=?windows-1252?Q?Torque_Values_depending_on_type_of_Nuts?
Tony
These torque values are presumably from the FAA Advisory Circular, which
can be found in this document, plus a wealth of other information:
http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentid/99861.
The torque values are listed in chapter 7.
However these numbers are for fastening metal parts. For composites I would
be reluctant to apply the maximum recommended torque. I believe the maximum
torque is a function of the compressive strength of the parts being
fastened and the tensile strength of the bolt itself. There was a document
---From Cirrus which had lower numbers for AN bolts on composites, but I can't
seem to find it now. So far I've been tightening the bolts based on how
much compression I feel after the parts become clamped.I know this is not
very scientific.
On the other hand, I am a bit surprised that your AN3 bolt broke during
normal torqing. Is it possible that the bolt bottomed out at the end of the
threaded portion? In that case I can see how that can break at the joint
between the shank and the threads.. In fact, I had to replace several AN
bolts called out in the Europa manual with shorter lengths because they
were bottoming out before clamping the parts.
On Mon, Oct 28, 2013 at 5:58 PM, Tony Renshaw <tonyrenshaw268@gmail.com>wrote:
> Gidday,
> Yesterday I was tightening by hand one of the two AN3 bolts that clamp the
> flap cross tube to the articulating/hinge arms that are attached in the
> floor. So, in case there is the slightest movement and this would
> exacerbate in my flaps I decided to do them up "tight". Guess what, I
> snapped one, yep snapped. It broke at the top of the shank where the thread
> started, and did NOT strip the thread as many might have presumed. This got
> me thinking that normally most bolts are designed to effect a shear load,
> and not normally a clamping load. Anyway, I know there is counter arguments
> to all of this, but what matters is the applicable torque loads we use if
> we torque them using a wrench, and I just stumbled upon a reference I think
> is important. I found this on an VansForce website, and why it matters is
> the torque values are NOT for locknuts, which have an inherent friction
> drag torque value of 14 in-lbs. So, referring to the attached table an AN3
> needs 20-25 in-lbw, but in actuality would be more like 34-39 in-lbs.
> I think this could be easily overlooked, and if the friction drag torque
> of locknuts is not taken into account, people are under torquing their
> bolts.
> Regards
> Tony Renshaw
> Sydney Aussie.
>
>
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