| Author | Message | ||
     John Harlow (Jharlow) |
The other day while flying in a light rain, I noticed that when I touched the radio I received a static shock. Are there any suggestions on how to discharge this to the air? Would static wicks do any good? I feel this may be what has caused my Garmin GNS 430 to loose the remote com transfer capability. The Garmin people have repaired the radio and I have checked out the circuits for this feature and found no stray voltages or other problems with my wiring. I feel it could be the static electricity that caused the transistor to fail in the radio. John | ||
| Bob Gisburne (Gisburne) |
John: I experience this quite frequently, as recently as today coming into San Diego through rain and some snow showers. It has gotten so severe that the VM1000 has gone off-line and resets itself. I've never had any damage to radios or anything else. I've tried several remedies, including static wicks, but to no avail. My theory is that there is no ground path given the composite nature of the airplane. I understand that the lightning protected Glasair III did not have this issue, but you may recall that this required a ground mesh imbeded in the fuselage/wing layups, all grounded to the electrical system. So, my solution has been to live with it, but NOT touch any metal during the flight through rain... I've had it JUMP from the control stick to my finger. Not much help, but comfirmation... Bob Gisburne N4382A | ||
| Anonymous |
John & Bob, I have flown my Express in rain, snow, mist, fog, ice (unexpected, not known icing) and solid clouds and haven't experienced the problem you are having. I have also shot approaches to 200' above minimums, all with no problems. My panel and airplane wiring was installed by Ted Gaston of Express. You might want to talk with him and find out what he did that is different from your airplane. Jim Butler | ||
| Tom R. Hutchison (Tomhutch) |
Is anyone bonding their control surface hinges electrically to ground, i.e. the engine block. A non-express composite builder recommended doing that. Also Bill Maddox of "speed brake fame" sells a static wick kit for composite AC that he says to bond together. See http://www.speedbrakes.com Tom | ||
| Wayne Norris |
Sure now all these type problems are cropping up as I get close to finishing my plane. I was wondering and looking into how these plastic planes faired in the weather flying. No one seemed to know and there appeared to be plenty of them flying, but are all those fancy radios just for show? Static buildup moves aft and discharges off the most rearward parts for the most part. Bonding the fixed surface to the control surface with a cable keeps the strong charges from welding your hinge pins together. Static wicks can help on carbon type skins but for our fiber glass it would be like wiring one insulator to another. current still won't flow through the whole thing. I plan to ground the radio rack to the battery/engine. FYI the worst static build up while flying will be where the OAT is Oc. and of coarse in precip. | ||
| Brian McKinney (Bmckinney) |
I still have my wings and fuse open. Any thought to glassing some sort of mesh to the inside of the surfaces & grounding that to eliminate the static? I'm sure it will take me at least a year or two (or three, etc.) to close them all, so I have lots of time to consider all options... | ||
| jharlow |
After some additional thought, it has occured to me that I have not grounded the radio rack to ground. My panel is constructed in three removable alum sections with each mounted to the common fiberglass panel.The VMS 1000 is in one section and has the DPU case grounded to the firewall and thus the engine and battery. The radio section is in a seperate sub-panel and the structure is not directly connected to ground. For beginners I plan to run a seperate gnd wire from this subsection to ground as well as my third section which has some misc gages and C/B's. Because of what Bob said about a discharge from the control stick I think I will also run a gnd wire from it also. What about running a wire from the battery ground to a static wick? John | ||
| Tom Hutchison (Admin) |
When I mentioned the static wick kit from Bill Maddox he had recommended bonding all the static wicks together with a electrical conductor (wire) and everything grounded to the engine. This was his recommendation for the Lancair ES which is simular to the Express. Tom BTW, in the April 2002 AOPA Pilot, there is an article about a school Lancair puts on for A&P's to learn how to repair composites. The author mentions they have a metal mesh imbedded in the wing skins and fuselage skins of the Lancair 300 & 400 for lightning protection. | ||
| wayne norris |
This is why it's an experimental, seeing that even the paid experts don't have any sure fire answers for us, I am going to tie all of my negatives together. From the engine,battery,instr panel, console and control rods back through a -16 cable and run that out the rear tail cone. I realize this will not get rid of the static build on the outside skin,(which is bad for RT and lightening) but may disapate the inside static you all are getting. | ||
| Reinhard Metz |
Similar to Jim Butler's comments, I have also flown through all kinds of precipitation under various conditions, and have had no problems whatsoever, no static discharges, radio malfunctions, or other electronics malfunctions. I have the VM1000, Garmin 530, King KX-155. In fact, I just flew back from Sun 'n Fun to Chicago, a 5.5 hour flight, about 4 of it solid IFR, mostly in clouds, with numerous periods of very heavy rain, passing build-ups and cells under ATC direction, verified by the Strike-Finder, and no problems. Touched stuff on the panel countless times. (Boy, it's sure nice to have "Otto" (STEC30) with you for this kind of flight!) The only anomallies I have are deflection of the SkySports fuel gages when transmitting (I would not recommend them - get the Vision Microsystems ones), and occasional ATC transponder complaints, but I got those with the Bonanza I had before as well. I made a concerted effort to tie all cockpit metal together with wire braid, including everything in the panel, control tubes, etc., but do not have any wicks. They would probably be a good idea to add. If anyone wants more details, or an electrical engineer's discussion of the theoretical aspects of it all, let me know. | ||
