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Sunfish
18th Sep 2007, 22:24
Make of this what you will. (Mods: Not sure if this is the right place)

A fired Engineer goes public. I've always wondered how Boeing was going to deal with the problem of catastrophic failure (handled in Aluminium hulls by tear strips), since the carbon fibre mast failures I've seen in yacht racing have always been 'spectacular"


Forty-six-year veteran Vince Weldon contends that in a crash landing that would be survivable in a metal airplane, the new jet's innovative composite plastic materials will shatter too easily and burn with toxic fumes. He backs up his views with e-mails from engineering colleagues at Boeing and claims the company isn't doing enough to test the plane's crashworthiness.

http://seattletimes.nwsource.com/html/boeingaerospace/2003889663_boeing180.html

bomarc
19th Sep 2007, 00:11
whether the man was fired or not isn't the question...but plastic planes bug me for all the reasons in this article.

TSR2
19th Sep 2007, 00:35
Reading the Seattle Times article a sudden chill ran up my spine and the name Roger Boisjolly immediately sprang to mind.

I hope history does not repeat itself.

AndyCirl
19th Sep 2007, 00:50
I second that.

http://en.wikipedia.org/wiki/Roger_Boisjoly

denachtenmai
19th Sep 2007, 01:11
Shades of Dan Applegate re DC 10's cargo doors:eek:

Two's in
19th Sep 2007, 02:15
Disaffected ex-employees are about as new and innovative as composite material airframes. If this individual truly has an axe to grind, he might well have reconsidered the timing of his "bombshell", saving it as he did until he himself has been accused of gross professional misconduct.

Not only are these materials being used extensively on aircraft today, but the techniques and methods required for testing and certifying are well understood. To give credence to his theory is to accept that both the FAA and Boeing are colluding in some mass conspiracy to short circuit the certification process for commercial aircraft. The FAA can certainly do incompetence, but they struggle mightily with conspiracy. As for Boeing's motive to expose the travelling masses to such an unquantifiable risk, has anyone noticed the propensity with which Americans sue each other? It's almost a given that composite materials will behave differently to traditional metals, they will produce different toxins under combustion, but does that greatly change the survivability index in a crash over a traditional structure? Only the certification process will establish that, not some shotgun blast of accusations and generic blame throwing.

Incidently, linking it with the Shuttle experience simply demonstrates that e-mail is the preferred media for communicating dissatisfaction within a large anonymous organization, but provides little additional insight.

411A
19th Sep 2007, 03:22
Hmmm, as I recall, a couple of Boeing engineers also thought that the original B707 was 'unsafe' yet it turned out to be quite a respectable aircraft.

Divergant dutch rolling tendancies and all....:}

lomapaseo
19th Sep 2007, 04:12
Presumably by going public, beyond the designer safety analysis and the regulators approval, the disaffected employee has a chance to see his views and concerns be discussed and analyzed by the myriad of real experts on the various internet discussion boards.

What we really need now is a poll and just skip the discussion:sad:

Brian Abraham
19th Sep 2007, 04:38
Both Boeing and the FAA are capable of running their own agendas when they see fit. The cargo door blow out on the United 747 over the Pacific is an example. It took the investigative abilities of the New Zealand parents who had a child killed in the event to find the truth as to the cause, both Boeing and the FAA acknowleged their findings were correct but were not about to alter the incorrect official findings.

archae86
19th Sep 2007, 05:41
A person posting on a military aviation newsgroup provided this link:
Weldon letter to FAA (http://seattletimes.nwsource.com/ABPub/2007/09/17/2003889769.pdf)
Assuming it is for real, which seems likely to me:
His criticism is so comprehensive, and so over-the-top that is has far less
credibility for me than would a more focused objection to specific design
problems or management actions.
Essentially he demands that no new structural material differ in any way from his beloved aluminum that could ever have any adverse effect under any subset of use conditions. He also takes a commitment to overall safety improvement, and translates it to a requirement for no adverse safety impact in any circumstance, no matter how implausible.
That not only rules out composites, but pretty much anything else. If one considered titanium in a similar mood, I'm pretty sure you could find some killer objections. It is hard to machine, for one thing, so with equal production skill, more likely to have some sorts of flaws.
I'm not saying none of his concerns have any validity. I think maintaining composites appropriately for cases of "hangar rash" and such may take some real field experience and learning before cost and safety get balanced properly, just to pick one.
I am not a pilot. I am a retired engineer, with some experience in arguing unpopular views in a large organization.

grumpyoldgeek
19th Sep 2007, 05:49
I can't help but wonder if Bill Boeing got a similar letter when he decided to build planes out of aluminum instead of sitka spruce.

Trashed Aviator
19th Sep 2007, 06:08
You are not supposed to crash land an aircraft.
Have also heard Carbon fibre is difficult to join to other materials such as metal or glass, and even in some light aircraft where carbon fibre has been used in conjunction with fibreglass, the carbon fibre has broken away. Im sure Boeing know what they are doing.
I may be a little concerned if:mad: a russian copy comes out though....

VH-Cheer Up
19th Sep 2007, 07:06
Interesting article (http://www.news.com.au/story/0,23599,22444080-2,00.html) cites claims by an ex-Boeing engineer that the Dreamliner will shatter on impact, give off toxic fumes in a fire, and will be less able to withstand a lightning strike than an aluminium tube.

