St. Elmo's Fire
- Thread starter c172captain
- Start date
Orange Anchor
New Member
Nope..
The positive strikes are reportedly much more powerful than a negative strike and one composite glider in Germany was exploded by a positive strike. The pilots were both wearing chutes so survived but the airplane was destroyed.
I spoke with a number of labs about lightning and what is required to certify an airplane against lightning strikes. Many homebuilts, especially composites, have NO defense against a strike.
Best quote was, "Lightning is like a teen ager.. it wants to go where it wants to go and gets real angry when it can't. So, we just channel that energy. It gets real nasty when is stopped and tends to start eating things."
And it is not like you, the aviator, have a choice. As another guy told me, 'When you have particles rubbing up against each other in the air, it creates friction which creates charges. Those charges tend to separate and what is that? It's a battery. And when something provides the short between the positive and negative BAM!!!!"
http://www.weatherimagery.com/blog/positive-negative-lightning/
http://www.weatherimagery.com/blog/lightning-facts/
http://en.wikipedia.org/wiki/Lightning
(There is a corridor in Florida that is a virtual lighting alley. I think it is between Tampa and Orlando..LOTS of strikes)
Boris Badenov
This is no laughing matter.
Seen it a bunch in minor ways (temp gauge on a 210/baron, windshield wiper attachment on a mitsi). Only once have I had the whole windscreen and prop phenomenon, in the mitsi. And yes, I was somewhere that in retrospect I probably shouldn't have been, for the big one. The others were "in the vicinity" of bad weather, but not in "danger city". Never had a strike. I guess I'd rather be lucky than good.
Baronman
Well-Known Member
Yep..Seen it on the ERJ (it's pretty rare) descending in the teens in an area of rain (don't think I saw lighting that night).
It started with St. Elmos fire on the windscreen, then we started getting white flashes. Every 15 seconds or so we'd get a white flash but there was no noise associated with it. I do remember as well the smell of ozone and the feeling that the thrust levers were getting warm to the touch. Not just my hands holding them but they got noticebly warm. (Perhaps their resistance?). All this and a really chitty ride made for an unpleasant minute or two.
It started with St. Elmos fire on the windscreen, then we started getting white flashes. Every 15 seconds or so we'd get a white flash but there was no noise associated with it. I do remember as well the smell of ozone and the feeling that the thrust levers were getting warm to the touch. Not just my hands holding them but they got noticebly warm. (Perhaps their resistance?). All this and a really chitty ride made for an unpleasant minute or two.
jynxyjoe
Queso King
(By the way, that's "rocket alley". Home of junk science. Their stuff has little to do with aircraft because they are setting off their own strikes. Some say that is simular to aircraft except the people in aircraft cert biz)
You know what there is this guy who used to do certification of aircraft for lightning. He's actually on this forum, his name is Jynxyjoe. We oughta get him on here.
I'd sure like to know which lightning labs you spoke to.
That composite glider would have blown up just fine from the negative strike by the way. I don't know why you keep talking about the homebuilts, they are not required to get lightning cert because they are for Day VFR. However many homebuilders told me they could make their RV's and other flying death traps IFR certified. Always found that interesting, but the results are going to be the same. When we tested the one aircraft recently, for instance, I was able to put my fist through the hole we made.
The evidence to support the positive strike, or what we called the "granddaddy strike", have been shown to be much more intense than negatives. The data is also based on ground observations from the 1970's. It's not new. Although it would be news to me that negative strikes cause little damage while positive ones cause damage (what I was actually disagreeing with). That would be fantastic since 95% of naturally occuring strikes are negative. Also it'd mean that job I had for a few years was all irrelevant. Man what a hoax we were pulling hu?
Again, i need to say nope to what you said earlier. The positive ones have the potential to add more charge to an airframe. However if the airframe is all metal it is irrelevant. All composite structures have bits blown off them from either positive or negative strikes. The new buzz word in the industry is "sacrificial parts" in zone 3a-c.
Also, another problem with the channeling energy, if this is the same glider we used to talk about, was they thought a couple gauge pipe running through the glider was some sort of protection. The pipe they put in would have been crushed by the associated EMF caused by any strike. I don't remember if that was pointed to as a contributing cause.
Composites have a very hard time with lightning and metal frames do not (pos/neg). Basically you're flying around in a giant resistor. Even on metal frames it's not uncommon for the lighting to hop across the frame tens (sometimes 100) times. On a composite it'll hop a lot more times and build an incredible amount of heat. Enough to melt the glue... i mean apoxy... sorry carbon fiber nuts. I love talking to structural engineers... they think composite structures have good bonding, electrical guys just have to shake their heads and move on.
