wing clouds

Can this be recreated in a lab? Any equations would be helpful if so. Also, why doesn't this happen during high angles of attack on a smaller wing, such as that of an R/C plane?

  • $\begingroup$ If the lab is inside a wind tunnel, yes. $\endgroup$
    – Koyovis
    Sep 10, 2017 at 4:59
  • $\begingroup$ This water comes from condensation of water vapor already in air after pressure is decreased suddenly due to lift mechanism, and temperature is decreased accordingly. Air must be near water saturation (near 100% humidity ratio). The value obtained with small wings at small speed cannot produce the pressure change required to lower temperature below the due point. See this general explanation. Which "equation" are you looking for? $\endgroup$
    – mins
    Sep 10, 2017 at 7:15
  • $\begingroup$ related: aviation.stackexchange.com/q/14327/1467 $\endgroup$
    – Federico
    Sep 10, 2017 at 12:27
  • 1
    $\begingroup$ @mins I believe you mean to say 'dew point'. $\endgroup$
    – Gerry
    Sep 10, 2017 at 13:04

2 Answers 2


The sudden fog due to the fast (and hence adiabatic) expansion of air is re-created, in many laboratories, in the simple cloud chamber.

For those that haven't seen one (they are fast disappearing from school labs due to 'radiation risk'): it is a small, usually round chamber with a window. Inside, there's a a small amount of water to ensure a water-vapor saturated air. As the chamber is closed, the water is in stable equilibrium with its vapor. The chamber is connected to a hand pump that resembles a bicycle pump, but working in reverse. When you pull the pump handle, you make a partial vacuum in the chamber, and due to the sudden descent in pressure, the temperature drops too, and some of the water vapor inside the chamber condenses. If the pull is light enough, the condensation will take place only along the trajectory of the alpha- or beta particles emitted by a suitable source placed inside. But if you pull hard enough, the whole chamber fills with fog.


As an addition to @xxavier's excellent answer: RC planes have far lower wing loadings, so the pressure difference between ambient and over wing pressure in case of model airplanes is far too small to cause that massive condensation seen in the photo above.

The pressure coefficient on the top side of a model airplane wing will rarely drop below -1 (except for a very pointy suction peak at high angle of attack) while the pressure coefficient on the top side of an airliner wing with slotted flaps extended can be as low as -2.5. Next, the dynamic pressure (which is needed to convert the pressure coefficient to an absolute pressure) is orders of magnitude higher for airliners than for model airplanes.

Typical airliner pressure distribution in landing configuration

Typical airliner pressure distribution in landing configuration (picture source). For comparison, a model airplane distribution can be found in the linked answer.


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