MCIGuy
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Revisiting Composites

Sat Nov 08, 2008 1:16 am

The 787 and A350 will obviously have more composites used than any other airliners ever, but is it worth it? Didn't Boeing say that 17% of the 20% gain in efficiency on the 787 would come from the new engines? With all the delays and difficulties it seems that the extra 3% efficiency gained form composites might not be worth it. Also, if only 3% is to be gained from the use of CFRP, does this not make it little more than a marketing gimmick?
Please, I'd like to know opinions as to whether these ideas are correct or incorrect and why.
Thanks!
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planewasted
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RE: Revisiting Composites

Sat Nov 08, 2008 1:38 am

Composites also have other advantages, such as maintenance costs, production costs and cabin comfort.
 
MCIGuy
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RE: Revisiting Composites

Sat Nov 08, 2008 1:47 am



Quoting PlaneWasted (Reply 1):
Composites also have other advantages, such as maintenance costs, production costs and cabin comfort.

You have point, it is all that and more, but what about the maintenence? What if an airline has to change a fastener more than once and the hole gets damaged and enlarged? Can it be backfilled and repaired or does it at some point become a major issue?
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tdscanuck
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RE: Revisiting Composites

Sat Nov 08, 2008 3:02 am



Quoting MCIGuy (Thread starter):
The 787 and A350 will obviously have more composites used than any other airliners ever, but is it worth it?

Yep.

Quoting MCIGuy (Thread starter):
Didn't Boeing say that 17% of the 20% gain in efficiency on the 787 would come from the new engines?

I believe it was 10%, not 17%. Or about half. But the major gain for CFRP was the maintenance cost, not the fuel burn...the 20% figure is specifically related to fuel burn.

Quoting MCIGuy (Thread starter):
With all the delays and difficulties it seems that the extra 3% efficiency gained form composites might not be worth it.

CFRP isn't there primarily to reduce fuel burn, it's there to greatly reduce maintenance and increase longevity. As a byproduct, it also enables some of the "softer" features like increased cabin altitude and humidity.

Quoting MCIGuy (Thread starter):
Also, if only 3% is to be gained from the use of CFRP, does this not make it little more than a marketing gimmick?

No.

Quoting MCIGuy (Reply 2):
You have point, it is all that and more, but what about the maintenence? What if an airline has to change a fastener more than once and the hole gets damaged and enlarged? Can it be backfilled and repaired or does it at some point become a major issue?

You don't normally backfill, you oversize. Normal practice is to allow for one or two oversizes in any particular fastener, and I don't have any reason to believe the 787 is different on that score. If you run out of oversize, you can always go to a doubler. This problem occurs in aluminum too, so it's not like CFRP suddenly opened a can of worms on oversizing.

Tom.
 
MCIGuy
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RE: Revisiting Composites

Sat Nov 08, 2008 3:17 am



Quoting Tdscanuck (Reply 3):
You don't normally backfill, you oversize. Normal practice is to allow for one or two oversizes in any particular fastener, and I don't have any reason to believe the 787 is different on that score. If you run out of oversize, you can always go to a doubler. This problem occurs in aluminum too, so it's not like CFRP suddenly opened a can of worms on oversizing.

Ah, I see, so it's akin to to using a larger bolt or a helicoil when you strip a bolt. So if the hole gets too big they'd just back it with a CFRP or metal plate?
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soon7x7
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RE: Revisiting Composites

Sat Nov 08, 2008 1:38 pm



Quoting Tdscanuck (Reply 3):

You believe that composite repairs will be less expensive that sheet metal repairs?...if so , how and why?...j
 
tdscanuck
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RE: Revisiting Composites

Sat Nov 08, 2008 4:26 pm



Quoting MCIGuy (Reply 4):

Ah, I see, so it's akin to to using a larger bolt or a helicoil when you strip a bolt. So if the hole gets too big they'd just back it with a CFRP or metal plate?

Basically, yes. The SRM (structural repair manual) normally specifies how many oversizes you can do an, if you go past that, there are standard doubler repairs. A doubler is a just a backing (or fronting, depending on your you assemble it) plate that carries the load over the area you can't repair. It's very commonly used for small dents, dings, puctures, bad holes, etc.

Quoting Soon7x7 (Reply 5):

You believe that composite repairs will be less expensive that sheet metal repairs?...if so , how and why?...j

Not less expensive, less of them. CFRP is almost immune to corrosion and fatigue, which are two of your big drivers on structural repair. Ramp rash is obviously more of an even thing but there are some great impact-resistance demos for CFRP so I don't see this being particularly worse. Boeing has stated (several times) that they can use conventional repairs for ramp rash, so the cost should be the same.

Tom.

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