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Torque Wrench with a Universal Joint

Meat

Active Member
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Hi All,

I'm torqueing the four AN-6 bolts on my RV-14 fuselage F-01442 Lower Drag Fittings. The two inboard bolts are pretty straightforward. The outer two are tougher to get at. The only way to torque the nut is by using a universal joint and extensions. I'd try torqueing the bolt but there's not enough space for the torque wrench ratchet to reengage and turn. A crows foot there doesn't help either.

Is using a universal joint acceptable with a torque wrench? If so must any torque setting adjustments be made? I can't find a clear answer or reference on that.

Thanks for everyone's time.

Scott
 
I would check the build manual, or contact Vans. Normally, use of universal joint or multiple extensions is not recommended due to the inaccuracies caused by said extensions. If Vans has recommended use of u-joints or extensions, they may have already done the math to ensure the torque values are met.
 
It depends on the angle the u-joint is subjected to and how "friction-free" the joint is supported. A picture of the setup would be helpful. I know of no rules of thumb for this, but my gut sense is if the u-joint is only through 10 or 20 degrees, you should be close.

There will be bolts that cannot reasonably have a torque wrench applied. I've typically just "calibrated" myself using a torque wrench, then applied this freshly calibrated hand to a box wrench on subject bolt, and moved forward.
 
I'll comment with the disclaimer that I went to A&P school 30 years ago, so take this for what it's worth;

U joints have some slop in them but it seems to me that any error would be caused by the angle. As far as I know, there isn't a specific reference for correcting this error, but there is a reference for correcting the error caused by using a crows foot.

AC43.13 had a chart that shows how much to bump the torque setting up based on the length of the crows foot, so if your u joint combination is causing you to be 2" out of plane (for example) you could use the calculation for a 2" crows foot, but this is going to be error prone depending on if your u joint is closer to the wrench end or the socket end.

I'd probably do what alex peterson suggests above and just calibrate my elbow, but if you really want to get down in the weeds you could simulate your situation with a bolt in a vice both with and without the u joint and approximate wrench angle, and see what the difference is.
 
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If you extend the length of your torque wrench in any direction, you need to adjust its setting to get the correct torque on the nut. This is true even if you use a crow foot, although the difference may only be an inch. Formula below:

https://www.norbar.com/Home/Torque-Wrench-Extension-Calculator

Another way of looking at it:

https://www.engineersedge.com/manufacturing_spec/torque_wrench_2.htm

And here is a handy calculator to do the math for you:

http://www.rv7.us/a_u-torquewrenchsetting.htm

Just plug in your numbers and select calculate. Makes it easy. If it’s impossible to get your torque wrench in there, what Alex says has worked for me many times. Sometimes you just don’t have a choice.
 
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Universal joint

Scott,

Unless the angle is very small, using a universal joint makes the torque reading meaningless. Universal joints are fairly complex to analyze because the transmitted torque depends on both the offset angle and the angle of rotation. As a universal joint rotates, the torque oscillates, which is why in drive chains, they are in matched pairs.

Jim
 
Thanks for everyone’s time and feedback. Much appreciated. After sleeping on it and a trip to the store for a proper extension I figured out how to attack the offending nuts without a universal joint.
Merry Christmas.

Scott
 
I guess “extension” can be taken two ways. I misunderstood what the OP was referring to. I thought when he said extension he was referring to adding length to the lever arm, in which case that calculator works fine. A socket extension obviously does nothing to the torque value applied to the bolt/nut because the force is being applied perpendicular to the wrench and doesn’t make the lever any longer. The universal joint torque variations is something I never thought about, and I’m pretty sure I couldn’t figure it out anyway.
 
I assume this thread is from step 7 on page 29-03 Rev 1. However I am confused about the verbiage Van's uses as they say
"Firmly tighten the bolts in the upper drag fitting and lower drag fitting."
vs. torque the bolts.
Is this a deliberate use of firmly vs torque?

Asking the mothership, but wondering if others have already asked.
 
I was confused by this also. After match and final drilling, Upper Drag fittings are removed (29-12, step 3) and rivetted to Center Section Side Plate (29-12, step 4). Bolts are reinserted and final torqued as part of Side Skin Assembly to Fuselage in (29-13, step 8).
 
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