[RV10Rob]

I checked the torque on the bolts attaching the aileron bellcrank to the spar on my QB wings, and they're all around 60 in-lb (these are AN3 bolts). They're bolted into nutplates, which have a relatively high run on torque, but not high enough to make a total torque of 60 in-lb within the correct range. Anyone else seen this? There was no torque seal on these bolts, which is why I checked.

This has me thinking: how confident should we be in the nuts/bolts on the QBs that *do* have torque seal on them?

-Rob

 

[Camillo]

In my 9A QB wings, I found all nuts overtorqued. When I disconnected the bellcrank and reassembled it, I had the terrible idea of retightening nuts at the same torque value (if I recall...70 inch./lbs.) and...they broke! They got loose and I had no other way of taking them out than disassembling the fuel tank. I also had to change the platenuts.

So, I think you should go per manual specifications torque values. Also Van's told me to untorque and retorque nuts to the correct value.

Camillo

 

[terrykohler]

You need to look at the full specification for the prevailing torque fastener that you are using. Normally, the spec. shows a first "on" value which is what most manufacturers (including Van's) utilize in assembly. Manufacturers of the fasteners are also required to meet a spec for first "off" as well as fifth "off". The first off is generally much higher than the first on due to both friction as well as some plastic deformation in the joint. In a fastened joint, this is generally referred to as "breakaway torque".
The specification you are working to incorporates both prevailing torque from the locking element as well the application torque specified for the joint. The fifth off is lower than both first on and first off due to loss of elasticity in the locking element. The expectation is that you will not re-use the fastener more than a couple of times. Another thing to consider is the clamping surface that the fastener come up against. This is one reason that hardened washers are used. With soft metals such as aluminum or un-heatreated steel, the rubbing of the surface as a fastener is clamped will generaly roughen the surface, leading to increased friction. When this happens, your torque value stays the same, but you're actually generating less clamping force on the joint itself. This is why fastening of critical joints is generally done using torque angle rather than torque.
Here's a question for you: When's the last time you had your torque wrench calibrated? For most backyard mechanics, the answer is never. If you don't unwind the wrench after each use, you're probably causing damage to it.

 

[SteinAir]

Terry is spot on here. It's somewhat of a falsehood that I don't know who started about "checking torque" on an already installed locking device. Typically (and especially on something like a nutplate or other locking device) you can really and truly only check torque in one direction accurately, that being the "on" torque. Simply putting a torque wrench on the bolt and trying to check the torque in the other direction won't tell you much of anything at all. In fact, you might end up doing yourself a disservice by loosening those up.

Anyway, just wondering how you were checking the torque of an already installed bolt into a locking type device such as a nutplate. Checking torque in the "off" or backwards direction isn't telling you much of anything IMHO.

My 2 cents as usual.

Cheers,
Stein

 

[jdeas]

Break force vs torqued value

About a year ago I attended a talk on torquing propellers. What stood out to me was the difference between the 'break free' force on a bolt already in place vs torqued value.
If memory serves it can take considerably more force to 'break a bolt free' beyond its torqued value. In the case of this seminar, the implication was that torque could not be properly measured unless the bolt was first loosened to some extent then re torqued. Just checking an already installed bolt with your wrench and seeing when it moves is not a valid measurement.

I have to agree that bolts on my QB7 also seemed well above listed torque values but perhaps this explains some of the discrepancy.


Perhaps I am wrong in doing this, but all bolts on my airframe are being re torqued as part of the QB inspection and assembly and yes, my torque wrench has been checked.

 

[RV10Rob]

Thanks, all... I should have described how I checked. Basically, I loosened the bolt slightly (about 20 degrees) and then re-torqued it. The wrench "slipped" right away at around 25 in-lb, so I kept increasing it until I got to around 60 in-lb, when the bolt finally moved. Not really scientific, and maybe I shouldn't have done that.

I also marked a couple bolts, then completely loosened them and re-torqued to the right value. They ended up almost 60 degrees (one "flat") off of where they were from the factory.

 

[Rick S.]

If you don't unwind the wrench after each use, you're probably causing damage to it.

Also the wrench should be "broke" before each days use. By this I mean at the lowest setting use the wrench three clicks on a nut that won't move. Most tool rooms have a set of adapters welded to the bench so you can break the wrench before heading out to work. I was told the reason for this is to disperse the lubricants inside of the wrench. If you have access to ANSI or ASME standards, all you ever wanted to know is here:

ASME B107.14-2004, Hand Torque
Instruments (Mechanical)

 

[Rivethead]

jdeas is absolutely right. It is folly to check torque by trying to move a nut from a resting position. Proper torque technique is to bring whatever is being torqued to torque while still moving and never from a resting position. If you come near to torque but can't finish for some reason you must back off and start over. You should be seeing what appears to an over torque condition on nuts or bolts at rest.

(edit) Just finished reading your method of checking torque and still think (imho) that something is missing in technique.