Torqueing of Bolts?

[CDBridgesRV7A]

Good Day,

Are we supposed to torque all the bolts on the airplane or just the ones that are for structure? In particular what about the AN3-4A bolts used to attach the Z brackets to the spar during the build of the fuel tanks? There were also bolts used to attach the aileron bell crank brackets to the spar. Are these supposed to be torqued as well?

If so, is there a guide somewhere that states for each size bolt, what the torque setting is?

Thanks for all the help!

Cheers

Chris

[Lemmingman]

Hi Chris,
You will find a table in your builders guide, 5-13 that shows the values. You can also refer to AC43.13. I torque my bolts then use torque seal to let me know that I've final torqued it to the proper value.

[MauiLvrs]

Yes ... torque all bolts.
The "good and tight" method will almost always excede the torque value for AN3 bolts

[flion]

If I'm understanding your question, what you are really asking is do bolts into nutplates get torqued and the answer is yes. How much to torque has been discussed previously in the forums. When you get to that point, castellated nuts also get torqued. The exception might be pivot bolts, but even then there is often a bearing that serves to allow you to torque the fastener without hindering the pivoting action, like in the control sticks. The torque on AN3 bolts is so low that even without a bearing, like in the rudder cable links, pivoting motion was not hindered. Even screws have a torque value. So, torque every threaded fastener.

[GAHco]

Weather you do it in a calibrated and measurable manner is what makes the difference!

It's your thing, do what you wanna do.......................

[Av8torTom]

Chris,

As others here have said, torque every bolt and put torque seal on it so A) you know it's been torqued, and B) you can tell if it has loosened up when you inspect. I recommend a beam style torque wrench as opposed to a click one. A) they never need to be calibrated, and B) you can see how much torque the nyloc nut is putting on the bolt, then add that value to the final torque value. i.e., if it takes 10 inch lbs to turn the nyloc nut on the bolt and the specified torque for the bolt you're using is 25 inch lbs, then the final torque value at the wrench should be 10 + 25 or 35 inch lbs. I'm always amazed how little it takes to achieve proper torque.

Tom

[frankh]

I take the opposite view.

The torque values maybe propper according to the book but in reality these values are way too low for a bolt in tension.

The get out of course is that all the bolts are used in shear so a low torque value is not that important.

Bottom line, bolts can be torqued into their plastic range (i,e permanently deformed) and still not break in service.

The problem is on the AN3 bolts it can be tricky to feel when you have gone too far.. i.e torqued beyond the yeild point..But they will usually break if you do that.

I would calibrate your hands and torque to right "correct" level..The deliberately break on in a vise with the torque wrench.

Feel by hand a point somehwere between the two values and leave the torque wrench in the drawer.

metallurgically speaking these so called "correct values" don't hold up from a metalurgical point of view.

I would still torque anything that is critical..wing splice plates and most definately prop flange bolts..which incidently I believe are torqued quite a bit more than the book values..Which if so suppors my argument above.

Flame suit on!

[rgmwa]

Originally Posted by frankh

Bottom line, bolts can be torqued into their plastic range (i,e permanently deformed) and still not break in service.

They can, but keep in mind that if you choose to torque into the plastic range rather than keeping to the recommended values, you will need to replace the fastener if you ever undo it.

Also, think about the load that a fully torqued bolt will be placing on nutplate and Nyloc threads.

[frankh]

Actually thats exactly my point..You can torque into that range and be perfectly safe. But the difference between the book values and the elastic limit (the point at which you will start to deform the bolts) is a lot, even for a AN3 bolt.

Thus "proper torqueing" by hand is easy to achieve.

We cantinually hear of "my bolts will break if they are over-torqued".

Well if by "over" torquing you mean more than the book values, but less than the yeild point..well that argument is simply bogus.

I have seen many bolts fail is under-torqued however, but these are normally when they see a cyclic stress in addition to the stress induced by torqueing. The prop flange bolts are a prime example of this and why you must always torque his kind of bolt.

[Walt]

There are lots of AN3's on the plane that you will not be able to get a torque wrench on, so as Frank said, you need to develop a good feel for how tight an AN3 should be by feel. I make it a habit to use only my "stubby" wrenches on small bolts and only 1/4" drive stuff with a short ratchet. You get a good feel when you use small tools on small hardware.

And just as an FYI, I seem to find a lot of under-torqued fasteners, so if you torque something down make sure that the bolt is actually providing the desired clamping force (bolts should not easily spin when in assembly if they are correctly 'torqued").