Date: Tue, 17 Oct 1995 12:52:46 -0600 From: reavesga@iamerica.net (Geroge Reaves) Subject: Static Electricity Hello I am curioius if I should be worried about static electricity on my Cozy. I want to set it up for full IFR as well as how about the gas cap and static disipation. FAR 23.954 address this for certified aircraft. Any help/suggestions will be appreciated. George Reaves Structural Engineer Kestrel Aircraft Company From: Marc J. Zeitlin Subject: Static Electricity Date: Wed, 18 Oct 95 9:17:32 EDT George Reaves writes: > I am curioius if I should be worried about static electricity on my >Cozy. I want to set it up for full IFR.......... There was a discussion about this topic on rec.aviation.homebuilt a few months ago. There didn't seem to be any consensus on whether composite planes had any major problem with static. People seemed to state that if you PLAN on flying in known T-storm conditions, you might want to bury a metal ground plane under the skin of your bird everywhere (of course, this negates the possibility of having antennae inside) and hook up your electrical system ground to that. On the other hand, some people also stated that if you were going to do this (fly in or near T-storms), you were an idiot, and had bigger problems than static. There have been cases of composite planes having MAJOR static buildup to the point where the pilot could not touch the radios or he would get major shocks. It was stated pretty categorically that you could have a full IFR composite aircraft without having static buildup avoidance - just don't fly near T-storms. If anyone else has recommendations and/or more info, I think we'd all like to hear it. >.................. as well as how about the gas cap and >static disipation. The COZY plans and Newsletters call for static dissapative chains connected to the gas cap which hang down into the gasoline. Nat makes the assumption that you WILL connect the grounding clip to the gas cap when you refuel. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 18 Oct 95 09:20:51 EST From: "Wilhelmson, Jack" Encoding: 10 Text Subject: Re: Static Electricity There are several ways to insure that static electricity is dissapated when fueling. The proven gas cap grounding method is discussed in back issues of the COZY builders newsletter. It is a simple SS cable attached to the metal cap with a screw or rivet and a triangular aluminium sheet metal tab, that will fit through the cap opening, on the end of the cable. The Tab extends into the tank fuel while fueling and is in contact with the tank filler neck and the fueling nozzel. The normal method of grounding to some metal part is not effective on composite airplanes. Date: Wed, 18 Oct 95 13:49:20 EDT Subject: Re: Static Electricity George; > I had heard about static build up and the >problem with getting shocked by the radios. How >on earth would you put a ground plane through >out the aircraft. Would it be a mesh of sorts burried as >a ply in the layup or is it something else. is there a material >out there that I can put into the layup process..... I think that what was recommended was to put a crosshatch mesh of the same copper tape that we use for NAV and COM antennae under the outer skin of the fuselage. Tight, and interconnected. Of course, no one has actually done this and tested it, so we have no clue if it would actually have any effect. >...................DO I even >want to do this ?? My opinion, and it is ONLY an opinion, would be don't bother (I didn't). The incident with the Glasair occured quite close to known T-storm activity, so if you plan on avoiding it, there shouldn't be a problem. It would be a LOT of extra work, for a completely unknown and untested goal. -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 18 Oct 1995 12:38:37 -0600 From: reavesga@iamerica.net (Geroge Reaves) Subject: Re: Static Electricity Marc Thanks for the comment on the gas caps and on flying near T-Storms. I don't plan on going anywhere near T-Storms in my Cozy or anyother aircraft for that fact as I agree with statement about there being something elsewrong besides the aircraft if you are intenionally flying near and in T-Storms. I had heard about static build up and the problem with getting shocked by the radios. How on earth would you put a ground plane through out the aircraft. Would it be a mesh of sorts burried as a ply in the layup or is it something else. is there a material out there that I can put into the layup process..DO I even want to do this ?? Thanks George Reaves Structural Engineer Kestrel Aircraft Company Date: Fri, 20 Oct 1995 00:21:35 -0400 From: JIMWHI@aol.com Subject: Re: Static Electricity The ground strap connected to the fuel cap is a good idea, but what happens if a spark occurs when the fueler grounds to the cap? Especially that close to the fumes and fresh air. In addition to the fuel cap ground line mentioned in the newsletter and other e-mail responses, I also plan on installing a thin copper or aluminum strip inside surface each gas tank adjacent to the fuel site gauge. The strip can then be grounded to the fuel line which is conductive all the way back to the firewall. The fuel truck can connect the ground to the exhaust pipe instead of the filler cap. The copper/aluminum strap would be there to remove any static charge build-up that might occur on the surface of the fuel during refueling. Maybe this idea is way overkill, but the extra gram or two of weight seem worth the peace of mind. That's my 2 cents worth. Jim White Date: Fri, 20 Oct 95 08:45:38 EST From: "Wilhelmson, Jack" Encoding: 27 Text Subject: Re[2]: Static Electricity The method I use to elliminate a static discharge when fueling a composite aircraft is as follows: (These methods are my own and I have had no fueling fires in over ten years of flying composites, however, they are not offered as a safety tip only not as fool proof method). 