Re: Sonic Boom

From: (Anthony Pilon)
Organization: University of Minnesota, Twin Cities
Date:         07 Oct 93 00:54:19 PDT
References:   1 2
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  or MIME structure (Robert Dorsett) writes:

>In article <airliners.1993.618@ohare.Chicago.COM> you write:
>>>>P.S. Can somebody please elaborate on the original question:
>>does the sonic boom arise only on passing through the sound barrier,
>>or during the whole supersonic flight?

>The sonic boom is a byproduct of a shock wave created as the airplane 
>flies through the air.  It travels with the airplane, leaving a series
>of "booms" in its wake.

I'm doing my graduate research on sonic booms, and would like to clarify
the above answer.  The supersonic motion of the aircraft creates shock waves
originating from the structures of the aircraft (wings, nacelles, tail, etc).
As these shock waves propigate toward the ground they are overtaken by the 
two main shocks, those created at the bow and tail of the aircraft.

When these shocks reach the ground they first cause a sudden rise in pressure
from ambient conditions.  This is followed by a decrease in pressure to a
level significantly lower than ambient conditions.  The tail shock then brings
a sudden increase to approximately ambient conditions.  This pattern of 
pressure rising, falling, and rising again is referred to as an "N-wave".

Since shock waves are created whenever the aircraft moves supersonically this
N-wave is felt on the ground at all times during supersonic travel.  One
way of reducing the destructive effects may be to modify to shape of the 
aircraft so that the shock waves created interfere with each other in such a 
way as to lessen the noise on the ground; If the aircraft is flying at the 
proper altitude.

I hope this explanation was helpfull (and factually correct).

    "It could be worse....                     Anthony Pilon could be rainin'"         Aerospace Engineering, U of MN