LV
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Lightning And Composit Frames

Sun Apr 04, 2010 4:59 am

I was just watching a show on the History Channel, it said every commercial airliner is likely to be hit by lighting at least once a year... and that what makes getting hit safe is the aluminum that makes up the air frame. That got me thinking, with manufactures moving toward composite frames... how will the lightning react when it hits. Will we be more likely to see accidents because of this? I assume Boeing and Airbus has done a tremendous amount of research as obviously this would be a huge liability no matter what the cost savings.
 
macsog6
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RE: Lightning And Composit Frames

Sun Apr 04, 2010 5:06 am

Beech did extensive testing on the airframe for the Model 2000 Starship which involved lightning strikes. Woven into the composite structure was a metallic layer, which looked amazing like window screen, which served to conduct the electricity much as the metal skin of a non-composite aircraft does.

The Starship handled hits just about as well as any conventional aircraft. I can only asume that since the 1980's, when the Starship was being tested, the technology for this has gotten better.
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baroque
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RE: Lightning And Composit Frames

Sun Apr 04, 2010 5:11 am

Quoting LV (Thread starter):
Will we be more likely to see accidents because of this? I assume Boeing and Airbus has done a tremendous amount of research as obviously this would be a huge liability no matter what the cost savings.

Well if there was an incident due to lightning, it would not be an accident as it would be by design. The folk that know, say it is taken care of by ?copper mesh for the 787. Not sure what the A350 solution is, but they have so much plastic in existing models they must have some experience of what happens.

It is quite dramatic being struck on the ground. I was in a 747 in Singapore when its tail was struck. APU went out and some hours to repair.

Overall sounds exciting, but aside from the weight associated with the fix, probably nothing more than a point of interest.
 
NoWorries
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RE: Lightning And Composit Frames

Sun Apr 04, 2010 8:02 pm

Quoting Baroque (Reply 2):
it is taken care of by ?copper mesh

I think it's a copper alloy -- bronze.

There've been quite a few threads about this over the years, with a lot of good info -- I'd recommend a topic search; it'd probably answer a number of questions.
 
GST
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RE: Lightning And Composit Frames

Sun Apr 04, 2010 9:10 pm

A few weeks ago I was at a royal aeronautical society lecture, during which two samples of composites were passed round. They had both been lightning strike tested by Bombardier, and were the same material pegged to make up much of the C Series. The first, without the metallic mesh there was complete burn-through where the hit was located (you could put two fingers right through), the sample that utilised the metallic mesh was barely discoloured, and tests had shown negligible internal damage also.

I do not expect to see any commercial airliners being brought down by lightning & composites disagreeing with each other. I do expect to see a possible rise in the number of lightning strike crashes and serious damage incidents with light sport aircraft, as they increasingly utilise composite construction and they are not supposed to be anywhere near spark clouds in most cases, so many will not have the mesh protection.
 
soon7x7
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RE: Lightning And Composit Frames

Mon Apr 05, 2010 3:25 am

The internal mesh is one method of distributing the charge on composites while other methods use a sprayed aluminized layer underneath the topcoat. The panels are then bonded by a metal braid to the alloy airframe. I once saw a Gulfstream llB with an all metal airframe peperred with lightning exit points, so much so that it was considered a write off. Depends on the circumstances. Normally nothing will happen...one Cessna Citation I saw had a strike on the nose bowl, passed ball lightning through the cabin and blew out a football sized hole out the tail cone. On a WN flight out of MDW we flew right into a squalline and sustained some real snotty weather...the environment outside the windows was green/pinkish, I knew we were in for it...we did take two hits but one had both wings wrapped in a hot pink spider web of electricity. Nothing happened...the lights did not even blink...upon landing at ISP however the MX found an exit wound from the strike underneath where I was seated...(comforting).
 
TSS
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RE: Lightning And Composit Frames

Mon Apr 05, 2010 6:06 am

Quoting NoWorries (Reply 3):
Quoting Baroque (Reply 2):
it is taken care of by ?copper mesh

I think it's a copper alloy -- bronze.

