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Beth Stackpole
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Its fair shair of problems
Beth Stackpole   6/19/2012 7:53:28 AM
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Some how knowing there are cracks in the wings and knowing they aren't on track to be fully fixed until 2013 would make me very reticient to hop on one these babies, even though they are undoubtedly a beautiful example of A&D design.

Interesting that Airbus has suffered its fair share of setbacks on this plane, due mostly to miscommunications and missteps in the design process. To whit: One of the highly publicized delays related to the project was due to problems around the wiring harness system and the structural design--a miscue some attributed to interoperability and incompatibility issues between CAD platforms.

 

Jerry dycus
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Re: Its fair shair of problems
Jerry dycus   6/19/2012 8:24:16 AM
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  I agree with Beth.   I wouldn't ride on one until fixed.

Facts are fasteners in composites if loaded are rarely that good unless very good design.  For lower labor, weight, higher strength they should have been glued together.

Bede glued his alum designs together from the 60's and many fighters, etc have too.  Not new tech at all.

Next why are they different materials?  It should have been one material or the other to keep  this from happening.

CF alsocan  cause corrosion in Alum, fasteners if not insulated well electrically.

naperlou
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Re: Its fair shair of problems
naperlou   6/19/2012 9:22:09 AM
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Beth, I agree with you.  I wouldn't fly one yet.  If they really could tell if it was safe they would not have had the problem.  This is new stuff.  They can't really know. 

I saw a similar situation on the Landsat spacecraft.  The structure was a large space frame made of composite tubes.  The joints were of metal (titanium, I think).  It was clear that if you put the fastrner holes in the normal position, as for an all metal structure, that there would be problems with cracks.  This was becuase of the use of dissimilar materials.  This was found by building a test sub-structure.  I wonder if Airbus did enough testing of actual materials, or whether they relied on CAE.  When using new materials it is important to understand that the CAE tools may not be able correctly predict what is happening. 

Ann R. Thryft
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Re: Its fair shair of problems
Ann R. Thryft   6/19/2012 12:31:00 PM
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The fastener problem makes me, too, wonder about safety issues, regardless of what Airbus says. In a previous feature on fasteners, manufacturers told me they were designing new ones to go into new composite materials, which have very different requirements from metal. So what does that say about whatever fasteners or insertion techniques are currently being used? OTOH, composites in aircraft are not at all new and you'd think they'd have figured out that part by now.

Ann R. Thryft
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Re: Its fair shair of problems
Ann R. Thryft   6/19/2012 12:32:16 PM
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naperlou, I think the potential gap between existing modeling techniques and assumptions and the new realities of a new material is a good point, and one that the GAO was concerned about in its report addressing repairs to the Boeing 787's composites: http://www.designnews.com/document.asp?doc_id=235037 They focused on the back end of repair and maintenance, not the front end of design, but the concerns were similar.

sensor pro
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Re: Its fair shair of problems
sensor pro   6/19/2012 1:25:25 PM
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I would expect that these type of problems of material incompatibility would be first tested and then applied on smalled jet designs. The stress may be better detected at faster speeds and fuselage deformations under changing Gs.The chance of serious accident with many lives lost is a clear possibility. I would avoid this plane as a plague for now.

What concerns me the most a fast fixes.

Ann R. Thryft
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Re: Its fair shair of problems
Ann R. Thryft   6/19/2012 2:27:28 PM
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The main problem seems to be where composites interface with metals: and that is a new problem. It happens because a commercial plane is made of both materials: composites have not been designed to replace everything yet and metal can't be used everywhere due to weight/fuel reduction requirements. These problems took about 10 years to show up in in-service planes.

Jerry dycus
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Re: Its fair shair of problems
Jerry dycus   6/19/2012 5:51:07 PM
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  Ann, composites and metals is not a new problem at all. Been dealing with it for 40 yrs.   Most aircraft were made from a combo of them.

The problem is the engineers or above can't bring themselves to do composites as they have always worked in alum, etc.  So instead of doing it right, glueing, they use a bastard mechanical fasteners because they are scared of doing anything new.  Sadly this goes through many industries.

Naperlou just the expansion, contraction of the Composite tubes in the metal joints from the 1000F to -200F of space temps as it comes into and out of sunlight would be enough to destroy it as their rates are so different.

Rob Spiegel
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Re: Its fair shair of problems
Rob Spiegel   6/19/2012 6:57:38 PM
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Ann, is this the kind of problem that could cause a re-think on the use of composites in aviation?

greg
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Iron
Re: Its fair shair of problems
greg   6/20/2012 12:31:48 AM
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titanium and carbon fiber have similar thermal expansion rates. aluminum is quite different... titanium also does not corrode when placed next to carbon fiber, aluminum must be well insulated with fiberglass or something else...

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