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787 Composites And Lightning Strikes  
User currently offlineTockeyhockey From United States of America, joined Feb 2005, 950 posts, RR: 0
Posted (9 years 6 months 3 weeks 5 days 11 hours ago) and read 16814 times:

I read about a lighning strike on a recent thread and it got me thinking about how the 787 will deal with lighning strikes since it is going to be a mostly composite airplane. As I understand it, normal airliners withstand lightning strikes because they are made of very conductive materials -- mainly metal. If lightning strikes a composite airliner, it won't conduct the energy through the plane; instead, the lightning will essentially get "trapped" in the non-conductive material and explode.

does anyone have any insights on what boeing is doing to deal with this problem?

55 replies: All unread, showing first 25:
 
User currently offlineAsstChiefMark From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 6 months 3 weeks 5 days 9 hours ago) and read 16708 times:

Hmmm... Good thought. I witnessed (and heard) a carbon-fibre pole get struck by lightning. It got blown into millions of carbon "needles." The carbon was glowing a bright white because it was so hot.

Mark


User currently offlineSunriseValley From Canada, joined Jul 2004, 4953 posts, RR: 5
Reply 2, posted (9 years 6 months 3 weeks 5 days 8 hours ago) and read 16640 times:


I understand that there are military aircraft in service that use this construction. Thus surely the issue of lightening strikes has been solved. Thus it is a non-issue.


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5771 posts, RR: 11
Reply 3, posted (9 years 6 months 3 weeks 5 days 7 hours ago) and read 16542 times:

Here is my theory.
Aircraft electrical equipment is generally wired much like your car- one wire to the device, and the device grounded through its frame and the aircraft skin. The negative lead on the generator is also connected to the skin (believe it or not, folks, our cars are wired the same way).
Composite general aviation aircraft (the Beech Starship I am discussing here) have a "ground plane" of metal mesh between layers of the composite material. When you go to add a new electronic device, you sand the composite down to the wire mesh, and ground your electronics into the mesh.

SO- my theory is that the lightning will go into the wire mesh, and dissipate out the back.

ALSO- another idea... How much of the 787 fuselage will actually be composite? I think it's just the skin.. which would mean that longerons and whatever else might still be metal.. maybe they could link these metal components together and create a path for lightning to exit the plane???

If someone else has the answer, feel free to shoot my ideas down.
Have a good weekend,
R


User currently offlineTockeyhockey From United States of America, joined Feb 2005, 950 posts, RR: 0
Reply 4, posted (9 years 6 months 3 weeks 5 days 7 hours ago) and read 16504 times:

not sure about the % of composite in the wing, but from the looks of the photos of the construction methods, almost the entire fuselage seems to be "wrapped" in composites. my guess is that lightning would tend to strike wings (tips, especially) and not the fuselage. not that it couldn't hit the fuselage, just that it seems less likely.

will the wing be metal? if so, maybe this explains their plan to ground the airplane.


User currently offlineLMP737 From , joined Dec 1969, posts, RR:
Reply 5, posted (9 years 6 months 3 weeks 5 days 6 hours ago) and read 16463 times:

There are several ways to dissipate an electrical charge in composite structures.

1)An aluminum screen can be laminated under the top layer of fabric. This is typically used on a carbon/graphite component.

2)You can flame spray aluminum on a composite component.

3)A thin aluminum foil can be bonded to the outer layer.

4)Aluminum wires can be woven into the top layer of the composite fabric. This is found in fiberglass and Kevlar components.



User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1608 posts, RR: 52
Reply 6, posted (9 years 6 months 3 weeks 5 days 5 hours ago) and read 16446 times:
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If I remember right, the Lear Fan had a layer of aluminum plasma sprayed on the outside of the airframe. Again, trusting my memory, the Starship had a copper mesh included in the layups. Including a mesh in the layups is the most common protection used.

User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 7, posted (9 years 6 months 3 weeks 5 days 5 hours ago) and read 16460 times:

To clear up a couple of points. First, according to the Boeing 787 website, the entire fuselage including the skin, formers, and stringers, and the wing of the 787 will be made of composites. Second, for some reason, I'm not sure why, but lightning seems to strike the fuselage much more frequently than the wings. I've repaired damage on literally thousands of fuselage lightning strikes but could probably count on both hands the number of wing strikes that I've seen. Also when lightning strikes it usually emerges out the bottom of the fuselage on it's way to the ground. Lightning pulses very rapidly and often times leaves a track of strikes as if machine gunned down the fuselage.

