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Old Today, 04:30 AM
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United Kingdom, Pardshaw
Joined Oct 2012
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Analysis of failure.



The structure failed in compression on the top cap strip.


The lower cap strip bent continuously under tension with no difficulty at all and did not fail.



The details of the upper cap strip compression failure are simple. The glue bond to the plywood remained intact. The glue bond to the foam failed in shear, releasing the plywood and allowing it to snap, creating two new ends. These ends slid one over the other as the beam failed. Its all over in a fraction of a second - classic catastrophic failure.


The initiation of the first fracture is the stress increase at the sharp brick edge.
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Old Today, 04:33 AM
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United Kingdom, Pardshaw
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What does this mean?


Spars are not needed. Thin, wide spar caps top and bottom provide ample strength for foam wings.


Remember .... the test was a CONCENTRATED load, wings take much less severe DISTRIBUTED loads which are far more easily handled.
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Old Today, 06:15 AM
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Bristol,UK
Joined Feb 2007
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Very interesting and thorough test Dave. I wonder what the result would be if you used the iron on formica edging instead of the plywood?
Just thinking that instead of priming an EPP wing and then applying xtreme type crossweave tape you could just use iron on edging in a similar pattern. A lot less hassle and probably lighter. Wouldn't degrade like cross weave does if exposed to sunlight either. Just need a little crossweave on the le for ding protection.
I say this as I'm just about ready to cover my EPP-Modelle Pluto wing
Andy
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Old Today, 06:51 AM
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