Building the 787 | When lightning strikes

Seattle Times ^ | Sunday, March 5, 2006 | Dominic Gates

[phantomworker]

Off-loaded to Wichita?

[cpdiii]

I know there is a special electrical conductive like paint made here in Phx for special applications...wonder how that might work in discharging lightning??

The less paint on a plane the better so far as fuel burn is concerned. To paint an entire airplane the size of a 787 would add a few thousand pounds to the airframe. That is expensive.

[Question_Assumptions]

I'm still looking for information on (A) how fast this carbon composite will burn when contrasted to a conventional aluminum airframe (what happens when one of these things goes on fire -- yes, I know aluminum melts and burns, too) and (B) how will they repair these composite one-piece airframes if an impact damages the structure of the composite (I assume you can't just rivet on a new piece of carbon composite, or can you?)?

[nightdriver]

"I'm still looking for information on (A) how fast this carbon composite will burn when contrasted to a conventional aluminum airframe (what happens when one of these things goes on fire....

Ol' Bill Lear (of LearJet fame) learned that the carbon fiber composits have a nasty fire characteristic. Even using chasis as electrical ground runs the danger of igniting the stuff and the fire gives off some very toxic fumes.

As an old alum of Boeing (747 project), I'm not really very optimistic about their new plastic and electric airplane.

[phantomworker]

Composites are not new in commercial aviation, he said. And although the safety team's conclusion was "absolutely true at the time" it was written, he said, by the end of the testing and analysis now in progress, the 787 will meet strict Federal Aviation Authority (FAA) requirements.

Plus

... the safety systems combined will assure the 787 exceeds the one-in-a-billion probability target.

I think there is a lot to be optimistic about! These are all new state of the art composites in a super efficient new airplane model. The 747 was once just a glint in Bill Boeing's eye as well. (Was he still alive when the 747 was designed?)

[Question_Assumptions]

Thanks for the honest answer. That's what worries me about this thing. I know aluminum has it's problems but plastic gets really nasty when it burns.

[phantomworker]

I think there is a lot of titanium on this plane. Doesn't Ti have a high burning point? (it is good in fireworks, lol)

[knew it all the time]

Approximately 40% of the F/A 18 airframe is composite construction. It appears to be working in that application.

[Jonah Hex]

Years ago, I was a pax on a B-747 when our aircraft took a hit on the wing during descent into San Francisco. There was a flash/bang which scared the hell out of everybody (including me) as we looked at each other with an "oh sh*#, what the hell was that?!?" expression on our faces. A few minutes later, the captain announced we'd taken a lightening strike on the port wing, but everything was okay and we'd arrive on time.

This occurred prior to 9/11. I'd hate to think of our reaction if it'd happen after that day. (Probably a sudden drop in cabin pressure as a few hundred sphincters tightened at once.)

[griffin]

Boeing "will have to do a lot of testing, a lot of analysis and provide the FAA a lot of data"

Knowing the way reliability engineers calculate their "analysis" I'd be very interested to go through the report they cook up for the FAA to prove the one-in-a-billion compliance! LOL!

[phantomworker]

"One-in-a-billion" seems like pretty tight reliability, but safety is paramount. Not sure how they test FoM (first of model) and how much is done by analysis. Probably not like military planes where they actually break the plane to test its limits.

[Paleo Conservative]

If you want on or off my aerospace ping list, please contact me by Freep mail.

[COEXERJ145]

William Boeing died shortly after the 367-80 was rolled out.

[Paleo Conservative]

William Boeing died shortly after the 367-80 was rolled out.

It's hard to believe how much progress was made in just the first 50 years of aviation. Literally going from the Wright Brothers' first flimsy flyer of 1903 to the B-47, XB-52, and the design of the 367-80.

[Zuben Elgenubi]

Thank you PC. I understand, now.

[PAR35]

(I assume you can't just rivet on a new piece of carbon composite, or can you?)?

I would think that you'd use glue instead of rivets. I'll leave any discussion about structural issues to the engineers.

[phantomworker]

I'm not a structural engineer, but I'm pretty sure you can't just use glue instead of rivets, unless you have a portable autoclave. Interesting idea, though.

[orionblamblam]

> carbon fiber is conductive.

In the direction of the fiber, but not *between* fibers. And I don't think it's really all *that* conductive. I find electrical resistance for carbon fiber (raw) to be on the order of 0.00155 ohm-cm , while for 5000-series aluminum it's 5.5e-006 ohm-cm. That's several orders of magnitude.

[Yo-Yo]

To paint an entire airplane the size of a 787 would add a few thousand pounds to the airframe. That is expensive.

They're going to paint every inch of the 787 fuselage no matter what. Unless they want a black aircraft.

[narby]

I find electrical resistance for carbon fiber (raw) to be on the order of 0.00155 ohm-cm , while for 5000-series aluminum it's 5.5e-006 ohm-cm. That's several orders of magnitude.

Lightning operates a bit wierd compared with normal electricity. You can put a lightning rod on your house with a relatively small wire that could in no way carry the real load of the strike. Yet the lighting will follow it, as long as yoy lay it out correctly (no sharp bends in the wire).

I'm sure there will be inter-fiber damage in a strike where the lightning jumps between fibers, but it's not going to be like an S glass airframe that basically explodes, even if there's no fuel present.