Date: 10 Dec 97 04:05:03 From: firstname.lastname@example.org (Stephen H. Westin) Organization: Program of Computer Graphics -- Cornell University References: 1 2 3 4
View raw article or MIME structure
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.