Re: 757 engine (fan?) noise during freewheel

From:         Steve Lacker <slacker@arlut.utexas.edu>
Organization: applied research laboratories
Date:         28 Sep 95 03:52:45 
References:   1
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hjl@thelaws.demon.co.uk (Henry Law) wrote:
>Frequently when boarding a BA 757 (RR engines) by steps rather than
>through an air bridge I hear a distinct metallic clanking from the
>engine closest to me, which is nearly always still freewheeling from the
>previous sector.  It's regular, but with gaps - rather like the sort of
>noise you'd make by rattling something metal along some iron railings.

FWIW- I've heard this same sound on a 727-200 once. I was seated in the
tail, and the galley staff opened the rear door to take on supplies shortly
after reaching the gate, so the engines were still freewheeling. I leaned
over and looked down the throat of the engine, and best I could guess
there were about 3 rattles (clanks) per rotation of the fan.
Chink--a-Clank---Chink--a-Clank.  (best conversion to ASCII I can muster).
I'm curious as to what this is also.  Its interesting to note that the
two of us have observed this sound on *very* different engine types
(high-bypass 3-spool RR vs. an older JT8D).

--
Steve Lacker	/	Applied Research Laboratories, The University of Texas
512-835-3286	/	PO Box 8029, Austin TX 78713-8029
slacker@arlut.utexas.edu