Re: Concorde's other customers

Date:         09 Dec 97 03:54:26 
From:         Steve Lacker <look@the.sig>
Organization: Applied Research Laboratories - The University of Texas at Austin
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tassio@watson.ibm.com wrote:
> Andrew Weir wrote:
> >Surely the main reason was very simple, and it is in the heart of why all civil
> >supersonic transports are fundamentally unsound (...)
> >Nobody will tolerate
> >sonic bangs overland. To the uninitiated, describing a sonic bang ("boom"
> >is a complete misnomer) is simple: it is the loudest noise you ever
> >heard in your life.
>
> I am so glad you posted because we finally have a participant in these
> forums who is an expert in sonic booms.

No offense to the initial poster, but those were not the comments of an
"expert" in sonic booms.... or at least not the comment of someone who's
stood at Cape Canaveral while a Saturn V lifted off (I understand the
Shuttle is a bit loud too...:-) There are non-sonic-boom-generated
sounds that are as loud as sonic booms. I'm certainly not an *expert* in
booms, but I have had a bit of acoustics, including non-linear
acoustics. (translation: I just know enough to be dangerous... :-)

> I am one of these "uninitiated"
> and here is what I've been wanting to know for ages:
> The noise level generated by a sonic boom is a function of the distance
> from the source of noise.

Yes, it is. If a supersonic airplane flies overhead at 60,000 feet, it
will not necessarily rattle the foundations. In fact, depending on the
size of the aircraft, you might not even notice it. Bigger aircraft
generally produce bigger shock waves (sonic booms). Once the sonic boom
is generated, it propagates as a more-or-less ordinary sound wave
travelling at the local speed of sound, experiencing the normal
attenuation effects due to spreading and absorption. I say "more or
less" ordinary, because near the source it is a "finite amplitude"
(non-linear) sound wave. Far enough away, it transitions to a normal
sound wave. There are many other ways of producing finite amplitude
sound waves, by the way.

> Sitting at the nose of the plane, I'll hear the
> loudest thing on Earth.

Careful there! Inside the airplane (or even, hypothetically, sitting
outside it but *moving with it*) you won't here a thing.

>  Now imagine the Concorde takes off from
> JFK, goes up to is cruising level (60000ft?), and then crosses the sound
> barrier right above my head. How much noise will I perceive?

See above: probably not more than a gunshot. The Concorde is *big*
compared to most supersonic A/C, and thus has a pretty big shock
footprint. It could very well be an annoyance to those along
regularly-flown routes who might have to hear it several times a day.

--
Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
PO Box 8029, Austin TX 78713-8029
512-835-3286 slacker@arlut.utexxas.edu (Remove the extra 'x' to mail me)