Composites

[Michiel Nijkamp]

Gents,

I just read the (closed) thread about the 787 beaing a death rattle and things about Dan Rather.

Now, i have no idea who Dan Rather is, but I do know a lfew things about composites that I would like to mention as I thought they needed to be said in regard to the article. I am a structure technology engineer at the Dutch National Aerospace Laboratoy (NLR) and designing, producing and testing composites structures is what I do for a living.

I wanted to chime in and say that there really is some truth to the story, biased or not. Carbon Fiber Reinforced Plastics ((CFRPs) just one general composite material type)) are very vulnerable to impact damage (birds, FOD e.g. runway debree, aircraft smashing large hard objects such as the earth). Carbon composites shatter in countless pieces once broken and do not plastically defrom as they are indeed brittle. Though just how brittle they are widely depends of what kind of thermoset or thermoplastic polymers are used. Sames goes for toxic fumes. It depends on the used matrix. But I can tell you that there are a lot more and worse material used that do not smell nice when they are burned.

The brittleness and all other material performances are all taken into account in the design and is not necessarily unsafe. We alway design with saftey in mind. In fact, safety always comes first!!! To break the matrix (resin that binds the fibers) and fibers in CFRPs, a lot of energy is absorbed which is good on impact (though it will often not safe you). That is one of the reasons why race cars are made out of CFRP monocoques (next to saving weight ofcours). Having said that being in a crashing aircraft is unsafe to start with in the first place, it is true that impact damage itself is a serious hazard. It causes delaminations and microcracks that are difficult to detect and do weaken the material significantly. But I am convinced that they (all manufactures) have proven the authorities (FAA, EASA etc) that they are able to cope with that problem. Otherwise, they would nog be allowed to fly.

An even more serious issue would be monitoring fatique. We (composite structure engineers in the industry worldwide) often say that CFRPs do not suffer from fatique. But that is not entirely true. As it does suffer from fatique, but not far as quickly or easily as metals. In fact, within the expected service live of an aircraft, we do not expect fatique symptoms. Obviously, every part that flies on a aircraft is certified and found safe after being tested extensively before it is put into use. Test samples are exposed to the same or higher load levels as they suffer in a plane and are tested for its entire expected service live. But it is still interesting to see how a CFRP materials in primary structures perform after 30 years of use on a. I can tell you that no-one has all the answers.

To conclude things. Aircraft are tested in severe and hard conditions and manufactures have to convince and proof the authorities that they can assure safety within the expected service live conditions. Especially when new materials are used such as composites, whether it being CFRP, Glass fiber composites, Aramid fiber composites, metal/glass/carbon/armid hybrids or even new pure metal allows. So the A380, A350, B787 etc, they can all be considered safe. However, accidents do happen. Not oft, but surely they do and obviously you don't want to be the unlucky one. No matter what aircraft I am flying. However, composites are pushed forward for there enormous weight savings in comparison to metals (about 40% on average) while there is still a lot to be learned and researched. So is this wise? Even while the authorities seem to satisfied and convinced, that is still no garantee. We simply do not know all we need to know and that is where the danger lies. We should not fear what we know is dangerous, we should fear what we do not know that is dangerous. And in the world of composites, there are still a lot of unanswered questions.

In the end (it sounds harsh), developement will cost lives. The risk is minimized as much as we can, but it will always be there. Its inherent. But we are definately ready to push composite aircraft structures forward.

Cheers,

Michiel

[PBoilermaker]

Gents,

I just read the (closed) thread about the 787 beaing a death rattle and things about Dan Rather.

Now, i have no idea who Dan Rather is

He's the guy that sucks.

:)

[Trigger]

Michiel

Thank you; I appreciate your taking the time to share your knowledge and experience with us on this topic.

[vanilla gorilla]

:)

He's the guy that sucks.

:D

[hazmatt]

Good to have a certified expert weigh in.

Matt

[Aggressor Supporter]

Thanks Michiel for the insight on the subject.

He's the guy that sucks.

:D

:lol:

[toadwbg]

Michiel

Thank you; I appreciate your taking the time to share your knowledge and experience with us on this topic.

Ditto. I have my bachlor's degree in composites annd your analyis is an accurate one to my knowladge.