1. Always fuel your own aircraft. 2. grasp the end of the fuel nozzel with your hand and rest the lower part of your hand on the strake at the leading edge. (FAR FROM FUEL VAPORS). 3. slide your hand with the fuel nozzel over to the filler neck and release your grasp lightly to let it slide down into the tank. 4. Always carry a small CO2 or Halon(If you can still find one) fire extinguisher in your plane and keep it handy during fueling. This method allows a static buildup to bleed off through your hand. Skin resistance is fairly high but it will elliminate any chance of a spark. The other precaution is push the nozzel into the tank far enough so that the fuel in the tank is in contact with the metal nozzel while fueling. These methods work with or without grounding straps. Date: Mon, 13 Nov 1995 22:11:21 -0700 From: psalm@axxis.com (Peter Salm) Subject: Lighting vs Composite Materials I don't know if this topic has been addressed in past letters. It seems if I miss reading the mail for two nights, it takes four nights to get caught up again. A few nights back I watched a Nova special on lightning. It appears that lightining and non-conductive composite materials don't mix well. Let me state right up front that I have no intension of flying near any kind of weather which will transform my plane back to its original condition (lots of foam and fiberglass pieces). The first time I heard about this issue, was in the AOPA artical about the Cozy (DEC 1994)"...lightning strike concerns aside, it ought to make a fine instrument platform." I asked Nat about that, and he indicated he had only heard of one incident in a Long Easy, and the pilot landed safely. A couple of months later, AOPA did a lengthy artical about a lightning-proof Glasair, which involved putting a conductive layer (I think it was copper mesh) under the skin of the plane. This NOVA special showed the composite nose section of a Lear Jet, after it had been zapped by labratory induced lighting. It did not look to good. It also showed some of the things they were experimenting with, like copper strips attached to the skin, etc. Does anybody know of other incidents involving lighting and composite aircraft. Should I be concerned about such a rare occurence, and should I consider some kind of safety measure while building. I just thought I would ask for some other input. Peter Salm From: Marc J. Zeitlin Subject: Lightning vs. Composite Materials Date: Tue, 14 Nov 95 11:08:25 EST Peter Salm writes: >.... A few nights back I watched a Nova special on lightning. It >appears that lightining and non-conductive composite materials don't mix >well. Let me state right up front that I have no intension of flying near >any kind of weather which will transform my plane back to its original >condition (lots of foam and fiberglass pieces)...... >...... Does anybody know of other incidents >involving lighting and composite aircraft. Should I be concerned about such >a rare occurence, and should I consider some kind of safety measure while >building. I just thought I would ask for some other input. We did have a short discussion about this a while back - those comments are on the "mailing list" web page under the topic "stat_elect". There were no other known incidents of composite planes flying in lightning, and the rec.aviation.homebuilt concensus was "stay away and you'll be fine - the protection scheme may or may not work, and it's not worth the effort because you're an idiot to fly in or near lightning anyway". YMMV (Your Mileage May Vary). -- Marc J. Zeitlin Email: marcz@an.hp.com Date: Wed, 15 Nov 1995 14:50:10 -0500 From: JHocut@aol.com Subject: Re: Lighting vs Composite Materials My 2 cents worth: I was at the forum at OSH a couple of years ago where they discussed the lightning hardened Glassair. What I got from that in regards to the Cozy is that it would be a MAJOR task to get anywhere near the protection that they achieved with the test Glassair. (Major $$$ too.) (I was really interested in this because I intend to outfit my plane for hard IFR and put it to use - I just hope the pilot will be up to the task!) My solution to lightning protection: a Stormscope and enough sense not to get anywhere near a thunderstorm, and at a fraction of the cost of lightning hardening a composite airplane. Jim Hocut jhocut@aol.com Date: Thu, 16 Nov 1995 16:47:58 -0800 From: ljansch@ix.netcom.com (Larry Jansch) Subject: Fwd: Lightning vs. Composite Materials >I have no intention of flying near any kind of weather which will >transform my plane back to its original condition (lots of foam and >fiberglass pieces)...... You really don't have to. In FLYING a bunch of months ago (last year?), they told the tale of some bizjet which descended through a light layer of ice crystals ... and built up a healthy charge in the process. -*KAPOW*- Then they went on to tell how the flight crew managed to get their aircraft under control. I don't have the physics background, but does anyone know if static discharge wicks would work on a composite structure? I've seen them on MD-11 empennages, which are skinned in composite materials, but I suspect the wicks are connected to the metal skeleton. -Larry Still in Chapter 4 Date: Fri, 17 Nov 1995 00:15:06 -0800 From: stetson@speed.net Subject: Re: Lighting vs Composite Materials (1 of 2) (long) On Mon, 13 Nov 1995, psalm@axxis.com (Peter Salm) wrote: >A few nights back I watched a Nova special on lightning. It >appears that lightining and non-conductive composite materials don't mix >well. Should I be concerned about such >a rare occurence, and should I consider some kind of safety measure while >building. I just thought I would ask for some other input. > Some years back there were some interesting articles