The grounding and bonding of the composite structure on the 787 will be a non-issue as Boeing has I'm sure already taken care of it. The general public will not be informed of the methods used just as they probably haven't been informed of the exact grounding and bonding requirements and methods of any other of Boeings products. When the planes enter service the technicians that work them will be trained on the methods employed and how to maintain them, perhaps then one of us will be able to share that info. Until them maybe a Boeing employee can share the info we're looking for.

Dl757Md



757 Most beautiful airliner in the sky!
User currently offlineMrocktor From United States of America, joined Jan 2005, 1668 posts, RR: 50
Reply 8, posted (9 years 6 months 3 weeks 5 days 5 hours ago) and read 16445 times:

As stated, a wire mesh is laminated into the composite parts to provide conductivity. I imagine on the 787, with most of the plane being composite, they will have to take specific care in "grounding" the wire meshes of the different components to each other and to the metal structure. This is unusual for structural components but is already a standard procedure for all equipment on the aircraft.

I imagine that special "grounding points" will exist on the main structural components both to interconnect them and to allow equipment to be grounded.

One issue that, in my opinion, is more relevant than how this will be done is the extent of damage in case of a lightning strike. In metal planes lightning usually does no structural damage whatsoever, except to antennae, composite control surfaces or poorly grounded equipment. On the 787 any lightning strike would most likely prompt a careful inspection of the whole airplane, as conductivity will be lower and the potential damage much more serious. Delamination can be notoriously hard to detect.

mrocktor


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 9, posted (9 years 6 months 3 weeks 5 days 5 hours ago) and read 16427 times:

mrocktor

In metal planes lightning usually does no structural damage whatsoever

I couldn't disagree more. While catastrophic structural damage is never a consequence, minor structural damage usually occurs to the skin and sometimes stringers and formers. The skin suffers pinholes or pock marks at the point of the strike. Since cracks can propagate from these defects they have to be evaluated and either burnished out or, if the depth of the damage is too great, drilled out and filled with a rivet. I've seen aircraft with over 100 rivets in a meandering path down the side of a fuselage from a severe strike.

On the 787 any lightning strike would most likely prompt a careful inspection of the whole airplane

True. This is however no different from any other aircraft. All AMMs have a procedure for lightning strike inspections. In a nutshell it's a careful inspection of the whole airplane.

The big problem I see with the composites on the 787 are that for the most part composites are hygroscopic. This means that they absorb moisture from the ambient air. Carbon is not nearly a susceptible to this as fiberglass or kevlar, but even small amounts of moisture are instantly turned to steam by the heat of a lightning strike. This is very explosive. The damage that occurs form this is usually quite obvious as panels are literally blown apart. Bonding can help but not completely eliminate it as an area about 1/4 to 1/2 inch around the strike point is heated by the plasma of the lightning bolt itself. The damage caused by this would still be abundantly evident with just a visual inspection. As I see it, bonding is important, but moisture protection via surface finishing(paint) and it's subsequent mtc. will be at least as important although it's mtc. has historically been far more neglected.

Dl757Md




757 Most beautiful airliner in the sky!
User currently offlineAirgypsy From United States of America, joined Nov 1999, 130 posts, RR: 2
Reply 10, posted (9 years 6 months 3 weeks 4 days 20 hours ago) and read 16334 times:

Like lightening rods, there are screws installed through composites to provide safe paths for lightening, there are "lightening strips" on radomes and other places to control the attachment and direction of lightening as it passes through structures. Composite aircraft requirements for lightening strike inspections will be more rigorous because there are fewer and harder to detect paths for lightening.

User currently offlineMrocktor From United States of America, joined Jan 2005, 1668 posts, RR: 50
Reply 11, posted (9 years 6 months 3 weeks 4 days 9 hours ago) and read 16254 times:

Dl757Md,

I see where you are coming from. Let me rephrase:

In metal planes lightning usually does no structural damage whatsoever outside the entry/exit points.

I wanted to setress that the post lightning incident inspection for a "full composite" aircraft must be extremely careful, not downplay the procedures for current planes.

mrocktor



User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 12, posted (9 years 6 months 3 weeks 4 days 7 hours ago) and read 16234 times:

mrocktor

I agree that the the lightning strike inspections will need to very comprehensive and detailed. One thing that I think will aid in the detection of strike points is that the entire structure will be required to be painted. The burn marks that the lightning leaves behind in the paint will be obvious and will be a clue in detecting possible structural defects caused by the strikes.

