What is that mist that forms around wing root shortly after takeoff

[eji]

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?

[Dockjock]

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.

[Shemptol]

The sudden extreme pressure drop on the top of the airfoil causes the moisture to condence out. You are seeing lift in action!

[eji]

Thank you very much, I understand it now

[thx1138]

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.

[BEagle]

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........

[4dogs]

Folks,

In my distant youth, the condensation was referred to as "ectoplasm", presumably as a consequence of it's wraithlike or ghostly appearance.

[OverRun]

And there I was thinking it was the fumes from the Gin and Tonics in first class being vented overboard

[Slasher]

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!

[eyeinthesky]

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.

[Truckmasters]

You'll also get this effect of the propellors of a lot of aircraft in early morning conditions