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.
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5$\begingroup$ You saved me from asking the same question, thanks! :) $\endgroup$– shortstheoryCommented Mar 26, 2014 at 17:48
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3$\begingroup$ You didn't save me from asking the same question. Whoops! I tried searching for "static wing" but this question never showed up. Oh well! $\endgroup$– Jeff BCommented Sep 4, 2014 at 13:32
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3 Answers
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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:
answered Mar 25, 2014 at 19:28
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$\begingroup$ They also show damage in a lightning strike, so I would assume they help with that too. $\endgroup$– ptgflyerCommented Feb 3, 2015 at 16:13
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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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3$\begingroup$ 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! $\endgroup$ Commented Mar 26, 2014 at 19:29
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1$\begingroup$ @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.) $\endgroup$– reirabCommented Mar 27, 2014 at 3:17
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7$\begingroup$ 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. $\endgroup$– reirabCommented Mar 27, 2014 at 3:26
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4$\begingroup$ Yes, typically kilovolts are required before the corona will ignite on the carbon fiber tips of the "wicks." Corona is required to exist on the sharp tips before they can function. If the voltage on the aircraft drops well below kilovolts, they stop working. Also, it's easily measured, but using an "Electrometer" type of voltmeter, where the meter impedance is upwards of 10^20 ohms, not the usual 10^7 ohms of typical DMMs. For electrostatic measurements, 10 meg ohms acts like a good conductor, a near-short circuit. Instead we use a "field mill"-based electrostatic voltmeter. $\endgroup$– wbeatyCommented Jun 8, 2016 at 7:58
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3$\begingroup$ You don't even have to travel at high speeds: skydivers (~120mph terminal velocity) in relatively large formations -- say anything over 20-30 people-- can pick up enough static electricity across the formation that you can feel the shocks ripple through your body. They don't hurt, but you can definitely tell that you're getting zapped. $\endgroup$– ljwobkerCommented Mar 26, 2018 at 22:42
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It's called static dischargers since aircraft body or fuselage is made up of metal and carrying tonnes of fuel and electronic devices, we will have to remove the static electricity charge from the fuselage to the air in order to not ignite the fuel or disturb the electronic devices, and that's how it's done ! :)