Dl757Md



757 Most beautiful airliner in the sky!
User currently offlinePilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 11
Reply 13, posted (9 years 6 months 3 weeks 4 days 2 hours ago) and read 16196 times:

Tockeyhockey,

Welcome to the fourm! You have a valid question and that's one of the neat things about this particular fourm on Anet. You'll find many professionals here who will provide valuable insight.

Another nice feature here at tech/ops that separates this particular fourm from the rest of the message board is the respect displayed by everybody here. There are mechanics, pilots, ramp agents, fuelers, industry professionals and enthusiasts from every part of the globe flying and working on everything from piper cubs to 747s. This unique blend offers insight into how differently a question can be approached. As a result of this, disagreements do come up and you may have a few people that add their opinion or an answer that you don't like but again, respect reigns. Please refrain from making comments like the ones you made in response to SunriseValley in the future.




DMI
User currently offlineMD-90 From United States of America, joined Jan 2000, 8507 posts, RR: 12
Reply 14, posted (9 years 6 months 3 weeks 2 days 18 hours ago) and read 16108 times:

One thing that I think will aid in the detection of strike points is that the entire structure will be required to be painted.

Yet another reason why American is going to have to come up with something new if it buys 787s, even though the polished fuselage is a very strong part of brand awareness (I'm discounting the ugly A300 paint).



If the comparatively tiny companies of Stoddard-Hamilton and Lancair were able to solve this problem for their Glasair III and Lancair IV(P) respectively, then I'm sure Boeing will do so as well.


User currently offlineTockeyhockey From United States of America, joined Feb 2005, 950 posts, RR: 0
Reply 15, posted (9 years 6 months 3 weeks 2 days 11 hours ago) and read 16081 times:

Pilotpip,

I think that whenever someone disrespects a question that is posed in a forum, the person who posed the question reserves the right to fire back. Basically, what sunrisevalley was saying was that "everybody knows how it's done, so don't bother to ask." well, i don't know how it's done and i wanted to know!

since i posted my retort, the comments on the board have started to get me closer to an understanding of the technical aspects of lightning strikes on a composite plane. sometimes, you have to get the idiots out of the conversation before people start making sense.

respectfully yours -- tockeyhockey


User currently offlineVzlet From United States of America, joined Mar 2004, 835 posts, RR: 0
Reply 16, posted (9 years 6 months 3 weeks 2 days 11 hours ago) and read 16075 times:

Tockeyhockey,
Disagreement is often a part of the discussion process here and isn't of itself a bad thing, but insult and escalation contribute nothing to the forum. Even if you formed the personal opinion, after reading one post, that SunriseValley is an "idiot", what's the purpose of extending your insult to all Canadians?

I'd urge you not to be so quick to disregard Pilotpip's gently worded advice.



"That's so stupid! If they're so secret, why are they out where everyone can see them?" - my kid
User currently offlineTockeyhockey From United States of America, joined Feb 2005, 950 posts, RR: 0
Reply 17, posted (9 years 6 months 3 weeks 2 days 8 hours ago) and read 16050 times:

sorry to offend the canadians out there. i actually love canada. but please, if anyone agrees with what surisevalley was saying, they wouldn't be on this board in the first place.

here's essentially what he said: there is no purpose for this message board. it's like saying "the wright brothers invented the airplane. the issue of lift has been solved, so it's a non-issue."

you have to admit that it was a really stupid comment.

let's get back to discussing the 787, which seems to be a very exciting plane. i want to figure out hoe boeing is going to deal with lightning strikes!


User currently offlinePilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 11
Reply 18, posted (9 years 6 months 3 weeks 2 days 2 hours ago) and read 15974 times:

Tockeyhockey,

You'll find pretty often on these boards that those comments happen. You'll get one or two that throw their two cents in without any sense that they have any idea of how things actually work (a great thread in general topics about the A380 being able to glide demonstrates this perfectly). Blow it off, and move on. You'll more than likely get many good answers from people that do know what they're talking about. This is one of the challenges of being on a fourm that accepts anybody willing to pay the price of admission.

