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Faro
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Cfrp Airliners: How Long A Useful Life?

Fri Sep 02, 2011 10:18 am

Given that CFRP presents much less fatigue issues, how much longer useful life will the likes of the 787 and A350 have in terms of hours and flight cycles? Will this increased life actually be used by airlines or will it translate into a glut of freighters on the market in 20 years' time from now?

Faro
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tdscanuck
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RE: Cfrp Airliners: How Long A Useful Life?

Fri Sep 02, 2011 1:55 pm

Quoting faro (Thread starter):

Given that CFRP presents much less fatigue issues, how much longer useful life will the likes of the 787 and A350 have in terms of hours and flight cycles?

Tough to tell. However, if other examples of very long-life airliners are any guide, we're probably talking 30-40 years (+50-100% hours/cycles). They will likely become economically obsolete before their structure gives out.

Keep in mind that there is still metal in there in crucial places and it's all got a finite fatigue life. It might not pay to replace, say, a fuselage splice plate 30 years from now.

Quoting faro (Thread starter):
Will this increased life actually be used by airlines or will it translate into a glut of freighters on the market in 20 years' time from now?

Some of both, I expect. 20 years from now we'll have to have made more progress in efficiency, so only some airlines will have route and business models where a then "antiquated" 787/A350 can make money.

Tom.
 
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Faro
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RE: Cfrp Airliners: How Long A Useful Life?

Fri Sep 09, 2011 2:27 pm

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):

Given that CFRP presents much less fatigue issues, how much longer useful life will the likes of the 787 and A350 have in terms of hours and flight cycles?

Tough to tell. However, if other examples of very long-life airliners are any guide, we're probably talking 30-40 years (+50-100% hours/cycles). They will likely become economically obsolete before their structure gives out

I wonder then if the airframes can last such a long time whether re-engining will become the trend of the future. Barring the development of practical BWB aircraft (commercial obstacles, costly) or some spectacular breakthrough in wing aerodynamics (unlikely), engines are where the majority of future efficiency gains are likely to come from. Don't be surprised if a significant proportion of 787/A350 frames are still plying the skies +40 years from production date...

Faro
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Stitch
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RE: Cfrp Airliners: How Long A Useful Life?

Fri Sep 09, 2011 4:50 pm

Quoting faro (Thread starter):
Given that CFRP presents much less fatigue issues, how much longer useful life will the likes of the 787 and A350 have in terms of hours and flight cycles?

A CFRP structure eventually reaches a "fatigue floor" at which point no further degradation occurs regardless of how many cycles / hours of wear are generated. So in theory, the fuselage and wings of a 787 or A350 have no limits. I say in theory because the fasteners and such do have a maximum-rated life along with the other systems.

However, we have DC-9s today that are approaching the half-century mark so I fully expect that we will see 787s and A350s in passenger revenue service a half-decade after delivery. And if the passenger airframes are suitable for conversion to freighters and the systems can be kept up to date for a reasonable cost, it just may not be outside of the realm of possibility to see a 787BCF or A350P2F crossing the 75 year mark or even the century mark.   
 
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Faro
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RE: Cfrp Airliners: How Long A Useful Life?

Fri Sep 09, 2011 4:57 pm

Quoting Stitch (Reply 3):
it just may not be outside of the realm of possibility to see a 787BCF or A350P2F crossing the 75 year mark or even the century mark.

Or even doing the pax charter circuits with refitted open-rotors or 70,000 lb GTF's...

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474218
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RE: Cfrp Airliners: How Long A Useful Life?

Fri Sep 09, 2011 6:59 pm

Does any you know how many cycles the the 787 fatigue test airframe was subject too. Common practice is to divide the number of test cycles achieved and then divide that number in half for the designed service fife.
 
tdscanuck
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RE: Cfrp Airliners: How Long A Useful Life?

Sat Sep 10, 2011 1:36 am

Quoting Stitch (Reply 3):
A CFRP structure eventually reaches a "fatigue floor" at which point no further degradation occurs regardless of how many cycles / hours of wear are generated. So in theory, the fuselage and wings of a 787 or A350 have no limits.

That's only true if the fatigue floor is high enough that it's still good for limit load...that's unlikely to be the case (too heavy).

Quoting 474218 (Reply 5):
Does any you know how many cycles the the 787 fatigue test airframe was subject too.

They passed 10,000 back in May:
http://www.flightglobal.com/blogs/fl...boeing-passes-10000-cycles-on.html

Quoting 474218 (Reply 5):
Common practice is to divide the number of test cycles achieved and then divide that number in half for the designed service fife.

That doesn't determine design service life...design life is a target established at the beginning. The requirement is that the fatigue test article has to go (at least) to double the design life but it doesn't have to do that before certification. According to the flight global article, they just need to stay 10,000 cycles ahead of the fleet leader.

Tom.
 
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RE: Cfrp Airliners: How Long A Useful Life?

Sat Sep 10, 2011 1:20 pm

Quoting tdscanuck (Reply 6):
That doesn't determine design service life...design life is a target established at the beginning. The requirement is that the fatigue test article has to go (at least) to double the design life but it doesn't have to do that before certification. According to the flight global article, they just need to stay 10,000 cycles ahead of the fleet leader.

That may be way Boeing is doing it now but, when the Aging Aircraft Task Force was established, and all commercial aircraft with a MGTO weight of over 75,000 lbs had to provide a Design Life Goal what I stated was the criteria used. Additionally if the OEM did not provide a DLG the FAA would establish one for them using that basic criteria.

I must use my experience on the L-1011. If you have seen pictures of the L-1011 fatigue test airframe it did not have a flight station. Instead it had had a metal fitting that was used to pressurize the fuselage, which meant the flight station had to be tested separately. So while the entire airframe, less the flight station, was tested to 84,000 flight cycles. The separate flight station test stopped at 72,000 flights. One half of 72,000 is 36,000 the design life goal of the L-1011.
 
cmf
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RE: Cfrp Airliners: How Long A Useful Life?

Mon Sep 12, 2011 2:16 am

Quoting tdscanuck (Reply 6):
they just need to stay 10,000 cycles ahead of the fleet leader.

A bit picky but IIRC it is minimum twice the number of cycles and not less than 10,000 above the fleet leader.
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