Re: Geared turbofans

Date:         21 Mar 98 16:31:31 
From:         Steve Lacker <no@spam.thanks>
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Campfire wrote:
> 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?

Pratt is hoping to run the fan at its optimum speed while simultaneously
running the LP compressor at *its* optimum speed, withouth having to use
a 3-shaft arrangement with its associated inefficiencies. The drawback
to geared fans has always been the gearbox, but Pratt is saying they can
use all the gearbox expertise they gained with their UDF (unducted fan)
program to get a reliable, small, efficient gearbox.

> 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?

Nope. They're aiming at a midsize engine. In fact, they're aiming RIGHT
at the CFM-56 family, hoping to cut into its market dominance. <opinion
mode on> They should have done this YEARS ago- Pratt was once THE
dominant maker in that market with the JT8D, and it still stands to this
day as one of the best aero engines of all time, bar none. But after the
JT8D 200 series, Pratt let that market segment go except through their
rather unsuccessful collaboration on the IAE V2500. I just hope they
haven't waited too long- CFM has a TIGHT hold on that market. </opinion
mode>

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

They are OBLIGATED to say that, aren't they ;-) The truth will come out
in the end- either the gearbox will be the engine's downfall, or else
Pratt will knock some wind out of CFM's sails and get back to a better
market share. I would never bet any serious money *against* Pratt &
Whitney...

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Steve Lacker
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