Re: Sighted a shock wave above airliner wing

Date:         13 Oct 98 02:48:16 
From:         "S.L." <look@the.sig>
Organization: Applied Research Laboratories - The University of Texas at Austin
References:   1 2 3 4
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J. W. Dawson wrote:
> But no, not condensation. What I saw looked like - this doesn't describe it
> very well but I can't think of a better description - more like a ripple
> would appear in glass, with a definite edge to it. And it wasn't in the
> glass of the window, either. But there was no whiteness or gray fuzziness
> that you would get from condensation.

Yep- localized shock wave. I've seen those little things dancing over
airliner wings for years and years, and only recently heard an aerospace
engineer confirm the explanation I had suspected. There is sufficient
change in the density of the air around the shock that the index of
refraction is changed, so it reall does *exactly* what a ripple in glass
would do- bends the light waves passing through it.

Its really not that farfetched- think about it. Heated air just above
the hood of your car on a hot day causes visible "shimmer", so only a
very minimal change in air density is required.

--
Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
slacker@arlut.utexxas.edu (Remove the extra 'x' to mail me)