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Todays Composites Vs Yesterdays On Boeings  
User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Posted (6 years 1 week 1 day 20 hours ago) and read 2780 times:

When the 727's, 737's and 747 were in production, honeycomb composites became widley used. They were comprised of fibreglass and Nomex honeycomb, sometimes aluminum skinned aluminum honeycomb. Then later on, the 757's and 767's incorporated a mix of carbon fibre, fiberglass and kevlar panels throughout the airframes. Can anyone tell me if todays n/g aircraft ,777's 747/400.s etc are ONLY carbon fibre and have they done away with kevlar and fiberglass ? I wonder about kevlar as it has strange properties and needs special tooling and think some production costs would be aleviated by replacing it with all carbon fibre construction in locations where composites are required.

19 replies: All unread, jump to last
 
User currently offlineDynamicsguy From Australia, joined Jul 2008, 873 posts, RR: 9
Reply 1, posted (6 years 1 week 1 day 9 hours ago) and read 2680 times:



Quoting Soon7x7 (Thread starter):
Can anyone tell me if todays n/g aircraft ,777's 747/400.s etc are ONLY carbon fibre and have they done away with kevlar and fiberglass ?

Kevlar and fibreglass still have their place. Kevlar fibre in particular is generally tougher (less brittle) than carbon. Looking at the colour of the 787 barrels it doesn't look like the outermost ply/plies are carbon.

In our parts we use fibreglass mainly as a barrier ply between aluminium fittings and carbon structure to reduce the risk of galvanic corrosion, or where we need to pad up an area to machine it flat later.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (6 years 1 week 1 day 8 hours ago) and read 2667 times:



Quoting Soon7x7 (Thread starter):
Can anyone tell me if todays n/g aircraft ,777's 747/400.s etc are ONLY carbon fibre and have they done away with kevlar and fiberglass ?

737NG definitely does. Since the 747-400 predates it, I would assume it does also. The 777 radome is certainly not metal and certainly not CFRP, so it's probably one of the others. It's something of a mistake to assume that carbon is a successor to fiberglass and kevlar...it's just different. In some applications, carbon makes sense. But not in all.

Quoting Soon7x7 (Thread starter):
I wonder about kevlar as it has strange properties and needs special tooling and think some production costs would be aleviated by replacing it with all carbon fibre construction in locations where composites are required.

For this reason, Kevlar is typically only used when you're in a situation where you need those odd properties, or you need higher strength than you can get with fiberglass but can't handle the conductivity of carbon.

Tom.


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 3, posted (6 years 1 week 20 hours ago) and read 2612 times:

I know that the wing panels on the 747-8 are fiberglass.

Quoting Dynamicsguy (Reply 1):
Looking at the colour of the 787 barrels it doesn't look like the outermost ply/plies are carbon.

The outer plies are definitely carbon epoxy tape plies. The outermost ply is a different type of CFRP than the other outer plies, but they're all CFRP nonetheless.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 4, posted (6 years 1 week 19 hours ago) and read 2596 times:

Conductivity of Carbon? I never thought Carbon was an electrical conductor....

Blackbird


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 5, posted (6 years 1 week 18 hours ago) and read 2588 times:



Quoting Blackbird (Reply 4):
Conductivity of Carbon? I never thought Carbon was an electrical conductor....

Yes. Carbon is a conductor. Obviously not as good as metal, hence the need for the large CRN (current return network) throughout the 87. However, there is enough conductivity present in carbon to cause problems where a CFRP/CFRP stack-up can't have current going through it.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 6, posted (6 years 1 week 17 hours ago) and read 2564 times:

Can anybody back me up on this...I seem to remember when Southwest placed orders for N/G 737/700's, they specified aluminum only engine cowls.

Blackbird....yeh, my friend has a Freedom yacht with a 38-40 foot carbon fibre mast. He has sustained three lightning strikes from three different storms yet his aluminum neighbors escaped all three times untouched...so either carbon fibre likes electricity or his Karma really stinks.

I'm curious about the fabrication of composite parts and the use of carbon fibre, when regarding large transport structures. Seems to me to be too brittle...I've seen a 757 aileron fail in flight, a 737 h/stab trim tab fail in flight,both were 100% carbon fibre. Not to mention an Americas Cup yacht split in two, AA 587 V/fin break at the lugs which were repaired carbon fibre...(yes I'm aware of the aggresive rudder inputs by the pilot)...I've just never seen such material behavior on similar surfaces made from aluminum/fibreglass composites.

