Home' Asian Aviation : AAV_March_2013 Contents 34 AsianAviation | MARCH 2013
with a slightly lower 45:1 on the PW1524G.
The greater overall pressure ratio means a higher
gas temperature, with the bigger engine running
some 24oC (75oF) hotter, according to P&W. The
manufacturer uses advanced cooling techniques to
maintain normal combustor-hardware temperatures.
Although CFM and P&W agree that double-digit
bypass ratios are required to obtain the desired levels
of fuel efficiency, as with basic engine architecture, they
have followed routes to a solution. P&W puts more
store by its reliance on cooling, while its competitor has
chosen to work with new ceramics materials.
To avoid the necessity for introduction of complex
cooling arrangements, CFMI adopted ceramic matrix
composites (CMC) material technology. CMCs have
been around for almost 30 years, but their earlier
adoption for production has been deterred by
manufacturing costs and the challenge of ensuring
durability under extreme ranges of temperature
change. Now, the technology is seen as a likely
standard feature of future engines.
UNDER THE GAZE
CFMI's adoption of CMC technology for the
Leap, the first such commercial-engine production
application, has brought the engine under the gaze
of airworthiness officials at the Federal Aviation
Administration (FAA) and the European Aviation
Safety Agency (EASA).The CMCs are used to
encase the first stage of the HPT, where the low-
weight material can accommodate high temperatures
that otherwise could melt even cooled metal blades.
Partner GE has used CMCs in ground-based
industrial gas turbines and had US Government
funding for F414 military-engine demonstrations.
Regulators have been considering CFMI's
component- and engine-test and certification plans
ahead of preliminary type board meetings for the
Leap-1A and -1C engines in the coming three
months that will be followed next year by a review of
Leap-1B test and certification plans.
For its part, P&W has rejected so large an adoption
of CMC technology in favour of established materials.
The company continues its development of so-called
"ceramic coatings" that apply a sprayed-on "thermal
blanket" to insulate metallic materials. P&W claims not
to have suffered thermal shock (leading to cracks) that
has occurred with some sprayed ceramics, creating
safety hazards. It suggests that such problems have
arisen when coatings have been applied at too high
a temperature, which allows embrittlement (and
detachment).of the ceramic coating.
The Leap engine benefits from GE90- and
GEnx-derived technologies, such as a carbonfibre-
composites fan case that already has passed a blade-
out rig test. CFMI reckons that a metal fan case (two
per aircraft) would have weighed 500lb more.
Finally, CFMI uses an advanced combustor
to reduce nitrous oxide (NOx) and unburned-
hydrocarbon emissions. The Leap design again
benefits from GE large-engine technology. Through
the use of a "Mark 2" variant of the twin-annular
premixing-swirler (TAPS) combustor developed for
the GEnx powerplant in a bid to get NOx emissions
50% below the CAEP/6 standard. The "TAPS II"
equipment has smaller, improved mixers said to
produce a 60% NOx-emission improvement.
Currently, the CFMI Leap engine orders for
narrowbody jetliners are ahead, if only because it
is the only engine on all three Airbus, Boeing and
Comac narrowbodies. P&W's PW1000G family
has a monopoly position on the new Bombardier,
Embraer, Irkut, and Mitsubishi designs, while it is also
offered on the A320 Neo.
It has been said that the initial example of superior
principle is inferior to the perfected example of
established practice. CFM International and Pratt
& Whitney have jumped in opposite directions, the
former following traditional architecture while the
latter explores a new configuration. Whichever of the
Leap or GTF engines proves the more successful,
both manufacturers now have a lot more time to
prepare designs for that next-generation of A320 and
737 replacements, for which the timing is no longer
Mulally's "not before 2011", but is now, according
to senior Airbus executives, "not before 2030".
CFM International and Pratt & Whitney have jumped in opposite directions, the former
following traditional architecture while the latter explores a new configuration.
The 737 Max will feature CFMI's LEAP-1B engines.
The Mitsubishi Regional
Jet is exclusively offered
with the Pratt & Whitney
PRATT & WHITNEY
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