Re: breaking sound barrier movie

[William Beaty <billb@ESKIMO.COM>]

On Wed, 12 Jul 2000, S.Goelzer wrote:

> Hi All
> I took a protractor to the screen ( in the last few frames the plane is
> almost in profile) and  measured the cone angle. Then I used the
> standard formula ( sin angle =  v sound/vobject)  to computed the speed
> of the plane. I got (with reasonable error) the plane going right at
> Mach 1.

But the reasonable error makes all the difference: it converts a moving
disk into a moving cone.  If the aircraft only exceeds the speed of sound
by a few percent, each percentage point translates into about five extra
degrees of conicalness


Separate issue: I wonder if the aircraft distorts the air density around
itself in advance of the shock wave.  If so, then the "speed of sound"
might be higher near the aircraft.  The shock wave in the video might only
be conical near the fuselage, and have a curved shape which flattens out
further away like so:


                 |
                 |
                 |
                 |
                 |
                 |
                |
               /   _
           ___/___/ |
        -=/_________|
              \
               \
                |
                 |
                 |
                 |
                 |
                 |


If the above is how it works, then I'm confused.  How is the plane able to
communicate this density variation outwards?  Wouldn't the moving wave of
extra density itself become a shock wave?


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William J. Beaty                             SCIENCE HOBBYIST website
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