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RPMcMurphy
11-07-2008, 06:32 PM
Okay, so somebody start splaining.
Any aerodynamic gurus please, your thoughts on this picture:

http://i363.photobucket.com/albums/oo71/11072008/0981791.jpg


Myself:
I think the plane is taking off since I don't seem to see much landing flaps going on and the conditions were just right in the areas of low pressure above the wings to cause condensation of water molecules. A demmonstration of the wings ability to generate unequal airpressures but it looks like there is a high angle of attack, it looks to me like it is stalling.
Passengers probably freaked out.

X32Wright
11-07-2008, 06:42 PM
'Lucy!!! I'm Home!!!!!!!.......'

Skoshi Tiger
11-07-2008, 06:59 PM
Clouds form when the ammount of water vapour contained with in exceeds the maximum ammount of water vapour it can hold.

The ammount of water vapour that the air can hold depends on it's temperature, and pressure. The hotter the air and the more pressure it is at allows it to hold more water vapour.

When an airfoil (ie wing) is passed through the air, an area of low pressure is formed above the airfoil. When air reduces in pressure it also reduces in temperature.

So as the air passes above the wing it reduces in pressure and temperature. Thus the ammount of water vapour the that the air can hold is reduced. If the ammount of water vapour in the air is almost at maximum and the airfoil reduces the temperature and pressure so that there is excess water vapour in the air a cloud forms. (notice that the cloud is only above the wing!)

If in this case the there is a high angle of attack on the wing the area of low pressure above the wing is fairly big.

So it's either that or some Nazi plot to take over the world or aliens!!!!

RPMcMurphy
11-07-2008, 07:38 PM
http://forums.ubi.com/images/smilies/11.gif

halfcool
11-07-2008, 07:59 PM
Sonic Boom.
http://en.wikipedia.org/wiki/Sonic_boom

Ahh **** wait that sucker is taking off... my bad.

Skoshi Tiger
11-07-2008, 08:59 PM
Similar effect in the cloud around the F/A-18 but you'll notice that the cloud on the Hornet goes all the way around the aircraft.

I doubt the plane pictured above would be breaking the sound barrier at any time during its flight with it's wheels down.

WeedEater9p
11-07-2008, 10:37 PM
Originally posted by halfcool:
Sonic Boom...
With gear down too? http://forums.ubi.com/images/smilies/34.gif
(Just kiddin' http://forums.ubi.com/images/smilies/partyhat.gif)

WhiteKnight77
11-08-2008, 12:31 AM
While not as large, said condensate can be removed from the air in other ways too.

http://www.whiteknight77.net/images/hm14thumb.jpg

Bremspropeller
11-08-2008, 07:06 AM
I think the plane is taking off since I don't seem to see much landing flaps going on and the conditions were just right in the areas of low pressure above the wings to cause condensation of water molecules. A demmonstration of the wings ability to generate unequal airpressures


Very correct.


but it looks like there is a high angle of attack, it looks to me like it is stalling.
Passengers probably freaked out.

That's not the case.
The a/c is climbing.
You can visually tell the a/c's AoA by comparing the wing-tip vortice's trail with the wingtip's chord-line.
That's gonna give you a rough impression of what the current AoA is like - this does not take wingwash and other stuff into account, though.

M_Gunz
11-08-2008, 07:26 AM
And it's not that they allowed smoking on board and the windows are open to let smoke out.
Even if it is the Marlboro Special.

Divine-Wind
11-08-2008, 09:20 AM
Originally posted by halfcool:
Sonic Boom.
http://en.wikipedia.org/wiki/Sonic_boom

Ahh **** wait that sucker is taking off... my bad.
I didn't know airliners were allowed to break the sound barrier?

Kettenhunde
11-08-2008, 09:29 AM
it looks to me like it is stalling.

Bremspropeller is right from the pilots POV but let's take it deeper!

Actually there is local stalling from the frame of reference of wing but I doubt the passengers are even noticing it much from due to the fact the gear are still down. It is not stalling from the frame of reference of the aircraft. Only a portion of the wing is actually stalling and to our pilot it is perceived as "buffeting".


So as the air passes above the wing it reduces in pressure and temperature. Thus the ammount of water vapour the that the air can hold is reduced. If the ammount of water vapour in the air is almost at maximum and the airfoil reduces the temperature and pressure so that there is excess water vapour in the air a cloud forms. (notice that the cloud is only above the wing!)


Good explanation Skoshi Tiger. Allow me to expand some on this concept by explaining some of the lesser known details of boundary layer mechanics for the readers.

