Wednesday - March 03, 2010

rotorhead II

Since Vilmar put up a post today on a new helicopter rotor design, I figured I’d add to the mix with a link and a small bit of science.

If you rub an amber rod with a cat you get static electricity. If you touch that cat to a grounded water pipe in a dark room you get sparks. Then you get your face clawed off as the cat discharges the room at near light speed. Don’t try this experiment at home kiddies, unless you have bandages at the ready and it’s someone else’s cat.

The old amber rod thing is an example of the triboelectric effect. In very dry and dusty environments you can get a similar thing with helicopter rotors. The blade builds up a static charge as it moves through the air, and when the hard metal of the blades impact the dry sand or dust in the air, they discharge a small spark as the sand etches away a tiny little bit of their surface. Perhaps a bit similar to Saint Elmo’s Fire on ships, the effect is very unpredictable, quite beautiful, and can be very dangerous. And it just goes to show that helicopters are high maintenance machines in a desert environment.

You’re thinking, “Oh, Ok, a little spark. No big deal.” But it isn’t just one or two. It’s millions of them at a time. Enough so that the rotors can create a shimmering halo that can be visible for miles. Not what you want when you’re flying in a combat zone at night. The phenomena is nothing new; it’s been known about for years.

A secondary concern with the erosion of metal abrasion strips pertains to the visible signature that occurs when microscopic metallic pieces are eroded away. In the erosion process, they often oxidize, giving off a visible spark and causing a corona effect in sandy environments

Although both Ni and Ti are hard metals, their hardness values are significantly lower than that of sand, which is primarily made up of quartz. This hardness differential results in the excessive erosion/degradation of rotor blades in desert environments. An equally important problem with Ti protection is that a visible corona or halo is generated around the rotor blades at night from the sand impacting the Ti leading edge and causing Ti to spark and oxidize.

To everyone’s surprise, Science, which lives to pin names on things, has not given this variation of the triboelectric effect it’s own name. And it is a variation, since erosion is involved.

Half a year or so ago Michael Yon took some fantastic photos of this effect in action, and after much research decided that it should be called the Kopp-Etchells Effect. I think it’s a good name, and his reasons for it are just as good or better than some beaker shaker’s attempt at immortality. I’ll respect his copyright even though hundreds of other sites haven’t, and instead send you over to take a look. Sure, it’s “only” “a plasma phenomena of ionized particles”, but all cool and rare things deserve a decent name.

This little update link implies that The Powers That Be may be agreeing that he coined a new phrase. Very cool.

Yeah, I’m six months late to this party. So what? It’s the neatest bit of helicopter news I could find on just one cup of coffee.

Posted by Drew458     on 03/03/2010 at 09:51 AM   
Filed Under: • Amazing Science and Discoveries • Military •  
• Comments (3) • Trackbacks(0)  Permalink •  

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