in Rutan's CP's about this subject. The first is given below. Because of length, the others are given in a following post. They're long, and I think there's some limit to the length of an email message. Hope this works! Stet ------------------------------------------- **From CP44-3** LIGHTNING STRIKES ON FIBERGLASS AIRCRAFT We recently received information from NASA and from Andy Plummer of Lightning Technologies Inc, a recognized expert in this field, regarding lightning strikes on fiberglass aircraft. At this point in time there is not one single documented case of a fiberglass sailplane being struck by lightning. This is surprising, especially in Europe, where sailplanes do fly in the clouds. There is no documented evidence of any EZ or composite type having been struck and damaged. There is however, one documented case of an all wood sailplane which was struck, with catastrophic results. There are many cases of radomes, glass tail fins, etc. on airlines being struck with damage from insignificant to quite considerable. The expert opinion from both NASA and Mr. Plummer, is that it could happen and if it did, it may be possible to suffer catastrophic damage. Mr. Plummer states, "I am firmly convinced that fiberglass aircraft are just as likely to receive a lightning strike as a metal aircraft of the same size". The consensus of opinion is to stay well away from thunderstorms or cloud formations that may generate lightning. **From CP53-9&10** The following three letters are concerning a lightning strike on a Long-EZ flown by Dick Kreidel. We certainly thank Dick for taking the time to write the account which Burt sent to Andy Plummer for his comments. Mr. Plummer is one of this countries leading authorities on lightning strikes and his letter is, also, reproduced here for all of us to read and inwardly digest. Pay attention, guys, our EZs are not indestructible, although many of us fly them as though they were. "I deliberated for a long time whether to publish this account of poor judgement and foolish mistakes. When I read it now, on the ground, three months later, the faulty reasoning is easy to see. But I assure you, that the decisions and events on May 23rd were made to the best of my ability and skills. My hope is that someone will benefit from my errors. It is a fine line between being around to tell a story and not being around. This account was originally sent to RAF for their comments. Burt passed it on to Andy Plummer of Lightning Technologies who is reputed to be the foremost lightning expert. Mr.Plummer's comments follows my tale...... I departed New Orleans Lakefront Airport IFR to El Paso at approximately 9:30 a.m. local on Sunday, May 23rd. I had received a thorough weather briefing from Flight Service only 20 minutes earlier and they indicated that westbound I shouldn't have much problems; rain showers and multiple cloud layers with tops at 14,000' to 16,000' MSL with a thin cirrus layer at 25,000'. Live Radar and FSS painted a line of thunderstorms about 20 miles south but it probably wouldn't arrive at Lakefront for at least an hour. I was cleared to 16,000' and had gone through multiple layers of cloud and picked up some light clear ice after a climb through 12,000'. I requested from ATC to hold at 14,000' for a while since I was between layers and the next ceiling didn't look as thin as advertised. The OAT at 14,000' was +1 degree C. I flew through some heavy rain and more ice accumulated on the plane, especially the canard, elevators and vortilons. The wing did not appear to have much ice on it and I could not see any on the winglets or the intersection between the wing and winglets. Indicated airspeed at 2400 RPM was 122 KIAS. The ice on the canard covered about 20-25 percent of the chord with some "streamers" that went back to perhaps to 50 percent chord line. Ice formed below the trailing edge of the elevator about 1/8" thick with a uniform spanwise distribution. The ice on the canard was definitely clear ice but what was below the trailing edge of the elevator looked more like mixed or rime ice. The elevator position was about 5/16"-3/8" T.E. down. The airplane was very controllable with good elevator responsiveness. I could have easily climbed if I had wanted to so I was not overly concerned. ATC was giving me radar vectors to stay clear of any CB's but indicated that contrary to my preflight weather briefing, the "weather west of New Orleans is really wicked with the big boys having trouble going through!" Center advised that the only way they felt would be O.K. would be to deviate approximately 60 nm due North - obviously I followed their recommendation. After a few minutes I was again in cloud and it became increasingly difficult to hear radio transmissions - static was all that came through the headset. I started receiving small electrical shocks from the roll trim lever through my jeans and shocks from the microphone to my lips. I became aware of the transparent blue glow that was on the nose and canard. I say blue but somehow it seemed blue with a pink tinge. The color was similar to the bright blue from a gas welders flame. This halo was about one chord width above the canard and seemed to "move" - it is very difficult to describe in words. I was now getting shocked through the speed brake handle and from the rudder pedals to my ankles (my feet were in the relaxed position forward of the pedals). The B&D tachometer was bouncing erratically from 500 RPM to full scale and both Nav CDI displays were swinging from stop to stop. The electric engine instruments were also useless - I didn't notice what the wet compass was doing. Here I was: IFR conditions, icing, no communication or navigation, thunderstorms and weird light. So far the ride was smooth with no rain or hail in the cloud - the cloud was not a dark, heavy