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Steel vs carbon fiber test


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Keep in mind that this is one complete wind, and tests in the fiber direction. If it was a stress test in any other direction, steel would probably come a lot closer. Finally, our aircraft undergo very different stresses than just tortional.


Still, it is very impressive how carbon fiber lasted for almost four times the forces that steel withstood.

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Notice metal shaft bent, carbon fiber shaft shattered. The failure modes of the two are vastly different.


This is an extremely important point that people forget about. One of metal's advantages is it's ability to control damage. Since it is ductile, it can deform and yet still contribute to structural strength (engines for example). Composites however, tend to hide damage and deformities until the damage becomes moderate, and at that point a significant amount of strength is lost.


Metals also perform much better with forces that they were not designed for. Composites are extremely weak in the shear direction. It's fortunate we can build up composites though, so we can partially make up for the shear direction weakness.


These two things considered, composites are superior to metallics, as long as we stay within the design parameters. Metallics, however, have a zone outside of design parameters where damage occurs, but it will hold together.

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I do agree with with nearly everything you said. I would be interested in seeing a good ceramic engine though; from what I know they are still extremely sensitive to heat. I've heard of ceramic cores wrapped in carbon fiber, but how well can it hold tight tolerances?


I'd love to see metals completely displaced with lightweight materials, don't get me wrong. However, for every technology that succeeds, thousands fail, and every one of them touted "the future of x". In the example of electricity in aircraft, aluminium conducts extremely well and is very lightweight. We don't use it anymore though, because it falls apart after a while due to work-hardening, so we are back to heavy weight copper.


We have yet to see how well FD aircraft hold together with age. We still have metallic airplanes flying that have 70 year old structure, but even though composite aircraft were basically invented in the 70's, the 30 year mark seems to be a death sentence in civil aviation for composite aircraft, because the materials break down and fall apart and stop being economical to repair.


Fabrics are also extremely lightweight, and are used in aircraft that are equipped like FD aircraft, with similar speeds, climbing characteristics, load factors, etc. But they have the same problem, after so long, you have to reskin them. Imagine if we have to do that to a CT...


All that said, there's good reason people still prefer tried and true metal. Metals are incredibly versatile and proven, whereas carbon fiber, graphene (electrical), and kevlar require immense engineering. I do see composite materials (not just carbon fiber, but a variety of others are still being discovered) eventually displacing metals, but until the cost comes down, metals will stick around for quite a while longer. Composites are the future, but we're just not there yet.

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Bad grammar on this site is really the sort of thing up with which no one here should put.

Are you trying to somehow equate Churchill and Yoda? On second thought..."This is not the end, or even the beginning of the end, but it may be the end of the beginning" is pretty Yoda like.

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How often does one see a bent wing from just flight (not running into a hangar or another plane)?   If metal was so great, FD would use it at least on the landing struts.  But they don't.  Likewise, note how Cessnas still use wing struts on their metal wings, FD got rid of theirs because their materials allowed it.


Airplanes DO get bent just from flight. There are many airplanes with wrinkled skins; this is caused by metal over stressing and reaching its yield strength, where it permanently deforms, but not yet reaching its failure point. Carbon fiber has no yield, it goes straight to failure. Some of the thousands of airplanes with wrinkled wing skins would not have landed if they were carbon fiber, and would be listed in the NTSB reports as in flight structural failures.


As for wing struts, you are just wrong -- their use is purely a design decision, and has nothing to do with materials. Struts allow thinner pass through spars and less overhead mass in the cockpit. Google the Cessna Cardinal...it is all metal and has no struts, starting in 1968. There is no high tech wizardry there. The reason your CT has a giant spar box over your head is because it has no struts.

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Cessna 210 went strutless as well. As you get closer to 200 knots these things really start to matter - not so much at 120 knots.


Not making a case one way or another, but this V-tailed Bonanza landed at Hollywood N. Perry after what was described by the pilot as "light turbulence":






General consensus was that there had to be much more to the story than "light turbulence".


What's scary is that in the typical "semi-monocoque" metal plane, the skin itself carries much of the load.



And then there's this: http://en.wikipedia.org/wiki/Air_Transat_Flight_961





Although most of the cockpit voice recorder and flight data recorder were erased due to the long span of time in which the incident occurred, there were several findings as to the cause of the incident. The aircraft probably had a stress fracture in the tail that went unnoticed for several flights prior to the incident flight and the A310 does not have a mechanism in the tail that suspends the growth of the fracture(s).[1]

The Transportation Safety Board found that inspection program of composite rudders was inadequate.[2] In particular, the durability of the rudder was questioned."



And also this: http://startelegram.typepad.com/sky_talk/2007/12/rigorous-airbus.html


Scroll down in the article for discussion of a second American Airlines crash where composite structure might have been a factor.


No material is perfect, and there's still a lot of learning to do with composites. This from someone who's last two planes were composite.

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