787 and lightning strikes
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787 and lightning strikes
from WSJLightning Hazards Prompt Boeing to Fix 787 Jets
Manufacturer aims to eliminate chances of cockpit displays failing due to lightning events
https://www.wsj.com/articles/lightni...s&page=1&pos=2
"Boeing Co. BA -0.02% is enhancing software on current and future 787 jetliners to prevent electrical spikes generated by lightning storms from potentially disabling cockpit instruments.
Manufacturer aims to eliminate chances of cockpit displays failing due to lightning events
https://www.wsj.com/articles/lightni...s&page=1&pos=2
"
By
April 25, 2018 6:30 a.m. ETAndy Pasztor
The moves were initially prompted by an incident years ago when three of five primary cockpit displays on a United Airlines 787 Dreamliner suddenly stopped functioning after the plane was hit by lightning. The incident surprised regulators and company safety experts alike, as such equipment failures were considered extremely improbable on such models.The issue, and Boeing’s responses, were revealed in a recently released report by investigators from the U.S. National Transportation Safety Board. The document describes, among other things, the hazards posed by a ”high intensity electric field radiated inside the cockpit” from nearby lightning. Such dangers historically weren’t considered part of mandatory airliner certification standards because the underlying technical reasons weren’t understood until the safety board and Boeing joined forces to investigate the unusual United incident."
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Oh Dear
We had a few lightning strikes on the Dornier 328 TurboProp , and one took out 3 screens:
This was old TV style CatodeRay tube , not flat screens.
I had some fantastic St Elmoes Fire the other day over some buildup and was sure I was going to get hit. Turned out it was Calima dust that caused the St Elmo in cloud.
Anyone have any screens lost in lightning strike?
We had a few lightning strikes on the Dornier 328 TurboProp , and one took out 3 screens:
This was old TV style CatodeRay tube , not flat screens.
I had some fantastic St Elmoes Fire the other day over some buildup and was sure I was going to get hit. Turned out it was Calima dust that caused the St Elmo in cloud.
Anyone have any screens lost in lightning strike?
I wonder exactly what sort of software enhancement they are installing to mitigate a problem that interferes with systems at a hardware level. The solution in the United case appears to have been rebooting the affected systems. So it appears that there was no (evident) permanent hardware damage. But since susceptibility to electrical transients usually involves stopping a system from running it's software, the only fix I can see them implementing is a better watchdog system. Essentially, a routine that once stopped (by a software crash, for example) forces a restart or reboot by a hardware timer. The displays will still go down. But barring any hardware damage by the lightning, they will come back up.
This is just my guess. But if anyone close to the systems knows, It would be interesting to hear.
This is just my guess. But if anyone close to the systems knows, It would be interesting to hear.
Engr - no first hand knowledge here, but s/w can indeed protect a system from a lightning transient, depending on the nature of the lightning transient. The example I saw was for something called "multiple burst" - as it was explained to me lightning strikes are often made up a very rapid series of smaller electrical pulses as the strike finds it's way to the big strike (this would probably make more sense if I could draw it for you, but think of a series of small sparks connecting into one massive spark). The problem is, those smaller spikes can mimic a the wave form of a valid digital electrical input - and the LRU can't tell the difference. The fix was to change the software so it could differentiate between actual digital inputs and the lighting induced inputs.
In a way, it's ironic - as an industry we've spent decades convincing everyone that lightning wasn't a big threat - we design for it. Except that isn't entirely true - we can't always protect from the most severe lightning effects. For example, we protect the engine control from the electrical transient, but if the lightning attaches to the inlet the shock wave into the inlet can cause the engine to surge and flameout (yes, it's happened). There was an event roughly fifteen years ago (memory says it was a 767, but don't hold me to that) where the lightning attached to the aircraft nose - the resultant electrical field around the flight deck incapacitated one pilot (the other pilot was 'affected' but fortunately was still able function). The bottom line is we can design for the lightning effects, but we can't completely protect for the worst case strike. We still need flight crews to do their best to avoid it...
