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Date: Sat, 13 Oct 2012 08:32:56 -0400
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From: "Dan Schaefer" <dfs155@roadrunner.com>
Subject: Re: [LML] Torque
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Paul, over-torquing even the high quality (125,000 - 160,000 psi) AN bolts 
can be as bad as under-torquing. With enough torque, the bolt shank can be 
stretched to failure. If you don't know how much force with which your main 
spar bolts were installed, you could - repeat "could" - be set up for a real 
problem. Over-torquing the spar bolts has an additional problem you probably 
haven't considered (aside from a catastrophic failure under load i.e. 
failure in flight) - should an outboard bolt fail while it's being 
installed, I doubt that getting the broken remainder out of the spar without 
cutting into the wing-skin is possible. At least on the LNC2's.

Use the published dry-thread torque values for which these fasteners are 
designed. A good (calibrated) torque wrench is a small but invaluable 
investment for an airplane builder if you really intend to commit aviation 
in it.

Regards,

Dan Schaefer