Structural Integrity of Carbon Monocoque chassis like the Enzo Porsche GT? Dangerous?

Everything cannot be made fail-safe due to physical, situational, and financial reasoning. Du-uh. Aircraft are quite redundant anyway with lots of backup systems and such...maybe they should put two rudders on the tails, in case one snaps off in the off-chance an aircraft gets caught in the wake of a 747

You want safety? Don't drive and live in a bomb shelter. If you have to drive, get an Abrams tank -- lots of steel in those suckers. You'll be very safe.

 

I don't happen to have any knowledge of the subject, but, I do have to say, nice attitude.

Welcome aboard.





Darrell.

 

Fact is, the composites broke. People died. Fact is, if the composite section of the plane that failed had been, say, aluminum or titanium 265 people may well be alive today.

Now, this brings us back on topic: Is a carbon tub safe (long term and short term) for street cars, particularly ones costing lots of money that will be used and around for many decades?

Or is there a better solution?

 

The fact is that you are ignoring the cause of the failure and instead blaming one specific material part in the plane that you have some kind of bias against.

You are also ignoring the many planes that have crashed due to various metal issues.

You are also ignoring the hundreds/thousands of planes flying around today that have plenty of composites in them, including planes many of us have flown on (made by both Boeing and Airbus) along with dozens of smaller plane manufactures and a few military planes as well.

 

There's always good old Mother Nature LOL!
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Quick question...The flight that lost its roof which landed in Hawaii about 20 years ago(?); how would a composite have held up to this type of stress? The airframe basicly bent because of the lack of upper support. Would a composit have stood up to this type of incident, or would it have just snapped off.

 

Whether they were stressed or not, the fact remains that a composite part failed in an environment in which a metal part probably would have bent. You can argue the fact that metals break/fatigue/snap as well, but in this case, the difference was one of life and death for a lot of people.

When I initially brought up the A300, I was not speaking only of the crash in Queens. I was speaking of many Airbus aircraft having horrible service/inspection intervals, or none at all, for critical composite parts. This is extremely bad on an aircraft, and very bad on a sports car designed to go real fast. The fact that Airbus uses composites with little or no x-ray/etc inspections is the reason that, as a pilot, I flat out refuse to fly on their aircraft.

To use another example in which there was no excessive load, was an A310 Air Transat flight that had its rudder go away under normal flight conditions. In this case, again, a critical composite part became fatigued, and eventually failed, as there was no sufficient material inspect procedure beyond "looks fine on the outside, let's fly!". That's very similar, if not better, than the "inspection" most carbon cars get before they're taken on the road.
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Depends on many things. How badly the structure was compromised, how it was put together, what kind of loads were present, etc, etc. It's hard to conclusively say how a composite airframe would have handled it, but, I'd put my money on a complete failure of the airframe.

In the specific case of Aloha 243, given how the incident happened (ruptured panel due to failed epoxy resulting in explosive decompression) a composite aircraft probably would have snapped in half.

It's interesting to note that Boeing specifically designed the 737 (and basically everything else they make) with controlled failure zones, so that if a given chunk of the plane is compromised be it by explosive decompression, an impact of some sort, a bomb, etc, the airframe on the whole will retain much or all of its integrity. A lot of people owe their lives to that design.

Wanna guess whose airplanes I fly on when I go commercial?

 

I HAVE read the report. I have also read countless articles in AOPA magazine, among others. Pilots are the yayhoos that have to fly the SOB's, and they are sometimes just as qualified to make assesments as anyone. In fact, most of the NTSB investigators are pilots. Whodathunkit. The problem is that politics gets involved. Right at a time when the entire aiviation industry was struggling post 9/11, this crash sent shockwaves all over the world. Grounding Airbusses would have NOT helped.

I can guarantee you if ANY light aircraft, say a Cirrus SR-20, or a Diamond DA-20 suffered the same failure, the entire fleet would be grounded. When a Bonanza failed in flight and the cause was found to be cracks in the carry through spar, they grounded them. When the rudder failed on a Bonanza, they grounded them. And when a crankshaft seperated at the propellor on a Lycoming, and rust was found, they grounded all aircraft with Lycoming engines until they could be inspected and deemed safe. In fact, in every single case of aircraft having failures, the entire fleet are grounded or put on emergency notice to have the aircraft inspected or repaired ASAP. Aircraft are just not supposed to fail that way

NEVER can I recall an aircraft being passed off as okay, and having pilots instructed to be more careful on putting pressure on control surfaces. Aircraft are instead, designed to be fully controlable up to redline airspeed. Go take a flight lesson. The Cessna 152 you will probably take off in will probably be 30 years old and have from 7,000 to 12,000 hours or more of time on it. And no one will ever teach you not to make hard inputs into the airplane. This would be akin to telling you to be careful driving your F-50 or Enzo at high speed on rough road, because the chassis could fail. Telling a pilot to be careful putting in rudder inputs is rediculous.