BTW, shortly before I retired, I was on a 747-8 flight test when we took a major lightning strike - I was in the flight deck at the time and it was quite a shock (emotionally, not physically). No adverse affects to the aircraft systems, but it did significant airframe damage. But what I really recall is the flight crew's reaction to ATC - basically ATC had put us into a spiraling decent right in the middle of a cell until we finally got hit - and the flight crew didn't appreciate it...
In a way, it's ironic - as an industry we've spent decades convincing everyone that lightning wasn't a big threat - we design for it. Except that isn't entirely true - we can't always protect from the most severe lightning effects. For example, we protect the engine control from the electrical transient, but if the lightning attaches to the inlet the shock wave into the inlet can cause the engine to surge and flameout (yes, it's happened). There was an event roughly fifteen years ago (memory says it was a 767, but don't hold me to that) where the lightning attached to the aircraft nose - the resultant electrical field around the flight deck incapacitated one pilot (the other pilot was 'affected' but fortunately was still able function). The bottom line is we can design for the lightning effects, but we can't completely protect for the worst case strike. We still need flight crews to do their best to avoid it...
BTW, shortly before I retired, I was on a 747-8 flight test when we took a major lightning strike - I was in the flight deck at the time and it was quite a shock (emotionally, not physically). No adverse affects to the aircraft systems, but it did significant airframe damage. But what I really recall is the flight crew's reaction to ATC - basically ATC had put us into a spiraling decent right in the middle of a cell until we finally got hit - and the flight crew didn't appreciate it...
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IN the mid 1960's- on a 707 flight from frankfurt toVancouver BC, as we were near/less than 10K feet approaching vancouver we took a lightning hit_ It was like being in a large tin can with someone hitting it once with a large hammer. it was LOUD and startling- I was near the tail and had the impression that that was what/where we were hit. After a minute or so- capt made an announcement that we had been hit by lightning- no problem. I recall a few cabin lights may have blinked- but no other issues apparent.
Yes, there is a copper mesh imbedded in the carbon fiber on the 787. While carbon has reasonable electrical conductivity, it's still considerably worse than aluminum (order of magnitude). That higher resistance means that the electrical current/voltages induced by a lightning strike are much higher than for aluminum structure. The copper mesh dramatically improves the conductivity of the carbon, but it's still a bit worse than aluminum. As a result, the lightning transient requirements for the 787 systems are somewhat higher than for aircraft with aluminum primary structure (I don't recall specifics, but IIRC the voltage requirements were about twice as high for carbon fiber aircraft).
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Disclaimer - I'm not a lightning/EMI expert, but I did have to deal with it for my engine systems - I know just enough to be dangerous
Yes, there is a copper mesh imbedded in the carbon fiber on the 787. While carbon has reasonable electrical conductivity, it's still considerably worse than aluminum (order of magnitude). That higher resistance means that the electrical current/voltages induced by a lightning strike are much higher than for aluminum structure. The copper mesh dramatically improves the conductivity of the carbon, but it's still a bit worse than aluminum. As a result, the lightning transient requirements for the 787 systems are somewhat higher than for aircraft with aluminum primary structure (I don't recall specifics, but IIRC the voltage requirements were about twice as high for carbon fiber aircraft).
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Yes, there is a copper mesh imbedded in the carbon fiber on the 787. While carbon has reasonable electrical conductivity, it's still considerably worse than aluminum (order of magnitude). That higher resistance means that the electrical current/voltages induced by a lightning strike are much higher than for aluminum structure. The copper mesh dramatically improves the conductivity of the carbon, but it's still a bit worse than aluminum. As a result, the lightning transient requirements for the 787 systems are somewhat higher than for aircraft with aluminum primary structure (I don't recall specifics, but IIRC the voltage requirements were about twice as high for carbon fiber aircraft).
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For but one example - the commercial boys wanted to use aluminum mesh for weight savings over copper. Thenit was pointed out that aluminum v carbon and a bit of moisture made a almost useable battery
Last edited by CONSO; 30th Apr 2018 at 01:04. Reason: fat fingers
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I remember reading about lightning protection on the 787...IIRC there is a copper mesh embedded in carbon fiber
I thought it was titanium due to the weight of the copper? I know they could use aluminum, but would have to thicken the composite for galvanic protection..
