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Topic: Article: Lightning Protection On The B787
Username: Grantcv
Posted 2006-07-12 05:53:48 and read 7356 times.

Interesting article on lightning protection and its effect on weight for the B787.

http://seattlepi.nwsource.com/business/277220_air12.html

Topic: RE: Article: Lightning Protection On The B787
Username: GBan
Posted 2006-07-12 06:41:11 and read 7284 times.

On the composite fuselage or wing skin of the 787, although the impact area would be about the size of a baseball from the lightning hit, there would not be penetration of the skin, Sinnett said.

Still, the lightning will look for any path of least resistance into the composite material, such as through a wing-skin fastener. Making sure that does not happen has meant adding materials or changing the design, which has increased the weight of the wing.


Does anyone know what they actually do to prevent this?

Topic: RE: Article: Lightning Protection On The B787
Username: Eirjet
Posted 2006-07-12 08:41:37 and read 7189 times.

".....On average, lightning strikes a commercial jetliner once or twice a year......"

- I would have assumed it the average was higher!!!

- Reading the rest of the article, it seems like promotional material for boeing....


"""....making sure the 787 is safe from lightning strikes in flight has driven up the plane's weight......"

- I am sure boeing are not the only airline who have encountered this problem?????  Wink

Topic: RE: Article: Lightning Protection On The B787
Username: AF1624
Posted 2006-07-12 09:20:48 and read 7143 times.

Remembers me of the movie "Cast away" with Tom Hanks, when the MD-11 gets hit by a lightning strike, and consequently its AFT cabin explodes because of "unregistered explosive materials".

Usually, the lightning would be drawn towards the lightning rod/conductors that are on the aicraft, like on this picture :


View Large View Medium
Click here for bigger photo!

Photo © Christian Galliker



And not on the wing/body surface...

Is such a situation realistic ? Can a lightning strike really dig a hole, as small as it would be, into an airframe ? Not very reassuring actually, i thought those lightning rods were enough to protect the airframe for breaking apart.

Topic: RE: Article: Lightning Protection On The B787
Username: Rheinbote
Posted 2006-07-12 09:47:07 and read 7100 times.

If the aircraft is 2,5% over weight target, and this extra weight is allegedly attributed to the wing, I'd rather believe that this is due to the first six wing skin shipsets being manufactured in hand lay-up fashion than due to lightning strike protections issues.

Maybe this "lightning strike protection issue" is the Boeing equivalent to the Airbus "electric harness" smart excuse?

Topic: RE: Article: Lightning Protection On The B787
Username: Joni
Posted 2006-07-12 09:56:49 and read 7082 times.

Quoting Rheinbote (Reply 4):
If the aircraft is 2,5% over weight target, and this extra weight is allegedly attributed to the wing, I'd rather believe that this is due to the first six wing skin shipsets being manufactured in hand lay-up fashion than due to lightning strike protections issues.

I think they've taken that issue into account and the 2,5% refers to the final configuration. The way they're dealing with the lightning-strike protection is to insert some metal mesh inside the fuselage structure, and this will of course weigh something.

Topic: RE: Article: Lightning Protection On The B787
Username: N8076U
Posted 2006-07-12 10:10:59 and read 7050 times.

Most aircraft parts that are composite like the wing and belly fairings on the 747 have a flamesprayed aluminum coating applied to conduct the electricity. They are also connected to structure with bonding straps. A newer technology is a wire mesh imbedded into the top layer of the composite panel.

Lightning strikes are fairly common. It wasn't too out of the ordinary to have an aircraft in the hangar for a check, and to find a dozen "hits" on the side of the fuselage, in a line.

Chris

Topic: RE: Article: Lightning Protection On The B787
Username: Rheinbote
Posted 2006-07-13 11:16:27 and read 6871 times.