Back on topic, Check out Lancair and Sirrus. While building only small GA aircraft, they have lead the way for some years in composite development and as a result have had some interesting hurdles in certifying their aircraft for IFR flight mainly as a result of the problems that composites have when struck by lightning. I've read a couple stories on how they achived this but looking through my "archive" of magazines such as "Flying", "Plane and Pilot" and "AOPA Pilot" has not netted any results.



DMI
User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 19, posted (9 years 6 months 3 weeks 21 hours ago) and read 15899 times:

you have to admit that it was a really stupid comment.

What an insensitive thing to say. His comment was no more "stupid" than your question TockeyHockey.

You could have just ignored it if you felt it added nothing to the discussion.

the lightning will essentially get "trapped" in the non-conductive material and explode.

Another brilliant statement....but nobody is calling you stupid. I think most have a little more tact than that. And what exactly does SunriseValley's nationality have to do with anything?

Step back a bit and reconsider your comments....


User currently offlineTockeyhockey From United States of America, joined Feb 2005, 950 posts, RR: 0
Reply 20, posted (9 years 6 months 3 weeks 11 hours ago) and read 15868 times:

actually, my language on lightning strikes is pretty accurate -- because composites are not conductive, the energy does not flow through them. instead, it expands outward (explodes) and splinters the carbon-based material. see post 3.

his nationality has nothing to do with his stupid comment -- you are correct. but why does everyone feel the need to be the feeling police on this board? sorry if i offended canadians, but i'm an american and i reserve my right to offend everyone!

anyway, my main point about sunrisevalley was that it is incredibly dumb to post something just to say "let's not talk about this." THIS IS A CHAT BOARD! that's what we do -- talk about things! who has the time to go on a chat board about airplanes to tell people that we shouldn't talk about airplanes?!

rather than attack me personally for what may be perceived as a nasty response, lets examine the post that i was responding to. if you're not going to do that, then stop talking about it.

anyway, this thread seems to be dead. thanks to everyone who took my question seriously and gave me some new information to think about.


User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6429 posts, RR: 54
Reply 21, posted (9 years 6 months 3 weeks 2 hours ago) and read 15826 times:

Some clarifications:

"Composites" is a very unspecific word. But for non-technically minded journalists it is often as technical as they can go.

Composite means exactly as the word says - some things composed together:

For aircraft four different composite types are used, and they are very different:

1. Glass fibre
2. Aramid fibre (often called "Kevlar", which is the DuPont trademark name)
3. Carbon fibre (sometimes also named graphite fibre)
4. Boron fibre.

What will be used for the main structures of the 787 is carbon fibre. Unlike the other types of composites carbon fibre is a quite good electrical conductor. Not nearly as good as aluminium which is second to only copper. But still quite good. Therefore carbon fibre cannot be used for radomes and such.

At least here in the tech/ops forum it should be banned to use the word "composites" since it's a generic name of so many different materials with extremely different properties.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 22, posted (9 years 6 months 2 weeks 6 days 23 hours ago) and read 15799 times:
AIRLINERS.NET CREW
DATABASE EDITOR

At least here in the tech/ops forum it should be banned to use the word "composites" since it's a generic name of so many different materials with extremely different properties.


Hear, hear. I agree 100%, Preben. It's like saying "metal", instead of "aluminum", "titanium", etc.


2H4



Intentionally Left Blank
User currently offlineMrocktor From United States of America, joined Jan 2005, 1668 posts, RR: 50
Reply 23, posted (9 years 6 months 2 weeks 5 days 12 hours ago) and read 15740 times:

"actually, my language on lightning strikes is pretty accurate -- because composites are not conductive, the energy does not flow through them. instead, it expands outward (explodes) and splinters the carbon-based material. see post 3."

No, actually it is not. The energy does flow through the composite material. In fact saying that "energy expands outward" or "energy explodes" makes no sense.

What happens is that while flowing through non conductive material, a large portion of energy is converted into heat. While electrical current does no damage to structures, heat does. The overheated material cracks and splinters - or explodes if you will.

Now, maybe that is what you meant, but your "language" was far off the mark.

mrocktor


User currently offlineJHSfan From Denmark, joined Apr 2004, 469 posts, RR: 2
Reply 24, posted (9 years 6 months 2 weeks 3 days 12 hours ago) and read 15638 times:

How about gliders?
A lot of them are made by composites. And although they mostly fly in good weather (am I right or wrong?) some gliders must have been hit by lightning.