I thought it was titanium due to the weight of the copper? I know they could use aluminum, but would have to thicken the composite for galvanic protection..
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And a little bit more as to lightning vs EMP
Go to page 69-70
http://www.northropgrumman.com/Capab...Innovation.pdf
benthere
Go to page 69-70
http://www.northropgrumman.com/Capab...Innovation.pdf
benthere
Again, no first hand knowledge, but I was 'told' the 787 used copper mesh - never even heard of them wanting to use titanium. It's all about the electrical conductivity - adding copper to the composite matrix makes it more conductive - which due to electrical laws that I'd need to refer you to a text book to explain, the induced current due to an external current is a function of the electrical resistance - the lower the resistance, the lower the induced current. Hence if they'd used aluminum they would have needed so much more to get the same conductivity that I doubt it would have saved any weight as copper is much more conductive (i.e. lower resistance) than aluminum. I believe titanium is even worse than aluminum.
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Again, no first hand knowledge, but I was 'told' the 787 used copper mesh - never even heard of them wanting to use titanium. It's all about the electrical conductivity - adding copper to the composite matrix makes it more conductive - which due to electrical laws that I'd need to refer you to a text book to explain, the induced current due to an external current is a function of the electrical resistance - the lower the resistance, the lower the induced current. Hence if they'd used aluminum they would have needed so much more to get the same conductivity that I doubt it would have saved any weight as copper is much more conductive (i.e. lower resistance) than aluminum. I believe titanium is even worse than aluminum.
https://www.azom.com/article.aspx?ArticleID=1298Specific electrical resistance
(ľOhm-cm)
55
72
2.7
4.3
9.5
1724
note the 1724 for copper is a misprint s/b 1.724 so look at the ti and aluminum ratios by comparison
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Flying the 787 for last 4 years,I've seen a series of eight strike marks,,on the underside of the fuselage after one encounter.Also,a flaperon that opened up on the top rear surface with the texture of blackened cotton wool.
Certainly have a bit more respect for flying in their vicinity than I did whilst flying this 767,some years ago!
sorry,failed cut n paste
Certainly have a bit more respect for flying in their vicinity than I did whilst flying this 767,some years ago!
sorry,failed cut n paste
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In the ' early ' days of composites for structural use on airplanes ( other than feathers- flaperons, etc ) there was significant discussion as to conductivity of carbon " dust " from machining and cutting of composite structure. A lot of trimming and cutting was done with abrasive ( brazed industrial diamonds on high speed cutters ) really a grinding process. Abrasive high pressure water jets were /are also used.
Anyhow to settle the question- a simple test method was used . A half/pound or so of ' carbon composite grindings' was put into a small plastic box over 90 percent full. As I recall, the box was an inch or so deep and about and size of a binder. On opposite sides an simple wire probe was inserted and sealed. resistance between the two probes was measured as the box was shaken - no reading indicating no conductivity. My very ancient recollection seems to be that low to moderate voltages ( dc ? ) were also applied. Results indicated zip current.. IMO not to surprising when one considers the fact that tdo establish a conductive path with carbon ' strings' covered with some epoxy- several thousand would have to line up end to end in close contact to pass any current. So much for composite ' dust ' conductivity.
Anyhow to settle the question- a simple test method was used . A half/pound or so of ' carbon composite grindings' was put into a small plastic box over 90 percent full. As I recall, the box was an inch or so deep and about and size of a binder. On opposite sides an simple wire probe was inserted and sealed. resistance between the two probes was measured as the box was shaken - no reading indicating no conductivity. My very ancient recollection seems to be that low to moderate voltages ( dc ? ) were also applied. Results indicated zip current.. IMO not to surprising when one considers the fact that tdo establish a conductive path with carbon ' strings' covered with some epoxy- several thousand would have to line up end to end in close contact to pass any current. So much for composite ' dust ' conductivity.
