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Posted by on July 31, 2008, 3:24 pm
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>
>Tony Jeffree Wrote:
>> On Tue, 29 Jul 2008 23:24:22 GMT, etpm@whidbey.com wrote:
>>
>> >From my friends who work at Boeing the
>> >word is that the new composite wings have far exceeded the calculated
>> >maximum stress where failure should occur. So far the wings have not
>> >been destroyed because the flexing has so far exceeded the design and
>> >calculated failure point. Word is that some folks think it's not
>> >needed but I bet that they will ultimately be stressed to the
>> breaking
>> >point if only to see where they really fail and for bragging rights.
>>
>> If that is really the case, then they've over-engineered them & they
>> will probably be looking into reducing the weight.
>>
>> Regards,
>> Tony
>
>It's a little more complicated than that.
>
>Both the Boeing and the Airbus wings have been tested far beyond the
>maximum stress expected on the wings, more or less the point where
>either the wing, the fuselage or the passengers would have failed.
>
>If I remember correctly the safety factor is Maximum *1.5. The Airbus
>designs failed at around the critical point (actually slightly below it
>but within 3%) The Airbus wing flexed 7.4 metres before rupturing.
>http://www.cs.york.ac.uk/hise/safety-critical-archive/2006/0031.html
>
>I remember reading somewhere (High Performance Composites?) that a
>Boeing design had had a similar failure.
>
>The design problem is enormous, whereas one can look as a piece of
>aluminium as a single piece, the equivalent composite part may be
>mutiple layer of a material in a matrix . Each layer may be laid at a
>different angle and where the material is woven, there is a stress point
>whereever one thread crosses another.
>
>So instead of the fairly precise data that is available to the metal
>engineer, one has to work with approximations of behaviour.
>
>Another problem is that effectively you 'create' the material every
>time you make a component part. Imagine if you had to mix, melt, roll
>and treat and test every piece of aluminium instead of relying on the
>manufacturer to do so. Indeed the Americans have the AGATE database
>which defines how to put the various materials and resins together to
>make a standard material and the various figures that one can use for
>that material to avoid some of the problems.
>
>So 'overengineered' is a relative term, given the large variables
>possible and the many modes of failure that have been identified.
>
>
>--
>rsss
>------------------------------------------------------------------------
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>View this thread: http://www.rcgroups.com/forums/showthread.php?t=901037
>
I've seen video of composite wings being laid up. They use a big CNC
device which applies the fabric in strips in a certain pattern. The
machine lays down the fabric remarkably fast. The angle of the fabric
changes depending on which layer it is and where on the wing it is. So
the effector at the end of the arm applying the fabric is constantly
turning. 5 degrees of freedom, or maybe 6. There are the X,Y,&Z axes
along with roll and yaw. Maybe tilt too. And different weaves are used
also. Must be hard to get all the bugs out the first time.
ERS
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>Tony Jeffree Wrote: