Re: Sighted a shock wave above airliner wing

Date:         05 Oct 98 00:26:45 
From: (Clive Leyman)
Organization: CIX - Compulink Information eXchange
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In article <airliners.1998.1497@ohare.Chicago.COM>,
(Peter Chapman) wrote:

> A couple days ago I saw a fascinating sight I had never yet come
> across -- seeing the shockwave of local transonic flow above the wing
> of an airliner in flight.

 Yes, I've seen that as well, once on a VC10 flying the Atlantic in the
afternoon , and once on a Raytheon (nee BAe) 125 flying to Toulouse  early
morning. On both occasions the sun was low and shining through both cabin
windows. First time I saw it (my discipline in aerodynamics also) we got
so absorbed by what was going on that the stewardess asked us to desist as
we were un-nerving the other passengers!.

Although the aircraft may be flying at 0.8M, it is quite usual to have a
region of locally supersonic flow over the top surface - hence the
description of a supercritical airfoil. One tries to get the flow to re
compress without shock waves though, because as you say they cause drag.
Boeing might be interested in that one!. What did surprise us on the VC10
was that the shock wave danced over a large part of the chord - obviously
not a stable aerodynamic situation, and very different from the impression
of stable flow you get from wind tunnel tests. I guess that the balance
smooths out most of the force and moment variations.

Clive Leyman