Lv 7
Regwah asked in Science & MathematicsWeather · 9 years ago

Can you tell me what's going on with this little cloud forming on the tip of the helicopter rotor blades?

10 Answers

  • 9 years ago
    Best Answer

    The two answers above are correct: The air is compressed under the rotor and when released, it cools down and that condenses moisture into a visible tiny cloud. This is called the adiabatic effect of a lesser pressure and it is the same that happens in your fridge when a coolant is released through a nozzle; it cools down.

    To happen, the air temperature must be close to dew point or, in other words, the relative humidity must be close to 100 percent.

    Where OURScott is wrong, though is that a helicopter rotor or an aircraft propeller tip NEVER exceed the speed of the sound. If it did, it would create a vibration that would disintegrate at once the propeller or rotor. I own and fly a Kitfox, a homebuilt aircraft and I know for sure that my propeller tip at maximum RPM is right under be NEVER over the speed of the sound. This is, actually, the way we calculate the maximum diameter of a propeller for our aircraft. Incidentally when it rains and rainwater meets the tip of the propeller at at speed right under that of the sound, it is so hard that even the best wood propeller get dented. That's why we never fly at maximum RPM in the rain. But ... I digress :-)

    What you see on the photo is what you can see often from many aircraft: the visible vortex at the end of a wing or rotor. Incidentally, what even some pilots ignore is that the vortex effect that can cause great turbulence to the following plane, is the greatest not when the plane flies fast but rather, when it flies slow and the angle of incidence of the wing is great to gain enough lift to sustain flight.

  • 9 years ago

    The tips of the rotors are breaking the sound barrier and the compression of the air from the shock wave make vapor in the air visible Here's a big cloud and a wake in the water from the same phenomena.


  • Joe K
    Lv 5
    9 years ago

    Well, I know nothing about helicopters, so I thought the pilot is a smoker, and that he has devised a kinda of ventilation duct :)

    I like Michel Verheughe's answer (among others).

    Nice shot, BTW.

  • Skywriting, that looks like a comma or the start of a shorthand sentence, or perhaps a cobweb for my darling Francine!!!

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  • A.C.R.
    Lv 7
    9 years ago

    the name for that is a contrail. or condensation trail.

    formed by natural condensation of water vapor showing blade tip vortex wake

  • jenny
    Lv 7
    9 years ago

    Wow shot, I'd be more concerned about what's that bomb doing up there,

    looks like the blade is shaking a cobweb off.

  • It looks like water vapor, I don't know what to call it. Cool pic, {{{Regwah}}}

  • 9 years ago

    Small hair on the camera lens perhaps.

  • Anonymous
    9 years ago

    activating cloaking device

  • Anonymous
    9 years ago's called a "talented photographer"

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