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When Will Boeing Know If 787 Design Details Worked  
User currently offline2175301 From United States of America, joined May 2007, 1022 posts, RR: 0
Posted (1 year 9 months 1 day 13 hours ago) and read 11496 times:

When Will Boeing know how well various 787 Design details and features worked (which is what I wanted for a tittle but it would not fit).

Now that the 787 is established in routine service and rolling off the production line (even if slower than desired); the question is how much time will it take to figure out how well certain design choices, and conservatism's, have worked out given that this is the first full size composite commercial jetliner.

While it is certainly true that it will take 20 years to validate some things - other things should take much less.

For example: The 787 composite barrels should be more resistant to "ramp rash"; and their are reasonable repairs available when it occurs. My personal guess is that it will take 2-3 years before there will be enough experience to see how much that is true; although it may take 5-7 years before someone hard drives a truck into a plane (as occurs once in a while).

I have read several times that Boeing designed in tons of extra reinforcement into the composite frame to be sure that it worked. When will they know how over-conservative they were; and have a good idea for when they can remove extra layers and the resulting weight? 5 years, 10 years, etc?

Did they properly design for the higher cabin humidity; and they can confirm that their is no unusual degradation. I suppose that will show up in the D checks.

I am sure that many fellow A-netters have their own list of specific items that need some kind of time limit to determine how well it worked. Everyone can join in.

Have a great day,

19 replies: All unread, jump to last
 
User currently offlinelightsaber From United States of America, joined Jan 2005, 12421 posts, RR: 100
Reply 1, posted (1 year 9 months 1 day 13 hours ago) and read 11393 times:
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Aerodynamics: Done

Engine Fuel burn: Will require 2 more PIPS, about 5 years

Range: Requires getting the aircraft down to promise weight, about two more years

Maintenance costs: Let's not forget this was a big promise, about 7 more years. For full understanding, it will be a bit longer to get through the first D-checks, but most of the cost reduction is the software that diagnosis if there is an issue. The humidity shouldn't be an issue for CFRP.

Recall much has been proven by material or component qualification. For example, corrosion life.

I'm a fan of the A330, but once the 787 is proven out, it isn't going to sell. A long time ago I put the end of the A330s sales life at 2017. Thanks to further PIPs, it should go a little longer, but eventually the 789 will be out in number forcing some tough competition. But note, despite my flag, that opinion is technically driven. Its also driven by A350 promises.   


Lightsaber



I've posted how many times?!?
User currently offlineSEPilot From United States of America, joined Dec 2006, 6681 posts, RR: 46
Reply 2, posted (1 year 9 months 1 day 12 hours ago) and read 11251 times:

One of the big advantages is lower airframe maintenance costs, and while you are correct that a lot of that will not really be known until the first ones undergo major maintenance, I believe that it will still show up fairly early. I believe that routine maintenance costs (which includes fixing ramp rash) will be lower starting early in the life of the airframes, but the real advantage will show up at major maintenance.


The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlineJAAlbert From United States of America, joined Jan 2006, 1491 posts, RR: 1
Reply 3, posted (1 year 9 months 1 day 12 hours ago) and read 11238 times:

How about the bleedless engine design? Has that lived up to expectations?

User currently offlinezeke From Hong Kong, joined Dec 2006, 8643 posts, RR: 75
Reply 4, posted (1 year 9 months 1 day 12 hours ago) and read 11153 times:

Quoting 2175301 (Thread starter):
When Will Boeing know how well various 787 Design details and features worked (which is what I wanted for a tittle but it would not fit).

I think they already know, they have their own internal historical data to compare with.

I think airlines are eager to get them. The 787 has had a great EIS, proved to be very reliable. They have been misused somewhat initially, placing them on shorter routes, however that is to be expected while the airline gets used to operating the new type.

The airframe will continue to improve, and continue to impress.

Quoting 2175301 (Thread starter):
The 787 composite barrels should be more resistant to "ramp rash"; and their are reasonable repairs available when it occurs.

A lot of ramp rash happens around openings in the aircraft, be it passenger doors, cargo doors etc. Most of these still have metallic components either in the frame or the actual mechanisms. I think if people try hard enough, they will still get damaged.