Nice article on lightning strike protection in airplanes in general and some on 787 in Composites World

"For its composites-intensive midsize 787 commercial passenger jet, The Boeing Co. (Seattle, Wash.) has developed a multilayered approach to its lightning strike protection strategy. Boeing plans to use a thin metal mesh or foil in the outer layers of the composite fuselage and wings to quickly dissipate and route charge overboard and shield onboard electronics. To avoid slight gaps between wing-skin fasteners and their holes, which could enable sparking, Boeing will install each fastener precisely and then seal it on the inside. Boeing will use nonconductive goop or glass fiber to seal edges where wing skins meet internal spars in order to prevent gaps, which could permit electrons to spray out during a lightning strike, a phenomenon referred to as "edge glow." In the fuel tanks, Boeing will eliminate the threat of exploding fuel vapors by installing a nitrogen-generating system (NGS) that minimizes flammable vapors in wing tanks by filling the space with inert nitrogen gas."

http://www.compositesworld.com/hpc/issues/2006/July/1366/1

Topic: RE: Article: Lightning Protection On The B787
Username: CHRISBA777ER
Posted 2006-07-13 11:18:34 and read 6868 times.

Quoting Eirjet (Reply 2):
".....On average, lightning strikes a commercial jetliner once or twice a year......"

- I would have assumed it the average was higher!!!

Ive had it happen at least once that I know of, and I have flown less than thirty times in my life.

Topic: RE: Article: Lightning Protection On The B787
Username: Grantcv
Posted 2006-07-13 15:24:20 and read 6749 times.

I am wondering how heavy the wire mesh is and how much of the 2.5% excess weight it accounts for? Was it originally planned for and allocated a weight. It strikes me that this mesh must be quite heavy to be the primary reason for the B787 being overweight. Especially if it was originally allocated weight.

Topic: RE: Article: Lightning Protection On The B787
Username: Stitch
Posted 2006-07-13 15:28:37 and read 6742 times.

Boeing appears to always have expected to use the mesh. It may need to be more extensive then they expected, or perhaps they have chosen to - or have been forced to - "overbuild" it a bit since it is not something that can be "field-replaced" if damaged by a significant strike, which might have kicked up the weight. Or they may be using a heavier alloy than originally planned to improve effectiveness/longetivity.

Topic: RE: Article: Lightning Protection On The B787
Username: LAXPAX
Posted 2006-07-14 01:18:22 and read 6606 times.

I once saw a fascinating documentary about lightning on PBS. One segment was about scientists who were researching the effect of lightning on composite aircraft skins.

First, they demonstrated how a lightning strike on a typical aluminum airliner is conducted along the skin, until the bolt dissipates (as illustrated in the video frame below).

Then they triggered a lightning bolt at a section of composite fuselage. The bolt simply punched a hole directly through the skin. THAT'S why Boeing is so serious about perfecting technologies that give the composite fuselage the same lightning-resistant characteristics of aluminum.

ANA 747 lightning strike
(see video footage at: http://www.ebaumsworld.com/planelightning.html)

Topic: RE: Article: Lightning Protection On The B787
Username: FoxBravo
Posted 2006-07-14 01:35:15 and read 6589 times.

Interesting article--thanks. I am even more fascinated by the third part of the article, regarding the gust suppression technology. That sounds pretty incredible! I am strongly in favor of anything that reduces motion during turbulence.  Smile

Topic: RE: Article: Lightning Protection On The B787
Username: Zvezda
Posted 2006-07-14 01:56:12 and read 6554 times.

The idea here is to establish a Faraday cage. Copper mesh turns out to be the lightest and most robust way to do so.

Topic: RE: Article: Lightning Protection On The B787
Username: DfwRevolution
Posted 2006-07-14 02:12:30 and read 6529 times.

Quoting Rheinbote (Reply 4):
Maybe this "lightning strike protection issue" is the Boeing equivalent to the Airbus "electric harness" smart excuse?

Except that the A388 was already into production when the wiring issue became aparent, then yes.

And except that the 787 represents an entirely new way to build an aircraft, while aircraft have required complex wiring for generations, then yes.  Yeah sure

Topic: RE: Article: Lightning Protection On The B787
Username: Antares
Posted 2006-07-14 03:25:31 and read 6483 times.

Just curious, if wire mesh is sandwiched into the composite layers, and it gets vapourized in a lightning strike, what happens to the integrity of the bond? How do you repair the panel? Or doesn't it need repairing?

It seems to me that the whole idea of the Dreamliner was to reduce metal and weight, right?

I know composites have been around a long time in military aircraft and in components of passenger jets. But I don't think these military planes were pressurized high cycle air frames. I wonder if the challenges Boeing is addressing are more of a quantum leap that some ordinary travellers like myself had realized.

Antares

Topic: RE: Article: Lightning Protection On The B787
Username: Zvezda
Posted 2006-07-14 04:30:59 and read 6426 times.

