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Torque for HS + VS AN3 bolts?

A

ao.frog

Well Known Member
Hi.

WARNING! Stupid question below....

We're about to permantely install the tailfeathers and I'm wondering about the torque values for the AN3 bolts?

The table for torque values in the manual for -3 bolts seems so very low for such "important" parts like the HS and VS.
I mean; 20-25 is just alittle more than "snug"...?
I'd feel better if we used alittle higher torque.... I think...??

Of course alot of parts are "important" so I guess this could apply to alot of parts, thus: this question is probably very stupid... but like they say: "if you don't ask, how are you gonna learn?"

Can anyone out there give me the reason why torque values are never to be exeeded?
(I think the answer to THAT question is really what I'm looking for to make me feel good when sticking to the low values for -3 bolts)

Thanks
 
As I understand it, and someone PLEASE correct me if I'm wrong, but if you over-torque any fastener, it basically starts to stretch, and will become weak.

It doesn't take a whole lot more than the recommended torque on AN3's to snap 'em right off...I've done it. Probably more than I remember, but they will break.

Figure out the amount of drag torque (the force needed to get the nut down to the material, then add that to the recommended value. Typically, I've found most the nuts for AN3's (10-32's I think) take about 7 in-lbs of drag torque to run the nut down the bolt. I add that to 23, mid range, to get 30 in-lbs as a final torque.
 
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Hi Alf,
Don't forget to add the run-on torque to your ~22 in/lbs. I've also heard directly from another builder (who's built several RVs) that they "just go to 35 or so and call it good". I think the AN3 bolts can handle well over 100 inch lbs, so I don't think overtorquing them by 7 in/lbs is going to hurt anything. (heck, your torque wrench calibration may be off by that much).

That being said, I'm sure I'll get verbally beaten senseless for saying so. :eek:
 
Hi Alf! I know 25-30 in/lbs doesn't seem like much, but that's the spec. For what it costs, I sent my torque wrenches in for calibration...I figured the cost was minimal and there was no sense using a torque wrench on every fastener if it wasn't right.
Thanks for reminding me...I need to send in my torque wrenches for calibration before starting my next airplane. I love doing business with these folks:
http://www.teamtorque.com/main.html

I do suggest using a torque wrench for final install...and I'm glad to see you're in the home stretch. We're waiting for the news that you're flying!
 
AC 43.13-1B

Alf,
You can take the advice of a first time builder (like me:rolleyes:) or check chapter 7 section 3 of AC 43.13-1B
It can be found on www.faa.gov/library and search for "AC 43.13-1B"
This Advisory Circular should be in every builders library...
 
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Well, here is the best reason I can think of not to give it a little bit more. I was very surprised to find out how easy it is to twist off a 1/4 -18 bolt in the engine case. I was loosening a bolt from the front of the engine and pulled a little the wrong way looking at it backwards. I'm probably the only fool to ever have done this but after having to pull the engine back off to drill it out, I am very careful not to overtighten anything.

Guess where the rest of this bolt is ? :confused:






When you think it's tight,.... it's probably too tight. Use a torque wrench and crows feet,... life will stay easy. :)

Bill S
7a
 
Thanks

Hi.

Thanks for the responses folks!
I learned alot (as usual) and I'll stick to the planes (as usual) then....
 
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