Quoting 2175301 (Thread starter):

Did they properly design for the higher cabin humidity; and they can confirm that their is no unusual degradation. I suppose that will show up in the D checks.

That technology has been in service now for around 6 years, I am not expecting the 787 to have significant issues with it.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (1 year 9 months 1 day 8 hours ago) and read 10597 times:

Quoting 2175301 (Thread starter):
The 787 composite barrels should be more resistant to "ramp rash"; and their are reasonable repairs available when it occurs. My personal guess is that it will take 2-3 years before there will be enough experience to see how much that is true

There's nothing to experience that hasn't already been experienced; the 787 is made from the same materials as nacelles have been made from for 20+ years. And nacelles get ramp rash all the time.

Quoting 2175301 (Thread starter):
I have read several times that Boeing designed in tons of extra reinforcement into the composite frame to be sure that it worked. When will they know how over-conservative they were;

On the static side, they already know; the static testing is complete. On the fatigue side, the fatigue frame has to stay, I believe, at 3x the fleet life so it will take, maximum, about 6 years. Likely much less. As others have said, almost all these properties are material properties, not design properties, and this particular material has been in active service for about 20 years.

Quoting 2175301 (Thread starter):
and have a good idea for when they can remove extra layers and the resulting weight? 5 years, 10 years, etc?

They know now. They just can't easily remove it now.

Tom.


User currently offlinerwessel From United States of America, joined Jan 2007, 2238 posts, RR: 2
Reply 6, posted (1 year 9 months 1 day 7 hours ago) and read 10402 times:
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Quoting tdscanuck (Reply 5):
On the static side, they already know; the static testing is complete. On the fatigue side, the fatigue frame has to stay, I believe, at 3x the fleet life so it will take, maximum, about 6 years. Likely much less. As others have said, almost all these properties are material properties, not design properties, and this particular material has been in active service for about 20 years.

I'm curious. What's the design life of the 787, and how accelerated is the fatigue testing on the static frame? Six years continuous is only 52k hours actual time. Obviously there has to be some acceleration factor, I can't imagine someone left a 747 on the test stand for 300k+ hours (~35 years).


User currently offlineaztrainer From United States of America, joined Oct 2011, 517 posts, RR: 1
Reply 7, posted (1 year 9 months 1 day 6 hours ago) and read 9295 times:

Quoting zeke (Reply 4):
A lot of ramp rash happens around openings in the aircraft, be it passenger doors, cargo doors etc. Most of these still have metallic components either in the frame or the actual mechanisms. I think if people try hard enough, they will still get damaged.

There was a show on TV about three weeks ago about the 787 and one of ANA's biggest concerns was the ability to fix ramp rash with a new material. Boeing provided them with a peace of the fuselage to test and they could not damage it. Then the person took a sample of the skin and a hammer and whacked it without any damage. They stated that ANA being so tech savvy could of killed the 787 if they did not like the new technology.

Boeing Impact Test (This is not what I saw, but it is the same idea) http://www.youtube.com/watch?v=-DE8LZcZgn4

I think the metal will be damaged way before the carbon fiber skin.

My question is about drilling into the "skin" How much does drilling into it lessens the strength of the skin? Also is/are there special procedures for drilling? I know the strength is in the angular lament of the carbon fiber, but can a hole be refilled by an epoxy type material?


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 8, posted (1 year 9 months 1 day 5 hours ago) and read 9255 times:

Quoting rwessel (Reply 6):
What's the design life of the 787

I think it's about 20 years but I've never seen that written down. That seems to be typical for modern generation widebodies.

Quoting rwessel (Reply 6):
how accelerated is the fatigue testing on the static frame?

I think it's about 5-10x on average but it goes in fits and starts...they go for x thousand cycles and then stop and inspect every nook and cranny. The time plot would look like a bunch of square waves.

Quoting rwessel (Reply 6):
Six years continuous is only 52k hours actual time. Obviously there has to be some acceleration factor, I can't imagine someone left a 747 on the test stand for 300k+ hours (~35 years).

