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Braybuddy
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Condensation Over Wings

Fri Aug 27, 2004 12:34 am

Can anybody tell me what causes condensation to form over the wings, and, seeing that the aircraft is flying fast, why it does not dissipate in a trail of vapour at the back?
 
AUAE
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RE: Condensation Over Wings

Fri Aug 27, 2004 12:58 am

Condensation usually occurs after the plane has been at altitude for a while. At altitude the fuel in the wing gets very very cold, and then as the plane descends the warm air condenses on the wing ecause the fuel is still cold. The reason you don't see the condensation blow off is because the air very close to a moving body is actually not moving (ie how static ports work).

shawn
 
Airbus_A340
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RE: Condensation Over Wings

Fri Aug 27, 2004 1:09 am

Air is flowing over the wing like a big venturi. And according to Bounoulis theory, air travelling over a venturi moves faster, not only that, but it is less dense.

When you make air travel faster, it cools, and you sometimes see condensation form over the wings as the air flowing over is rapidly cooled to (near) dew-point temperature (i.e. 100% humidity).

Hope that helps, and I hope it's right from what I understand of it!

Airbus_A340
 
SUPRAZACHAIR
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RE: Condensation Over Wings

Fri Aug 27, 2004 2:12 am

Bingo. Airbus_A340 nailed it. Faster, lower pressure air moving over the wing's surface cools below dewpoint and a condensation cloud will appear above the wing. Its Bernoulli's effect in action.
 
nealcg
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RE: Condensation Over Wings

Fri Aug 27, 2004 2:26 am

Braybuddy

Can anybody tell me what causes condensation to form over the wings, and, seeing that the aircraft is flying fast, why it does not dissipate in a trail of vapour at the back?


Airbus_A340 hit it on the head pretty well. The lack of "dissipation" you see is an illusion. The condensation does indeed "dissipate". As air moves over the wing it condenses due to the Bernoulli effect and dissipates as it moves back. because the process is continuous it appears that it is a staitonary "cloud" over the wing when the air is actually moving at hundreds of miles per hour.


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AGGIES WIN !!
 
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Braybuddy
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RE: Condensation Over Wings

Fri Aug 27, 2004 6:56 am

Thanks guys, sounds pretty complicated, but it sounds like it makes sense
 
FLAIRPORT
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RE: Condensation Over Wings

Fri Aug 27, 2004 7:34 am

Air is flowing over the wing like a big venturi. And according to Bounoulis theory, air travelling over a venturi moves faster, not only that, but it is less dense.
That would explain what I saw today. a CO aircraft was making its turn for final and everytime the (I'm assuming) spoilers were opened, I'd see this air rushing from the wings. It was quite a site!
 
Santhosh
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RE: Condensation Over Wings

Fri Aug 27, 2004 8:23 am

After the Aircraft flies off,for how long does the condensed cloud (Contrail)persists in the sky? I have a seen some of them lasting for and hour or so after flies over the area and alt the same time I have also seen them dissipating in minute or two. What is that phenomenon that influences the time for lasting of contrails?

Actually I was under the impression that the hot flue gases comming out of the jet exhaust vapourizes the moisture in the surrounding air and as the temperature at high altitudes comes around -40 to -50, as soon as the aircraft moves off the vaporized moisture is again exposed to the cold atmospheric condition and that causes condensation of the vapour and thus forms the white contrail.
 
JeffDCA
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RE: Condensation Over Wings

Fri Aug 27, 2004 10:27 am

The contrails are formed by the water vapor from the engine exhausts freezing in the high altitude environment as ice crystals. The length of time they stay in the air depends on the relative humidity of the air, if it's close to 100%, the contrails will persist for a long time, if the relative humidity is low however, the contrails will only last a short while.

Cheers,

Jeff
 
planemannyc
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RE: Condensation Over Wings

Fri Aug 27, 2004 10:48 am

Typically, condensation over the wing happens for a brief few moments....and in my expereince, only when landing. Here is a shot I took on final approach to JFK:


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Photo © Wasim Choudhury



Best,

Wasim / Planemannyc
 
Flyinround731
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RE: Condensation Over Wings

Fri Aug 27, 2004 12:28 pm

I'm not sure if this is the same thing, but this morning, I witnessed a WN 737 flying by, turning for finals to 12R at HOU, and it had the gear down, and the flaps down a little, and from the outside edges of the flaps, little trails were being left behind, I think it was condensation, I'm not sure though. Was it?
-Joe
 
B2707SST
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RE: Condensation Over Wings

Fri Aug 27, 2004 1:11 pm

Contrails are formed by water vapor freezing out of jet exhaust at altitude. Contrails are relatively permanent because the ice crystals persist in the cold upper atmosphere.


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Photo © Bailey - AirTeamImages



Condensation over wings is caused by a drop in air pressure, which also causes a drop in air temperature according to the laws that govern the behavior of gases. Once the air passes out of the zone of low pressure over the wing, its temperature returns to normal and the condensation disappears. You usually see wing condensation during landing on humid days.

Vortices are similarly caused by low-pressure condensation, but they occur in the "tornadoes" of air trailing from wingtips, flaps, stabilizers, etc. Vortices form where high pressure air (such as air beneath a wing, in front of a flap, etc.) tries to spill over into a low-pressure region.



Strictly speaking, the vortex itself is always present, but it is made visible when water vapor condenses in the low-pressure core. Vortices also don't last long and are most often seen on takeoff or landing.


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Photo © Tim de Groot - AirTeamImages
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Photo © PixAir



--B2707SST
 
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Braybuddy
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RE: Condensation Over Wings

Fri Aug 27, 2004 7:48 pm

Thanks B2727SST, that explanation makes perfect sense and is also easy to explain to others.

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