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Strange Distortion  
User currently offlineMclaudio From Portugal, joined Jan 2005, 170 posts, RR: 0
Posted (6 years 9 months 3 weeks ago) and read 2044 times:

Hi.
I would like to ask a small help so that I can understand what happened on the following photo.
I was shooting in Funchal airport in Madeira (FNC) and as a 757 from Finnair was landing I kept on shooting until the touch down. Only later I saw that strange distortion which only happened with that aircraft.
I remember that a while ago there was a topic with a similar situation, but I wasn't able to find a logic explanation to that effect.
The photo:
http://i19.photobucket.com/albums/b200/mclaudio/Finnair_ldg05_funchal.jpg
and fyi I was using a 30D plus a 100-400mm L IS
camera settings: M mode, ISO 160, and the photo was done at 340mm, f 7,1 with 1/250 shutter speed.

Is that...wake turbulence  Confused (or something similar)

thank you very much for any help


Proudly one of the 6 million Portuguese that support SL Benfica!! Champions 2009-2010!
9 replies: All unread, jump to last
 
User currently offlineFly747 From Canada, joined Apr 2005, 1497 posts, RR: 9
Reply 1, posted (6 years 9 months 3 weeks ago) and read 2031 times:



Quoting Mclaudio (Thread starter):
Is that...wake turbulence Confused (or something similar)

Yes, pretty much. That is the vortex coming off the tip of winglet. Weird effect.

Ivan


User currently offlineBeechcraft From Germany, joined Nov 2003, 828 posts, RR: 41
Reply 2, posted (6 years 9 months 3 weeks ago) and read 2007 times:

That´s really weird. I´ve only seen these effects in high speed low passes of fighters.
the distorion here goes all the way up the the red sign...strange strange.

Denis



That's it! You people have stood in my way long enough. I'm going to clown college!
User currently offlineIngemarE From Sweden, joined Mar 2005, 285 posts, RR: 5
Reply 3, posted (6 years 9 months 2 weeks 6 days 23 hours ago) and read 2001 times:

Hey Miguel!

Quoting Fly747 (Reply 1):
That is the vortex coming off the tip of winglet. Weird effect.

I agree.
The visual distorsion is due to pressure changes within the vortice.
This is probably caused by the fact that he/she is touching down with a slight crab-angle, to compensate for x-wind.
The winglet then slices through the in a manner it wasn't intended to (...'cause winglets are originally designed to decrease wingtip vortices/induced drag, remember?!) and hence creates its own wake/vortice.



In thrust I trust.
User currently offlineMclaudio From Portugal, joined Jan 2005, 170 posts, RR: 0
Reply 4, posted (6 years 9 months 2 weeks 6 days 23 hours ago) and read 1987 times:

Hi again.
Thank you for the input. It really makes sense what Ingemar wrote and if you don't mind...another question. Do you think that high humidity increases that effect on the photo, or should I say that it makes it more visible on a photo? The day was cloudy so I presume that the air was quite dense and this has some influence on the induced drag.
Note that I also cropped the photo in a way so that the windsock could be visible leaving no doubts that there was a slight x-wind.
Once again thank you very much. I am only trying to learn a bit more with the photo  Smile



Proudly one of the 6 million Portuguese that support SL Benfica!! Champions 2009-2010!
User currently offlineOly720man From United Kingdom, joined May 2004, 6817 posts, RR: 11
Reply 5, posted (6 years 9 months 2 weeks 6 days 23 hours ago) and read 1979 times:



Quoting IngemarE (Reply 3):
pressure changes

strictly speaking it's density changes. The refractive index of air changes with density (or temperature --> mirages in the desert). It's the same sort of effect (known in the trade as a shadowgraph) where you get light passing over somewhere warm (e.g. radiator) and you see wavy patterns on a wall behind. Alternatively if you mix hot and cold water in a glass, the interface between the hot and cold water will be seen as lines/surfaces due to the respective refractive indices and the way the light is distorted.



wheat and dairy can screw up your brain
User currently offline777MechSys From United States of America, joined Apr 2006, 350 posts, RR: 3
Reply 6, posted (6 years 9 months 2 weeks 6 days 22 hours ago) and read 1955 times:
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Here is another example:


View Large View Medium
Click here for bigger photo!

Photo © Mike Paschal



User currently offlineIngemarE From Sweden, joined Mar 2005, 285 posts, RR: 5
Reply 7, posted (6 years 9 months 2 weeks 6 days 21 hours ago) and read 1953 times:



Quoting Mclaudio (Reply 4):
The day was cloudy so I presume that the air was quite dense

Well, that would depend on what type of clouds you were having?
Cumulus clouds usually "vacuum" the air, so to speak, of its moisture. This usually leads to good visibility and more dense air.
While stratus clouds can trap moisture between clouds and earth, usually leading to hazy conditions with rather poor visibility and less dense air.

Quoting Mclaudio (Reply 4):
Do you think that high humidity increases that effect on the photo, or should I say that it makes it more visible on a photo?

No, I wouldn't think so, but rather the propriety of ambient light created by an overcast sky. Overcast gives a more "omni-potent" light, if you see what I mean!?  scratchchin 
You know, the kind of light that makes your cam's light-meter go bananaz!  Wink

One effect that humid air have though, is the need for a higher TrueAirSpeed and/or Angle of Attack on final approach, since moist air is less dense than dry air. (Lower air density means, for a given airspeed/angle-of-attack, a lower lift-capacity.)
With a higher AoA, the wing-tip vortices will also become more intense.

Quoting Oly720man (Reply 5):
strictly speaking it's density changes

Strictly speaking #2; You don't get one without the other. Right?  Wink
Good point though!, and a couple of good examples to clarify!  thumbsup 



In thrust I trust.
User currently offlineOly720man From United Kingdom, joined May 2004, 6817 posts, RR: 11
Reply 8, posted (6 years 9 months 2 weeks 6 days 21 hours ago) and read 1943 times:



Quoting IngemarE (Reply 7):
Strictly speaking #2; You don't get one without the other. Right?

Depends. For a mirage effect it's all due to the temperature/density varying at constant pressure.

For vortex pics like this I wonder if it's a pressure interaction with humidity giving density changes.



wheat and dairy can screw up your brain
User currently offlineFly747 From Canada, joined Apr 2005, 1497 posts, RR: 9
Reply 9, posted (6 years 9 months 2 weeks 6 days 21 hours ago) and read 1941 times:

Just to make a correction to my statement in reply #1, it's actually vortex coming off the flaps.

Ivan


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