From: Dan Schaefer <dfs155@roadrunner.com>
Subject: [LML] Re: Torque
To: lml@lancaironline.net
Date: Saturday, October 13, 2012, 8:32 AM
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


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