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The next generation of regional jets – the Mitsubishi Regional Jet (MRJ).
The MRJ is a 70-to-90-passenger commercial
transport to enter revenue service in 2013.
The MRJ70 will be rated at 67 kilonewtons,
the larger MRJ90 at a takeoff thrust of 76
kilonewtons. Its market volume is estimated
at 1,500 units. Official program launch is
expected to occur this year. The Japanese
opted for the geared turbofan on account of
its 15 percent lower operating costs. “A
major part of that is due to its lower fuel consumption,”
Winkler says.
Compared to today’s best-selling engines in
this thrust class the new design offers a
reduction of maintenance costs of 40 percent
according to Robert Saia, Vice President
Next Generation Product Family at Pratt &
Whitney. “Additionally it is about ten decibels
quieter.”
The big advantage afforded by geared turbofans
is their reduction gear, which decouples
the fan from the remaining low-pressure system.
That allows the components to run in
their respective optimum speed ranges to
improve efficiency. “By decoupling the fan it
turns at a third of the speed of the rest of the
low-pressure system. This way we can increase
the speeds of the low-pressure compressor
and turbine. Thus, for a given thrust
range we can reduce the number of stages of
the low-pressure compressor and the lowpressure
turbine,” the American engineer
says.
The concept also enables bigger fan diameters
to be selected, which in turn makes for
larger bypass ratios and hence lower fuel
consumption. “We try to make the fan as
large as possible. The slower it turns the more
efficient and quieter it gets,” explains Saia.
At this time, negotiations are underway between
MTU and Pratt & Whitney regarding
the size of MTU’s stakes. “We’re seeking
module responsibility in development and
manufacturing,” Winkler confirms. The
Munich people have set their sights on two
components, hoping to bag a stake in the
compressor, apart from the high-speed lowpressure
turbine. For MTU, the bargaining
position looks compelling, not least on account
of the Germans’ low-pressure turbine
expertise. That turbine is a key component of
the geared turbofan. Says Winkler: “On the
high-pressure compressor, we’re targeting
the stake we already had in the experimental
compressor. That would be the first four
stages, which is about half the compressor.”
Developed in partnership with Pratt &
Whitney, this eight-stage high-pressure compressor
has its first test phase behind it. “In
the process, it attained its efficiency and stability
goals throughout,” Winkler says. “It has
a high 17:1 pressure ratio and its size is targeted
at the potential successor models of
the Airbus A320 and Boeing 737. In a downscaled
version, the compressor will be used,
for instance, also on the MRJ and
Bombardier’s CSeries engine.”
The aircraft of the Canadian CSeries are conceived
to seat 110 and 130 passengers, and
enter revenue service in 2013, like the MRJ.
MTU estimates its market volume at roughly
3,000 units in the approximately 102-kilonewton
thrust range. The decisions made by
the regional aircraft makers may point the
way for the industry in general. The MTU
manager is confident that “if the geared turbofan
actually prevails and meets expectations
in this domain, that is sure to have a
ripple effect on the next-generation singleaisle
aircraft.”
First results coming in from a geared turbofan
demonstrator based on the PW6000
speak for themselves. “We’ve met specifications
for specific fuel consumption and effi-
The geared turbofan demonstrator on Pratt & Whitney’s advanced test facility in West Palm Beach, Florida. The high-pressure compressor developed jointly by MTU and Pratt & Whitney on MTU’s test stand.
ciency,” Winkler emphasizes. The demonstrator
features a gearbox and a new lowpressure
system including MTU’s high-speed
low-pressure turbine. Compared with the
standard PW6000, fuel consumption is much
superior, albeit not yet comparable with later
product applications that will come with a
new core. Flight tests planned for mid-year
are expected to demonstrate that capability
also when airborne. But even idling on the
test stand, the engine has impressed Winkler
and his colleagues. “It’s so quiet you can keep
up a conversation standing right next to it.”
For additional information, contact
Dr. Christian Winkler
+49 89 1489-8663
For interesting multimedia services
associated with this article, go to:
www.mtu.de/108GTF_E
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