one. The blue (pink) glow increased in intensity and its movement was more rapid. I am not sure but I believe that the blue glow was now inside the cockpit between my face and the instrument panel, but I could still easily read the gages; it was right out of the Twilight Zone. I saw a bright flash way ahead of me that seemed to go from left to right that really lit up the cloud I was in; I assumed that it was cloud to cloud lightning and that I was definitely in deep grease! The com was still all static and calls to center were unanswered (or perhaps unheard). I was so scared that I was sure that this would be the way it would all end and Kay (my wife) would really be pissed! I smelled a thick sweet odor, got one good shock from the microphone and then there was a tremendous flash of light and an incredibly loud "crack" - I felt it in my bones and chest as opposed to hearing it. I had been looking out at the right wing trying to figure out why the blue halo was not on the wings, only the canard, when the flash occurred. I was temporarily blinded so I removed my hand from the stick hoping I wouldn't enter a spiral dive. When I could see again (10-15 seconds), to my amazement 1) I was still alive and 2) the plane was still level at 14,000' on my last assigned heading of 060 degrees. The blue halo was gone and I heard a transmission on the com for a Delta jet. I called center to see if my radio was blown and they immediately answered my call! Apparently they had been trying to reach me to give me a new vector and immediately turned me to 330 degrees. The airplane was again between layers and the visibility was good, I could even see patches below. Everything appeared to be working O.K. but the plane still had a lot of ice on it and I didn't think I was in any mental state to fly an approach. The airspeed now read less the 50 knots so I knew that the pitot tube had iced over. The weather seemed to be improving rapidly with a broken layer above and below with some beautiful blue sky far in the distance. Since the plane would easily climb with full power and the remaining aft stick I saw no reason to descend and kill myself making a lousy IFR approach after all of this! I then saw several dark patches on the wing and winglet leading edges that upon later inspection were areas where only the glass skin remained. In about 20 minutes all of the ice melted and the elevator position returned to 1/16" T.E. up and the airspeed increased to 140 KIAS at the same power setting of 2400 RPM. The flight continued normally in IFR and I landed at El Paso International four hours later. So what is there to learn from this unwanted experience? Probably several things. First, that the invincibility I felt in B888EZ contributed to my cavalier attitude in flying in bad weather - this certainly was not the "California IFR" that I was used to. After nearly 1100 hours of flying in a plastic cocoon, I had developed a false sense of immortality - after all, the EZ had gotten me through some tough situations before. Also, I learned to never, ever trust ATC and/or FSS - the pilot must make his own decisions and evaluations on when to commence or terminate a flight. Another significant revelation is that although the Long-EZ is a great plane and can leap tall buildings with a single bound, it is not suited for hard IFR flights with embedded thunderstorms. I consider myself extremely lucky to have survived this flight - my skill and judgment (or more correctly - lack of both) hopefully will serve me better in the future. Dick Kreidel" **From CP44-3** LIGHTNING TECHNOLOGIES, INC., 10 Downing Parkway, Pittsfield, Massachusetts 01201 (413)499-2135 22 July 1987 Subject: Long-EZ Lightning Strike Reference: Your Letter of 3 June 1987, Same Subject, with Dick Kriedel's Letter Attached Burt Rutan Scaled Composites, Inc. Hangar 78, Mojave Airport Mojave, CA 93501 Dear Burt: I have studied the interesting account of a lightning strike to a Long-EZ by Pilot Dick Kreidel, accompanying your letter of 3 June, and have the following comments: 1. After beginning the deviation North, the aircraft entered an electrically charged region, as indicated by the static in the communications system, "small electrical shocks" and "blue glow" (corona) on aircraft extremities. The electric shocks were due to electric field penetration of the non-conductive fiberglass airframe. The erratic behavior of the instruments was also due to electric field interaction with the interconnecting wiring. It is very likely the the corona was indeed occurring inside the cockpit as Mr. Kreidel suspected. 2. The synoptic weather conditions reported by the pilot are very characteristic of those reported by other operators when lightning strikes have occurred (~14,000 ft; icing, precipitation, within a cloud, OAT +/- 5 degrees of freezing). Apparently the aircraft was near embedded thunderstorm cells, though lightning strikes have been known to originate in "layered" clouds as well as CB clouds. 3. The "flash of light" and "loud crack" indicate a lightning strike, although evidently one of mild intensity as indicated by the comparatively minor effects on the aircraft. At 14,000 ft. it is likely that the aircraft encountered a branch of a flash, rather than the main channel of a cloud-to-earth flash; as illustrated in the following sketch. **SKETCH OMITTED** 4. The electric currents in a branch (of which there are a lot in a typical flash structure) are usually much less than that in the main channel. Even so, the flash and noise can be frightening if experienced close at hand. 5. Apparently the lightning current entered one wing tip (take your pick) and exited from the other, being conducted by internal metal conductors between. The amount of damage to the fiberglass and foam structures indicates a very mild strike - perhaps 5 kiloamperes or less (Part 23 rules require an airframe to tolerate 200 kiloamperes). Comments 1. Pilot Kreidel was lucky! A more severe strike may well have caused major structural damage and lethal voltage difference among metal objects in the cockpit (column, pedals, headphones, etc.) as well as severe damage to internal electrical conductors such as control cables, hinges, bearings, rods, electrical wiring, etc. These voltages and currents can be far in excess of fatal levels. Electric fields and lightning strikes themselves will directly penetrate unprotected fiberglass structures, attracted by metal objects within - not matter how small. 