Personally, I think it's unsafe to be in any kind of a crash, and would recommend avoiding it.

Can't help wondering, though, if a glass ship like the 787 would simply shatter if it hit a tall building, leaving just the small, solid heavy bits to plough on through.

Thus, the 787 might be a lot less appealing to sociopathic organisations like Al Quaeda than aluminium bodied vessels?

Cloud Cutter
19th Sep 2007, 07:23
I agree, all aircraft are unsafe in a crash. That's why they are designed not to crash.

RedTBar
19th Sep 2007, 07:56
An article by an EX-Boeing engineer,no question of an axe to grind.As far as toxic smoke in an accident is concerned the interior fittings give off anough toxic fumes in a fire.

ARINC
19th Sep 2007, 07:58
Every single frame on the A380 Main deck (98 of them) is Carbon fibre. and in the interests of accuracy they are manufactured completely differently and with far higher tolerances than boat masts ! (I had to laugh at that one) Furthermore only Titanium fixings are used to secure other structural items to them.

aero junkie
19th Sep 2007, 08:01
"Fired engineer calls 787's plastic fuselage unsafe"

Well after surviving a crash, you also have to avoid breathing in carbon fibre particles and (if a fire happens) composite material burning in Jet fuel, both not good for the human body. No doubt Boeing are doing their homework:hmm:

kiwiblue
19th Sep 2007, 08:09
As others have pointed out already all aircraft are inherently unsafe in a crash... the very idea of a "crash-safe" aircraft is an oxymoron.

This thread strikes me as completely pointless, and quite possibly a wind-up. Get over it.

cwatters
19th Sep 2007, 08:20
I believe the russians make a lot of carbon fibre (raw material) for the world market.
It will be interesting to see how composite aircraft tollerate lightening strikes. I've seen the wing spar of a model plane burn when it acidentally shorted out a small nicad battery. It doesn't conduct as well as Aluminium and the extra resistance causes more heat to be produced - at least that's how I understand it. I'm not a professional composite engineer!

Edit: This report details what can happen to a composite glider (not normally provided with lightening protection). Good job they had parachutes...

http://www.pas.rochester.edu/~cline/ASK%20lightning%20strike/ASK%20accident%20report.htm

wobble2plank
19th Sep 2007, 08:56
I remember doing a post crash management course which bedeviled the properties of Man Made Fibres in the post crash environment especially in fire. But lets be patently honest here, F1 cars crash at ridiculously high speeds and the drivers walk away.

The majority of materials contained within the cabin attribute a vast amount of toxic fumes to the cocktail. Even in an aluminium tube.

The impact survivability of Carbon Fibre structures has been proven to be greater that that of aluminium due to the ability of the composite structure to absorb the impact energy whereas the aluminum deforms.

We all pray that a crash will never occur, however the global pressure from ill informed Governments and environmental groups forces more and more towards lean, light and efficient aircraft. The industry cannot stay in the 60's.

Personally I look forward to flying it :)

thabo
19th Sep 2007, 09:13
hey aero junkie

"Well after surviving a crash, you also have to avoid breathing in carbon fibre particles and (if a fire happens) composite material burning in Jet fuel, both not good for the human body."

plane crashes in and of themselves are not very good for the human body, and all the safety devices in the world aren't going to help anyone.

we all know that the sardines in the back of the airplane cant breath un pressurized oxygen at 36000ft. if there is a depressurization, the pilots' job is to land a plane with a whole bunch of either dead or brain-damaged passengers.

also, the life jackets are only intended to help rescuers find the corpses of the passengers in the "unlikely event of an emergency landing on water"... no one is going to survive that...

the fact that no one died in the China Air fire is probably better classed as "miracle" than "luck".

A and C
19th Sep 2007, 09:37
A some one who's maintenance engineers licence covers a range of composite aircraft I fail to see how this aircraft will be any more of a problem in terms of risk to passengers involved in an accident that aa aircraft of convetional construction, in fact the ability of composites to absorb energy may well be an advantage keeping the structure intact and allowing more people to escape before the (undoubtedly toxic) fire gets going.

For me the main promlems that I forsee are ones of maintenance. Boeing repair manuals are using "dark ages" methodes that would not be used on any light aircraft or glider and are not fit for primery structure due to the glued contact area between the layers of cloth being so small. these practises may well be satisfactory for floor boards and non critical panels but won't do for a pressure hull.

I have no doubt that Boeing have given this much consideration but will an industry that has for so long been wedded to metal put enough effort into re-traininng staff to repair and inspect these "new " structures that are so much better at hiding defects and dammage than metal ever was!

A and C
19th Sep 2007, 09:43
The China Air fire evacuation was not a miracle or luck it was due to the correct and speedy actions of the crew putting the safety training that they had receved in to practice.

old,not bold
19th Sep 2007, 09:46
Two small observations responding to comments above;

First; I don't understand the use of the word "spectacular" connected to failures of carbon yacht masts; they just break, exactly like aluminium ones do if a stay breaks or the tensions are set up wrongly.