Rarely is our dew point spread such that just the difference in pressure from un-separated flow will cause water molecules to change state. Commonly the energy to force the water to change state is from flow reversal. That is why you only notice this phenomenon in high angle of attack flight or in high speed flight.

Our boundary layer itself is not moving. Think of the wing being wrapped in a very very thin cocoon of absolutely still air. This is the actual boundary layer. Above this layer, we have a region of stratified uniform flow originating upstream leading edge termed "laminar flow". Behind this the layers begin to mix and our flow becomes "turbulent". The ratio between our laminar to turbulent flow is termed the Reynolds number. This is how engineers scale a model in the wind tunnel to the full sized aircraft by manipulating the Reynolds Number (Re).

Whenever that boundary layer of absolutely still air separates from the skin of the aircraft the consequence is a change in direction of the flow above it. This causes the molecules to slam into each other and provides the energy to change the state of gaseous water in the air to liquid. Thus we see our water vapor.

The denser liquid water causes more high energy collisions which result in more liquid water!

In the transonic and supersonic realm anytime we have normal shock formation, we will have flow separation and reversal just behind the normal shock. The airflow proceeding the normal shock is transonic, the shock itself supersonic, and the flow behind it subsonic.

Here is a page with some great applets explaining shock formation:

http://selair.selkirk.bc.ca/Training/Aerodynamics/shockwave-formation.html

Here in this tuft test, you can easily see the flow reversal.

http://uk.youtube.com/watch?v=sKzbeWwe0wM

Hope this wasn't confusing and brings some deeper understanding.

All the best,

Crumpp

edited for clarity on boundary layer mechanics.

SeaFireLIV
11-08-2008, 09:32 AM
What`s a splanation?


Don`t tell me, you spelt it wrong on purpose.

RPMcMurphy
11-08-2008, 09:57 AM
Originally posted by SeaFireLIV:
What`s a splanation?


Don`t tell me, you spelt it wrong on purpose.
You never saw I love Lucy on TV? It's either that or perhaps you should call the cops;
somebody has stolen your sense of humor.


For the responders:

Good explainations so far everyone, and thanks.

Except for the sonic boom theory.

However I assume that the little trail of visible moisture created by the wingtip vortcies is pretty much the same thing.

Thanks RP

halfcool
11-08-2008, 10:58 AM
It's the 'I Love Lucy' Pronunciation.

Aww god damn this guy beat me to it :P ^^^^^

i still think it's a sonic boom....... http://forums.ubi.com/groupee_common/emoticons/icon_biggrin.gif

Clan_Graham
11-08-2008, 11:17 AM
Originally posted by M_Gunz:
And it's not that they allowed smoking on board and the windows are open to let smoke out.
Even if it is the Marlboro Special.

Close. But the windows are open.
The plane is obviously arriving from Jamaica. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Airmail109
11-08-2008, 11:59 AM
Oh look its Iceman flying an Airliner

VMF-214_HaVoK
11-08-2008, 04:25 PM
Originally posted by halfcool:
Sonic Boom.
http://en.wikipedia.org/wiki/Sonic_boom

Ahh **** wait that sucker is taking off... my bad.

That is a myth.

SeaFireLIV
11-08-2008, 04:36 PM
Originally posted by RPMcMurphy:

You never saw I love Lucy on TV? It's either that or perhaps you should call the cops;
somebody has stolen your sense of humor.



Thanks RP

Hey I`m English!

I`ve heard of the lady - had no idea she said that or anything else. Can`t recall it ever being on Brit TV.

The local joke shop was out of American-style humour last I visited... Not much call for it here.

RPMcMurphy
11-08-2008, 04:52 PM
Originally posted by SeaFireLIV:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RPMcMurphy:

You never saw I love Lucy on TV? It's either that or perhaps you should call the cops;
somebody has stolen your sense of humor.



Thanks RP

Hey I`m English!

I`ve heard of the lady - had no idea she said that or anything else. Can`t recall it ever being on Brit TV.

The local joke shop was out of American-style humour last I visited... Not much call for it here. </div></BLOCKQUOTE>

Oh okay.
I can call off the sense of humor police then.
Oh bloody- ell. Sorry bout that constable. http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

Uufflakke
11-08-2008, 04:55 PM
Come on guys, it's got nothing to do with a sonic boom, smoking on a plane or a flight from Jamaica with open windows but some aircompanies introduced new uniforms for their stewardesses recently.
And that's smoking hot!

http://i256.photobucket.com/albums/hh195/Uufflakke/S01.jpg

RPMcMurphy
11-09-2008, 01:06 AM
As a passenger if stewardesses looked like that I wouldnt give a damn what the plane was doing upsidedown or what ever.