Therefore...I don't trust carbon fibre for primary structures.

Out at the glider base we even had a sailplane with a carbon fibre spar and we noted a sharp pressure point in the skin...further investigation yield a delamination event in the spar. We now just fly all metal sailplanes.


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 7, posted (6 years 1 week 16 hours ago) and read 2558 times:



Quoting Soon7x7 (Reply 6):

Therefore...I don't trust carbon fibre for primary structures.

Honestly, me neither. And i know a lot of people (many of us work on 87 primary structure, mind you) that agree. I mean no material is used that does not have a complete set of allowables and test data so we *know* it'll be safe, but for some odd reason I completely agree with you. I've stood inside empty 87 fuselage barrels and touching the skin/stringers just doesn't seem "adequate" enough. I don't know....

But in the end we know how these materials act on their own, though maybe not as a system. The first hull loss of an 87 will, unfortunately, be the real test. There's no way of really knowing what will happen to the structure as a whole.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 8, posted (6 years 1 week 15 hours ago) and read 2552 times:



Quoting Pianos101 (Reply 7):

I agree with you 100%...I think this big black carbon tube venture is going to be a big white elephant. The price of the learning curve may be high as well. Go to the boneyards in AZ and look....look carefully at eye level...all you will see are aluminum airframes...some destined for the furnace, some destined for service again...THEN look on the ground...in the dirt...you'll find composite panels that no one wants...they don't make the rotable shelves unless they were stripped immediate from out of service birds. Also the aesthetic condition of them from the elements...the vacuum process acetate falls off, they are delaminating, top coat finish is cracked, the panels are warped...

I think that composite structures are incredible secondary structures, they have already proved value in weight savings, maintenance costs. But I think transport manufacturing has crossed a line. I'm aware that they have been flying large composite structures for a while but in my opinion, static tests don't REALLY replicate the real thing...it's just the best we have. The real test is time. I laugh at A380 wings...just how much man made material can you hang horizontally before it breaks....j


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (6 years 1 week 6 hours ago) and read 2511 times:



Quoting Pianos101 (Reply 3):
I know that the wing panels on the 747-8 are fiberglass.

Just to clarify, that would be the movable wing...the structural upper and lower wing skins almost certainly aren't fiberglass.

Quoting Blackbird (Reply 4):
Conductivity of Carbon? I never thought Carbon was an electrical conductor....

Yep...lots of batteries use a carbon rod as an electrode. It's also what most of the static discharge wicks are made from.

Quoting Soon7x7 (Reply 6):
I seem to remember when Southwest placed orders for N/G 737/700's, they specified aluminum only engine cowls.

I've heard that too...I think it was because cowls get ramp rash all the time and they liked doing the metal repair more than the composite repair.

Quoting Soon7x7 (Reply 6):

I'm curious about the fabrication of composite parts and the use of carbon fibre, when regarding large transport structures. Seems to me to be too brittle...I've seen a 757 aileron fail in flight, a 737 h/stab trim tab fail in flight,both were 100% carbon fibre. Not to mention an Americas Cup yacht split in two, AA 587 V/fin break at the lugs which were repaired carbon fibre...(yes I'm aware of the aggresive rudder inputs by the pilot)...I've just never seen such material behavior on similar surfaces made from aluminum/fibreglass composites.

It's very important to recognize that metals and CFRP have different failure modes. Just because metal bends while CFRP shatters doesn't really mean much, since in either case you've grossly exceeded the design load. I don't doubt your examples of failed composite parts, but don't forget that commercial aircraft have also lost wings, vertical tails, major chunks of fuselage, etc. and they're all metal. If you take any material beyond it's ultimate strength, it's going to break. If it's CFRP, it will show more brittle behavior than metal but, in either case, the part was going to fail. Old steel Liberty ships used to snap in half too...

Quoting Soon7x7 (Reply 6):
Therefore...I don't trust carbon fibre for primary structures.

Hmmm...best not fly on many current production commercial aircraft then.