And second; many years ago (late '70's) the FAA and CAA gave a mandatory mod on TPE 331 engines (up to a certain production number) a 4-year compliance period when it should have been 6 months or less, solely to allow the mod to be done on next overhaul, to avoid grounding the large fleet using those engines. Safety gave way to "commercial reality". Maybe things have changed for the better, maybe not. But no-one should assume that any National Aviation Authority will not give way to commercial pressures, and that applies to FAA and EASA.

thabo
19th Sep 2007, 10:14
you are right... i exagerated.

there are safety standards and proreedures which are there to save lives and they do.

I just hate to think what would have happened if that "missing washer" in the slats had started the fire while the plane was still in the air. (that is what I meant by "miracle")

A and C
19th Sep 2007, 11:06
It is unlikely that the fuel leak from a flap can would be a problem in the air as the airflow over the wing would keep the fuel away from the hot engine.

The fire started on taxi in because the fuel was running inbd along the underside of the wing and falling onto a hot engine.

Jabawocky
19th Sep 2007, 11:28
cwatters

Just a thought, I think you will find as resistence increases, current decreases, Mr Ohm might say E=I x R, and P = V x I.

Cheers

J:ok:

PAXboy
19th Sep 2007, 11:59
wobble2plankThe impact survivability of Carbon Fibre structures has been proven to be greater that that of aluminium due to the ability of the composite structure to absorb the impact energy whereas the aluminium deforms.Eerrr. As the aluminium deforms - it absorbs the impact energy. :rolleyes:

In order to ascertain whether one material is better than another, you would need to show us the formal tests of two items constructed to identical dimensions and for the same purpose from different material that were then subjected ... etcetera.

As to CF structures been 'proven' to be better in impacts, there is not as much evidence accumulated to compare with Al, due simply to the length of time that Al has been in use for aircraft. That does not mean that Al is better than CF materials but we do not really know. That question can be answered in another 20 years time.

Beeline
19th Sep 2007, 12:53
Does anybody know if Boeing has incorporated Aramid type upper layers into the stucture to help alleviate the impact resistance problems of CF, I cant recall a composite structure that has to date, only the polyurethane finish on prop blades and the GE90??
I have heard titanium patch plates and splice pieces will be used within repair schemes, the SRM will make an interesting read!
As for impact testing I think we can rely on a few catering trucks for that first!
:ok:

pythagoras
19th Sep 2007, 13:51
How would the composite structure cope with lightning strikes - not knowing much about the science behind them would they be an issue? There are still many metallic components on the aircraft.

Capn Bloggs
19th Sep 2007, 14:18
Thabo,

if there is a depressurization, the pilots' job is to land a plane with a whole bunch of either dead or brain-damaged passengers.

Really? You've been watching too many movies.

thabo
19th Sep 2007, 14:50
A&C:

youre right, i didnt think of that.


Captain B:

I don't even know what movies are, I have no time to watch them.

at 36000ft with a decent rate of what? 8000ft/min? its going to take you a while to get your passengers back to an altitude where they can breath the oxygen they are being supplied with.

with regard to absorbing impact energy... the vast majority of energy is absorbed during plastic-deformation. cars are designed to have crumple zones which absorb as much energy as possible so that the driver doesn't have to. thats the reason that car accidents look so much worse than they did 20 years ago.

when it comes to designing planes, you take into account maximum flight loads and then add a 5% safety margin or so. you can't design a plane to withstand a crash, the kinetic anergy is just too great and it can not be dissapated.

There is work being done on using composite fittings inside the airplane that produce less toxic fumes when they burn, but you can never produce a plastic for wall panels etc. that is light, sturdy & doesnt burn at all.

Tim Dawson
19th Sep 2007, 15:12
Thabo,

You're talking about 3 minutes to get down to an altitude where people could breathe the outside air. People can go from anywhere between 3 - 10 minutes without oxygen without suffering brain damage. Given that as the plane descends there will be _some_ (ok, not much) oxygen around, people would probably be ok. I assume you're talking about a worst-case scenario where oxygen masks have failed to deploy for some reason.

GOLF_BRAVO_ZULU
19th Sep 2007, 15:54
This reminds me of this thread; http://www.pprune.org/forums/showthread.php?p=3409994#post3409994

So after a heavy landing (very rare, I'm sure) how do you check for structural strains in a modern composite construction?

(when I were a lad, composite construction meant metal, wood and fabric)

wobble2plank
19th Sep 2007, 16:04
Quite true that aluminium absorbs energy as it deforms. However, to effectively distribute large amounts of impact energy there is normally an energy dissapating structure (crumple zone) behind the aluminium skin which transports the energy around the structure.

Carbon fibre however, due to the complex interwoven nature of its core structure, has the ability to disperse impact energy throughout its own structure in multiple directions therefore dispersing energy and reducing deformation without having to resort to complex energy distribution structures. Whilst this is possibly a good thing in a crash scenario, on the day to day ramp I wonder what will happen when loaders, catering trucks etc get near it. CF is very good at delaminating without it showing on the surface.