2. This is another example of the fact that ATC cannot be relied upon to vector an aircraft safely around- and clear of - hazardous thunderstorms. Controllers are not provided with sufficient (and timely) information for this purpose. Even though avoiding areas of heavy precipitation the aircraft ran into an electrically active region. 3. This incident is not a good example of what would occur to a Long-EZ in a lightning strike. A "full threat" stroke would likely have ripped a hole a foot in diameter through the composite and vaporized small diameter control cables and interconnecting wiring. The accompanying shock waves would have caused extensive internal damage, delamination, etc. I doubt very much whether the aircraft or pilot could have survived such a strike. Recommendation 1. Continue to warn pilots of this class of aircraft to stay VFR and avoid "weather" clouds, precipitation and icing within 5 degrees of the freezing level should especially be avoided. 2. This Long-EZ should be thoroughly inspected to be sure that there has not been damage to any internal metal parts. All internal parts should be inspected. It is quite probable, for example, that this strike burned some strands of control cables, electrical wires, etc. Thank you for sharing this interesting account with me. Please give me a call if you have any further questions. Yours truly, J.A. Plumer, President Lightning Technologies, Inc. **From CP79-9&10** LIGHTNING STRIKE! Long-EZ builder/flyer, Dan Worley, sent in a couple of photos and a report of a lightning strike. **PHOTOGRAPHS OMITTED** His Long-EZ, N63EZ, was parked, nose down, at his local airport within 50 feet of other airplanes and a metal hangar during a storm. As you can see from the photograph, the lightning vaporized the copper tape comm antenna under the skin of the left winglet and, in doing so, melted the blue foam core fully 2" wide and through to the outboard skin. The pressure of expanding gasses literally blew the inboard skin off the foam core and split the skin for almost 30". The rudder itself was undamaged and the structural attachment of the winglet to the wing was intact. In addition to the above damage, his nav/comm was burned out, a handheld wired into the airplane was destroyed, the voltage regulator, intercom and strobe power supply were burned up, a digital CHT monitor, a digital fuel flow meter and bus voltmeter were destroyed. One co-ax antenna cable was burned. No other wiring was damaged. The lightning entered at the NG-3/NG-4 nose gear brackets, burning a 2" hole in the nose gear fairing, then ran around burning out the various electronic items and, finally, traveling outboard along the antenna co-ax and exiting from the tip of the left winglet. This is what we are told probably happened. Andy Plumber is a lightning expert and Burt has talked to him about this incident. It is Andy's opinion that this was a very tiny lightning strike! He also informed us that had this strike occurred in flight that damage most probably would have been less, not more! He is absolutely adamant that no unprotected composite aircraft should fly within 50 miles of a thunderstorm! We have a friend who works on a fleet of 4 C-130 aircraft and he tells us that at least one of these airplanes experiences a lightning strike on an average of once a month! Damage is usually small but occasionally results in an antenna being blown off the aircraft! There is even a report circulating that the recent loss of a similar C-130 (not one of his) was caused by a lightning strike which hit a fuel tank blowing the wing in half! Lightning is not to be taken lightly, but for those who can afford it, there is a full, anti-lightning treatment available as written up in Sport Aviation on a Glasair III. A metal screen was bonded to every square inch of the airplane then it was struck by an artificial lightning bolt. There was some damage but mostly cosmetic. I cannot find the article right now but it is an expensive procedure and not something the average homebuilder would normally opt for. This article is reproduced here simply to let all composite flyers know that flying close to thunderstorms could, quite literally, ruin your day! Stay clear of them, fly well around them, heck, that's the advantage of our canard pushers, we can fly around this kind of hazard with the excellent range we have. Fly safe and report any incidents to RAF so we can keep everyone informed. From: Sid Lloyd "'Larry Jansch'" Subject: RE: Lightning vs. Composite Materials Date: Tue, 21 Nov 1995 08:20:02 -0600 ---------- From: Larry Jansch[SMTP:ljansch@ix.netcom.com] Sent: Thursday, November 16, 1995 6:48 PM Subject: Fwd: Lightning vs. Composite Materials >I don't have the physics background, but does anyone know if static >discharge wicks would work on a composite structure? I've seen them on >MD-11 empennages, which are skinned in composite materials, but I >suspect the wicks are connected to the metal skeleton. The following is from Bill Blatt, my father-in-law, who was on the team that developed the static wick system in the '40s. They used to fly a B-17 through any thunderstorms they could find to test it. "If the