At the frequencies we're talking about for aircraft fatigue cycles, the frequency doesn't matter much, just the number of cycles. So if you need 100 cycles it really doesn't make a difference if you go at 0.1 Hz (1000 seconds) or 10 Hz (10 seconds). The OEM's define a particular statistical combination of loadings (air loads, pressurization, takeoff/landing, turbulence) to be a "fligth" and then basically run them as fast as testing fidelity allows.

Tom.


User currently offlinelightsaber From United States of America, joined Jan 2005, 12421 posts, RR: 100
Reply 9, posted (1 year 9 months 1 day 1 hour ago) and read 7366 times:
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Quoting tdscanuck (Reply 8):
Quoting rwessel (Reply 6):
What's the design life of the 787

I think it's about 20 years but I've never seen that written down. That seems to be typical for modern generation widebodies.

Design life is 3X the D-check interval.
From:
http://www.leandesign.com/pdf/787.pdf


“We expect, working with the FAA, that maintenance intervals will be improved
over the 767, possibly by as
much as 60-100%.” In other
words, where a 767 inspection
interval now may be at six years,
the 787 D-check interval could
be as much as 10-12 years.


That implies a 30 to 36 year design life. It also implies a 20 to 24 year economic life in passenger duty with a longer life for freighters. But wait until my next link. If its maintenance costs prove true, we could see the 787 in pax duty for 30 years! We'll see 787s still flying in 2050.   

I recall reading the 10 to 12 year D-check interval elsewhere too.

There is evidence:
Note: Largish pdf: http://www.vaughn.edu/assets/downloads/atec-2008-01.pdf
The 777 fleet history reveals
ZERO non-routine labor hours
for the composite floor beams


I recommend that PDF. It goes into the fundamental reasons the 787 should fly longer than a 767.

Lightsaber



I've posted how many times?!?
User currently offlinefaro From Egypt, joined Aug 2007, 1515 posts, RR: 0
Reply 10, posted (1 year 9 months 15 hours ago) and read 4603 times:

Quoting lightsaber (Reply 9):
If its maintenance costs prove true, we could see the 787 in pax duty for 30 years! We'll see 787s still flying in 2050.

Indeed, see Reply 3 of: Cfrp Airliners: How Long A Useful Life? (by faro Sep 2 2011 in Tech Ops)

Quote:
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.

Faro



The chalice not my son
User currently offlineLHCVG From United States of America, joined May 2009, 1449 posts, RR: 1
Reply 11, posted (1 year 9 months 15 hours ago) and read 4378 times:

Quoting faro (Reply 10):
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.

I've been curious about how the fatigue floor works - is it really a floor per se, or just practically speaking where it still degrades but just at miniscule levels from there on out?


User currently offlineoldeuropean From Germany, joined May 2005, 2026 posts, RR: 4
Reply 12, posted (1 year 9 months 14 hours ago) and read 4159 times:

Quoting aztrainer (Reply 7):
Then the person took a sample of the skin and a hammer and whacked it without any damage.

That's ridiculous – there is a difference between the force of a hammer and the inertia of a truck with a weight of some tons.  



Wer wenig weiss muss vieles glauben
User currently offlinelightsaber From United States of America, joined Jan 2005, 12421 posts, RR: 100
Reply 13, posted (1 year 9 months 13 hours ago) and read 3791 times:
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Quoting faro (Reply 10):
Indeed, see Reply 3 of: Cfrp Airliners: How Long A Useful Life? (by faro Sep 2 2011 in Tech Ops)

Quote:
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.

  

And great corrosion...

It will be the fasteners and ironically fuel burn that limit the 787s service life. But we will have to 'reset' some of the normal estimates due to the very low maintenance costs.

Quoting oldeuropean (Reply 12):
there is a difference between the force of a hammer and the inertia of a truck with a weight of some tons.

Yes. But it means that throwing luggage is no longer of concern to dent and ding the airframe.  


Reading a link from the thread you noted:
" Boeing will push ZY998 to as many as 165,000 over the next three years to determine the long-term structural life of the 787."
http://www.flightglobal.com/blogs/fl...boeing-passes-10000-cycles-on.html

Or we could see a service life extension to 82,500 cycles! That is a narrowbody life! I wonder if JAL/ANA made demands to have a life > 44k cycles (plan, see above link) for resale value after domestic operations?