:rolleyes:

lomapaseo
19th Sep 2007, 16:17
with regard to absorbing impact energy... the vast majority of energy is absorbed during plastic-deformation.
very true and it relates directly to the area under the stress/strain curve taking into account strain rates, and their effect on the area that can be placed under strain in a very short time before the G-loads kill the passenger.
A car has much less velocity so it has time to bring in large crumple zones before the G-loads are exceeded.
With a composite (non-homogenous- metallic) you are dealing in energy absorption by friction between the fibers as they separate from the glue holding them together. Ideally if you had no glue the whole thing would act like a blanket, Unfortunately it wouldn't stay together long enough to fly.

er340790
19th Sep 2007, 17:20
What concerns me most here is that the FAA position, even if remotely true, seems to be satisfied with safety levels in a new generation aircraft meeting current aircraft saftey levels.

Stop. Rewind. Replay. That's rather like Ford launching a new hybrid vehicle and claiming it matches the safety levels of its 1978 offerings to wit: drum brakes, cross-ply tyres, no ABS, no airbags, no laminated glass, lap-belts.

Let's hope the new Boeing Pinto, sorry 787, doesn't have to be made safer via tombstone technology.:oh:

Capt H Peacock
19th Sep 2007, 18:45
My concern is the day to day repair of 'hangar rash'. Water ingress into composite laminates, the subsequent freeze/thaw cycles and weave ruptures would not be as quick to fix as a patch of speedtape.

I reckon it'll very quickly become a pain in the ahhhhs.:confused:

qwertyuiop
19th Sep 2007, 19:57
Makes me laugh.
All these armchair couchspuds know more than the Boeing designers. 787 will be as popular as 757 and 320. Both of which were ahead of their time.

lomapaseo
19th Sep 2007, 20:01
What concerns me most here is that the FAA position, even if remotely true, seems to be satisfied with safety levels in a new generation aircraft meeting current aircraft saftey levels.



Not true. There have been numerous updates of the FAR/JARS since 1969 and each "new" aircraft not grandfathered by acceptable service experience has to meet these new standards. Indeed where the technolgy is new and so novel that doubt exist about where it stands relative to historical experience than "special conditions" are proposed that it has to meet. As I recall there were several special conditions that the B777 had to meet beyond the then current certification standards.

The watchdog for such conditions are not only the Regulators but also include other aviation bodies, NASA and the general public through the petition process. So any of you may endorse the disaffected Boeing engineer and put together a technically sound petition to the FAA to issue special conditions against the A380 and the B787

boguing
19th Sep 2007, 22:31
I like that 'blanket' analogy.

After my Pa contacted Terra Firma at well over 100 Kts at 30 degrees in his Carbon fibre glider fuse, the nose did indeed resemble a blanket if you poked it, but it held it's shape - almost eerily. But, he survived it, although he was also quite badly broken. There is no possible way that any non CF machine would have protected him to that extent. It was the "bit by bit" disintegration that saved him.

So, crash-wise, I think I'd prefer my chances in the Carbon composite.

Having said that, I'd only want to crash in a newish one. The inspection problems and the way that CRP reacts to electricity, fire, freezing, de-icer etc.. does worry me.

Sunfish
19th Sep 2007, 22:51
ARINC:

Every single frame on the A380 Main deck (98 of them) is Carbon fibre. and in the interests of accuracy they are manufactured completely differently and with far higher tolerances than boat masts ! (I had to laugh at that one) Furthermore only Titanium fixings are used to secure other structural items to them.

As a former professional engineer, and having worked in the aerospace industry, and in an airline, and having visited both Boeing composite manufacturing facilities and mast and hull builders, you are simply wrong to sneer about the manufacturing technology employed and the tolerance achieved. Furthermore the car industry uses about ten times smaller tolerances on their manufacturing processes and use far more sophisticated processes than do airframe builders, but in any case thats not the issue.

The issue is as Weldon succinctly puts it, the very low amount of linear strain before the composite material fails. In other words, it's main failure mode is a brittle fracture. My observation is that the considerable number of carbon hull and mast failures I've seen are consistent with this failure mode, and as a result, are "spectacular" compared to the failure of, say, an Aluminium structure.

What Weldon is alleging is that Boeing has avoided subjecting the 787 fuselage structure to a type of test (A drop test from 14 ft. producing a 30 ft/sec) velocity that in an Aluminium structure produced a maximum 20g deceleration - which is regarded as the maximum for passenger survivability.

The implication of what he is alleging is that the B787 fuselage is not going to behave as well as an Aluminum fuselage in a "Phuket" or "Yogyakarta" type of accident - and the behaviour is going to be worse, not better, with higher G loads on the Pax followed perhaps by the shattering of the fuselage, and possibly the ejection of the contents.

Whether this is likely to happen and whether this is a good or bad thing is beyond my competence. I will be interested to hear Boeing and the FAA's response.

The one thing we can all count on is that whether Boeing wishes to simulate such a situation or not, the B787 crash worthiness is going to be tested by nature, and as Feyneman famously said, nature will not be fooled.

As for his comments regarding Boeing's conservatism and "soul", I can testify that the Boeing I had dealings with twenty-five years ago certainly evinced the qualities of integrity and ethics he talks about, and it would be sad if that ethic has gone. I'm still not sure for example, if the aviation industry is using lithium/aluminium, and high strength low creep magnesium alloys, despite these having been around and tested for forty years.

To sum it up, if the allegations are correct, then this is the same sort of **** that got Douglas into trouble.