| kdennes |
Reinhard, I would be most interested in knowing more about the subject as we are at the stage of building where this would certainly come in handy. I wonder if you could explain what you did to "tie all cockpit metal together . . . etc." Kevin (from Downunder) | ||
| Rob Jordan |
Look at the different types of paint the builders are using you might find a pattern. Different paints conduct electricity where some are insulators. | ||
| Reinhard Metz |
Before writing the following, I did a bit of research to refresh my understanding of atmospheric electricity. In the process of doing so, my attitude about the subject changed significantly. Initially, I figured I would end up describing what I've done to my plane that might explain it's relative success in not experiencing any ill effects, either in radio reception or lack of sparks or static in numerous IFR experiences (as previously noted by both me and Jim Butler in his Express). But now, I have concluded that, relatively speaking, I have probably just been circumstantially lucky, and I believe the same is probably true for Jim. No matter how you slice it, atmospheric electricity can be dangerous to any small plane, the mechanisms involved increase the risk for glass planes, and it is extremely important for anyone flying one in IFR conditions to understand the risks and have some rules for themselves to minimize those risks. So, here goes: First, there is still significant controversy on the subject of lightning, static electricity, and interactions with airplanes, so what follows is not gospel, just my understanding of things. I've organized this into several topics: 1) ATMOSPHERIC ELECTRICITY AND CHARGE BUILD-UP ON AIRPLANES: Electric charge is the dissociation of electrons from atoms that would otherwise exhibit a neutral charge. The electrons have a negative charge, the atoms that lose electrons have a positive charge. An electric current is the flow of electrons. Materials can become charged, which means a net gain or loss of electrons relative to a neutral balance of charge. Metals and insulators can both get charged. The big difference between them is that charge can readily move in metal, and is relatively immobile in/on an insulator, such as the bulk of our airplanes. Charge is imparted to a material simply by friction - the charge rubs off or is transferred by impact or proximity. That means charge can accumulate on an airplane merely by passage through the air. Flight through rain increases the charge accumulation, as there is more material contact, and for the most part the rain is non-conductive. Furthermore, in the vicinity of, or in storms, the air has more loose charge as charged particles or charged raindrops, and thus has more ability to impart charge. As charge builds up on an object, a voltage potential is generated that increases with the amount of charge, and is also inversely related to the effective "capacitance" the object has. The lower the capacitance, the higher the voltage for a given amount of charge. On a metal airplane, this voltage potential is the same everywhere on the airplane, because the plane conducts electricity. An a glass plane, the voltage will vary. The charge in turn generates an electric field, whose intensity is greatest at the areas of highest curvature, i.e. the "pointy" areas, like prop tips, trailing edges, etc. On the other side of the scale is the dissipation of charge. An object will lose charge in accordance to the conductive mechanisms around it to conduct the charge away. In general, the charge "wants" to get away, as like charges repel, and unlike charges attract. At lower altitudes, the air is slightly conductive, and an equilibrium of charging and leakage of the charge back to the air will under most conditions occur at a voltage build-up level that is relatively low. At higher altitudes, say above 15or 18K, the air is colder and drier, and static build-up can be a problem even in clear air. 2) RADIO INTERFERENCE DUE TO CHARGE BUILD-UP: When the normal conductive dissipation mechanisms are insufficient, the voltage will build up to a point where ionization of the surrounding air occurs, and charge dissipation occurs by a break-down mechanism, i.e. a spark. This can in turn range from an even, glowing, kind of discharge, to sudden, rapid, and repetitive spark discharges. In either case, ionizing discharges generate electrical noise, that due to the proximity to the radios, overloads their input stages relative to the low level of the received signals, and trashes your reception. This can take the form of anything from crackling, to a buzzing, motor-boating noise, to complete hiss or white noise. This is generally known as P-static. The standard way to reduce charge build-up and radio interference on metal planes is with static wicks. A static wick is a bundle of very fine conductors, usually attached at a trailing wing edge near the tip. Since the field intensity increases with curvature, the very fine wire tips create very high local fields at the wick's end, allowing the charge to dissipate via many tiny discharges. This works well for metal planes. While there are those who have commercialized wick products for composite planes, it is doubtful they are very useful, given the lack of conductivity of a composite plane. There's no way for the charge to get to the wicks. Attaching them to metal parts or the ground structure may help some, but can't do anything for the charge on the surface of the composite structures, which ultimately still poses the possibility of damaging discharges under the appropriate conditions. 