It just occurred to me to wonder about this: Wouldn't having bronze mesh throughout the aircraft's skin have the side-effect of making the fuselage a very large Faraday cage that would block external signals to devices such as cell phones?
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GST
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RE: Lightning And Composit Frames

Mon Apr 05, 2010 9:58 am

Quoting TSS (Reply 6):

It just occurred to me to wonder about this: Wouldn't having bronze mesh throughout the aircraft's skin have the side-effect of making the fuselage a very large Faraday cage that would block external signals to devices such as cell phones?

This is an interesting point, and now I'm kicking myself for not asking that at the RAeS lecture. It would be a really pleasant world when even those who arrogantly try to use their phones in the aircraft be it on the ground or airborne actually can't!
 
NoWorries
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RE: Lightning And Composit Frames

Mon Apr 05, 2010 1:03 pm

Quoting TSS (Reply 6):
Quoting NoWorries (Reply 3):
Quoting Baroque (Reply 2):
it is taken care of by ?copper mesh

I think it's a copper alloy -- bronze.

It just occurred to me to wonder about this: Wouldn't having bronze mesh throughout the aircraft's skin have the side-effect of making the fuselage a very large Faraday cage that would block external signals to devices such as cell phones?

I'm not sure that it would be any more effective that a plain old aluminum fuse -- the windows are the culprits, allowing signals to pass. An interesting quuestion is whether those new windows on the 787 block signals to any extent?
 
tdscanuck
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RE: Lightning And Composit Frames

Tue Apr 06, 2010 12:34 am

Quoting TSS (Reply 6):
Wouldn't having bronze mesh throughout the aircraft's skin have the side-effect of making the fuselage a very large Faraday cage

That's not a side-effect, it's the entire point. That's the main thing that protects the contents of the plane from lightning strike damage.

Quoting TSS (Reply 6):
that would block external signals to devices such as cell phones?

Nope. The holes in the fuselage are more than big enough to let cell-phone wavelengths in.

Tom.
 
NoWorries
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RE: Lightning And Composit Frames

Tue Apr 06, 2010 1:31 pm

Quoting tdscanuck (Reply 9):
Nope. The holes in the fuselage are more than big enough to let cell-phone wavelengths in.

Yep -- the rule of thumb is that a half-wavelength opening doesn't reduce signal power. Cell phone signals cover a variety of frequencies -- taking 1 GHz just as an example, that's a wavelength of 30cm. A 15cm opening allows full power to pass through. Once below half-wavelength, the power throughput drops off rather dramatically.
 
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akiss20
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RE: Lightning And Composit Frames

Wed Apr 07, 2010 4:51 pm

Interesting note on this and the future of nanotech. One of the guys I worked with in a lab had a separate research position on growing conductive carbon nanotubes. One of the primary industrial applications they are slated for is lightning strike protection in composite airframes. Obviously with a metal airframe you have a conductive path, and with current composites, as stated above, they have to inter-weave a metallic mesh into the airframe. This costs a good amount of weight and fuel efficiency. Conductive carbon nanotubes grown onto the composite itself can provide the necessary conductive path while costing a fraction of the weight.

Pretty cool stuff
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tdscanuck
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RE: Lightning And Composit Frames

Thu Apr 08, 2010 4:21 am

Quoting AKiss20 (Reply 11):
Conductive carbon nanotubes grown onto the composite itself can provide the necessary conductive path while costing a fraction of the weight.

At over $100/mg at current prices, I'm not so sure they can buy their way on the plane yet.

Tom.
 
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akiss20
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RE: Lightning And Composit Frames

Fri Apr 09, 2010 4:01 am

Quoting tdscanuck (Reply 12):
Quoting AKiss20 (Reply 11):
Conductive carbon nanotubes grown onto the composite itself can provide the necessary conductive path while costing a fraction of the weight.

At over $100/mg at current prices, I'm not so sure they can buy their way on the plane yet.

Tom.

Obviously we are the very beginning stages of using nanotech, especially carbon nanotubes. All manufacture processes as of yet are very expensive and purely for research, but the industrial process will get there eventually, especially once we learn to use the tech to its fullest. I mean, how expensive did memory on a computer used to be? Or industrial grade diamonds prior to growth via seeding?
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