Since there has been a lot of grounding messages lately I will throw in my two cents. I design electronics systems for ships and I also have a lot of experience with grounding on fiberglass boats, particularly with MF/HF radio grounding. I am by no means an expert on composite aircraft grounding so don't take everything I say as gospel.
First, there are two types of grounding. There is bonding which is essentially using wire to connect two different pieces of metal so they are at the same electrical potential. This is what you do when you put a wire from one side of a hinge to the other side to prevent a strong charge from arcing accross your hinge and welding the two halves together or to keep a metal fuel tank from arcing through the anodized and somewhat insulated AN fitting into the fuel tube it is connected to. These arcs can be caused from lightning or even just highly charged air near a thunderstorm. This can also cause crackeling in your radio even when there is not enough of an arc to weld the hinges together. It is critical to bond metal flight surfaces that are hinged together, but it is really not necessary on the small mass of metal on the hinges of a fiberglass plane. Bonding metal fuel tanks and lines though is a must. The other type of grounding is RF grounding. This is done so high frequency radio waves have a path to ground. It both gives noise sources like your strobe power supply a path to ground and it also gives your radios their necessary ground plane. On a fiberglass boat with a sideband radio you want as much metal connected to your ground plane as possible. You connect the ground stud on the antenna tuner and the ground stud on the radio to the engine, metal thru hull fittings, and as much other metal as you can. You also run 20-50' of ground strap or copper screen around in the bottom of the boat when there isn't a lot of metal to connect to. On a KR you want to run ground strap to the ground studs on the radios, the case of the strobe power supply, the engine, engine mount, stainless firewall, and whatever else you can within reason. One thing that is important in your RF ground is that you should use copper strap if you can instead of wire. There is something called skin effect which caused higher frequency RF to travel only on the outer surface of the conductor instead of through the center so you really want a concuctor with a lot of outside surface area, not just a big gauge round wire. On boats you use 2" copper strap that is about .030" thick. For a KR you should look for copper tape about 3/4" wide. My KR has a very effective RF ground that the original builder put in. There are three pieces of 3/4" wide thin copper tape running along the bottom of the fusalage forward to aft. There is also copper tape under the glass in the wings connecting to the wing attach fittings. I believe there is even some connecting to the elevator and rudder hinges. The builder soldered pieces together where they connect and even went as far as to solder short wire leads to the straps with alligator clips on the ends to clip to the control cables. There are also pieces running off to all the aluminum pully attach fittings, etc. and connected to the fuel lines with hose clamps Mine may have been done a little on the overkill side, but I probably have a good three square feet of ground plane in the copper strap alone and several more in everything else that is connected to it and the entire weight of all the copper tape, leads, etc. is well under a pound. One other thing about RF grounding is that it is sometimes more black magic instead of science. Sometimes you can get radio interference from something that should be connected to the ground plane that isn't and sometimes you can clear up interference from disconnecting something from the ground plane that you think should be connected. Good luck. -----Original Message----- From: Ross Youngblood <ross...@operamail.com> Sent: Sep 24, 2003 8:51 PM To: rfreiber...@swfla.rr.com, KR builders and pilots <kr...@mylist.net> Subject: RE: KR>Ground / Earth Wiring/ Stall Warning Well, I guess I should have prefaced my post with: "I was thinking about grounding my wing attach fittings." The idea was to run braid to the FWD fittings only so it would serve as a ground point. Then I don't have to run a third wire all the way back from wingtip lights fueltank etc to the firewall as any connection could pick up ground at the attach fitting. The main reason I had the idea as there was a bolt hole there already, and it's easy to add a star washer and a couple of wires. I should have also added that you probably want a seperate wire to connect the outer and inner fittings together, as if you rely on the bolts to give you good contact, you could have problems... i.e. radio noise, bad connections, hard to track down etc etc. That was when I was concerned about having a ground path for the fuel tanks to prevent static buildup. I'm relying on my grounded fuel sender to do this now. So, simply grounding the wing attach fittings is not a great idea in itself, but if you want to use the wing attach fitting on the removable wing as a ground point, it's an idea. -- Ross ----- Original Message ----- From: "Ron Freiberger" <rfreiber...@swfla.rr.com> List-Post: krnet@list.krnet.org Date: Tue, 23 Sep 2003 19:13:07 -0500 To: "KR builders and pilots" <kr...@mylist.net> Subject: RE: KR>Ground / Earth Wiring/ Stall Warning > Ross said, > I would recommend > running a 1/4" ground unshielded braid aft to the elev horn > mount, and mount it there. I would also consider running a > braid to the wing attach fittings, but I haven't done that. > > What possible electrical reason would you have for doing that? > > Ron Freiberger > mailto: rfreiber...@swfla.rr.com > > > > > _______________________________________________ > see KRnet list details at http://www.krnet.org/instructions.html -- ___________________________________________________ OperaMail free e-mail - http://www.operamail.com OperaMail Premium - 28MB, POP3, more! US$29.99/year Powered by Outblaze _______________________________________________ see KRnet list details at http://www.krnet.org/instructions.html