surface of the airplane is electrically non conducting, the local areas, when flying through precipitation, may build up a charge that will not communicate with other areas of the airplane; this is different than an airplane made of aluminum alloy. The effect will be somewhat like the charge on a comb as a result of running it through your hair, or like trying to get rid of the cellophane cover that's so hard to remove from a new CD, audio cassette, or a box of new software. The charge just stays there until it naturally dissipatges through moist air or contact with an oppositely charged body. An airplane made of a conducting surface will tend to have the charge migrate to another area on the airplane that has a lesser charge, or an area that "sees" an outside region of opposite charge such as a charged cloud. The wick dischargers on conventional airplanes permit the dissipation of the charge in such a manner that it does not interfere with radio communication. Hanging a wick discharge from the wingtips of a fiberglass structure doesn't make much sense." Date: Tue, 21 Nov 1995 09:07:57 -0800 From: ljansch@ix.netcom.com (Larry Jansch) Subject: Fwd: RE: Lightning vs. Composite Materials The charge just stays there until it naturally dissipatges through moist air or contact with an oppositely charged body. An airplane made of a conducting surface will tend to have the charge migrate to another area on the airplane that has a lesser charge, or an area that "sees" an outside region of opposite charge such as a charged cloud. Thanks. It sounds like a composite airframe would not conduct enough current to do much damage. What about installing (at great weight and expense, no doubt) a network of heavy gauge cable beneath the skin to conduct any lightning away from the occupants, fuel tanks, and engine? In effect, would this give the aircraft the same lightning resistance (or lack thereof) of a tube-and-fabric aircraft? -Larry Date: Tue, 21 Nov 1995 13:27:53 -0500 From: Phillip.Johnson@Lockheed.on.ca (Phillip Johnson) Subject: RE: Lightning vs. Composite Materials > Thanks. It sounds like a composite airframe would not conduct > enough current to do much damage. What about installing (at great > weight and expense, no doubt) a network of heavy gauge cable > beneath the skin to conduct any lightning away from the occupants, > fuel tanks, and engine? You could make the aeroplane out of carbon fibre at great expense (Carbon fibre is a good conductor) but with a good weight saving :-). Phillip Johnson Date: Tue, 21 Nov 1995 17:19:48 -0500 From: "Symetrics Industries Inc." Subject: RE: Lightning vs. Composite Materials > It sounds like a composite airframe would not conduct enough >current to do much damage. It is the fact that composites do NOT conduct a current that causes the problems. The most dramtic example of a static discharge is lightning, in which thousands of amperes of current flow. With a metal airplane, the any static charge is equally distributed across the airplane. When it is grounded for fueling, all of the charge can be easily and quickly discharged from one point. With a composite airframe, one cannot get all parts of the plane grounded as the static currents cannot move very well. Thus, grounding the airplane will only result in a relatively small area being neutralized. Eventually the charges will dissipate, but it may take a long time. The human body is not a good conductor of electricity, but walk on carpet in dry weather and touch something metalic and watch the spark! Now imagine doing this with a few drops of gasoline on your fingertip! Now imagine fueling your charged-up composite airplane! I would think that there would be a way of determining the degree of charge on a composite airplane. Electronics manufacturers make use of static meters to measure the amount of static electricity on an object. Perhaps something like this would be useful -- before refueling, just whip out your static meter and instantly you can tell if the airplane is charged or not. If it is, just wait a while for it to dissipate before fueling. I think thesemeters can be had for no more than a couple hundred dollars, if that much. I can research this if anyone has an interest. >What about installing (at great weight and >expense, no doubt) a network of heavy gauge cable beneath the skin to >conduct any lightning away from the occupants, fuel tanks, and engine? I doubt that it would work. If your plane gets hit by lightning, the currents might very well melt the wiring, perhaps causing an explosion from the out gassing, that might rip apart the airplane. Besides, if the metal is on the underside of the airplane, the lightning would go right through the top to get to it. Seems you would need a Faraday enclosure, where the entire plane is covered with metal so the currents would be routed around the occupants. Again, unless heavy enough, the metal could melt and blow apart the composite frame. With that much metal, you might as well build a metal airplane. Perhaps a thin copper mesh or series of interconnected thin guage copper wire embedded into the composite skin, all connected to static dissipators on the trailing edges of the wings and tail, as well as to a central grounding point (to ground the aircraft for fueling) would be of some advantage. Any localized static buildups might be dissipated by such an arrangement. If it would be effective, however, I do not know. How well the charges would flow in the composite skin to these metalic areas might make a good Ph.D. dissertation. I do know that two conductors seperated by a non-conductor forms a capacitors, which stores a static charge, and this sounds close to being a capacitor. As someone else mentioned, carbon fiber might be a good alternative to copper, especially if it could be substituted for some of