Re: Stalls

From:         fern@nosc.mil (David G. Fern)
Organization: NCCOSC RDT&E Division, San Diego, CA
Date:         06 May 94 18:02:14 
References:   1 2 3
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mdrews@dsd.es.com (Michael Drews) writes:

>This talk about stalls reminded me of an interesting "view out the 
>window" on a 757 flight from CVG to SLC a few years ago.  I was on 
>the north side of the plane directly over the wing, and noticed an 
>odd shadow on the wing which would shift several inches back and 
>forth in the light turbulence.  Then I noticed a line of distortion 
>in my view matching the position of the shadow.  It appeared to be 
>a vertical plane of distortion similar to the distortion seen from 
>heated air rising from a hot road.  The sunlight angle was perpendic-
>ular to the direction of flight, so I had ideal viewing conditions.

>   My guess is that this was a shockwave associated with flow over 
>the wing was at or near Mach speed.  I had never heard of shockwaves 
>with commercial transports until this stall thread came up.  Opinions?

I have seen the same thing-- yes, it is a shock wave.  It moves around
as the plane jostles lightly in turbulence and moves back and forth along
the wing as the plane changes spped.  I have only seen this once in many
years of flying-- and I too was curious as to the combination of 
conditions that combined to make the shock wave visible.  My flight was
over northern Canada in the winter (although at FL350 the season probably
doesn't matter too much).  

David Fern  fern@manta.nosc.mil