Quoting Soon7x7 (Reply 8):
I'm aware that they have been flying large composite structures for a while but in my opinion, static tests don't REALLY replicate the real thing...it's just the best we have. The real test is time.

Static tests don't replicate the real thing...fatigue tests (which are done exhaustively) are much better, but still not quite the same. I agree with you that time is the real test...but we've had composite primary structure in aircraft for several decades. How much time do you need?

Tom.


User currently offlineBaroque From Australia, joined Apr 2006, 15380 posts, RR: 59
Reply 10, posted (6 years 6 days 22 hours ago) and read 2474 times:



Quoting Pianos101 (Reply 5):
Quoting Blackbird (Reply 4):
Conductivity of Carbon? I never thought Carbon was an electrical conductor....

Yes. Carbon is a conductor. Obviously not as good as metal, hence the need for the large CRN (current return network) throughout the 87. However, there is enough conductivity present in carbon to cause problems where a CFRP/CFRP stack-up can't have current going through it.

To be more specific, graphitic carbons are conductors but only within the graphitic planes (the basal or {0001} planes). They are very poor conductors perpendicular to the graphitic planes, that is along the c or z crystallographic axis.

Note that many carbons used in composites are fibrous, and the graphitic "planes" may not be strictly planar as they are in Ceylon graphite for example.

Graphites are strongly anisotropic in all their properties that are directional.

Diamonds, by contrast are isotropic.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 11, posted (6 years 6 days 21 hours ago) and read 2460 times:



Quoting Tdscanuck (Reply 9):

You won't find me on dreamliner for quite a while...still feel monocoque aluminum construction is a proven wheel design along with limited composite use...I'm sure the 787 will perform as planned however I also feel many points I have raised in the past regarding super structure carbon fabrication still hold true but only time will tell....will be interesting to observe.

Quoting Baroque (Reply 10):

Apparently you have a firm grasp on this technology, I have trained in sheet metal repair and composite repairs...I find BOTH to actually be ART FORMS...so to speak. Composites are a real science with basic concepts that need to be understood...but knowing this stuff...I feel a wide margin for error exists in the fabrication of composite parts. Temps, vacuum pressures, weave direction, weave selection...resin hot batches...out of date resins being used...so much needs to be right on target to create the optimum component. Metal fabrication is somewhat more foregiving....NO?

The A300 tail section is the only large component I'm aware of that uses carbon fibre and HAS failed. What others are common. Do A320's have metal wing torque boxes or composite? I also am aware military uses carbon structure but they too have experienced many structural failures.


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 12, posted (6 years 6 days 20 hours ago) and read 2445 times:



Quoting Tdscanuck (Reply 9):
Just to clarify, that would be the movable wing...the structural upper and lower wing skins almost certainly aren't fiberglass.

or... the leading edge and trailing edge panels (fixed and moveable). between the spars is Al.


User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 13, posted (6 years 6 days 19 hours ago) and read 2433 times:



Quoting Pianos101 (Reply 7):

Honestly, me neither. And i know a lot of people (many of us work on 87 primary structure, mind you) that agree. I mean no material is used that does not have a complete set of allowables and test data so we *know* it'll be safe, but for some odd reason I completely agree with you. I've stood inside empty 87 fuselage barrels and touching the skin/stringers just doesn't seem "adequate" enough. I don't know....



Quoting Pianos101 (Reply 7):

But in the end we know how these materials act on their own, though maybe not as a system. The first hull loss of an 87 will, unfortunately, be the real test. There's no way of really knowing what will happen to the structure as a whole.

Woah, you're a Boeing employee, and an engineer working on the latest 747 no less, and you're announcing on a public forum that you don't believe Boeing products are safe? Including the 787 and the 747-8 you're working on?

At best you certainly shouldn't be saying these things in public, for your own sake. At worst this is a huge thing that has dramatic safety repercussions for your company and the industry.


