flyenforfun

flyenforfun

Well Known Member
Looking for a final answer on wing bolt torque. I've read many thread and even called vans and the answers are all over the map. Do I use the AN torque values or the NAS bolt values (much higher). So far I have torqued half my 7/16 bolts to the Nas value if 520 to 630 in lbs. the AN value is 450 to 500 I think. Problem?

Which is correct?
 
az_gila said:
If they are NAS bolts leave them alone....
Click to expand...

They are the NAS Wing bolts torqued to NAS spec of 520 to 630 inch lbs. so torque plus run on torque of the nut I did 600 in lbs, or 50 ft lbs.

Why do I feel like I am the only builder in the world who does some of the things I do. Someone always knows something I don't.
 
Last edited:
Am I correct in thinking that these bolts are loaded almost exclusively in shear, so the torque might not be as critical as it would be for a bolt in tension (like a connecting rod bolt), thus Van's recommendation that standard AN torque is adequate?
 
flyenforfun said:
Well now I feel a little better.

What are your wing bolts torqued to?
Click to expand...

Tell me this, torquing experts. Those of you who torqued any bolts from the head, did you incorporate the torque it takes to turn the bolt in the hole? I just measured 25 ft lbs to just turn the bolt in the hole, no nut. Does this mean when vans told me to torque to 40 ft lbs, head or nut, I am under torquing by 25 ft lbs?
 
I'm going to come up on this during final assembly pretty soon...why is this not something that is *very* specifically defined and instructed by Van's? I'd expect specific directions on how to insert each bolt and tighten to the proper torque, both for torqueing the nut and the ones where you have to torque the bolt head. This is, after all, a critical fastener, is it not?

Or did I miss something in the plans and instructions? Tell me I did (it wouldn't be the first time :) ).
 
don't get too worked up...

To accurately measure the torque on the nut you would have to consider the drag on the nut, or bolt head; wherever you are getting the measurement from.

There many variables with getting a consistent and accurate torque... mostly associated with measurement and technique.

Even though this is a critical connection it is critical in shear not tension... the nut is really there to make sure that the bolt stays put to resist vertical movement of the wing, not so much to pinch the spar together.

Imagine that the bolt was more like a C-clamp which would provide no shear, only tension... all that you would have to resist the wing load would be the frictional forces from the spar halves being held together... not much no matter how much you torque the nut. Now, as designed, use a very tight fitting pin and you will create a pure shear connection where failure can only occur from the bolt being sheared out by the wing spar from the wing load... a truly monstrous force. Note that if the pin is loose there is a bending load that gets introduced into the bolt that will significantly reduce the strength which is why they are very close tolerance bolts with honed holes and warnings ;)

Once the close fitting pin is installed they only need to stay put; at least to resist the wing load... they might still be factored into creating the main spar structure but I doubt it is significant since there is so little yaw load and the beam structure is clearly arranged to carry vertical loads...

The rear spar pins the wing in position so that the wing loads are transferred to the main wing spar vertically... these are critical to prevent the main spar from twisting... not much strength in twisting; recall how easy it is to move the trailing edge up and down before it is bolted in place.
 
Last edited:
People have flown forgetting to install one or more of those nuts and later discovered that the bolts hadn't budged a bit. You may be able to do a search to find the post from a few years ago, but I don't think stressing over the torque value of these bolts is necessary.

I torqued to the upper end of the AN spec and left it at that, and those bolts coming out over time are the least of my worries. Heck, I had to back several out to get the nuts on and it took a lot of time and effort to move those things even a quarter of an inch, they were in so tight. I would be more worried about properly lubing the bolt before you install it, or providing some sort of long term corrosion protection, that I would about what turning torque you need to add.

Keep things in perspective! If Van's felt the issue was critical, they would have highlighted it in the plans or instructions.
 
Torque

flyenforfun said:
Tell me this, torquing experts. