Page 25 - AAA NOVEMBER - DECEMBER 2013 Online Magazine

FEATURE ENGINE DESIGN

year. So with 15% savings on a 30-aircraft
fleet, that’s a pocket-filling US$67million-
plus a year. Not bad returns.
“With the new LEAP engine, which will
be used on Boeing 737 MAX, COMAC C919
and Airbus A320neo, we are introducing
a 3-D woven resin transfer moulding
(RTM) carbon fibre composite fan and fan
case that saves about 450kg per aircraft.
And in the high-pressure turbine, we are
introducing ceramic matrix composites
(CMCs) in the shroud,” she explains.

Hot technology
This move away from an all-metal power
unit gives better thermal behaviour in
the hottest part of the engine – with
temperatures in excess of 1,500deg C – so
what would previously have been cooling
airflow can be used for thrust instead.
Rolls Royce’s blisk (without adding extra mass), the possible “And this is just the beginning,” enthuses
technology has use of complex composites for key loaded Jewell. “As this technology matures, you
been developed assemblies, the design of shrouded will see more and more parts made with
for use in the fan blades with a high length-to-chord CMCs.” She sees CMCs used for turbine
next-generation of aspect ratio (possibly using hollow or with blades, as well as the combustor, and
gas turbines
honeycomb cores), the ability to cope with possibly in the coatings and cooling design
out of balance forces during a blade failure, for the high-pressure turbine blade.
the necessity for the housing to be strong Others are pioneering what are called
enough to contain broken or damaged blisks. These save weight yet maintain
blade parts, and lastly the ability to keep strength and heat resistance by behaving
flying if birds are sucked into the engine. like a single component in which both
That’s a lot of conflicting requirements. blades and support disc are one item. This
“Materials technology is totally reduces weight and improves the efficiency
changing the landscape,” says CFM’s of the compressor by removing the need
Jewell. “New materials with higher for blade roots and disc slots. Blisks will
temperature capability and lower weight be used Trent turbofans on the Airbus A350
are allowing us to design an engine that XWB. CFM is looking at the use of titanium
will bring 15% lower fuel consumption.” aluminide for specific high-strength, low
According to Jewell’s calculations, a 1% weight applications too.
improvement in fuel efficiency can save an And an increasing use of electric
airline roughly US$150,000 per aircraft, per controls and drives removes mechanical

OPEN AND SHUT CASE Farnborough in 1988, this is still
Engine makers are constantly looking at prototype stage. With rotors are
for new ways to squeeze more efficiency roughly 4m in diameter, the engine
from jet fuel. Pratt & Whitney is looks like a turboprop with the blades
promoting its geared turbofan, the hanging off the back. But the biggest
PW1000G. CFM has been evaluating problem is not the looks or size – it is
open rotor designs, which could boost the noise. Because open rotor engines
fuel efficiency up to 25% compared do not have a nacelle (cover) over the
to today’s engines. Although tested fan, noise is significantly louder than
in the 1980s and successful flown at an enclosed turbofan.

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