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 14, posted (6 years 6 days 19 hours ago) and read 2433 times:



Quoting Tdscanuck (Reply 9):

747 main wing torque boxes are all various aluminum alloys...7k series on top and 2k or 3k series underneath...Spars also alloys...Wing stringers are alloy extrusions.The attached leading edge skins, including the movable kruegars are now fiberglass...the inboards used to be aluminum. All leading edge caps are aluminum. Trailing edge upper and lower wing panels are fiberglass composite panels as well as flap segments...tear drop slat is nomex honeycomb, metal spars, nomex trailing edge. The large flap segment has forged and sheet aluminum box frame, skinned w/ aluminum honeycomb panels with nomex leading edge cap and carbon trailing edge, the last flap segment is nomex composite leading edge, alloy sheet metal spars connected by aluminum honeycomb construction, with nomex trailing edge...in short...about 40% of a 747 wing is honeycomb. In spar ribs are alloy sheet metal (really thin) rienforced with alloy extrusions...riveted and sealed...there...we just built a 747...whew!...Oh, spoilers are aluminum skinned aluminum honeycomb or at least they used to be however on the 757 and 767 I believe they converted the construction of spoilers to carbon fibre.


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 15, posted (6 years 6 days 18 hours ago) and read 2425 times:



Quoting 777236ER (Reply 13):
Woah, you're a Boeing employee, and an engineer working on the latest 747 no less, and you're announcing on a public forum that you don't believe Boeing products are safe? Including the 787 and the 747-8 you're working on?

Whoh hold on there!! Re-read what i said before you put words into my mouth. I NEVER said these planes are not safe. I said that we (as in not me, but people who've been working composites for years) know how these materials work, how they take various loads, and what their failure methods are. Boeing has some of the greatest stress analysts in the world, and I know that they know what they're doing. The plane would not have gotten this far if it wasn't perfectly safe.

That said, i PERSONALLY just feel "weird" about flying in a big piece of plastic. it's a personal opinion, NOT a statement of fact. Sorry if that was not clear. It's common knowledge anyway that the first few 87's are overdesigned so there is definitely nothing to worry about. My statement was opinion, not fact about the aircraft.

On the program side, obviously we all know about the partners' "gaffs," and that some of them are still struggling to get things back in order. There is still definitely quality control present throughout the process, and the FAA would never issue a ticket if they thought otherwise (errrr forget about the eclipse 500...).

And since the 87 is the first aircraft of its size made of (mostly) composite, I really don't think there is a way to know what will happen to all that graphite in an accident. I don't think that's a risque statement, I just think that's the truth.

I love my job and I love the company that i work for and the projects that I work on. I have complete faith in my coworkers and I really take offense to you insinuating otherwise.

And, for the record, my opinions were not about the -8, just the 87. The 47-8 is a great aircraft that is a follow up to the greatest commercial airliner ever.  Big grin


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 16, posted (6 years 6 days 17 hours ago) and read 2413 times:



Quoting Pianos101 (Reply 7):

Like I said earlier...static testing on the ground is just not the same as real time, real environment, the shortcomings of a radically changed technology will become evident in the air trials that are to follow. No one does this better than Boeing...the 777 proves that...never built a full size prototype, yet exhaustive testing...proving composites, catia and all the other happy hoarse ---- works. If Boeing feels this product is not worthy of service...no doubt it won't fly.

Pianos101 like myself just personally don't feel comfortable in a plastic plane. I did not take his comment any other way. Probably just a matter of tin knockers expressing their preference.


User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 17, posted (6 years 6 days 16 hours ago) and read 2403 times:



Quoting Pianos101 (Reply 15):
That said, i PERSONALLY just feel "weird" about flying in a big piece of plastic. it's a personal opinion, NOT a statement of fact.

That's fine, but you've identified yourself as an engineer of Boeing and you're putting this in the public domain.

Quoting Pianos101 (Reply 15):
It's common knowledge anyway that the first few 87's are overdesigned so there is definitely nothing to worry about

Again, the specifications of the first few 787s are between Boeing and the operator. Are you suggesting that later 787s will be less safe?

Quoting Pianos101 (Reply 15):
On the program side, obviously we all know about the partners' "gaffs," and that some of them are still struggling to get things back in order

Who needs a communications department when we can hear it from the horses mouth?

Quoting Pianos101 (Reply 15):
There is still definitely quality control present throughout the process, and the FAA would never issue a ticket if they thought otherwise (errrr forget about the eclipse 500...).

Here you're implying that the FAA certify aircraft that are unsafe!!