For those of you with some concept of the math behind this. Two strikes of the same potential hit two aircraft. Aircraft A is all metal and takes the charge with very little damage. The charge on the aircraft is measured to the idealized (waveform 1) of 6.4us by 69us (50% down the double exponential curve). Aircraft B is mostly composite, especially in areas with level 3a-3c current, and the waveform looks more like the idealized (waveform 5a or b) 50us by 500us. Didn't matter if it was pos or negative. Composite has a good chance of missing pieces (depending on MANY factors in the design)... the solution of late has been increasing the density and weight of the composite, thus eliminating all the benefits that are realized moving to composites.
Some say the pos waveform is a little more benign because of the indirect effects that won't come with it. Those are waveforms 2-4. Digital systems have a lot of trouble especially with waveform 3. I remember one aircraft, a very large one, which would cycle the gear up and down because of WF3. Funny to watch. If your aircraft is composite then a positive waveform may be more destructive, but it would depend on the attachment point. Of course when you are talking about experimentals it gets to be purely speculative because we don't certify experiementals very often. Usually because we'd have to change the way the aircraft is made so greatly the engineering costs are prohibitative. Also, positive or negative the plane is gone. Shotgun blast from point blank or 5 feet away. Your choice.
I see I've gone over my allotted time. I apologize. I yield my balance to the floor.
PS. I like the battery anology. I used that a little when I got started. Of course it's a lot more complicated than that, especially with aircraft. We can keep going. I did this for years.
jynxyjoe
Queso King
Interesting about the thrust levers. It's unlikely it had anything to do with the St. Elmo's fire, although the coincidence is hard to ignore.
EMF's (electro magnetic fields) bow into the cockpit because of the windows. It's possible there is enough flux to cause an electron flow on the metal underneath the plastic grips of the levers... but that's a tough sell. Elmo's has a lot of voltage and very little current, I don't know if it'd have the power to do that. I don't suppose there is anyway you or the other guy were gripping the levers much harder or hands were cold from touching the windscreen?
Orange Anchor
New Member
I think that has happened sans trumpets.
Don't have my notes but it wasn't Radio Shack or Bob's. They were companies that had dealings with OEMs. And like you, they were in the business of FAA certifying for lightning.
I mentioned the sailplane only as a point that lightning can take an airplane apart. And that it was attributed to a positive strike. The NASA stuff I read along with other documents supported the point that most strikes, negative strikes, didn't knock stuff off airplanes but could and often did knock autopilots off, fuzz 'glass', leave pock marks or scorch marks where it exited. But with lightning strikes the main thing was to keep flying the airplane. Some compounded the problem by being distracted by the strike and failing to keep the first rule (fly the airplane)
what's your beef with RVs and small aircraft being IFR? Death traps? The SR-22 I occasionally fly has more stuff than the Boeings or Airbus I used to fly?
Bandit_Driver
Gold Member
I've seen St. Elmo's fire in the C-310 and a lot in the 727. The 310 is great for St. Elmo's fire. It usually builds up on the tuna tanks and on the prop tips.
The 727 will have its windows covered and wipers will have blue or purple "flames" coming off the ends (looks like a mini butane torch). It is pretty neat to see. I have yet to get a good picture of it.
The 727 will have its windows covered and wipers will have blue or purple "flames" coming off the ends (looks like a mini butane torch). It is pretty neat to see. I have yet to get a good picture of it.
BobDDuck
Island Bus Driver
I wouldn't worry too much about the fuel in the tanks igniting. Or fumes for that matter. Every known incident of fuel ignition due to lighting strikes is with JP4. Since the military went to JP8 (which is the equivalent of JetA) there have been no known incidents of fuel explosions due to lightening.
I'd be more worried about plasma building at the engine inlet and potentially disrupting airflow and causing a flameout.
Bandit_Driver
Gold Member
I was more nervous about that in the 310 with 100LL
c172captain
Well-Known Member
I hope to one day have the equipment and cajones to make it through something like that
seagull
Well-Known Member
I hope to one day have the equipment and cajones to make it through something like that
Didn't look that bad, didn't see anything flying around the cockpit! As far as the rest, except for research aircraft, I don't think anyone tries to get there, just sometimes you don't have a choice, or it doesn't pick up on the radar from the angle you are approaching the storm, etc. Worst is when you're in light to moderate rain with imbedded storms around. Can be a challenge to avoid the real weather, especially close in when max up tilt doesn't put the beam high enough to distinguish the regular precip from convective activity.
