates the maintenance-prone D-door latches and
smooths bypass airflow, improving fuel consumption and boosting
thrust-reverser efficiency by as much as 10%. Nexcelle says the
O-Duct’s single-piece CFRP inner skin (see Fig. 3, p. 42) is a key
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