What is that mist that forms around wing root shortly after takeoff
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What is that mist that forms around wing root shortly after takeoff
Hello Gentlemen, I couldn't help but notice a fine mist that appears around the wing root of jets just after takeoff. It forms a perfect airfoil and disappears rapidly. Also, it forms on perfectly clear days with no visible moisture present. What creates this phenomenon? 
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With the airflow accelerated over the wing, the local static pressure is reduced (producing lift).
When pressure is reduced so is temperature, in this case to its dewpoint, which causes condensation. What you are seeing is water vapour.
You will see this frequently when the temperature/dewpoint spread is very small.
When pressure is reduced so is temperature, in this case to its dewpoint, which causes condensation. What you are seeing is water vapour.
You will see this frequently when the temperature/dewpoint spread is very small.
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If you ever have a window seat in the last row of a 727, when the power comes up for takeoff you can see mist shaped like a rope appear that wraps around from between the fuselage and the engine and goes into the engine when the power is applied.
Last edited by thx1138; 14th Oct 2002 at 20:40.
Unless, of course, it's because someone has opened the chem tank valves too soon and population-subjugating chemtrails are being generated at low level. But don't tell the loonies........ 
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I remember once taking off in my 737 FLUF and having pax complain of all this gray mist off the left wing starting at rotation and continuing unabated even at 320 kts. After I replyed its just condensation the penny dropped when I was told theres NO complaints about the RIGHT wing!
Yep! The left over-wing tank cap was loose!
Yep! The left over-wing tank cap was loose!
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You can get a good view of this phenomenon (the lift one, not the lose fuel cap!) from the ground if you watch aircraft departing on a nice day with some cumulus at about 2000'. As the aircraft approaches the cloud base, but about 200 ft before it gets there, you will see 'clouds' form around the wing root and some way along the span as the decreased pressure lowers the temperature to its dewpoint.
It is the same process which causes those narrow trails of vapour from the outboard edge of the flaps on final on a murky day. This time they are vortices.
It is the same process which causes those narrow trails of vapour from the outboard edge of the flaps on final on a murky day. This time they are vortices.
