Re: Concorde noise (was: Concorde's other customers)

Date:         10 Dec 97 04:05:03 
From:         westin*nospam@graphics.cornell.edu (Stephen H. Westin)
Organization: Program of Computer Graphics -- Cornell University
References:   1 2 3 4
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kls@ohare.Chicago.COM (Karl Swartz) writes:

> >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?

I think there's a misconception here; the sonic boom follows any
aircraft cruising above Mach 1. It's not just a transient when going
transsonic.

> I was at Edwards AFB for their recent airshow, which included an
> SR-71B doing a Mach 3 flyover at about 75,000 ft.  The boom sounded
> like a couple of gunshots from a few hundred yards.  I don't know if
> lower speed would reduce the intensity (I have a feeling it wouldn't)

I think it would; after all, boom intensity is zero below Mach 1. My
mental model is that the sound that should precede the aircraft all
gets squeezed into one nasty transient; the faster you go, the more
waves pile up, and the more intense the boom.

> but lower altitude and a larger aircraft would probably cancel out any
> advantage of lower speed.
>
> >If it is a heck of a lot, then you are right. If it is not, then the
> >ban imposed by the US on supersonic flights over its own land was a
> >political knee jerk to assure the Concorde was a failure.
>
> While not tremendous, I can see how the noise could be startling and
> thus worse than a conventional jet flying over at a few thousand feet,
> especially if it happened a number of times per day, every day.

Yeah. After all, *lots* of airliners cross the U.S. every day. If
every one boomed, life would be much uglier.

> There was also the matter of engine noise on takeoff.  Having heard
> a Concorde departure when the aircraft was about fifteen miles out
> from Heathrow, I can easily understand why nobody wanted the thing
> around.  The racket must be horrific up close.

Well, yes, but...

I happened to be visiting New York back in 1977 (?) when Concorde made
a demonstration visit to JFK, amid much frou-frou about takeoff
noise. Some enterprising TV reporter took a sound meter down to a
subway station, and recorded higher levels for the northbound express
train than for Concorde on take-off!

So yes, it's awfully loud, but so are a few other things about which
there is no public outcry.

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.