Engine noise question

Date:         25 Nov 96 06:18:49 
From:         jcb@interlog.com (Jeff Bowen)
Organization: InterLog Internet Services
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I was walking my dog in the park this afternoon in Toronto and
listening to the sound of passenger jets going over - a common
experience as I am about 20 miles from Pearson airport.

Some of the planes had a high-pitched whine and some a dull roar.
All were above the cloud cover.

Can anyone explain to this non-pilot what actually creates the
sound and why the sounds are different?  I seem to recall from
being at the airport that the high whine is more pronounced when
close to the planes and the dull roar more pronounced from a
distance.

Is the whine a mechanical sound (turbines or something) of metal
parts rubbing on one another?  Is the roar the actual sound of
combustion or of air rushing over the metal surfaces of the
engine?

These may be absurdly inaccurate guesses, but I've often wondered
and just found this newsgroup where I might find answers.

Thanks.

-- Jeff


| Jeff Bowen | <jcb@interlog.com> | Toronto, Canada |