Fareastdriver
19th Sep 2007, 23:15
I shall look at the composite construction components on my aircraft now with abject terror. They have been twisted, bent, stretched and despite this they have been on the aircraft for God knows how long without rectification.
They're called helicopter rotor blades.

mocoman
19th Sep 2007, 23:18
Just a thought, I think you will find as resistence increases, current decreases, Mr Ohm might say E=I x R, and P = V x I.


Yes, but the problem is that power dissipated is dependent on resistance and current.

It is true that P=V*I

However, V = I*R

so, P= I(squared)* R

Therefore, in order to get the same power dissipation you have to reduce the current by a factor of 4 if you increase the resistance by a factor of 2.

The only way to do that is to reduce the voltage.

Since the voltage for any serious electrical supply can be assumed to remain constant then current will also remain purely a factor of resistance from Ohms' law.

You will find that a higher resistance will increase the power dissipated through the fault given a constant voltage.
:ok:

bomarc
20th Sep 2007, 00:34
DAN RATHER to present 787 safety concerns on tv

Sunfish
20th Sep 2007, 00:43
Fareastdriver, you are missing the point. We are not talking about strength, we are talking about what happens when someone crash tests the B787.

ChrisVJ
20th Sep 2007, 04:55
Firstly, the demanded comparison of exactly the same designs being tested against each other is, of course, not the point. One would design an aluminium structure to suit Al and a CF structure to suit that material.

Second, If one wants an example one might care to look at, say, Formula one, (often mentioned on these pages,) where CF has been used for quite a while. The energy absorbing qualities of Cf are well known and tried and are said to be superior to Al, and even fancy honeycomb double skinned stuctures, just their deformation style is radically different.

armchairpilot94116
20th Sep 2007, 06:26
things that make you go "hmm"

http://www.atwonline.com/news/story.html?storyID=10276

llondel
20th Sep 2007, 07:50
You will find that a higher resistance will increase the power dissipated through the fault given a constant voltage.

No it won't. Power = V(squared)/R (the more appropriate form of the equation for constant volts) so if R is bigger, power goes down in the scenario you describe. You fail to cope with the fact that as you increase R, the current goes down.

The reality is more complex, because you're into impedance matching where maximum power is transferred when source and load impedances are the same, but as I don't know the source impedance of a lighting strike I can't work any numbers.

Volume
20th Sep 2007, 07:50
with regard to absorbing impact energy... the vast majority of energy is absorbed during plastic-deformation
This is a quite generic statement, and not entirely true for crashworthiness of aircraft. Aircraft structure, highly optimized for low weight, often fails in a buckling mode, not in overstress. Therefore the plastic deformation is restricted to a very small part of the overall structure, and the energy dissipation is low, compared to the overall volume of material.
For composite structure you can generally state, that it could be designed to have superiour crash resistance. Using monolithic, thick walled, woven fabric, hybrid material design (Carbon/Aramid, or even better Carbon/Polyethylen), gives you crashworthiness unparalleled by any metal structure. Formula 1 demonstrates this impressively.
If you want to have a structure optimized for low weight, you will use unidirectional tapes, thin walled structure and carbon fibre only. Such design typically fails without much energy dissipation.
So the 787 could be both, superior to all metal competitors with regard to impact resistance, or a total nightmare, depending on the knowledge of the boeing engineers and the ethics of boeing management. Future will tell us.
Looking at the pictures of the crash tests, I am not too convinced, that crashworthiness was the primary reason for chosing composites. Looking at the boeing advertisments also looks more light low weight and economy were the driving factors.

Wet Lettuce
20th Sep 2007, 08:17
Lightning and carbon fibre composites.

You ever seen a tree that has been struck, they explode.

Same with windmill blades.

Any water trapped in there flashes to steam and blows the structure apart.

Orographic
20th Sep 2007, 08:40
The issue is as Weldon succinctly puts it, the very low amount of linear strain before the composite material fails. In other words, it's main failure mode is a brittle fracture. My observation is that the considerable number of carbon hull and mast failures I've seen are consistent with this failure mode, and as a result, are "spectacular" compared to the failure of, say, an Aluminium structure.

I shall look at the composite construction components on my aircraft now with abject terror. They have been twisted, bent, stretched and despite this they have been on the aircraft for God knows how long without rectification.
They're called helicopter rotor blades.

yes, but in rotor blade, and props, this Brittle Fracture Failure mode is desirable. They are less likely to dig in and cause more problems for a crew, who it must be said, have enough on their plates. assuming there isn't some poor sod under them, then having them shatter and nicely dissipate their excess energy in a ballistic arc is , while spectacular, generally safer for the a/c as a whole.

The question is, is it as desirable when we are talking about the fuselage itself, and indeed is it a more desirable set of traits than aluminium shows?

One question that is partly tangential, is the mass savings of moving to this material significant as opposed to aluminium, and if so, how significant or otherwise would that change be in terms of impact energy? It seems a stupid question, but I am not an engineer, and I am sure Boeing has information that I don't.

GOLF_BRAVO_ZULU
20th Sep 2007, 10:04
As I mentioned earlier, I know sod all about modern composite structures. I am aware, though, that carbon fibre/epoxy resin structures do not suffer from many of the problems, such as osmosis, found in fibre glass reinforced polyester/acrylic resin ones.