KLB
Well-Known Member
:yeahthat:
Especially at night. The best thing you can do is stay out the places where you see lightning striking.
jynxyjoe
Queso King
Just reply'ing outside of the PM's to try and continue the knowledge base a little.
Generally the FAA looks at certifying an airplane at a 200kva level. Idea being it's somewhere in between a pos and a negative strike. Pos being the granddaddy. No one cares on the cert level about pos being stronger than the neg. We test both polarities equally. For us in the labs (indirect effects), we are just changing the way coils are oriented with reference to the ground. Sometimes in direct effects it means we charge the opposite polarity, same level. I guess for me, the difference between +100kva and 300 kva is sort of irrelevant. even if it's 20kva (weakest neg) and 300kva I personally don't get any easier feeling getting hit by the negative. it's still 20kva.
In the PMs to Orange I've made it clear that I feel the quote ".... there are positive and negative lightning strikes. One leaves tiny holes and exits. The other knocks stuff off airplanes." is too generalized. In fairness to orange he was trying to get a point across and not certify an aircraft. I think I understand that now but I still think it deserves yet another response.
Positive strokes and negative strokes both cause damage and can both cause things to separate from the aircraft. Apparently it makes people feel better to know that a positive strike (the uncommon of the two) is an order of magnitude greater than a negative and negatives are more common. I think it's a little naive to think that just because the positive is more powerful that the negative is just going to fuzz glass. At some point I have to realise what we talk about in the certification world and what pilots want to know is very different. Positive strikes do have more action integral (just a term meaning energy), it is likely you will have more direct damage off a positive than a negative. That doesn't really mean anything to you if the negative strike still punches a hole in the side of your composite frame but whatever... at some point I just give up illustrating the point.
Negatives can be weak or very strong. Positives are almost always strong (from the data we have recorded decades ago). The only difference (other than amplitude) is if it starts at the cloud or at the ground. The only way you the pilot are going to know (on a certified airplane) is if you had some sort of oscilloscope hooked up to the aircraft. Something we haven't done since the NASA F-106 decades ago. Also we find that positive's rarely have the indirect effects which make digital equipment go haywire. Positive strikes do cause the indirect effects, but because of it's nature they are not as complicated a waveform.
In our world (pilots, not engineers and cert guys), when we deal with lightning it is because we (the aircraft) triggered it. Bigger airplanes get more strikes than smaller ones (per flight hour). There are different reasons for it but mostly the larger the airplane the larger the potential for the trigger. I don't know if anyone has seen it on youtube but if you take some time you can find a 747 get hit 3 times after takeoff.
/certification rant
Another thing I want to emphasize is that airliners, Part 25 aircraft are certified for a severe lighting strike. Part 23, who are IFR cert'ed have to pass those tests as well. Aircraft determined to be day vfr under part 23 don't get tested, although I have seen them elect to do it but I don't know of any that passed.
"Many homebuilts, especially composites, have NO defense against a strike." By defense I think you mean a real test done on the aircraft. There is a provision in 23 for Day VFR that you have to show some engineering level (no actual testing, just some guy thinking about it) design put into the aircraft to defend against lightning. From what I've seen and heard, including that glider, the "design" is severely flawed, but it never gets worked out during testing. I'd have to guess that a lawyer would say there is some defense, but for practical purposes no. I worked mostly on part25 airliners and part 23's with ifr certs. Composites are very complicated when it comes to lightning. They are a giant resistor and they get hot enough to melt the apoxy resin that keeps them in one piece.
/end certification rant
I'd still like to know which labs you talked to.
Any airplane you fly into IFR that is not certified for IFR is, in my opinion, a death trap. I have seen the bad end of tests where avionics packages won't pass. Just not something I want to deal with. Give me the 172 anyday over the RV in IFR. I don't care if the 172 is bendix with /A and the RV has dual 430's. Just not worth the risk to me, and I haven't met anyone who is familiar with the cert process who thinks its worth it either. I believe in the cert process, even if it isn't perfect and is a little dated. It's better than what I see from these homebuilts and experimentals.
As far as the cirrus thing, just because it gives you lots of pretty data doesn't mean it is trustworthy. Class A software means it is certified and useful. Garmin would love to throw their 1000's in a airbus. Can't happen because they aren't trustworthy enough from a cert standpoint. I get this question a lot. Someday they may be.
Anyhow. That's it for a bit. I find myself writing this stuff at length and it taking quite a while. Hope it has been helpful.
braunpilot
What day is it?
Thanks!
