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danlist(at)syz.com
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 Posted: Fri Feb 03, 2012 4:20 pm Post subject: Proper nyloc nut torquing |
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Hi there.
When I first started building my RV10, I was introduced to "proper" torquing of nuts, and probably like most people, was surprised at how light typical torquing forces were. Most of my life, I'd been overtorquing nuts, and it's nice to finally know how to do it right.
But I'm the sort of person who when I learn something want to learn it fully, and now I'm not sure I actually *have* been doing it right. Like probably most people, I've been following Van's guidelines in section 5V for torquing. I've found that this corresponds with AC43.13-1B, Table 7-1 (with a small deviation for AN10 bolts, but I haven't ran into anything that big yet), so it seems like a reliable guide.
The only problem is that AC43.13-1B specifies those torque values are for oil-free cadmium-plated (but otherwise standard) fine threads.. not particularly for nylocs. And most of Van's nuts are nylocs.
Proper torquing values take into account friction between the face of the nut and the surface, force required to lengthen the bolt (which is ultimately what a specified torque is trying to control), and dry thread friction. But nylocs have far more dry thread friction than standard nuts - that's what they're for, after all. Measuring the prevailing torque on AN3- and AN4-sized nuts (before the face of the nut contacts the surface), I've found a few foot pounds of torque required to just overcome the nyloc's friction. Installing into nutplates usually requires even more prevailing torque than nylocs do.
| Quote: | From what I've read, this sort of prevailing torque should really be added to the final installed torque. And that makes sense - a nyloc or nutplate's internal friction does nothing to add stress to a bolt under load - it only adds stress while the nut is actually being torqued (and of course, helps prevent the nut from loosening later on its own)
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I know this is pretty much nit-picking - thousands of RVs have been built and are flying fine, and I'd be willing to wager than 90% or more of the builders never worry about this and just used the torque values that Van's quoted. The torque values specify a range anyway. But I'm doing this as more an exercise of understanding the engineering involved. Am I correct in this assumption, and that theoretically the prevailing torque of nylocs and/or nutplates should be added to the torque values Van's provides? That would add a few extra foot pounds to the torque values aimed for, which might at least have a small significance for smaller bolts like the AN3s which aren't torqued very high in the first place.
Dan
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Syzygy Research & Technology
Box 83, Legal, AB T0G 1L0 Canada
Phone: 780-961-2213
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n801bh(at)netzero.com
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rene(at)felker.com
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| Posted: Fri Feb 03, 2012 4:51 pm Post subject: Proper nyloc nut torquing |
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I think you have it correct. But, I just set my wrench to the high side of
the range and went for it. I could not figure out how to accurately measure
the resistance.....
Rene' Felker
N423CF
801-721-6080
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