3) LIGHTNING: The other nasty manifestation of atmospheric electricity, particularly in storms, is obviously lightning. There are lots of ways to think about it: You'd like to avoid getting hit, and if you do, you'd like to minimize damage. A metal plane minimizes damage by conducting the lightning relatively well, mostly on the skin surface, away from internals and occupants. Any current that does finds alternate paths can do damage to wiring, control cables, etc., but generally that doesn't happen much. It depends on the magnitude of the strike. In a composite plane, a lightning strike will seek the metal paths available, and has several devastating damage mechanisms. They include blasting holes in the composite by vaporization of the resin, vaporizing control cables and wiring due to high current densities, minimally the welding of bearings or hinges in control structures, and potential electrocution of the inhabitants. The obvious conclusion is that the occurrence of a lightning strike in an unprotected composite airplane is to be avoided at all costs. The embedding of metal mesh in a composite is therefore primarily aimed at providing a safe path for conducting lightning currents in the event of a strike. It's not experientially clear, but from a theoretical point of view, when a plane becomes highly charged, it should increase it's attractiveness to a lightning strike, though strikes are so random that the magnitude of the increased probability may not be much. You just don't want to be in the wrong kind of place to begin with. 4) SO WHAT ACTUALLY HAPPENS WHEN AND WHERE AND WHAT DO YOU DO ABOUT IT? The first thing is thunderstorm and lightning avoidance, and the generally agreed distances are in the range of 25 miles minimum away from major cells and lines. I think a Strikefinder or Stormscope is essential. The second thing is that it has been generally observed that the occurrence of damaging static build-up is by far worst with precipitation and temperatures in the range of 0 +/- 5 deg. C (some say +/- 10), particularly mixed snow and rain. So those are conditions to avoid flying through. Third, you can help your radios and minimize the chance of internal sparks with a comprehensive grounding plan that ties major metal in the plane together. MY OVERALL CONCLUSION is that despite my lack of radio problems, I have probably just been lucky. None of the IFR ha been in mixed precip, and likely was in temps. above +5 deg. C. And I use my Strikefinder to confirm what ATC tells me. 5) NOW,HOW I DID GROUNDING: First, I defined a bus bar of 3/16" by 1" by about 12" copper, located at the bottom right of my instrument panel as the central ground. It is drilled and tapped with an array of holes, and terminates a couple dozen ground wires from various instruments, radios, auto pilot, etc. That includes the big ground coming through the firewall from the engine, which in turn also has a fat cable to the battery and firewall. Then, I basically tied the accessible metal pieces in the cockpit to ground as well. For example, there is a flexible braid from the rudder torque tubes to ground. The radio stack and panel metal plates also need to each be grounded. They need not have a separate wire - chaining is ok. The same goes for the elevator torque tubes and aileron push-pull tubes - I have a braid that picks them up near the center console. There are some minor pieces that end up floating, but are inaccessible, like the nuts inside the tie-down points. The purpose of all this is to bring the major metal pieces, especially those you can touch, to the same electrical potential, so no inter-metal sparking can occur. Additionally, to avoid you getting zapped, you would like your body to have a relatively high resistance, but nevertheless conducting path, to your airplane's ground structure. For the latter, I have done nothing deliberate. I have, however, never gotten zapped, not the least. Maybe it's sweating, most likely it is a combination of leather seats (not the greatest insulator) and a wood (slightly conducting) stick grip in my hand, the stick itself being grounded, keeping me at ground potential, at least for the rate of charge build-up I've been exposed to. So, folks, that's it! Another time I'll post a list of interesting subject-related URLs. Reinhard Metz | ||
| jharlow |
Reinhard, WOW!!! Thanks for the great research and your thoughts. I have gone thru my plane and attempted to make all metal areas to have the same potential. I also plan to install a static wick tied to the bat ground prior to my planned trip in June. John Harlow | ||
| Kevin Dennes |
Reinhard. I want to thank you for your wonderful contribution. Trying to work things out now from Downunder without any assistance from EAA is a real nightmare. My only real hope of finishing our aircraft is with the help of people like yourself. I have had 50 years as a pilot but have had exceptionally little to do with the "nuts and bolts" that make these flying machines work. I am most grateful for this forum, for without it I am afraid the project would never be completed. With best regards Kevin (from Downunder) | ||
| Reinhard Metz |
Folks, In addition to the above, here are some interesting URLs for more lightning/static reading: A frightening dialog on someone's actual experience: http://cozy.canard.com/mail_list/topics96/static.txt Static wicks (again, I have some doubts about their effectiveness on plastic planes): http://www.speedbrakes.com/static1.html A company that speializes in lightning: http://www.lightningtech.com There's also a fantastic article on fuel handling and static by the Cafe Foundation, entitled "Fuel Handling Safety". Don't have a URL, but you should be able to find it on their site. Item on atmospheric electricity: www.auf.asn.au/meteorology/section11.html Reinhard Metz | ||
| jharlow |
Greetings from Alaska, Well I have grounded most everything metal back to the A/C ground and am pleased to report that on my present trip from Florida to Anchorage I have experienced just about every kind of weather condition possible. Rain, Snow, fog, and a few days of sunny weather have not reproduced the static problem SOOOOOOOOOOO I hope my problem is solved. I hope to stop by the factory in Olympia on my return and fly down the west coast of the US. John Harlow |