Re: Stalls

From: (Mary Shafer)
Organization: NASA Dryden Flight Research Facility, Edwards CA
Date:         13 May 94 11:31:44 
References:   1 2 3
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On 12 May 94 13:19:37 , (leishman) said:

jgl> Careful here!! The observation of flowfields containing shocks and
jgl> other density variations are routinely examined by means of a class
jgl> of density gradient flow visualization methods known, in general,
jgl> as schlieren methods. A simple schlieren system is direct
jgl> shadowgraphy - which is essentially what is being described by the
jgl> various observers of shockwave images on transport aircraft wings.

[Excellent explanation sacrificed to appease the bandwidth gods]

jgl> These schlieren methods are routinely used in the laboratory when
jgl> examining high speed flows containing shockwaves. Turbulence and
jgl> vortices can also be observed, such as those behind propellers and
jgl> helicopter rotors. In the field, obviously it is much more
jgl> difficult to visualize such flows, but the example of the "natural"
jgl> shadowgraph of the shockwave on a transport wing has been cited in
jgl> the literature for many years. It is indeed interesting to me that
jgl> so many of our friends on the internet have also observed such
jgl> phenomena.

We've just taken some schlierens of entire aircraft in flight, with
the camera on the ground and the airplane, an F-18, flying between it
and the sun at Mach 1.4.  Very impressive.  We have a little trouble
getting the actual aircraft in the frame, since we're trying to solve
a 4-dimensional problem, but we have gotten one picture with the
aircraft in the frame and a number of photos of the near flowfield
(having just missed the airplane).

We're considering whether to try this with the SR-71, too, as part of
a research program examining sonic boom signatures.  We have an array
of microphones that we use to record the booms.

Mary Shafer                                                   DoD #362 KotFR   
SR-71 Chief Engineer         NASA Dryden Flight Research Center, Edwards, CA                Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot