Article: 8482 of rec.aviation.misc Newsgroups: rec.aviation.misc,rec.aviation.owning Path: newshost.ncd.com!ncd.com!olivea!sgigate.sgi.com!sgiblab!swrinde!cs.utexas.edu!howland.reston.ans.net!europa.eng.gtefsd.com!fs7.ece.cmu.edu!cantaloupe.srv.cs.cmu.edu!dst From: dst+@cs.cmu.edu (Dave Touretzky) Subject: all about static wicks Message-ID: Sender: news@cs.cmu.edu (Usenet News System) Nntp-Posting-Host: dst.boltz.cs.cmu.edu Organization: School of Computer Science, Carnegie Mellon Date: Sat, 12 Feb 1994 03:38:54 GMT Lines: 89 Xref: newshost.ncd.com rec.aviation.misc:8482 rec.aviation.owning:1787 I've learned a little bit about static wicks recently. I had been dissatisfied with the static wicks on my Seneca; they were limp and kinked and generally looked like hell. Also they seemed to be of several different types; it looks like whenever a wick fell off, the previous owner had just grabbed another wick at random and bolted it on. One of mine fell off just recently, and I decided I wanted to replace my wicks with something better. I thought it might be cool to get those big plastic telephone pole-shaped static wicks (I called them "swizzle sticks") that you see on Citations. But my mechanic wasn't sure which types of wicks were OK for my plane; he thought (incorrectly, it turns out) that the different resistances of the different types of wick might be a problem. I ended up talking to a company called Dayton-Granger, which makes lots of different kinds of wicks for everything from puddle jumpers (top speed under 150 mph) to supersonic military aircraft. They sent me a catalog with pretty pictures, and spent a good chunk of time on the phone answering my questions. Turns out there are several variables to consider in selecting a static wick. First, motion of the wicks. As the plane flies, the wicks oscillate in the slipstream. If they move around a lot, they eventually weaken and break off. The faster the plane flies, the greater the forces on the wicks. Little puddle jumpers don't go very fast, so they can use simple wires (actually carbon filaments) that just hang out in the slipstream. Jets need something stronger. Hence, the "swizzle sticks". The purpose of all that plastic is simply to keep the wick stiff, so it doesn't vibrate too much. (I thought it might filled with inductors and "flux capacitors" and other obscure stuff. But noooooo....) A second factor is outside air temperature. Planes that fly really high operate in extremely cold conditions, where wicks can become brittle. The beefier and more expensive types of wicks are built to withstand vibration under these extreme temperature conditions. A third consideration is mounting hardware. Some types of wicks have a built-in fitting that you can bolt directly to the airplane. But most wicks are sold "bare", and you buy a separate base that the wick screws into. Bases come in different shapes and sizes, with different numbers of mounting holes. My Seneca apparently uses an "ASA-style" base, with two holes. Some of their supersonic bases come without holes; you get to drill your own as you see fit. According to the nice folks at Dayton-Granger, I can put Citation-style swizzle sticks on my Seneca if I want to. They don't weigh all that much more than the smaller types; total weight (minus the base) is under an ounce. And there's no need to worry about resistance values. But it still might not be such a good idea: those stiff wicks are frequently snapped off in "hangar rash" incidents. In fact, while I was pondering which type of wick to purchase, one of the line guys at my FBO pushed a Citation a little too close to the wall and snapped off a couple of its swizzle sticks. With all the traffic around my airplane, including clueless passengers not looking where they're going, I just know that I'd be finding snapped wicks all the time. Plus, I decided those big swizzle sticks would look ridiculous bolted to my plane's (relatively) tiny control surfaces. I also spoke with someone at Chelton, another manufacturer of static wicks. This guy recommended I talk to Dayton-Granger, as most of Chelton's products are designed for larger aircraft. But he did have some interesting things to say. First, I should be very careful to check the electrical bonding between my control surfaces and the wings, and between the doors and the fuselage. A poor bond will result in lots of electrical noise when static charge builds up on the airframe. Second, he warned me to stay away from the nylon filament type wicks offered by some manufacturers. These are the kind that eventually get worn due to static discharge; you're supposed to cut off a bit of the tip every so often to keep it fresh. These older-style wicks, in his opinion, are junk. Third, he told me a story about some military jet that had just come out of the paint shop, and the mechanics forgot to reconnect the bonding straps. The pilot took off, built up a static charge on the airframe, and promptly lost all his comm radios. So P-static really does have an effect on radio performance. It's generally more pronounced on higher performance planes. I decided to order a set of Dayton-Granger model 15330 Micropoint Trailing Dischargers, which include lightning diverter elements (a metallic stripe running the length of the wick.) This unit is thicker and stiffer than their smallest models, yet still flexible enough that it won't snap off if someone walks into it accidently. I also purchased a model 15660-1 ASA-style base (also called a retainer), which the wick screws into. Total cost for nine of these assemblies was about $360. I expect to receive this stuff next week, and will have it put on during the plane's annual inspection near the end of the month. If you would like to talk to Dayton-Granger about static wicks for your airplane, you can reach them at 305-463-3451. Ask for Cheryl Kincaid. You can also buy wicks directly from aviation supply houses (like Aviall), if you know the model you need. -- Dave Touretzky, CFI-AIM, Seneca N8147E (``The Anti-Static Beast'')