 

Then you also read hours upon hours of testimony that came from a dozen or so experts on the subject of composites. Since any initial look at the accident put the blame right on them, it was looked at very hard. Yet composites still came out with a clean bill for aviation use.

That is all true, but again the composite parts of many other planes aren't just failing all over the place. The Airbus in question has a weak spot in it, we have no idea how the rudder would handle the stress if it were made out of another material. Boeing has several planes out now with composite's in the exact same place as the Airbus, yet they don't fail. Why? Blaming all composites because Airbus designed a rudder control system that can be easily broken by "normal" inputs is just way off.

If it ain't Boeing, I ain't going!

 

"Notwithstanding the issue of light weight, what about (1) FAIL SAFE crashworthiness and (2) long term durability (and subsequent FAIL SAFE
crashworthiness?

ALSO, correct me if I'm wrong, but there are alternatives to aluminum chassis, carbon fiber chassis and steel tube chassis.

So, any suggestions as to what may be the most ALL AROUND optimal chassis construction?" - excelsiorZ



What is "Fail Safe" crashworthiness exactly? Do you believe that something perfect exists, but its behind withheld from the public? Do you believe that it is possible to build an indestructable vehicle?

Are you suggesting that nobody has ever died in a car made from steel, that only composite chassised cars kill people?

The closest thing possible to "optimum" is to have the strongest possible passenger cell with dedicated crush and impact absorbing zones in strategic locations. All this coupled with airbags and proper seat belt geometries.
....This can be achieved with whatever material you choose to build a car from, and is the current standard.


It is an understanding of how to design with the material that makes a difference. Carbon composite chassis are very stiff and light, which makes them ideal for racing. When using them on a road car, where crush zones and other impact requirementrs exist, the design must be tailored to suit. This is why composite road cars have a central passenger cell, with front and rear subframes designed to be sacrificial. Is it "ideal"? maybe-maybe not, but it is the state of the art which is why it is applied to enzos, mclarens, cgt's etc...which are made to mimic top level racing counterparts. The vast (99.99%?) majority of vehicles on the road are stamped steel welded up unibodies, which are cheap and work well. people still die in those when they hit other things at 100+mph.

So I am trying to understand if you are questioning composite materials in general, or the designing with them, or taking a stance that an automaker should be able to protect the end user from every imaginable harm?

Enzos are carbon chassis cars for the performance benefits of stiffness to weight, nowhere does ferrari state that it will allow you to crash into anything (oncoming cars in your example) at 150mph and live. Carbon chassis does not mean indestructible, you seem to have created that image in your mind. Ferrari have some very clever engineers, but i dont think they can change the laws of physics yet. F=MA, the human body will only take so much, regardless of what the capsule you are in can take.

 

I personally question the wisdom of flying in aircraft built by the French. Dinner and wine yes, risky technology no. Just because the NTSB gave the plane a GOOD rating doesn't mean that the copilot should be able to break the plane under foreseeable circumstances.

 

Boeing uses composites, but they generally don't use them for major structural members or control surfaces. The 787 is the first major departure from this, yet even there they're primarily using composite materials as wing and fuselage skins, but various metal alloys for structure and leading edges and such. Further, in critical areas that they do use composites, they use carbon sandwich layouts that have several layers of composite between more layers of aluminum and other alloys. That goes a very long way to preventing pieces falling off their planes.

Further, in the planes they already have in service using composites, they have a pretty rigorous inspection and overhaul schedule on those parts.

Those inspections don't exist at all in automotive applications outside of race teams, which, to get back to the original topic, is why I don't like composites for structural members in road cars.

Now, if those car builders using carbon were to go to a carbon sandwich method, they'd end up with the best of both worlds, albeit with significantly higher tooling and production costs.