Quoting Antares (Reply 15):
Just curious, if wire mesh is sandwiched into the composite layers, and it gets vapourized in a lightning strike, what happens to the integrity of the bond?

The wire mesh doesn't get vapourized. There would probably be some ablation of the resin on the outer surface, but that would be an easy repair if one were even needed.

Topic: RE: Article: Lightning Protection On The B787
Username: Antares
Posted 2006-07-14 05:46:55 and read 6366 times.

Zvezda,

How do you repair resin on the outer surface, and outer surface of what?

I thought the resin was holding together layers of reinforced carbon fibre, ratherer than one layer of resin being exposed to the elements.

If the resin is in fact in a sandwich that sounds like you have to undo the sandwich to get at the area that needs repair.

I know these are dumb lay person questions, but the dumbest questions in life are those you don't ask.

It will be pretty annoying all around if the 787 has to be held together with additional metal just to make the composite bits work properly. Not quite how I originally thought it was going to be.

Antares

PS One of the tribe has asked a 'duh' question too. If his composite sail board suffers from damage from ultraviolet over a few summers, what is going to happen to a composite jet in being exposed for many hours in a much fiercer UV regime.

Its school holidays. You get questions like this....

Topic: RE: Article: Lightning Protection On The B787
Username: N8076U
Posted 2006-07-14 06:50:22 and read 6326 times.

Quoting Antares (Reply 15):
Just curious, if wire mesh is sandwiched into the composite layers, and it gets vapourized in a lightning strike, what happens to the integrity of the bond? How do you repair the panel?

It is dealt with no differently than existing carbon fiber panels already in service, like the inlet cowls on the 747-400. Once in service, the 787 shouldn't cause too many problems, at least with smaller repairs like those from lightning strikes. You do a repair, and either bond in a small piece of mesh with it, or use a paint-on layer of conductive coating after the repair is cured, under the primer. You would cut away beyond the damaged area to make sure you get into some "good meat". The repair is vacuum-bagged to eliminate air and to compress it, and a heat blanket is used to bring the area up to the proper temperature required by the resin used.

Chris

Topic: RE: Article: Lightning Protection On The B787
Username: Rheinbote
Posted 2006-07-14 12:24:32 and read 6242 times.

Quoting DfwRevolution (Reply 14):
And except that the 787 represents an entirely new way to build an aircraft, while aircraft have required complex wiring for generations, then yes.

No A vs B flame intended. In terms of orders of magnitude, it's comparing apples with grapes, agreed.

Just thought that like the problems with the A380 cannot be entirely attributed to 'electric harnesses', the 787 being over weight target by 2,5% are unlikely to be entirely attributable to LSP.

Constituting 25% of aircraft empty weight, the wing would have to be 10% over its component target to achieve an overrun of 2,5% at aircraft level.

Topic: RE: Article: Lightning Protection On The B787
Username: Kaneporta1
Posted 2006-07-14 15:12:53 and read 6183 times.

Quoting Zvezda (Reply 16):
The wire mesh doesn't get vapourized. There would probably be some ablation of the resin on the outer surface, but that would be an easy repair if one were even needed.

That is not correct, I've read some research papers on this, and the mesh will be vaporised, maybe not all of it, but certainly around the point where the strike occurs.

Topic: RE: Article: Lightning Protection On The B787
Username: FLALEFTY
Posted 2006-07-14 15:47:10 and read 6152 times.

http://seattletimes.nwsource.com/htm...echnology/2002844619_boeing05.html

Here is another good article from the Seattle Times summarizing the steps Boeing engineers (and their subcontractors) are taking to protect the 787 from lightning strikes.

Topic: RE: Article: Lightning Protection On The B787
Username: FLALEFTY
Posted 2006-07-14 15:56:01 and read 6136 times.

http://seattletimes.nwsource.com/new...business/links/boeinglightni_b.pdf

Here is a graphic from the above article which summarizes Boeing's approaches.

Topic: RE: Article: Lightning Protection On The B787
Username: Derik737
Posted 2006-07-14 17:01:13 and read 6095 times.

Quoting AF1624 (Reply 3):
Usually, the lightning would be drawn towards the lightning rod/conductors that are on the aicraft,

Those are actually called static dischargers or static wicks.

Purpose
There are static dischargers on the airplane to decrease radio receiver interference. The static dischargers discharge static at points as far from the fuselage as possible. This makes sure there is the least amout of coupling into the radio receiver antennas.