Biggest problem I always encountered with composites were voids, or air entrapment in the resin matrix resulting in poor wet-out of the fibers. Did some ultrasonic testing to try and QC product, but this was not a 100 percent inspection. That's why a sizable safety factor is always engineered into the design.

[Dispatcher]

Wow, I just learned something! Thanks for the post.

[Johnopfor]

Here is Dan Rather's sign at CBS

[andyman_1970]

Awesome post Michiel, I could not have said it better myself.

As an engineer in the aircraft industry working with composite fuselage aircraft (Beechcraft Premier I and Hawker 4000), the lead engineer on the modification of the Hawker 800XP to it’s composite winglet version the 850XP (and now more recently the 900XP) and certified to perform composite “wet layups†by Flight Safety I have just a little bit of experience in the areas of composite structures on FAR part 25 aircraft.

Ditto. I have my bachlor's degree in composites annd your analyis is an accurate one to my knowladge.

Biggest problem I always encountered with composites were voids, or air entrapment in the resin matrix resulting in poor wet-out of the fibers. Did some ultrasonic testing to try and QC product, but this was not a 100 percent inspection. That's why a sizable safety factor is always engineered into the design.

Absolutely correct, that is exactly why the design on the front end has such huge margins with regards to the loads. The cool thing with composites is you can have greater margins than say an aluminum aircraft without the same weight penalty. Poor wet out is a big deal, when I was getting my wet layup training that was the number 1 thing the instructor emphasized was making sure our fabric was completely wetted out.

The cool thing about composites vs. aluminum is that damage tends to be very localized and thus easier to repair. We had a Premier that was involved in a mishap that resulted in the left hand fuselage skin above and aft of the wing being damaged. Our technicians cut out a 3' x 3' of the outer skin (the fuselage is made up of a nomex honeycomb with CF skins on the inboard and outboard sides), replaced the damaged honeycomb and bonded in a new outerskin and voila good as new (or better according to the regs)……………not only that but the repair is invisible once the aircraft is painted.

We’ve done repairs here in Little Rock on fuselage skins on the aluminum 800XP’s and they are ugly, you either have to remove the whole 6' x over 12' section of skin (which requires jigging up the jet) and risk oversizing fastener holes in the skin and frames or add external doublers which look terrible and customers hate.

From a durability stand point composites are certainly the way to go.

Edited September 20, 2007 by andyman_1970

[pablo189]

Here is Dan Rather's sign at CBS

[CiscoKid]

Ok, this has to stop. What we have here is a rational, intelligent discussion. What we really need to do is answer one question. Which is better, Boeing or Airbus?

Brian (ducking for cover)

[Johnopfor]

Ok, this has to stop. What we have here is a rational, intelligent discussion.

Well, that's just great, ruin it for everyone!!

BTW, what's intellegent? What's conversation?

What we really need to do is answer one question. Which is better, Boeing or Airbus?

Can I get fries with that?

BTW, Dan Rather SUCKS!!

Do you know Dan Rather's favorite magic trick?

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.

.

.

.

.

Watch me pull a story out of my @$$!!

Edited September 20, 2007 by Johnopfor

[jbrundt]

Composites in aircraft have been around for years and years. Of course now they are being used more and more in primary aircraft structure.

The AV8B wing, horizontal stab and forward fuselage are all composite and have held up very well for almost 25 years now.

Burt Rutan makes extensive use of composites in all his aircraft with minimal issues.

Many homebuilt aircraft are composite construction.

The F-18E/F, F-15E and many other modern fighters use composite in major structural members. (F-18 wing skins are carbon composite and are structurally integral)

Most all modern helicopters have composite rotor blades.

This is not new stuff. As long as care is taken during the manufacturing process you should not have any issues. It's true that poor resin prep, environmental conditions during lay-up, incorrect fiber placement, incorrect hole drilling and other issues can affect the eventual strength of the finished component. However, there are stringent quality controls in place to minimize these things.

I am quite confident the 787 wouldn't have been manufactured nor would it receive FAA type certification if there was any doubt in the materials and processes used.

Jeff (Boeing flight test engineer)

[Michiel Nijkamp]

You're welcome guys! ;-)

Michiel