The Kopp-Etchells Effect

November 21, 2009 1:42 PM

Stunning pictures by Michael Yon show what happens when helicopters land in dust storms: The Kopp-Etchells Effect is thought to be the result of static electricity created by friction as materials of dissimilar material strike against each other, in this case titanium/nickel blades moving through the air and dust, but a precise definition is as of now not known.

Von reports most pilots were unable to provide him with a satisfying explanation for why this occurred but within the comments at the end of the article some speculate this could be related to Triboelectric effect or the nature of the sand crystals in the dust.

posted by krautland (33 comments total)

The first picture on the second page kinda looks like something out of Halo. Very cool.
posted by threetoed at 1:47 PM on November 21, 2009

So, helicopters sparkle in daylight sandstorms? Are hordes of teenage girls about to become newly interested in aviation?
posted by justsomebodythatyouusedtoknow at 2:46 PM on November 21, 2009 [7 favorites]

I wonder if magnetism might not be involved somehow; rapidly rotating blades would probably pick up a heck of a static charge, and there's lots of iron in the Earth's crust. A rotating static charge would look like current, and moving current causes magnetic flux. If it's rotating fast enough, it might make ferrous particles glow, kind of like a magnetic range does to your pots and pans.

Might also explain why it happens some nights and not others; the air would probably need to be very dry for the static to accumulate, and you'd probably need a certain density of ferrous particles in the air for it to happen.

I'm suspicious that friction wouldn't do it, because the blade probably doesn't actually impact enough air to cause that kind of heating. Helicopter blades are designed to push air, not drag on it.

This is a wild-assed guess from someone with no particular qualifications to do so: if later, more-qualified comments suggest that this is a bad explanation, pay attention.
posted by Malor at 2:47 PM on November 21, 2009 [1 favorite]

They're opening dimensional portals?!
posted by Brandon Blatcher at 2:51 PM on November 21, 2009 [2 favorites]

Very interesting. My wild guess: The blades are whacking through flocks of giant desert fireflies.
posted by amyms at 3:02 PM on November 21, 2009 [2 favorites]

I wonder if this is related to the St. Elmo's Fire-like effect that pilots have reported when encountering volcanic ash clouds at night (where it's usually the first sign they're in big trouble)?

Also, my favorite simple demonstration of the triboelectric effect is this: take a roll of masking tape into a very dark room. Wait for your eyes to adjust to the darkness. Then peel some tape off the roll, looking at where the sticky side peels away from the layer of tape underneath. You should should see a nice bright blue glowing line.
posted by FishBike at 3:03 PM on November 21, 2009

Is this not too different from St. Elmo's fire?
posted by sundri at 3:04 PM on November 21, 2009

First hand account:

It's dark at the LZ. Both ground crew and rotory crew are using a combo of NVG and IR to make this work, so it's hard to see much. I had neither so I was at the edge of the LZ, facing away from where the bird will eventually land. Watching others and personal experience teach you to face away, pull your chin in as close as you can to your chest and squeeze your eyes shut. A wash of dust is coming right at you as the helicopter approaches

You fee the wind buffet your back and after the initial strong gust, you can tell the bird has set down. You turn around and see what these pictures show. In fact, with the exception of small lights people use to move around (never white, always colored) this is the only real light. It's not much.

It never gets old to look at. Every single time, it's awesome in the classic sense of the word

Once the bird has set down, the rotor speed drops a bit as people and things unload then load. The sparkle does die down but it's hard to tell if this is due to slower speed or less dust in the air.

And while these are great photos, you can't get a feel for the sheer movement that goes with the lights. They sparkle and dance.

Seriously, it never gets old.
posted by Dagobert at 3:08 PM on November 21, 2009 [22 favorites]

Note that we're dealing with very sensitive detectors here -- with your bare eyes, you wouldn't see much but handheld lights and the glow, and that's only once your eyes have adapted.