I think many of us accept that a carbon fibre structure that hasn't received permanent strain will allow as good an impact survivability as an aluminium alloy one, if not better. Perhaps I'm being blind or thick (or both!) but I've not seen any explanation of how post "hangar rash" (credit to Capt Peacock), heavy landing, tail scrape/strike events will be investigated and evaluated. Did I miss it?

Jaun Huw Nose
20th Sep 2007, 11:49
Race cars seem to absorb some huge impacts and protect the driver.The Beech Starship did a lot to further the certification of composite structures. http://en.wikipedia.org/wiki/Beechcraft_Starship

lomapaseo
20th Sep 2007, 12:27
The race car experience in my opinion is directly applicable. Also not directly mentioned is the current experience with current carbon fibre aircraft bodies themselves. The F-22 comes to mind. This plane fuselage was broken into three large pieces and not shattered into dust

mono
20th Sep 2007, 14:05
As I understand it the lightning strike protection will be provided by either the usual flame spray type coating or an impregnated conductive mesh such that usual airframe conductive figures would be obtained.

Slight thread creep here but llondel and mocoman need to go back to school to re-assess the effect of a lightning strike on an aircraft. They have both been saying the voltage is constant whereas if fact it is NOT.

The aircraft acts as a resistor WITHIN AN EXTERNAL CIRCUIT which is from the ground to the PD source (or vice versa depending on whether you are conventionally or electron minded). SO. If the resistance within the airframe is high then the PD across the aircraft (i.e. the voltage) increases (V=IR) and therefore so does the current. As we are talking about thousands if not millions of volts then even a small resistance can result in HUGE power dissipation. This why the bonding of aircraft is so important.

SLFStuckInTheBack
20th Sep 2007, 21:55
lomapaseo,
The thing about race cars (especially F1) is that although the body is made out of carbon fibre, it is bonded to an Aluminium honeycomb structure (at least in the nose cone). Its the honeycomb that helps absorb the energy, crumpling in a crash.
In other race cars like Nascar the driver is sitting in a huge steel cage onto which the body is attached.
Overall though I would rather be in an aircraft than a race car (parent of a 24 year old son who wants to take father round the nurburgring before son turns 25).

lomapaseo
21st Sep 2007, 01:15
The thing about race cars (especially F1) is that although the body is made out of carbon fibre, it is bonded to an Aluminium honeycomb structure (at least in the nose cone). Its the honeycomb that helps absorb the energy, crumpling in a crash.
In other race cars like Nascar the driver is sitting in a huge steel cage onto which the body is attached.
Overall though I would rather be in an aircraft than a race car (parent of a 24 year old son who wants to take father round the nurburgring before son turns 25).

I doubt that the honeycomb absorbs any significant energy. Crushing absorbs squat, it's deformation under the stress/strain curve that absorbs energy. You can take the honeycomb out lay it on a table and slap it flat with your hand, it's sole purpose is to provide stiffness to the supporting structure.

However I won't argue about the energy absorption capabilities of the race car composite cockpit shell. It simply provides lots of stiffness to distribute the g-loads evenly to the occupant. the real energy absorption takes place by the surrounding mangling of the frame and time extending bounces. One of the things that is applied is a basic crash recorder attached to the shell which records max G-loads. For the very serious crashes this is consulted before removing the occupant so as to lessen the internal trauma. (cutting out vs lifting the body out)

The argument about the composite was not it's excelent energy absorption but's it longevity throught the crash impact scenario.

So in simple opinion, in the same type of crash, both an aluminum airframe and a composite aircraft will protect or not protect the occupants relatively to the same level of survivability. in my experience I have seen both.

glad rag
22nd Sep 2007, 12:34
The F-22 comes to mind. This plane fuselage was broken into three large pieces and not shattered into dust

were these 3 pieces the marry up joins?

glad rag
22nd Sep 2007, 12:38
ARINC:


Quote:
Every single frame on the A380 Main deck (98 of them) is Carbon fibre. and in the interests of accuracy they are manufactured completely differently and with far higher tolerances than boat masts ! (I had to laugh at that one) Furthermore only Titanium fixings are used to secure other structural items to them.

Actually the cargo deck uses metal beams, don't know if there are any plant to go CF with these............. I've only manages to count 95 frames on the main deck and the pressure bulkhead.

lomapaseo
22nd Sep 2007, 13:44
were these 3 pieces the marry up joins?

Mostly....................

Minorite invisible
24th Sep 2007, 01:47
I saw the video. Vince Weldon does not actually claim that the 787 is unsafe. His point is that there are many questions to which Boeing and the FAA do not have the answers to yet, questions that should be looked into a little more than has been done.
An aicraft with so much leading edge technology should have a little more flight testing than the fast track program that was announced to make up for the production delays.
It is also said in the program that Airbus decided to use less composites in the A-350 but is under pressure from it scustomers to use more composites to save weight. There seems to be a reluctance......
One thing is for certain. The 787 will make or break Boeing.

GOLF_BRAVO_ZULU
25th Sep 2007, 10:02
Having established that the 787 is new and that racing cars crash "safely", was my question too difficult to answer or just too stupid to bother with?

Minorite invisible
25th Sep 2007, 12:38
Has anyone posted the link where the interview can be seen? I dont think so.

