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Video Standing Shock-Wave on Subsonic Commercial Aircraft

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Video Standing Shock-Wave on Subsonic Commercial Aircraft

Old 10th Jan 2007, 00:08
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Video Standing Shock-Wave on Subsonic Commercial Aircraft

I believe the following is a Standing Shock-Wave on Subsonic Commercial Aircraft !!?

Sorry Youtube over compresses videos.

1st
http://www.youtube.com/watch?v=TI_usGqlbjI

2nd
http://www.youtube.com/watch?v=duCHFaWm-ms

In the 1st few secs watch the large refraction "tall columns". Afterwards you'll see the "dancing" shock wave.

This was on a B757 (possibly B767) in Jan 1996 and there were approx 4 vertical fingers at the leading edge of the main smooth part of the wing.

There were also 4 of them on the trailing edge of the main smooth part of the wing.

They moved several feet along the edges back and forth as the plane slightly moved vertically.

They were not linked with the vortex generators.

A trick to see them is to pause the video see that they bend light such that they produce "kinks"/"bumps" on the wings surfaces such as the leading edge slats.

This is not distortions in the window !! and not a gremlin on the wing

You have to be seated just right to see them and few people notice them.





see also http://www.airdisaster.com/forums/sh...d.php?p=480115

Last edited by aardvark2zz; 10th Jan 2007 at 04:46.
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Old 10th Jan 2007, 01:10
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shocked

Its late, I've had wine - looks like a smudge in window. You know when your head is against it for a while. That or could be recompression shock. Only clever men in sandals and beards will know...
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Old 10th Jan 2007, 03:47
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Yes, they ARE shockwaves!

More than 20 years ago, I have been lucky enough to see shockwaves from an ideal position. It was during a DC-10 post-Heavy Maintenance test flight.
With the sun to our left, I was kneeling near one of the many shiny polished cabin windows, say near the inboard wing trailing edge. This was in an empty convertible freighter cabin: no seats in the way and choice of all windows. On the RH wing, I suddenly noticed something resembling the shadow of an 8 feet tall whip antenna (like you see on old army vehicles). I was fully aware that our faithful Tri-Jets don’t have anything like that, and ‘on top of that’ the shadow moved slightly forward and aft all the time, as if it was an antenna with the base moving forward and aft on some rail on the fuselage crown. I also remember it was noticeably less sharp than the shadow of the fuselage itself!
The test team confirmed that this visual effect could only be caused by shockwaves; they were just verifying the airframe behaviour at high Mach number and the MMO warning.

The sun was indeed roughly in the plane of the front spar of the RH wing, so several members of the team then took up positions slightly aft of the front spar where we had an excellent view of the sort of wrinkled glassy transparant curtain that kept wandering slightly forward and aft chordwise, but always close to just aft of the front spar.
The tell-tale ‘shadow’ I mentioned was caused by slight refraction of the sun’s rays almost in the shockwave plane separating colder and slightly warmer air!

Without the choice of windows, but luckily strapped-in just aft of the front spar, I have since seen these shockwaves also in an IL-62. The visual discontinuities moved and became more noticeable during turns, particularly against the background of the ground when “my” wingtip came down.

I have complete understanding for those who think to see something else, or even nothing at all, but trust me: these look fully like shockwaves (and can hardly be something else).

Shocking but true.

Plumb Bob

Last edited by Plumb Bob; 10th Jan 2007 at 06:40. Reason: ‘slight reflection’ corrected into ‘slight refraction’
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Old 10th Jan 2007, 04:44
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I remember seeing these years ago as a passenger in a 727. We were in a transonic dive and the sun was coming over the other side of the fuselage. I could see the shock waves shift and then disappear as slowed on level off.

This phenomenon has been used for many years to view shock waves in the lab and wind tunnel, see:

http://en.wikipedia.org/wiki/Schlieren_photography

Here's another picture from a pax window:

http://amasci.com/wing.html
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Old 10th Jan 2007, 06:31
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see here for more pictures of shockwave shadows.

Have seen it really nicely on a qantas 747-400 enroute FRA-SIN 6 weeks ago. You could see the trailing edge kink in the shockwave also. If I find some minutes time, I´ll add the pictures later today.
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Old 10th Jan 2007, 08:25
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Thumbs up

.
Ahhhhh the good old days of high fuel burning above Mach 0.85 (to overcome headwinds) in 1996 when fuel was cheap.
.
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Old 10th Jan 2007, 13:13
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Some 20 years ago, was seated by the wing of an L-1011 in climb and was treated to the sight of two shockwaves by the point of maximum thickness.

Yep, you have to be in the back by the front spar to see them with the right sun angle and wx.

They made the air look like a curtain with two rents in it.
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Old 10th Jan 2007, 13:43
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Here's a still of the phenomenon:
http://www.adastron.com/707/flyhome/nk-239.htm
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Old 10th Jan 2007, 15:45
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They are indeed shock waves aardvark2zz, not in the league of the big beggars we used to see in earlier days when we flew fast, but shock waves nonetheless.

The reason that we see them is because the vast majority of commercial jets are Trans-Sonic, not Sub-Sonic as suggested in the title of your thread. (There are some good folk oft appearing on these threads that still believe that we limit operating speeds to below Mcrit).

Regards,

Old Smokey
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Old 10th Jan 2007, 16:52
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Used to watch them all the way down to the Falklands when on a Tristar.
Quite hypnotic at times.
Nice to see that someone has filmed it and might now believe me if I said "I see 'Shapes' dancing on the wing outside".
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Old 10th Jan 2007, 17:11
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Check my post #6 here - and they still haven't locked me away!
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Old 12th Jan 2007, 06:39
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Thanks guys and gals for the info and stories

If you want some techical info and graphs also see:

http://www.airdisaster.com/forums/sh...d.php?p=480115

Anyone have any comments about the upward and downward bending of light depending if looking forward or aft ??
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