On Mon, 7 Apr 2008 17:43:27 -0700 (PDT), Jon
wrote:

"The Geared Turbofan will be available by 2013 and airlines don't have
to trade," Finger claimed. "They can get better fuel burn, better
greenhouse gas emissions, significantly lower noise and significantly
better economics."


Here's some more information:


http://www.flightglobal.com/articles...he-geared.html
Pratt & Whitney’s long-standing passion, some might say obsession, for
the geared turbofan (GTF) concept is well known. Equally familiar,
however, is the frequency over the past 20 years with which this
apparently promising technology has either failed to live up to its
promise, or been ruled out on the grounds of high cost, or risk, or
both.



http://www.prnewswire.com/cgi-bin/st...4398944&EDATE=
The expected benefits will include up to a 12 percent improvement in
fuel efficiency and a 30-decibel noise reduction over Stage III
requirements. A ground demonstration test is planned in the third
quarter 2007 and a flight demonstration test in 2008.



http://www.freerepublic.com/focus/f-news/1908833/posts
“We believe the [GTF] offers a technological breakthrough that will
provide the best economy and performance for the Mitsubishi Regional
Jet," said Kazuo Tsukuda, President, Mitsubishi Heavy Industries,
Ltd., in a statement. The MRJ is a 70-seat to 90-seat airliner.

Photo



http://en.wikipedia.org/wiki/Pratt_&_Whitney_GTF
Geared fan
As bypass ratio increases, the mean radius ratio of the fan and low
pressure turbine (LPT) increases. Consequently, if the fan is to
rotate at its optimum blade speed the LPT blades will run slow
(because they are on the same shaft), so additional LPT stages will be
required to extract sufficient energy to drive the fan. Introducing an
epicyclic reduction gearbox, with a suitable gear ratio, between the
LP shaft and the fan, enables both the fan and LP turbine to operate
at their optimum speeds. This increases the engine's complexity,
however, which is why it is not a common solution. Only the Honeywell
TFE731 has seen widespread use.

Pratt & Whitney claims the GTF will be 10% to 15% more fuel efficient
than current engines used on regional jets and single-aisle jets, as
well as being substantially quieter.