Re: Geared turbofans

Date:         21 Mar 98 16:31:30 
From: (H Andrew Chuang)
Organization: Concentric Internet Services
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In article <airliners.1998.452@ohare.Chicago.COM>,
Campfire <> wrote:
>This is my first posting to this apparently nearly deceased newsgroup(is
>ANYONE out there? :)
>My curiosity was piqued when I read about PW developing a new geared
>turbofan. PW put out a news release stating it was the last great
>improvement to be made with current technology(paraphrasing here, so I hope
>I got it right). Does anyone know what advantages PW expect out of this?
>I'm assuming they'll be running a bigger fan and will need to slow it down
>from the core speed, and that the bigger size is because this engine would
>be for the proposed superjumbo jets. Anyone have any info? Comments?

No. the engine will not be used for the proposed superjumbo jets.  It is
intended for the A320 and possibly for the B737.  Since the introduction
of high-bypass turbofan engines, there has not been any major
improvement to engines.  For the past decade or so, engine companies
have introduced incremental fuel cost and operating cost savings as well
as noise reduction of a few decibels every once a while.  The deregulation
of the US airline industry in the late 70s shifted the need for bigger
planes (like the B727 and B757) to smaller planes which are ideal for
hub-and-spoke operations.  Boeing reacted to the market and launched the
second-generation B737, while P&W didn't.  After all, only 600 or 700
B737s were ordered before the deregulation.  So, why should P&W believe
the B737 would transform the US domestic market?  On the other side, CFMI
had an engine, the CFM56, that it could not find any application with
a future (re-engining the B707 and DC-8 didn't really have much future).
Thus, CFMI sneaked in.  IMHO, I doubt that neither CFMI nor Boeing
foresaw the tremendous success.  P&W's market share tumbled as a result of
the success of the B737/CFM56.  To regain some of its lost market share,
P&W wants to introduce a product that can help Pratt differentiate itself
from the competition.  With the Boeing-CFMI exclusive agreement on the B737,
Pratt has to work its way in from the Airbus side.  If the A320 with the
PW8000 does have signifcantly lower operating costs than the B737, Boeing
will be forced to consider a new geration of B737 with the PW8000.

>about some of their competitor's comments that this is old technology with
>no inherent advantages?

That was a cheap shot from R-R.  P&W has the most extensive experience in
gear-driven fans.  Some of the development work that many people are aware
of include the propfan in the late 80s and the Advanced Ducted Propulsor
(ADF).  I don't think the R-R gear-driven fan in the 60s was anything
close to what P&W is proposing.  In a nutshell, the geared turbofan allows
fan, low pressure, and high pressure systems to operate at its optimal
speed.  One may argue that this is what R-R's three-shaft design is trying
to achieve.  However, the low pressure turbine in R-R's three-shaft design
is still limited by the fan speed.  Hence, more turbine stages are needed
to drive the fan which means more parts and lost efficiency.  Furthermore,
a two-spool design with a gearbox will have less mechanical complexities
than a three-spool design.

The comments from CFMI had more "meat".  CFMI announced its own
initiatives for improving the CFM56 with similar goals.  CFMI also said
that CFMI had never discounted P&W, but CFMI would not allow someone to
steal three quarters of the market share from CFMI, like they did to
P&W.  In addition, CFMI does not think P&W's timing is right.  It intends
to introduce the new improved engine two years later than the PW8000.  I
don't think P&W worries about R-R's cheap shot, but P&W does have to worry
about CFMI's comments.