Any which way, it looks like the 787 will have the cycles for a 36 year service life. Since Boeing makes a profit off service life extensions, I would expect to see one for the 787. Note: Only a profit if there are enough sold and the 787 easily passed that benchmark.

The only issues I see with the 787 today are:
1. Empty weight
2. Engine fuel burn (both missed)
3. How few are out there.

The last one is being fixed by a ramp in the production rate.
The engine fuel burn will require a new low turbine from both GE and RR (somehow both botched the same module).
I know quite a few engineers hired by Boeing to fix #1. That should cease to be a discussion point after LN120. Pick another LN if you so choose. What matters is 2014 on 787s won't have a weight issue just as the latest build 787s have a lesser issue.

What is the range of the current GE and RR examples entering the fleet? I've lost that bubble. We should be approaching 7,600nm.    The 787 should 'get its legs' as range increases to promise.

Lightsaber



I've posted how many times?!?
User currently offlineCM From , joined Dec 1969, posts, RR:
Reply 14, posted (1 year 9 months 13 hours ago) and read 3753 times:

Quoting rwessel (Reply 6):
What's the design life of the 787

Aircraft do not have a "design life", per se, at least not in the same way milk has a pull-date (i.e. there is no "expiration" for the aircraft). What aircraft do have is a DSO, an LOV and an "economic life".

DSO = Design Service Objective: DSO is an anticipated number of cycles the average airplane is expected to experience over a 20 year period. The DSO is useful for designers when sizing parts for fatigue and for helping to define certain parts of the maintenance program, but does not have any real practical implications for the airplane or its operators. Airbus call this measure DSG (Design Service Goal), which is similar in most regards, except Airbus uses a 24 year period rather than 20.

LOV = Limit of Validity: LOV is a relatively new measure for the industry, only having become law in the last year or so. LOV effectively defines the useful limit of an airplane's maintenance program. OEM's have had to declare their LOV's in the last year or so for all aircraft (I do not believe they have released an LOV for the A380 and 787 yet, but all other aircraft are done). Defined as a flight hours and cycles limit, LOV is a limit at which a new and more rigorous maintenance program must be implemented for a given frame. As such, LOV has a direct impact on an aircraft's economics and has a much more direct impact on when an operator may retire an airplane.

Economic Life: This is the real driver behind aircraft retirement. Aircraft become too inefficient compared to newer aircraft, and too costly to maintain compared to newer aircraft, at which point they are said to have reached the limits of their "economic life".

Quoting rwessel (Reply 6):
how accelerated is the fatigue testing on the static frame?

Not sure when Boeing started fatigue testing of the 787, but the fatigue frame just passed 1 DSO (see above), which is representative of 20 years of service for an average airplane. The test frame will be tested to 3 DSOs

Quoting oldeuropean (Reply 12):
That's ridiculous – there is a difference between the force of a hammer and the inertia of a truck

The test was done with two representative pieced of fuselage structure. One CFRP from the 787 and one Aluminum from the 767. It was not meant to demonstrate CFRP resistance to vehicle impacts. It was designed to show the ability of CRFP to resist the normal kind of ramp rash an aircraft experiences every day.

Quoting 2175301 (Thread starter):
although it may take 5-7 years before someone hard drives a truck into a plane

Even this has been tested and the results are known. This was done in a controlled test on the static frame (after completion of static testing) to demonstrate how a CFRP fuselage would respond to a low-speed, high-energy, wide area impact. It was an area of interest from the regulators, which is why the test was done.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 15, posted (1 year 9 months 11 hours ago) and read 3571 times:

Quoting LHCVG (Reply 11):
I've been curious about how the fatigue floor works - is it really a floor per se, or just practically speaking where it still degrades but just at miniscule levels from there on out?

Despite being a ~100 year old discipline, this is still a topic of philosophical debate among fatigue engineers and researchers. The problem is that fatigue is highly non-linear and "a really big number" and "infinity" start to look the same. Nobody has had enough time/money to definitively answer (the experiment would take decades and has almost no practical significance).

Quoting oldeuropean (Reply 12):
That's ridiculous – there is a difference between the force of a hammer and the inertia of a truck with a weight of some tons.

