Re: Geared turbofans

Date:         21 Mar 98 16:31:28 
From:         greg@sherrill.kiva.net (Gregory Travis)
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In article <airliners.1998.452@ohare.Chicago.COM>,
Campfire <dcampbell@navnet.net> 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? What
>about some of their competitor's comments that this is old technology with
>no inherent advantages?

I saw a blurb about this in AvWeek.  I too was struck by the author's
tone that this was something totally new under the sun.

Lycoming developed a geared turbofan, the ALF (Advanced Lycoming Fan)-502
back in the late 1970s.  I don't think they were the only manufacturer
to do so.

The ALF-502 went into the Avro/BAe-114 (hope I have the model right - the
high winged four-engined short haul commuter).  The early history, at
least, was not rosy with some wags suggesting that BAE really stood
for "Bring Another Engine."

Of course, IIRC, all of the ducted/unducted ultra-high bypass designs
fielded a decade ago were geared.

Gears and airplanes generally don't mix well.  I guess P&W thinks they
can lick the problems though.

P&W no doubt is trying to eek out the last bits of efficiency gains.  Most
turbofans are somewhat of a compromise since the fan is a direct-drive
off the turbine.   As a result, you tend to end up with a fan that's turning
too fast and a turbine that's turning too slowly for max. efficiency.  You
can try and fix this with double and triple spool designs (at a horrible
increase in manufacturing costs).  But, as the man says, that helps you
get better but you never get well.

greg