the glass cloth, as charge could flow through it. We should all try to find out about any static related accidents of composite aircraft and learn from them. As there appear to be few such accidents, the logic of adding 100 pounds of copper in an attempt to reduce static problems is questionable. BTW, the problems with my double postings to this group has not been resolved. Thus, if you see a repeat of this message, please ignore it. I regret any inconveniences this may be causing to any of you. Anyway, Happy Thanksgiving. ______________________________________________________ Jeffrey K. Rosson, P.E., KE4KZ Ph. 407-254-1500 Director of Engineering Fax: 407-259-4122 "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position that we are now in.'" Mr. Spock in "Tomorrow Is Yesterday" Date: Tue, 21 Nov 1995 22:34:18 -0700 From: chapman@ditell.com (Dave Chapman) Subject: RE: Lightning vs. Composite Materials >Jeffrey K. Rosson writes; >something like this would be useful -- before refueling, just whip out your >static meter and instantly you can tell if the airplane is charged or not. >If it is, just wait a while for it to dissipate before fueling. I realize that this thread is actually about lightning and our plastic airplanes but static electricity can happen and be a problem even on the ground. Several years ago Nat published an advisory in the newsletter directing builders to place a chain device in the fuel tanks to avoid static electric problems that had evidently caused a Long Eze to have a fuel fire during refueling. As I'm not quite that far yet (my tanks have yet to smell fuel!) I haven't gone back and done the suggested mod but it seemed to provide a method to ground the fuel in the tank prior to fueling. After a little research, the info is in newsletter #22 on page 2. Dave Chapman (chapman@ditell.com) "Man's flight through life USHGA #5742 is sustained by the power Park City, Utah of his knowledge" (801) 647-0319 Cozy 3 on gear, with the engine on, in other words, 80% done and 80% to go... ***************************************************************************** Wed, 22 Nov 1995 14:42:25 +1000 Date: Wed, 22 Nov 1995 14:33:27 +0200 From: parkyn@citr.uq.oz.au (Nick Parkyn) Subject: Lightning vs. Composite Materials In his email Jeffrey Rosson wrote: >As someone else mentioned, carbon fiber might be a good alternative to copper. Carbon fibre skinned aircraft must still be protected with copper mesh in the laminate. Because of electrolytic action, carbon fibre laminates need copper mesh and glass fibre composites can use aluminium mesh. There are other problems like antennae etc which can no longer be embedded in the structure without special provisions. The mesh would be very difficult to use in a moldless composite - you really need a female mold with vacuum bagging and pre-preg materials. Wet layup would fill the voids in the mesh further adding to the weight. Once lightning protection is complete you would still have to have it tested in the "lightning lab" to ensure that the design works for that particular aircraft! Lightning protected versions of the high-end kitplanes are being developed eg. Glasair III, Lancair IV. Lancair IV is also being fitted with de-icing equipment. For others the best approach seems to be to fit a Stormscope and keep away. Nick #0018 Subject: Re: Lightning vs. Composite Materials Date: Wed, 22 Nov 1995 08:40:05 -0500 (EST) From: "Randy Smith" > > > It sounds like a composite airframe would not conduct enough > >current to do much damage. > > It is the fact that composites do NOT conduct a current that causes the > problems. The most dramtic example of a static discharge is lightning, in Would there be any benefit to making the epoxy conduvtive? Is it do-able? --* --- -* **-* *-** -*-- -* Crash Rescue Team 7 - Don't PANIC! _____|_____ AT&T Randy.Smith@ColumbiaSC.attgis.com -(X)- Global Support Center Voice 803-939-7648, V+ 633-7648 ___o/o\o___ West Columbia, SC 29170 "I am the way, the truth, and the life..." -JC (post.office MTA v1.9.1 ID# 0-11525) with SMTP id AAA353 for ; Sun, 17 Dec 1995 20:17:20 -0600 From: TODDC@why.net (TODDC) Subject: re: lightning versus composites Date: Sun, 17 Dec 1995 20:17:20 -0600 Just a thought. could you add the foil/wire mesh around, say a 1.5-2 ft dia, the fuel filler? and then ground it to the engine or wick. If The major concern is spark during refueling, and static charge will not readily move through a composite structure, why not ensure it doesn't happen where there will be fuel. Then just leave the rest of the fuse. alone. Is this a viable solution or am I barking up the wrong tree? also, we can make adhesive conductive (for a cost) I would think we could make epoxy conductive too. Finally, On tube and rag aircraft, we spray "silver",(dope with aluminum particls in suspension) to block out UV radiation. Could this provide enough conductivity to allow static elec. to disipate faster? If the structure cannot be made conductive, why not the paint? my $.06 :-) Todd C (post.office MTA v1.9.1 ID# 0-11525) with SMTP id AAA352 for ; Thu, 21 Dec 1995 21:49:33 -0600 From: TODDC@why.net (TODDC) Subject: re: lightning versus composites, again. Date: Thu, 21 Dec 1995 21:49:33 -0600 in reply to my own letter, i'v done some research (should have done that first :). At 08:17 PM 12/17/95 -0600, you wrote: >Just a thought. >could you add the foil/wire mesh around, say a 1.5-2 ft dia, the fuel >filler? and then ground it to the engine or wick. If The major concern is >spark during refueling, and static charge will not readily move through a >composite structure, why not ensure it doesn't happen where there will be >fuel. Then just leave the rest of the fuse. alone. Is this a viable >solution or am I barking up the wrong tree? does this sugestion even hold water? >also, we can make