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Thread: Why there is white smoke giving out from the wings?

  1. #1 Why there is white smoke giving out from the wings? 
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    Why there is white smoke giving out from the tip of the wings of a plane?
    thx very much


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  3. #2  
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    It isn't smoke, but condensed water. In the wake of the aircraft wings there are zones of reduced air pressure. If the humidity is at or close to 100% then the sudden reduction of pressure will trigger condensation of water droplets. In essence the passage of the wings is creating miniature clouds.


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  4. #3 wing tip vapor 
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    just to add to Ophiolite's note,
    the air moves from the lower surface (high pressure)
    to the upper surface (low pressure) over the tips in a vortex flow,
    creating the low pressure area of condensation. It can also occur
    at other parts of the plane.
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  5. #4  
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    Interestingly, I never saw this happen anywhere else than on the wing tips
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    I think that is because airplanes are the only ordinary objects that move at speeds capable of producing such large differences in low pressure.
    I demand that my name may or may not be vroomfondel!
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  7. #6  
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    Quote Originally Posted by oracle
    Interestingly, I never saw this happen anywhere else than on the wing tips
    Coming in to land, with full flaps, so that the aircraft is close to stall and the pressure difference is (I think) at a maximum, the effect can extend along much of the wing. This is seen best in tropical climates where the humidity is routinely high.
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by oracle
    Interestingly, I never saw this happen anywhere else than on the wing tips
    Coming in to land, with full flaps, so that the aircraft is close to stall and the pressure difference is (I think) at a maximum, the effect can extend along much of the wing. This is seen best in tropical climates where the humidity is routinely high.
    I've seen this at my resident local airport in central Florida.
    It's butt-stinking hot down here.
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  9. #8  
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    Quote Originally Posted by Ophiolite
    It isn't smoke, but condensed water. In the wake of the aircraft wings there are zones of reduced air pressure. If the humidity is at or close to 100% then the sudden reduction of pressure will trigger condensation of water droplets. In essence the passage of the wings is creating miniature clouds.
    You seem to be proposing that gases will spontaneously condense into liquids if their partial pressure is lowered, which is definitely not correct. If you had a container filled with a mix of nitrogen and water vapor, then removed the nitrogen through a filter that wouldn't pass the water vapor, this would not cause the vapor to condense.

    And in any case, water vapor in the air would presumably be “pushed out” with the other gas molecules in the air when the low-pressure zone is created, leaving the ratio of water vapor to other gases unchanged.
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  10. #9  
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    Quote Originally Posted by Scifor Refugee
    Quote Originally Posted by Ophiolite
    It isn't smoke, but condensed water. In the wake of the aircraft wings there are zones of reduced air pressure. If the humidity is at or close to 100% then the sudden reduction of pressure will trigger condensation of water droplets. In essence the passage of the wings is creating miniature clouds.
    You seem to be proposing that gases will spontaneously condense into liquids if their partial pressure is lowered, which is definitely not correct. If you had a container filled with a mix of nitrogen and water vapor, then removed the nitrogen through a filter that wouldn't pass the water vapor, this would not cause the vapor to condense.

    And in any case, water vapor in the air would presumably be “pushed out” with the other gas molecules in the air when the low-pressure zone is created, leaving the ratio of water vapor to other gases unchanged.
    Tell me, what happens to a gas when its pressure lowers? Maybe just maybe its temperature goes down? Maybe enough to cause it to condense? :wink:

    OTOH, I would think it is high pressure what causes condensation around aircraft fins... it is complicated as, well, there is a high pressure right in front and a low pressure right behind the fin, so where does condensation come from? My bet still would be high pressure "melting" together several microdroplets, too small to be visible unleess when they're pushed together by a passing fin and temporally make a macroscopic, visible, droplet... :?


    BTW, this sort of condensation happens too on the tip of propeller blades.
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  11. #10  
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    This effect also happens generally around the midpoint of an aircraft just as it hits the sound barrier. There are several pictures of this happening - it's rather impressive. It also takes either a movie camera or very impresive timing (bordering on precognitive) to take a still of the effect.
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  12. #11 vapor 
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    air is never totally without water content.
    if you do high g maneuvers, you can generate wing tip flows at will.
    catch an air show sometime, they are awesome.
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    Quote Originally Posted by Archie
    This effect also happens generally around the midpoint of an aircraft just as it hits the sound barrier. There are several pictures of this happening - it's rather impressive. It also takes either a movie camera or very impresive timing (bordering on precognitive) to take a still of the effect.
    this acually lasts for more than 2 seconds.
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  14. #13  
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    From what I understand you people are saying, the vapor in the air condenses due to a partial vacuum left by the flying aircraft.

    If this is true, would it be possible to condense the water into ice if you, say, fired a bullet fast enough?
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  15. #14  
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    Quote Originally Posted by Lucifer
    Tell me, what happens to a gas when its pressure lowers? Maybe just maybe its temperature goes down? Maybe enough to cause it to condense? :wink:
    You seem to have it backwards. A reduction in temperature can cause a drop in pressure, but the temperature doesn't drop just because you are lowering the pressure. Here it's being proposed that the pressure drops because air is "pushed out" of the space, so the pressure drop should be proportional to the decrease in the number of moles of gas in the space that the air passes through.
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