Impulse is impulse. A hammer is a high force/short duration event, a truck is the opposite, but as long as you test both types (which has been done) you know the different responses.

Tom.


User currently offlineSEPilot From United States of America, joined Dec 2006, 6681 posts, RR: 46
Reply 16, posted (1 year 9 months 5 hours ago) and read 3315 times:

Quoting tdscanuck (Reply 15):

Despite being a ~100 year old discipline, this is still a topic of philosophical debate among fatigue engineers and researchers. The problem is that fatigue is highly non-linear and "a really big number" and "infinity" start to look the same. Nobody has had enough time/money to definitively answer (the experiment would take decades and has almost no practical significance).

My grandfather was the pioneer in gear design, and as part of it he did a lot of pioneering research into material durability for gear materials. He designed a wear test machine for United Shoe Machine; after they were finished with them my father ended up with one of them and ran tests in his garage for many years. With steel, a fatigue floor exists when the load is below a certain level, which is where "infinity" and a "very, very big number" are for all intents and purposes the same. Steel does fatigue, however, over this load threshold; and aluminum will fatigue no matter what the load (although with light loads it can work harden and thus gain substantial additional life, but it will ultimately fatigue.) From what I understand about CFRP it behaves a lot like steel except it does not have the threshold at which it starts to fatigue; it does lose strength with initial cycles but then when it reaches its "floor" it does not degrade any more no matter how many cycles it goes through, as long as its load limit is not reached.



The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
User currently offlinejustloveplanes From United States of America, joined Jul 2004, 1002 posts, RR: 1
Reply 17, posted (1 year 9 months 4 hours ago) and read 3196 times:

Quoting SEPilot (Reply 16):
From what I understand about CFRP it behaves a lot like steel except it does not have the threshold at which it starts to fatigue; it does lose strength with initial cycles but then when it reaches its "floor" it does not degrade any more no matter how many cycles it goes through, as long as its load limit is not reached.

Also assuming it is protected from UV radiation?


User currently offlinebikerthai From United States of America, joined Apr 2010, 2011 posts, RR: 4
Reply 18, posted (1 year 8 months 4 weeks 1 day 13 hours ago) and read 2874 times:

Quoting tdscanuck (Reply 5):
the 787 is made from the same materials as nacelles have been made from for 20+ years.

Technically, the 787 fuselage material is more like the 777 tail structure. The nacelles uses honeycomb panels which have a different cure cycle than solid laminate.

Quoting aztrainer (Reply 7):
My question is about drilling into the "skin" How much does drilling into it lessens the strength of the skin? Also is/are there special procedures for drilling? I know the strength is in the angular lament of the carbon fiber, but can a hole be refilled by an epoxy type material?

Holes in composite produce the same stress concentration as is in metal. However, the stress concentration is dealt differently. The only potential is any delamination at the hole caused by the drilling operation. Usually the clamp up load of the fasteners will help with the delamination.

The thing with drilling in to the composite is that you need to keep your drill bit extra sharp to get a clean hole and prevent fraying etc.

As the hole in composites do not pose a fatigue crack propagation issue, you don't need to fill the hole as typically what a rivet does in aluminum. The holes are typically close tolerance (not interference fit) to improve load transfer properties and wet installed for corrosion protection.

bt



Intelligent seeks knowledge. Enlightened seeks wisdom.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (1 year 8 months 4 weeks 1 day 12 hours ago) and read 2784 times:

Quoting bikerthai (Reply 18):
Quoting tdscanuck (Reply 5):
the 787 is made from the same materials as nacelles have been made from for 20+ years.

Technically, the 787 fuselage material is more like the 777 tail structure.

I meant more that they're both CFRP. You're right that the exact material spec for the 787 solid laminate is closest to the 777 tail solid laminate.

Quoting bikerthai (Reply 18):
The nacelles uses honeycomb panels which have a different cure cycle than solid laminate.

True, but it's still CFRP. More importantly, in this context, honeycomb panels are considerably less durable and harder to repair than solid laminates, and we know how the honeycomb panels behave in service. Solid laminates will only be better from a damage/repair standpoint.

Tom.


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