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Bolts for HS

D

dsm8

Well Known Member
Patron
I went to install the AN3-4A bolts that hold the WD-1207 and WD-1208 horns to the HS spar via the K-1000-3 nut plates. It was very difficult to get them tight requiring increased torque, greater than the 25 inch pounds called out in the torque tables. I have an EAA tech visit scheduled for tomorrow, but thought I would put it out to the RV-12 experts. Any advice would be greatly appreciated.:confused:

Thanks,

Don
 
You need to add the "run-on" torque (the torque required to turn the bolt in the nutplate before it begins clamping) to the specs appropriate for the bolt size. For example, if it requires 8 in-lbs just to turn the bolt without it clamping anything, then you need to add that 8 in-lbs to the standard 20-25 in-lbs used for an AN3 bolt.
AC43.13 is your friend here. You really should have a copy of it in your shop.
Hope this helps.
 
Run-on Torque

I measured the run-on torque on the nutplates for the hinge brackets that install using AN3 bolts. The run-on torque was about 10 to 12 in lbs. So I torqued the bolts to 34 in lbs.
 
Do a search on "nutplate" and "torque". You be pointed to quite a few posts regarding nutplates, including one that I started five years ago early in my build. (Can't believe it's been five years!)

You will see several suggestions re the use of nutplates. The only one I really don't think is a good idea is running a tap through them.
 
Thank you to all who replied. I took your advice and with the addition of the drag torque you suggested to the recommended torque values I was able to get an additional turn or two from each bolt. I was also able to fall asleep last night knowing that the horns would not fall off. Off to buy a beam torque wrench, shucks I have to buy another tool.

Thanks again, Inspection tonight with EAA tech counselor.

Donnie Mac
 
Dial Torque Wrench

For really low torque values, it's hard to beat a Dial type torque wrench. I bought a Proto 0 - 75 in lbs dial torque wrench for $100 + shipping on ebay a couple of weeks ago.
 
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