Its here:

http://www.hd.net/drr231.html

Intruder
25th Sep 2007, 20:15
Having established that the 787 is new and that racing cars crash "safely", was my question too difficult to answer or just too stupid to bother with?
The dynamics of car and airplane crashes are quite different. The regulatory requirements for race cars, passenger cars, transport airplanes, and light GA airplanes are quite different. How can you assume the experience with race cars applies directly to airplane fuselages?

GOLF_BRAVO_ZULU
26th Sep 2007, 08:44
Intruder; personally I don't and I suggest that the entire comparison is a pointless red herring. Please read my earlier and, I believe, pertinent question at Srl 51. How easy/possible is it to detect the effects of seemingly minor damage in composite fabrications?

Taking it to the simplistic, we all know that "used" motor bike crash helmets are supposed to be consigned to the gash bin as they are only likely to protect you the once, even if they look only scratched.

lomapaseo
26th Sep 2007, 13:35
The dynamics of car and airplane crashes are quite different

How so:confused:

The regulatory requirements for race cars, passenger cars, transport airplanes, and light GA airplanes are quite different.

What do the regulations have to do with the differences between race cars and comercial aircraft relative to composites?

Intruder
27th Sep 2007, 03:39
Intruder; personally I don't and I suggest that the entire comparison is a pointless red herring. Please read my earlier and, I believe, pertinent question at Srl 51. How easy/possible is it to detect the effects of seemingly minor damage in composite fabrications?
My experience in composites is limited to building and repairing small boats. Even in that very limited domain, though, I am aware that there is such a significant difference in the behavior of different composites (e.g., glass/polyester, glass/epoxy, Kevlar/epoxy, wood/resin...) that one cannot generalize about their responses to various types of stress and damage. I suspect that even within the context of the single 787 airplane, there will be several different composite layups, each with their individual inspection/repair criteria. I'll leave it to an expert in the specific composites to tell us what some of those criteria may be.

IIRC, the issue with motorcycle helmets has more to do with the foam liner than the composite shell. While the shell may still do what it is supposed to do, the foam liner may be permanently compressed in some places after a significant impact. Since that liner gives the bulk of the actual protection, its failure (or actually, its planned response to the impact) may make it significantly less able to provide the specified protection in a subsequent impact.

nick2007
27th Sep 2007, 13:55
Re: Damage assessment/detection
I imagine significant events (tail strike) would trigger a thorough Non Destructive Testing programme for surrounding structure to look for delaminations etc. I don't know much about NDT in composites, but as far as I know, acoustic methods are the most effective (there may be others). I know of one method used for quality control in the manufacture of CFRP flight control surfaces that involves passing running water over the part, and then elsewhere on the part monitoring the sound waves generated by the running water - thus irregularities can be detected this way.
In the field I imagine conventional ultrasonic testing would be used. Though this is only one NDT procedure, and it has its limitations. Anyone have some more details about composite NDT?

Re: Carbon fibre ship masts
As far as I know - these are generally constructed with a lot of unidirectional material. I am guessing that unidirectional material would not be used to so great an extent in 787 fuselage primary structure, thus the failure modes can't really be compared.

ChristiaanJ
18th Jan 2008, 21:12
Just saw reference to this thread. Will read first, but logged in to get the e-mail updates.

BarbiesBoyfriend
20th Jan 2008, 11:20
What happens when a GPU or catering truck knocks a hole in a 787 (or other plastic a/c)?

Is the patch going to have the same longevity as the rest of the fus'?

Also, said patch is going to need curing time and quite a lot of extensive and careful grinding and prep work.

Not sayimg it can't be done or anything, but........

satos
21st Jan 2008, 08:23
Quote:
Having established that the 787 is new and that racing cars crash "safely", was my question too difficult to answer or just too stupid to bother with?
The dynamics of car and airplane crashes are quite different. The regulatory requirements for race cars, passenger cars, transport airplanes, and light GA airplanes are quite different. How can you assume the experience with race cars applies directly to airplane fuselages?
A modern formula 1 car's tub is made entirely of carbon fiber.Watch a race where a f1 car has hit a solid retaining wall at high speed and see how well the tub absorbs the impact without breaking and the driver walking away with the only injury concussion.
F1 is a technically highly regulated sport and the tub has to pass stringent crash tests in order for it to be allowed to race.Teams spend millions in order to pass these crash tests.
I agree the dynamics of an airliner and an f1 car are not the same but if a f1 car tub can now be perfected to resist breaking in an accident and absorb the impact I'm sure the same can be done with a new aircraft such as the Boeing 787 dream liner.

NigelOnDraft
21st Jan 2008, 08:50
satos... I am afraid you miss the point... Having crashed into the wall, do they now reuse the CF tub? How do they view? assess? repair? the damage, and then certify? the repaired tub?

This is the real worry. Look around on "old" airliner, typically 10+ significant and visible patches rivetted on. Who knows how many unseen or repeated patches have been done....