Quoting Pianos101 (Reply 15):
And since the 87 is the first aircraft of its size made of (mostly) composite, I really don't think there is a way to know what will happen to all that graphite in an accident. I don't think that's a risque statement, I just think that's the truth.

You're opening yourself up for disiplinary action, and putting the company at risk. Imagine the headline in Flight on Monday "Exclusive: Boeing engineer says 787 not safe in crash!" "Boeing engineer: "I wouldn't be comfortable flying on a 787".

Quoting Pianos101 (Reply 15):
I love my job and I love the company that i work for and the projects that I work on. I have complete faith in my coworkers and I really take offense to you insinuating otherwise.

I'm not insinuating otherwise, I know what your point is, but I'm just saying be careful what you write in public forums.


User currently offlinePianos101 From United States of America, joined Jan 2008, 365 posts, RR: 0
Reply 18, posted (6 years 6 days 15 hours ago) and read 2396 times:



Quoting 777236ER (Reply 17):
Are you suggesting that later 787s will be less safe?

How do you get "less safe" from "overdesigned?" I'm stuck with figuring out that logic. The FAA requires testing to 150% of ultimate load. If the first few aircraft are built to 185%, but then weight is taken out where it was found it can be taken out and the next few aircraft are built to withstand 160% of ultimate load, how the hell is that unsafe?

Quoting 777236ER (Reply 17):
Who needs a communications department when we can hear it from the horses mouth?

Show me where i said something that has not already been publicly released. Boeing said that it's supply chain was the reason for the delays, and they said that the one positive stemming from the strike is that it gives suppliers a chance to catch up. I didn't say anything that wasn't already put out there...

Quoting 777236ER (Reply 17):
Here you're implying that the FAA certify aircraft that are unsafe!!

What do you think happened with the Eclipse 500? Did Eclipse pay off the FAA inspectors? I have no idea what happened, but apparently something did to cause an investigation about why the 500 got its ticket with unresolved issues. Do you think that plane is unsafe?

Quoting 777236ER (Reply 17):
"Exclusive: Boeing engineer says 787 not safe in crash!"

Huh??? I didn't say it's unsafe in a crash!!! Jeez do you guys not understand English over there???? I said no one knows how, in real life, an all composite airframe will act in a real-life accident. I didn't say it won't be safe, nor did I say it will be more safe than a metal airframe. I DON"T KNOW THE ANSWER!!!!!! I'm simply saying that time will tell!!!

Quoting 777236ER (Reply 17):
I'm not insinuating otherwise

Sorry man, but that's what it sounds like....


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (6 years 6 days 11 hours ago) and read 2366 times:



Quoting Soon7x7 (Reply 11):
Composites are a real science with basic concepts that need to be understood...but knowing this stuff...I feel a wide margin for error exists in the fabrication of composite parts. Temps, vacuum pressures, weave direction, weave selection...resin hot batches...out of date resins being used...so much needs to be right on target to create the optimum component. Metal fabrication is somewhat more foregiving....NO?

Sort of...composites are definitely different beasts with a different skill set but, like anything in aviation, you have to follow the instructions.

With metals you could have wrong temper, wrong finish, bad deburr, a knick, a scribe mark, an unseat rivet, etc. More variables in compsites, I suspect, but they're relatively forgiving of being out by a few %.

Quoting Soon7x7 (Reply 11):
The A300 tail section is the only large component I'm aware of that uses carbon fibre and HAS failed. What others are common.

That's the only commercial primary structure composite failure that springs to mind, but I'm sure there are others. Right now we've got composite floor beams (777), composite vertical stabs (A300 and 777), composite horizontal stabs (777), and composite fan blades (777).

Quoting Soon7x7 (Reply 11):
Do A320's have metal wing torque boxes or composite?

Metal.

Quoting Soon7x7 (Reply 11):
I also am aware military uses carbon structure but they too have experienced many structural failures.

They have, but their safety margins and load conditions are very different. It's also not particularly exclusive to composites...the B2 has almost entirely CFRP primary structure and hasn't suffered any structural failures. The F-14 and F-111 are almost all metal structure and have suffered major structural failures.

Quoting Soon7x7 (Reply 16):
the shortcomings of a radically changed technology will become evident in the air trials that are to follow.

Radically changed? It's the same stuff in a new shape. What's the radical change from a materials point of view?

Tom.


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