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.

ARINC:

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.

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 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:

DAN RATHER to present 787 safety concerns on tv

Fareastdriver, you are missing the point. We are not talking about strength, we are talking about what happens when someone crash tests the B787.

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.

things that make you go "hmm"

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

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.

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.

Yes!!! Finally a thread I can be an expert on!
 

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.

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.

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

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

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.

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).

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.

lomapaseo
 

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?

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.

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

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.

To see the interview video
 

Has anyone posted the link where the interview can be seen? I dont think so.

Its here:

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

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?

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.

How so:confused:

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

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.

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.

Just saw reference to this thread. Will read first, but logged in to get the e-mail updates.

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........

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.

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

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.

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" ;)

As I said in my previous post,they ultrasonic test the tub for hidden damage such as delamination etc.

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

If they need to 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.

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:

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.

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