NoD

satos
22nd Jan 2008, 05:21
satos... I am afraid you miss the point... Having crashed into the wall, do they now reuse the CF tub? How do they view? assess? repair? the damage, and then certify? the repaired tub?If the car hit a wall and is damaged they can patch repair the tub which makes it stronger in that area than before but heavier which can be a disadvantage in F1 as lightness is the key objective in this sport.
The tub is also tested regularly by ultrasonic inspection for any imperfections and before and after repairs are carried out to make sure it is structurally sound.
Production and maintenance of these cars is A1 with quality control on par with aviation.
Most of the top teams spend between 300-400 million dollars (USD) a year in research and development of these cars.

NigelOnDraft
22nd Jan 2008, 07:50
satos... You still have not answered "see". Let me put it another way - how do they "know" to look for damage? * CF etc. tend to "spring back" when struck, and on the exterior show no damage, yet internally there is delamination etc. - a typical airliner scenario when struck by a servicing vehicle, which is the cause of 90%+ of the patches discussed above.

<<they can patch repair the tub which makes it stronger in that area than before >> This is easy in "basic structures", say boats. Surprised so at F1 where you are presumably using unidirectional fibres, and you have to strip the damaged area back and somehow link in the "repair" fibres into the original long fibres... Remember we are not talking a sport - we are talking a certified passenger vehicle :eek:

* The answer cannot be "because the driver of said vehicle says so" ;)

satos
23rd Jan 2008, 08:08
As I said in my previous post,they ultrasonic test the tub for hidden damage such as delamination etc.

Blip
23rd Jan 2008, 11:55
A modern formula 1 car's tub is made entirely of carbon fiber.Watch a race where a f1 car has hit a solid retaining wall at high speed and see how well the tub absorbs the impact without breaking and the driver walking away with the only injury concussion.

How can any structure absorb energy if it does not significantly deform?

If they need to ultrasonic test the tub for hidden damage such as delamination etc. after an accident well then it was not the carbon fiber structure that absorbed the energy of the crash, it must have been the soft bits of car around it that did.

If you put a raw egg in a tin can and drop it onto the road, the can is hardly going to deform at all, meaning that it absorbs very little. It will simply transfer that sudden deceleration to the poor little egg inside.

NigelOnDraft
23rd Jan 2008, 12:02
As I said in my previous post,they ultrasonic test the tub for hidden damage such as delamination etc.satos... I ask again, how do they KNOW to do the ultrasound? Presumably because telemetry and the driver and the wreck say "we crashed it".

Translate that to a 787. How does one KNOW to ultrasound it? Unless the structure shows visible damage when it is whacked, which as you say composites do not, yet are damaged internally, then the engineer / pilot does not know... The person causing the (possible) damage will not, in general, say a thing :oh:

Burnt Fishtrousers
23rd Jan 2008, 13:31
What about work hardening of metals as they become brittle with age and stress imposed on them. Bend a piece of metal enough and it becomes brittle and will fracture easily. Do composites react in the same way and/or have a more "elastic" property giving rise to longer life?

How after an accident on a composite aircraft do you try to find the cause if its structural and not the obvious.If its metal you can detect age hardening of the metal by detailed analysis,( Comet disaster) This physical property I would suspect, may not be present in composites...i dont know??, so when faced with millions of pieces of composite you dont know which let go due to stress and which are a result of the impact during the accident ...do composites show signs of aging etc etc that can be scrutinised in the event of failure?? if the composites have melted away in the ensuing fireball would this leave forensic analysis more difficult..i'd suspect so. I only did metalurgy to OND level as a small module of a general engineering qualification ..and composites werent in abundance then.

Whitehatter
23rd Jan 2008, 14:09
I do recall seeing some talk of Boeing using implanted metal fibres both for lightning and electrical conductivity as well as detecting fuselage damage. Any break or distortion in the grid would be detectable by a system that they have cooked up under various patents.

Obviously all top secret and patented but along the lines of an electrical pulse being sent out and any deviation from the norm provides an 'echo' pinpointing the area to be looked at. They can then do something akin to those whizzy Autoglass type repairs where a resin is forced into any crack and it then sets harder than the original. :8

smala01
23rd Jan 2008, 16:32
Blip,

I agree with you that energy cannot be absorbed without distortion of the structure.

Race cars absorb energy based on known failure rate of the structure. The structure is based on layers of composite that “commit suicide” and disintegrate to manage the force of impact.

http://img30.picoodle.com/img/img30/4/1/23/f_CrashStructm_15b7ca8.jpg (http://www.picoodle.com/view.php?img=/4/1/23/f_CrashStructm_15b7ca8.jpg&srv=img30)

What I’m confused about is the assumption that the composite failure strength is less than that of “absolute Failure” of Aluminium (after buckling and distortion). In my (limited) experience on GA types I was always taught to make sure the composite failure rate was equal or greater than that of the “Absolute failure” of traditional material.

I have tried to demonstrate this in the following diagram.

http://img30.picoodle.com/img/img30/4/1/23/f_Absolutefaim_6ea2532.jpg (http://www.picoodle.com/view.php?img=/4/1/23/f_Absolutefaim_6ea2532.jpg&srv=img30)


Impact 1 – Composite structure Integrity remains intact; Aluminium Structure is deformed but some strength remains.

Impact 2 – Both Composite and Aluminium structure fail – no integral strength remains.

So are we to assume the Boeing intends for the Composite structure failure to be LESS that the absolute failure of alternatives?

Smala01