I do suspect it's related to St. Elmo's fire -- that it's a type of plasma discharge caused by high voltage static discharge. Given that dry air is one of the most positive things on the triboelectric scale, all you need to do is move something on the negative end through air rapidly, and avoid a path to ground, to build up a pretty amazingly high voltage, and once you reach the breakdown voltage of air, you get ionization plasma and glows.

But, hey, I don' t really know -- and St. Elmo's fire is different, in that it requires a path to ground and a very charged atmosphere, where this is the opposite, no path to ground and the charge is building up on the helo, not in the air.

Dust would be a big factor as well. There's a reason that there are special vacuum cleaners for electronics. Merely pulling dust through a plastic tube can build up a surprisingly high voltage in a very short time -- indeed, the actual mechanism of charge migration is very similar to how a Van de Graff generator works. I and a friend sketched out a VDG using dust as the charge carrier, we think it could work, but the technical issues of how to drive the dust in a closed loop are pretty complicated.
posted by eriko at 3:28 PM on November 21, 2009

Kopp-Etchells Effect on wikipedia.

Those pictures are pretty cool.
posted by cjorgensen at 3:29 PM on November 21, 2009

The pictures are cool. The explanation of the naming squicked me out.
posted by signal at 3:50 PM on November 21, 2009

The naming is rather disingenuous because those sorts of [name] Effect terms are supposed to trace back to the discovery of the principles behind a phenomenon, not simply memorialize dead people.
posted by Burhanistan at 3:55 PM on November 21, 2009

An example of the triboelectric effect.
posted by Mojojojo at 3:58 PM on November 21, 2009

The abovementioned Wikipedia article currently has a couple of references saying the effect is caused by sand in the air chipping off tiny hot particles of titanium from the anti-erosion strips on the leading edges of the rotors.

If this is true then the effect is actually not electrical; you're instead looking at a lot of little metal sparks, like when you take an angle-grinder to any similarly spark-y metal.
posted by dansdata at 4:09 PM on November 21, 2009

Yeah, my first thought was frictional sparks, rather than microscopic electrical arcs. You can get an enormous volume of sparks off a workshop grinder without removing very much matter at all, so I'm kind of in the friction sparks camp on this one for now.
posted by crapmatic at 4:52 PM on November 21, 2009

Kopp-Etchells, bitches! In EFFECT!
posted by flapjax at midnite at 5:15 PM on November 21, 2009

Given that one of titanium's uses is for non-sparking tools for use in explosive atmosphere, I think the grinding-wheel-hot-sparks explanation is less likely than the electrical-discharge explanation. OTOH, I gather that erosion of the rotors by sand and dust is a real problem over there, so it's not like there's nothing getting ground off the rotors at all.

eriko: There are also pelletrons, which are VdG generators with a linked chain of pellets instead of a belt. It seems to me that using non-linked pellets or dust would leave you with the problem that if you're transporting any significant amount of charge, there'll be a corresponding electrostatic force on the particles, probably pushing them in the least desirable direction. Kelvin's Thunderstorm is a little bit like a particle Van de Graaf generator, with each particle only going through the machine once; and it'll self-regulate: once the voltage gets high enough, the droplets are repelled from the collector and don't actually pump any more charge.
posted by hattifattener at 5:30 PM on November 21, 2009

Wouldn't you be able to determine if this is a static electricity issue fairly easily by grounding the chopper via a cable before it lands? Think Batman-style launched grappling spike shot into the ground.
posted by Decimask at 5:36 PM on November 21, 2009

Also, my favorite simple demonstration of the triboelectric effect is this: take a roll of masking tape into a very dark room. Wait for your eyes to adjust to the darkness. Then peel some tape off the roll, looking at where the sticky side peels away from the layer of tape underneath. You should should see a nice bright blue glowing line.

You might want to put on a lead apron first.

Apparently this same process also releases x rays.

Whether or not this is one of the causes of temporary insanity during various Winter Solstice holidays involving the frantic wrapping of gifts awaits further experimentation.
posted by loquacious at 5:41 PM on November 21, 2009 [4 favorites]

Decimask: If it's an electrical thing, my guess is that the circuit would be something like rotor tip → dust particles → air → rotor blade, so it wouldn't matter if the helicopter's body is grounded or not.