Characteristics
Each discharger has a carbon fiber tip at the end of a slender rod. The rod is a resistive (conducting) material and attaches to a metal base. The base attaches and bonds to the airplane surface.

There are trailing edge and tip dischargers. The tip dischargers are smaller than the trailing edge dischargers.

While lightning can "exit" through a discharger, it is my experience that most of the time it won't.

Topic: RE: Article: Lightning Protection On The B787
Username: AirSpare
Posted 2006-07-14 17:48:46 and read 6043 times.

War story warning-

A guy from the Comm shop came into our shop and said that a 135 declared an IFE due to a strike and was on final. It was more like "A 135 was hit by lightning and is going to crash!". We went out to the flighthline, watched a high speed landing and the crash trucks. That was it (the damaged wing was on the other side so we could'nt see any damage).

I did'nt have a reason to go over to the 135 side much, but a few days later I was stuck driving the line truck (parts deliveries for red-balls, etc.) and drove by it. It was hit on the nose radome, the strike exited the starboard wing and it blew off about 23 feet of wing. From the starboard engine pylon out, it was gone. I stopped and talked to the crew chief, he said there was a FLASH/BANG!, the AC rocked then continued straight and level.

Quoting AF1624 (Reply 3):
Can a lightning strike really dig a hole, as small as it would be, into an airframe ?

Yea, and a lot more!

I'm curious, if the copper mesh under a strike location would be vaporized by a strike, if that would cause a delamination. at least locally.

Topic: RE: Article: Lightning Protection On The B787
Username: HB88
Posted 2006-07-14 20:22:48 and read 5961 times.

I think the issue is more complicated than most people think. In a fully CFRP a/c there is no metallic substructure to provide charge dissipation in the event of a lightning strike - so you need to provide one one way or another and that is going to involve metal. Fundamentally, you need to be able to dissipate charge away from an attachment point towards a static wick or other sharp point on the a/c. This will cause local ionisation of the gas proximate the wick so as to allow the charge to 'bleed off' into the atmosphere.

For a composite aircraft, at the lightning attachment point (assuming it hits a region where there is a metallic surface mesh), there will be sacrificial ablation of the mesh or mesh layers on the surface of the composite part and if the conduction isn't sufficient, the strike will almost certainly affect the structural integrity of the composite at the attachment point. This is an issue because the damage can occur deep inside the composite layer and thus is extremely difficult to inspect conventionally. This is made even more problematic as the attachment point 'wanders' backward across the wing surface as the aircraft moves in relation to the stationary attachment location. So, you get a series of pits and damage to the surface layer and hidden damage which needs some form of reliable inspection technique.

Another further problem is that unless the localised charge caused by the attachment isn't dissipated away quickly (to where?), the charge will induce edge glow and arcing on any gap where a potential difference is set up. Around fuel tanks this is clearly not a good thing if, for example, you get a spark or worse still, blowthrough, in the region of a fastener. Backups such as fuel inerting, interference-fit fasteners and insulating heads are not ideal as fasteners and insulators will work loose over time (and would be an inspection nightmare) and fuel inerting is not a complete solution.

A further interesting issue is that if you have a structural metallic component with an outer surface part which is struck by lightning, in a non-conducting composite a/c structure, the strike can 'tunnel' into the interior structure of the aircraft as the charge will 'follow' the least resistant conduction path. Unless there is an effective way of dissipating the induced charge, the strike will, along the way, cause a myriad potential differences which could cause sparking inside the aircraft wing or fuselage structure itself and possibly damage to internal electrical systems.

For all their sins, metallic aircraft provide an extremely effective and safe protective faraday cage for flying in high EM environments such as thunderstorms. Any a/c with a high percentage of CFRP such as the 787 provides no such inherent protection. So it needs to be designed in and certified as being reliable and safe.

Personally, I'm not surprised that this issue is causing some headaches in Boeing. A 100% CFRP aircraft would be incredibly dangerous in terms of lighting protection. Until a highly conductive CFRP material is developed, there is always going to be metal in such an aircraft.

(you can also see that in relation to the aircrafts internal electrical systems, having no conductive substructure is another headache in terms of 'grounding' electric component failure currents. This issue is exacerbated by a "more electric" (eg bleedless) aircraft.)


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