Re: Engine Design

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         16 Mar 95 14:38:56 
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>Despite what I just said about R-R engines being better candidates
>for mixed-flow configuration, the RB.211-524 is much heavier than the
>JT9D, the PW4000, and the CF6.

Sure, but the added weight is mostly because of the third set of
shafts and bearings for the third stage, with the longer duct being
a comparatively modest increment, right?

>Surprisingly, the Trent 800 is the lightest engine for the B777 (but
>it has the highest specific fuel consumption).  R-R claims that the
>Trent is at least 3,000 lb lighter than the competitor (i.e., 6,000
>lb per aircraft)!!!

I assume you're reading the same ad I saw in AW&ST.  Like any sort of
advertising, read carefully:

    "The Trent 800 is also the lightest engine for the new Boeing,
    weighing UP TO 6,500lb less PER AIRCRAFT than its competitors."
             ^^^^^              ^^^^^^^^^^^^

The emphasis on key phrases is mine.  They'd *really* like you to
think their engine is 6,500 lbs less than any of the competitors, but
like most folks you caught that.  The first set of weasel words are
the real killers though.  RR is really only comparing their engine to
the heaviest competitor -- the GE90, which suffers a substantial
weight penalty on account of that enormous fan and perhaps some extra
hardware to easily allow the fan and core to be separated for shipping.
They in effect say nothing about the PW4000, which could only be an
ounce heavier, or perhaps even lighter than the Trent 800!  (I don't
know how the PW4084 compares in weight to the Trent 800, though my
guess would be that it's a little heavier.)

Karl Swartz	|INet
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