 

In regards to the Jag E types and how they broke in half. They are not a tube frame chassis. It is a monocoque shell around the cabin and tail section, and a tube frame engine and front suspension carrier assembly that attaches to the firewall. As far as I am familiar, the tube section was designed to break away from the car at the firewall in a major collision to rid the car of excess mass. That was pretty fantastic imagination back in the late 1950's. That entire tube frame wieghs less than 30 pounds IIRC, and was filled with nitrogen to keep it from rusting internally.

No, I didnt listen to hours and hours of testimony from experts on the subject. And I doubt you or anyone else here did either. The point is, there are politics involved in keeping commercial aircraft flying. Unlike general aviation where the Government will find any reason to ground a bunch of aircraft, they will do just the opposite to keep the airlines flying, purely for economic reasons. So I dont believe everything the Government tries to tell me. I also dont blindly believe everything a bunch of "expert" witnesses with a direct monetary interest have to tell me. I prefer instead to listen to myriad sources and make my own assumptions. And as far as I am concerned, we dont know enough about composites yet to make a lot of assumptions or statements. And I am not about to say its better or worse than other materials. Its different. Thats about all any of us can say. The tail came off simply because it was weak. The materials its made from are of only a secondary issue. The question regarding the materials only needs to be how long they last, how to repair it, and how to engineer it to be of useable strength.

The problem with cars like the F-50 or the Enzo is that, unlike steel or aluminum chassis, we really have no way as of yet to judge its continued useability. With steel or aluminum we can visually see stress cracks or corrosion, and both are rather easily repaired. Composite chassis may not only be unrepairable, but may be un-testable for useability. Short of an X-ray of the entire tub, and we dont know if that would tell us anything, I have no idea how you could certify it. But keep a watchful eye on aircraft and see what happens as composite aircraft age. That should be an indicator of what we should expect to see with composite car chassis.

 

There is a transcript, in a nice PDF format (searchable and all), and yes I did read it.

Really? Out of the witness list who has direct monetary interest in making sure Airbus keeps flying? Since you have zero idea who those witnesses are (I doubt you've even been to the NTSB's page on the crash), how can you make such a damning statement? I don't disagree that the NTSB can have a political slant to it.

In the 50+ years of using CF (and hundreds of years of using composites in general), we as humans don't know enough about them?

Just a repost of what Valence posted earlier and leave it at that. I'll drop out of this back forth train wreck.

 

As a little aside, your bones are akin to a honeycomb compostite material...

 

Perhaps we should have all bones declared unsafe because they can be broken with severe impact.

Anyone know of a replacement for bones, and any ideas how to retrofit 6 billion people with the replacements?

 

Titanium hips anyone?

 

It would appear that devolution has rather replaced many brains with bone, as some sort of defensive all purpose safety measure.

 

How about adamantium?

 

Exceptional points on the Airbus and the industry. Now I really want a Boeing!

It's great to have pilots and people familiar with flight on this site! Some real expertise!

And now, to the next question for people with more knowlege then me:

"So I am trying to understand if you are questioning composite materials in general, or the designing with them, or taking a stance that an automaker should be able to protect the end user from every imaginable harm?"

I've been reading investigative material from NASA regarding other materials (e.g., rated at something like five times speed of sound integrity).

Frankly, carbon fiber is anything but new!

Given what I've read on this post I think there are better materials ou there: Materials investigated by NASA and determined to be extremely strong.

Planes, and cars, are not optimal for many reasons, including technology at the time and technology often equals money.

Anyone here familiar with honeycombs of the non-aluminum type?

LID bonding process and graphite/titanium? If someone has expertise out there with these materials please feel free to send me a PM if you like.

A ten year lifespan and mode of failure convinces me carbon fiber tubs are not the way to go.

 

You mean like paper, Nomex, or something else?
What have you got against aluminium honeycombs?

You want to know about liquid interface diffusion bonding process then?

 

"Insisting on perfect safety is for people who don't have the balls to live in the real world." Mary Shafer, NASA

 

Bump... I'm incredibly intrigued by this, please share.

And which are the other low-service time components you mentioned?

 

I spoke to an engineer today (one noted for designing the chassis for a current exotic car). He tells me of a story where a man did welding on a car with carbon fiber panels. Apparently the welder attched the ground to the vehicle for his welding. The electric current was said to have made the carbon fiber extremely brittle, literally changint its properties and making it very weak. Is this an issue for carbon fiber? That its fiberous make up can be altered by electrical current?

This thread has grown cold. No chassis or structural engineers out there with an idea as to the chassis material of the immediate future?