🚀 go-pugleaf

In article <SHAFER.89May18154504@drynix.dfrf.nasa.gov> shafer@drynix.dfrf.nasa.gov writes:
>In article <4453@ttidca.TTI.COM> hollombe@ttidca.TTI.COM (The Polymath) writes:
>
>> In article <9090001@hp-lsd.HP.COM> paulc@hp-lsd.HP.COM (Paul Carroll) writes:
>>  }By the way, can anyone inform me as to why there are 2 sonic
>>  }booms, and not just one, from the shuttle?  ...
>
>>   One from the Shuttle, one from the chase plane.
>
>One boom is from the nose, one is from the wings.

There's something I don't understand about this explanation.  Even if one
boom (shock wavefront) were emanating from the very tip of the nose, and the
other from the very rearmost part of the craft, that would only separate the
wavefronts by the length of the craft, which is approx. 120 ft.  If the
craft is travelling at, say, 300 mi/hr, then the time difference between the
first wave and the second (as perceived by a stationary observer on the
ground) would be 

    300 mi   5260 ft      120 ft
    ------ x -------  =  --------
      hr       mi          N hr

Solving that for N in seconds, I get 0.27 seconds.  My impression was that
the booms were obviously separated in time.  I'd expect that people might
have a hard time distinguishing booms that were only 0.27 seconds apart.

I read an explanation once that said the second boom was just the first boom
reflected off an upper atmosphere layer.  When the craft is going faster
than a certain speed, the angle at which the primary boom leaves the nose is
such that a significant portion of it can reflect directly back down, and
the additional path length accounts for the time delay between booms.
Supposedly there's some critical angle (hence critical speed) that allows
the second boom.

Bob Colwell               ..!uunet!mfci!colwell
Multiflow Computer     or colwell@multiflow.com
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