Yours in realtime
JHSfan



Look at me, I´m riding high, I´m the airbornmaster of the sky...
25 Airplay : The airworthiness standards, even for gliders require that all external surfaces be electrically bonded. If not, can you imagine the huge static disch
26 Tockeyhockey : "No, actually it is not. The energy does flow through the composite material. In fact saying that "energy expands outward" or "energy explodes" makes
27 Dl757md : Tockeyhockey You are correct that most composites are insulators. The problem is that with the voltages involved with lightning they can conduct elect
28 Tockeyhockey : thanks DI757Md -- i guess my main point was that regardless of the technical aspects of voltage thresholds, it's clear that metal is better at dealing
29 Prebennorholm : Once again, carbon fibre, as will be used for main structures on the 787, is a fine electrical conductor for any voltage. Not as good as aluminium whi
30 Prebennorholm : For those interested in history - a lot of people think that carbon fibre is something new. Not really so. It was invented already in 1962 by Royal Ai
31 Post contains links Reporter : You'll find answers to many of the questions raised here in a Seattle Times article published Sunday Feb. 5, 2006, which provides inside scoop from 78
32 Post contains links and images Starlionblue : COMPOSITES! COMPOSITES! COMPOSITES! COMPOSITES! COMPOSITES! COMPOSITES! I just got this image in my head from the A.nut version of Life of Brian: MAT
33 Dougloid : Concur. I've worked on a couple metal airplanes that got hit by lightning. The damage is found at the point of ingress and any place where the curren
34 ContnlEliteCMH : An excellent example of why high school physics courses are routinely covered in a scant few weeks of college-level material: they don't actually tea
35 Starlionblue : Same with any other subject. Math, economics... High school is just much less focused.
36 Post contains images ContnlEliteCMH : It has to be because it's job is to impart a successful education to nearly everybody regardless of potential. College, well, they'll throw you out i
37 Post contains images Starlionblue : I could rant at length about how much I agree with you.
38 YYZYYT : Fascinating technical info here - thanks all. Is this readily possible? If so, how much weight would it add (compared to, say, paint) and what would t
39 Post contains images David L : Sorry for the late reaction but I didn't see that at the time!
40 Texfly101 : While I'm not disclosing anything new that hasn't been added, the fact that there is a wire mesh embedded in the composite material says that a high v
41 Post contains links Hmmmm... : Here is a real life accident caused by lightning striking a composite structure. Concerns about this issue are not totally unfounded. They don't alway
42 Tdscanuck : That's the primary reason why the contents of the airliner are protected...it doesn't do a whole lot to protect the aircraft itself. The radome is a
43 Nomadd22 : Carbon fiber is conductive. Epoxy, not so conductive. Do you actually get contact between layers of carbon tape in Boeing's CFRP? My totally uneducate
44 Rwessel : Just to pick nits, both silver and gold are better conductors than aluminum, and silver is even better than copper. And both have noteworthy uses as
45 Tdscanuck : Given the high fiber fraction and cure pressure, it's probably pretty difficult to avoid having contact between tape layers. Keep in mind that any li
46 Rheinbote : On the wing box expanded copper/aluminum foil is employed where the skin is attached to ribs and spars by fasteners. Arcing between the skin and fast
47 Nomadd22 : I I'd guessed that the bronze mesh wasn't so much to carry the current from the lightning strike to "ground, since there isn't really any ground in an
48 Tdscanuck : It's there to carry it from the entry to the exit point. The lightning will go to ground (the real ground) and there's nothing the airplane can do ab
49 Nomadd22 : I think we're pretty much saying the same thing. The way you carry the current "safely" is to keep all areas of the plane at pretty much the same pot
50 Baroque : As is pointed out by Nomad22: The carbon has conducting properties, but the resin bonding them is a pretty fair insulator up to the point where it is
51 Nomadd22 : Maybe not so much irrelevant as unpredictable. You need the current to follow predicatble paths to keep the plane undamaged and the mesh gives you th
52 Baroque : That too!! Which is presumably why B said they were including metal paths. The predictability will depend upon contact, but also upon exact orientati
53 AcNDTTech : Where I work, we use copper wire mesh......but for the same reason. You should see the reading that I get on my ultrasonic scope when I'm inspecting
54 JayinKitsap : On structural parts having an aluminum foil on a CFRP structure requires careful consideration of strains. If E (and G) are different between layers n
55 Starlionblue : Heh. The Mosquito fighter was also in large parts built of the same composite.
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