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What are these things hanging off the trailing edge of the wing?

I've seen them in almost all of the aircraft I've flown in, and can't remember if they're exclusively Boeing or Airbus.

wing trailing edge

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You saved me from asking the same question, thanks! :) –  shortstheory Mar 26 at 17:48

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up vote 34 down vote accepted

Those are static wicks -- Basically these are little wires screwed to the airframe.
Their purpose is to discharge the static electricity that an aircraft picks up moving through the air - especially in clouds.

The static discharge tends to happen at "pointy" protrusions from the aircraft - if this happened through antennas it could cause radio and navigation interference, so to prevent that static wicks are installed, providing a low-resistance protrusion for the charge to dissipate through (and as an additional benefit, dissipating the charge helps ensure your aircraft doesn't attract lightning strikes).

Here's a couple of closer pictures:
Static Wicks installed Static Wick close up

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These are static wicks or static dischargers. They dissipate static electrical buildup caused by the friction of air flowing over the surface of the aircraft. The air friction tends to separate electrons from their atoms just as rubbing a balloon tends to do, causing an imbalance of electrical charge on a body. The wicks work by providing a pointed surface where airflow separates from contact with the aircraft body. The excess charge tends to flow into the air and is swept away from the aircraft.

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At the speeds aircraft travel, and over the large distance between their wingtips - hundreds of volts potential difference are commonly produced. Impossible to measure, though, as your multimeter experiences the same PD across it's leads, and shows a zero difference! –  DefenestrationDay Mar 26 at 19:29
    
@DefenestrationDay, I'd be a bit surprised if it's not actually thousands of volts or more. You can't measure the potential difference between the air and the skin of the airplane with a meter, though. Air isn't conductive enough (without being ionized first, at least) for the ground lead to be a true ground. It's the same reason you can't just hold the ground lead in the air to measure a voltage on anything else. Also, if you did ground the ground lead and attempt to measure a static charge on something, it would discharge through the meter itself (though relatively slowly.) –  reirab Mar 27 at 3:17
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Even the static charges that you accumulate on yourself on a cold, dry winter day that cause you to get shocked when you touch something grounded are often up into the thousands of volts. Almost any time you see a visible arc from a static charge, it's a kV or so. Since it's just static, though, once current starts flowing, the potential difference drops very quickly. –  reirab Mar 27 at 3:26

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