A sensitive spectrophotometer ought to be able to tell you a lot about what's producing the glow. Or for that matter just keeping a record of conditions each time it's seen or not seen.

(Also, cool post and impressive photos.)
posted by hattifattener at 5:53 PM on November 21, 2009

threetoed: "The first picture on the second page kinda looks like something out of Halo. Very cool."

That's exactly what I thought. Crazy vehicles plus the omnipresent crates.
posted by aerotive at 6:41 PM on November 21, 2009

loquacious: "Apparently this same process also releases x rays."

From that link: "tribology, the science of things rubbing together".

That is probably the kinkiest science I have ever heard of. I wonder if there have been any studies linking Tribology and Knot Theory.
posted by idiopath at 6:44 PM on November 21, 2009 [1 favorite]

So yeah, contributions to science are usually named after the people who, you know, contributed to science.
posted by kiltedtaco at 7:05 PM on November 21, 2009

Hey those of you chimping out about the naming conventions of helicopter sparks are are as bad or worse than deal-with-it-mom atheists, loud-n-proud evangelican christians, or don't-have-a-tv guy/don't-use-social-networking guy.

We get it. You read a wikipedia article or half-remembered something your teacher told you. Happens to all of us.

Somebody chose a name for something based on what they felt was important to them. Popularize something else with a name that's important to you (or better yet, "contribute something to science") if you don't like it.
posted by hamida2242 at 9:51 PM on November 21, 2009

The pictures are of an interesting subject and technically well-done. I don't support either of the wars or dead-soldier-flogging jingoism; but since neither of those facts has any affect on the pictures or the phenomena they portray I'll refrain from trying to post some pedantic bullshit in an effort to look educated or intellectual, or to reinforce my already well-known political views.
posted by hamida2242 at 9:58 PM on November 21, 2009

Yeah, about that naming thing: what about the bugs and whatnot named after cartoonist Gary Larson?
posted by spacely_sprocket at 10:13 PM on November 21, 2009

Popularize something else with a name that's important to you (or better yet, "contribute something to science") if you don't like it.

I don't know about you, but in my experience the names of these sorts of things are either a) the first person(s) to describe the effect in detail in scientific literature, b) the theoreticians who predicted it, or c) (usually in medical scenarios) the person(s) subject to the effect/issue/disease.

While I'm entirely sympathetic to naming something after people who had nothing to do with it, I find it scientifically odd and potentially misleading. Calling this the "Kopp-Etchels Effect" tends to imply that Kopp or Etchels had something to do with discovery or description of it.
posted by chimaera at 10:15 PM on November 21, 2009 [3 favorites]

This is a photo journalist doing his job in a war zone and being amazed by the men and women he met and the weird, unexplainable effects of helicopter rotors and sand. Do you really think his poignant act of naming the effects after a couple of war casualties is going to stick in the world of science?
posted by birdwatcher at 4:22 AM on November 22, 2009

update: The Smithsonian Air&Space Magazine wrote about this as well. I wasn't aware of it even though yon mentioned it on his site as well.
posted by krautland at 7:36 AM on November 22, 2009

The Spice....must flow.....Arrakis, Desert Planet....Dune.
posted by Lipstick Thespian at 11:41 AM on November 22, 2009

Just because they're neat looking and involve helicopters (though unmanned ones), some of Jack Crossfire's photos are worth a look.
posted by morganw at 1:17 PM on November 22, 2009 [1 favorite]

From the comments on the photos page: "Since 9/11/01 I knew this. I'm convinced this is a Good fight fought by Good people against an Enemy that is fighting an Eternal struggle to control the World".

That's some science you've got going there. Oh, it's Journalism? Never mind.
posted by sneebler at 5:10 PM on November 22, 2009

sneebler: I don't think this ex-military man reporting on a military mission is exactly impartial but did you just conclude he had to be full of it because of what a commenter wrote? by that logic there isn't anyone in the world I couldn't take down.
posted by krautland at 12:04 PM on November 23, 2009