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Date: Sat, 16 Jan 1999 06:34:23 -0800
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From: Buchanan & Newcomer <bnn@abac.com>
Subject: Flutter Modification
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Rob,
	I'm also confused about Martin's material orientation. The most
conservative design solution would be to mimic the orientation of the
original material. That way you don't introduce any stress risers. Industry
standard nomenclature would orient 0 degrees with the fabric warp. (I.e.
the strongest direction. 7781 has 11% more yarn in warp, (i.e. the long way
off the roll,) than in fill.) Thus Martin seems to specify in words that
the fabric be oriented 0/90. However, his installation sketch implies that
the fiber might be oriented +/-45. THIS IS EXTREMELY IMPORTANT. One is not
the same as the other. You MUST call Martin and obtain clarification, and
Marv, you might ask Martin to clarify the web article, as well.  

[[I'm headed out of town on business but will be back in a week.  I'll try
to get Martin to clarify this upon my return.  Naturally, if anyone else
out there manages to get in touch with him in this regard in the meantime,
please pass the info along in a normal LML posting.  I'll clean up the
details on the flutter page of my site when I have a chance.   <M>]]

	From what I can see reading Martin's article, he tried some FEA solutions,
found a good one, and presented it. I see no indication of WHY that
particular solution worked. This makes variation from his analytical
solution extremely dangerous, as you don't know what caused the flutter
speed to increase. Was it increased bending stiffness? Was it increased
torsion stiffness? Was it additional shape control? (When a thin tube
bends, it flattens, decreasing the bending inertia, reducing the stiffness,
allowing it to bend more, flatten more, etc.) Without knowing exactly how
the improvement worked, your modification might completely miss the mark,
leaving you with a WORSE potential flutter problem because all you'll have
done is add weight.

	Martin's cavalier response is unconscionable. (And, I hope, taken out of
context.) He should have told you all of this and more.

Guy Buchanan 
Buchanan & Newcomer