Tockeyhockey From United States of America, joined Feb 2005, 940 posts, RR: 0 Posted (8 years 10 months 3 weeks 4 hours ago) and read 15604 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?
AA737-823 From United States of America, joined Mar 2000, 5547 posts, RR: 11 Reply 3, posted (8 years 10 months 3 weeks ago) and read 15332 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,
Tockeyhockey From United States of America, joined Feb 2005, 940 posts, RR: 0 Reply 4, posted (8 years 10 months 3 weeks ago) and read 15294 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.
AeroWeanie From United States of America, joined Dec 2004, 1605 posts, RR: 52 Reply 6, posted (8 years 10 months 2 weeks 6 days 23 hours ago) and read 15236 times:
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.
Dl757md From United States of America, joined May 2004, 1560 posts, RR: 18 Reply 7, posted (8 years 10 months 2 weeks 6 days 23 hours ago) and read 15250 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.
Mrocktor From United States of America, joined Jan 2005, 1662 posts, RR: 50 Reply 8, posted (8 years 10 months 2 weeks 6 days 23 hours ago) and read 15235 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.
Dl757md From United States of America, joined May 2004, 1560 posts, RR: 18 Reply 9, posted (8 years 10 months 2 weeks 6 days 22 hours ago) and read 15217 times:
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.
Airgypsy From United States of America, joined Nov 1999, 130 posts, RR: 2 Reply 10, posted (8 years 10 months 2 weeks 6 days 13 hours ago) and read 15124 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.
Dl757md From United States of America, joined May 2004, 1560 posts, RR: 18 Reply 12, posted (8 years 10 months 2 weeks 6 days ago) and read 15024 times:
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.
Pilotpip From United States of America, joined Sep 2003, 3119 posts, RR: 11 Reply 13, posted (8 years 10 months 2 weeks 5 days 19 hours ago) and read 14986 times:
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.
MD-90 From United States of America, joined Jan 2000, 8479 posts, RR: 13 Reply 14, posted (8 years 10 months 2 weeks 4 days 11 hours ago) and read 14898 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.
Tockeyhockey From United States of America, joined Feb 2005, 940 posts, RR: 0 Reply 15, posted (8 years 10 months 2 weeks 4 days 5 hours ago) and read 14871 times:
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.
Vzlet From United States of America, joined Mar 2004, 827 posts, RR: 0 Reply 16, posted (8 years 10 months 2 weeks 4 days 4 hours ago) and read 14865 times:
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
Pilotpip From United States of America, joined Sep 2003, 3119 posts, RR: 11 Reply 18, posted (8 years 10 months 2 weeks 3 days 19 hours ago) and read 14764 times:
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.
Tockeyhockey From United States of America, joined Feb 2005, 940 posts, RR: 0 Reply 20, posted (8 years 10 months 2 weeks 2 days 4 hours ago) and read 14658 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.
Prebennorholm From Denmark, joined Mar 2000, 6136 posts, RR: 55 Reply 21, posted (8 years 10 months 2 weeks 1 day 19 hours ago) and read 14616 times:
"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
Mrocktor From United States of America, joined Jan 2005, 1662 posts, RR: 50 Reply 23, posted (8 years 10 months 2 weeks 5 hours ago) and read 14530 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.