adhesive conductive (for a cost) I would think we could >make epoxy conductive too. Conductive adhesive is conductive, kinda. it seems the resistance is normally to much to allow low voltage electricity an easy way out. They make adhesive conductive by mixing in something conductive. Tradeoff is it gets proportionaly weeker as you add more conductor. >Finally, On tube and rag aircraft, we spray "silver",(dope with aluminum >particls in suspension) to block out UV radiation. Could this provide >enough conductivity to allow static elec. to disipate faster? If the >structure cannot be made conductive, why not the paint? I would think the same would be true about resistance being to high between particles of alluminum. Todd C Date: Fri, 22 Dec 1995 10:09:19 -0500 From: Jeff Rosson Subject: re: lightning versus composites, again. Hi, all, Thought that I would add my own thoughts to this recurring topic: >>could you add the foil/wire mesh around, say a 1.5-2 ft dia, the fuel >>filler? and then ground it to the engine or wick. If The major concern is >>spark during refueling, and static charge will not readily move through a >>composite structure, why not ensure it doesn't happen where there will be >>fuel. Then just leave the rest of the fuse. alone. Is this a viable >>solution or am I barking up the wrong tree? >does this sugestion even hold water? I think we are forgetting here that a "static" charge isn't necessarily non-moving. When a portion of a surface, i.e. a composite, become "charged", that charge will tend to spread out across the surface. So, the "static" charge actually moves, at least until it reaches an equilibrium of essentially equal charge across the entire surface. After that, there is no place else to go, so the charge then becomes "static". The charge will remain until it either dissipates or is discharged in some manner. For a metal airplane, if you ground one point of the airframe, all of the built-up charge can easily flow out. For a charged material which is not as good a conductor, it takes longer for this discharge to occur. For example, I build up a terrific static charge on my body here in the office as I walk about. The charge originates in my shoes and distributes itself across my body. When I touch something metallic (i.e. ground) with my fingertip, I can get a visible spark (and an ouch), as the "static" charge discharges itself. Now, what happens if I carry a metallic object in my hand and touch it to ground? I still get a spark, but it is between the two metallic objects so my fingertip is spared the pain A human body is a fair conductor of electricity, probably better than composites, in which the charge would be harder to move. However, whenever a charge gets built up, it must somehow dissipate itself. My little experiement shows that we can move the location of where the spark occurs, but that we cannot prevent it from occurring at all (without taking additional measures, anyway). Placing a metallic ring around the fuel filler will allow that area to assume ground potential when grounded. Any spark that results should occur at the ground attach point, well away from the fuel. The question remains as to what about the charge on the other 99.99% of the aircraft? Yes, the built-up static charge will tend to flow to ground through the metallic ring, but might there occur a spark between the ring/composite interface? If this occurs on the outside, it might not be significant, but what if it occurs on the inside, in the fuel tank itself? My own thoughts are that this all deserves some additional thought and study, and perhaps should even be implemented (I don't see how it can make anything worse), but that the techniques recommended by the designer and RAF still be followed. >>also, we can make adhesive conductive (for a cost) I would think we could >make epoxy conductive too. This is out of my area of knowledge. In our electronics assembly area, we use a conductive wax on the floors to help prevent static electricity buildup. It is expensive, but I suppose one could wax their airplanes with it and gain some added measure of safety. >>Finally, On tube and rag aircraft, we spray "silver",(dope with aluminum >>particls in suspension) to block out UV radiation. Could this provide >>enough conductivity to allow static elec. to disipate faster? If the >>structure cannot be made conductive, why not the paint? >I would think the same would be true about resistance being to high between >particles of alluminum. As I understand it, flakes of aluminum are mixed in with the paint to serve as "umbrellas", providing shade for the paint below it. In this case, each flake of metal would be surronded by fairly non-conductive paint, thus keeping the overall conductivity low. Special metallic paint, like the kind used to line some computer cases, might work, but the constant mechanical vibrations of an airplane might cause small cracks to develop that would destroy the conductivity. So, again, this might provide a margin of safety, but should not supplant the recommendations of the designer or RAF. This has been an interesting topic which, if nothing else, will cause my to check out my old Sears and Zemanski physic book tonight to see if I can gain any more insights. If so, I will post them. Otherwise, please note that I am not an expert on this subject, and my comments are given freely, which is exactly what they are worth. :-) Otherwise, Merry Christmas to all. Jeff ( maybe someday she will let me build ) Rosson ______________________________________________________ Jeffrey K. Rosson, P.E., KE4KZ Ph. 407-254-1500 Director of Engineering Fax: 407-259-4122 "Logically, it could work. Also, logically, there are a hundred variables, any one of which could put us in a worse position that we are now in.'" Mr. Spock in "Tomorrow Is Yesterday"