Over torqued bolts on QB?

[Rick_A]

The aileron bellcrank brackets were mounted on main spar when I received my QB. The brackets have to be removed to install the bellcrank. During the course of removing them, it seemed to me that it took a lot of force to remove these bolts, so I decided to measure the break out force. Using a new CDI torque wrench, I measured 48 in lb before the bolt started to turn. Since these go into a nutplate, do the bolt torques still apply? What's the difference between tighten vs loosen torque? Should these bolts be replaced with new ones?

[jcoloccia]

I don't know the specifics of this since I'm not there yet and I'm not building a QB, but since no one else has chimed in here yet, I'll put in my $.02. The whole reason you torque a nut (or bolt, in this case) is to get the proper tension on the bolt (torque's way easier to measure than tension). Typically, you don't worry too much about the breakout force 'cause it's typically pretty small, but on something like nutplates, if you want to get it right you first measure the breakout force, and then you ADD the required torque to that (resulting in the proper tension on the bolt).

I'm guessing the bolts were torqued properly.

[fodrv7]

Makes sense to me.
I have a document from an engineer which specifies adding 5"lb for an AN3 Nylon Lock Nut and 15"lb for an AN4.

From what John is saying the break-out torque would be 5"lb and 15"lb for an AN3 and AN4 respectively.

I shall dash down to the workshop and check.

Pete.
Down Under
Australia.

[jcoloccia]

Originally Posted by fodrv7

Makes sense to me.
I have a document from an engineer which specifies adding 5"lb for an AN3 Nylon Lock Nut and 15"lb for an AN4.

From what John is saying the break-out torque would be 5"lb and 15"lb for an AN3 and AN4 respectively.

I shall dash down to the workshop and check.

Pete.
Down Under
Australia.

4:23 pm: Some dude in Texas has a question.

4:56 pm: A loud mouthed know-it-all in California has a hypothesis

5:16 pm: A guy in Australia runs the experiment

The internet is an amazing thing.

edit: FYI...I'm the loud mouthed Californian in case anyone is wondering

[fodrv7]

I put an AN3 Nutplate in the vice, screwed an AN3 bolt in until thread protruded and fiddled with my Torque wrench until it would just move the bolt without clicking.
The torque required was between 12 and 15"lb (This is near the bottom of the torque wrench calibration and so might be a bit suspect.)

The torque setting for an AN3 bolt is 20-25"lb so this would suggest with a Nutplate you ought to use between 35 and 40"lb.

Now have a look at my Sniffle Valve Interference posting and give me a solution.

Pete Down Under.

[fodrv7]

Actually, I thought the hypothesis from the Texan pretty astute.
Pete.

[LettersFromFlyoverCountry]

Originally Posted by jcoloccia

I The whole reason you torque a nut (or bolt, in this case) is to get the proper tension on the bolt (torque's way easier to measure than tension).

You know, I've heard people say this before and believed it. but then I picked up a copy of AC 43.13 (Acceptable Methods, Techniques, and Practices - Aircraft Inspecition and Repair )

On 7-40.c. (Page 7-6 in the Jeppsesen version), it says Run the nut down to near contact with the washer or bearing surface and check the friction drag torque required to turn the nut. Whenever possible, apply the torque to the nut and not the bolt. This will reduce rotation of the bolt in the hole and reduce wear.

Is there somewhere in AC43.13 that provides additional guidance on bolt vs. nut?

//adding 5"lb for an AN3 Nylon Lock Nut and 15"lb for an AN4.

I believe the An3 is 20-25 and the AN4 is 50-75. It seems that torquing to the upper end of the parameters would suffice. Wouldn't it?

I also recall someone saying if you add an extension to a ratchet wrench, you would have to calculate a higher torque (using the formula that presently escapes me). But I believe this would not be the case for extensions perpendicular ro the wrench, but for extensions that add length to the wrench (i.e. extend the wrench's centerline). . Is that correct?

[jcoloccia]

Originally Posted by Bob Collins

You know, I've heard people say this before and believed it. but then I picked up a copy of AC 43.13 (Acceptable Methods, Techniques, and Practices - Aircraft Inspecition and Repair )

On 7-40.c. (Page 7-6 in the Jeppsesen version), it says Run the nut down to near contact with the washer or bearing surface and check the friction drag torque required to turn the nut. Whenever possible, apply the torque to the nut and not the bolt. This will reduce rotation of the bolt in the hole and reduce wear.

Is there somewhere in AC43.13 that provides additional guidance on bolt vs. nut?

//adding 5"lb for an AN3 Nylon Lock Nut and 15"lb for an AN4.

I believe the An3 is 20-25 and the AN4 is 50-75. It seems that torquing to the upper end of the parameters would suffice. Wouldn't it?

I also recall someone saying if you add an extension to a ratchet wrench, you would have to calculate a higher torque (using the formula that presently escapes me). But I believe this would not be the case for extensions perpendicular ro the wrench, but for extensions that add length to the wrench (i.e. extend the wrench's centerline). . Is that correct?

You can pretty much do anything you want and rig up any setup you'd like as long as ultimately the centerline of the wrench's drive is inline with the centerline of the bolt. So you could make a big C shaped thing with the wrench on top and the bolt on the bottom, and everything works out fine. The only time you need to change anything is when the wrench's drive is off center because you're giving it a mechanical advantage.

re: the nut vs. bolt thing. Honestly, I don't really think it matters one hoot with the small bolts we're using. I've heard every explanation from "It reduces wear" to "it screws up the torque measurement because the friction between the bolt and the material is not taken into account". The only thing they all have in common is they all seem to suggest turning the nut for whatever whacky reason they've managed to invent. LOL....so I try to turn the nut because it makes me feel like I'm more compliant, or something

[LettersFromFlyoverCountry]

Thanks, John. Your advice is always solid and very much appreciated!

[RudiGreyling]

Originally Posted by jcoloccia

<SNIP>
re: the nut vs. bolt thing. Honestly, I don't really think it matters one hoot with the small bolts we're using. I've heard every explanation from "It reduces wear" to "it screws up the torque measurement because the friction between the bolt and the material is not taken into account". The only thing they all have in common is they all seem to suggest turning the nut for whatever whacky reason they've managed to invent. LOL....so I try to turn the nut because it makes me feel like I'm more compliant, or something

I definetly think is got to do with both, but people take it to the extreme, and it might not matter on our small bolts:

1) If you do a lot of repition on fastening and loosening it is better to turn the nut, than the bolt. The bolt remains stationary in the airframe hence no wear on the airframe i.e the hole sides. It is ease to replace the bolt, but not easy to replace the hole..

2) on long bolts the shank surface is in contact with the airframe hole side surface area. The additional surface area and hence the additional friction can be significant in extreme cases to influence the torque value.

Therefor it is "best practise" to turn the nut
AND
The "best practise" to torq...determine the torque required to overcome the initial force to turn the nut when fastening, then add what the handbook says to this value and torq down.

Regards
Rudi