Re: Sighted a shock wave above airliner wing

Date:         12 Oct 98 00:02:12 
From:         "Russell Farris" <russf@prodigy.net>
Organization: Prodigy Services Corp
References:   1 2 3
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Phil Dunn <pdunn@nospim.circumnavigator.org> wrote in article
<airliners.1998.1576@ohare.Chicago.COM>...
> Do you think this could be condensation instead of shock wave?
>
> I have flown lots of supersonic formation and you don't see shock waves.
> You can feel them though.
>
> But as the pressure gets very low, you can see transient condensation of
> water and this appears like shock wave.
>
> Much like the stuff you see coming off the wing with high lift
> configuration entering high humidity area.
>
> And shock wave formation will kill lift aft of it pretty suddenly, no?

I disagree. An aircraft operating in the transonic range (about Mach .65
and above) has a shock wave on the wing, about 1/3 to 1/2 back on the
wing.  The airflow ahead of the wave is supersonic, the shock wave
itself is the transition, and behind is subsonic flow. Any text on high
speed aerodynamics tells you this. I have seen the wiggly line of the
shock wave on two occasions...in 1973 on a Delta 727 and 1984 on a
Western 727. It was exactly as our friend described. One fascinating
thing was when we banked, it moved aft, as the wing loading went up,
just as I learned in school. At some point the shock wave will disrupt
lift, either as speed is increased or bank angle increases. I remember
remarking to my seat mate about seeing the shock wave, and he turned
white! He felt a little better after I explained to him it was perfectly
normal.To see it is a rare privilage, like the Green Flash and Blue
Jets.

Russ Farris, Boeing 767 First Officer, US Airways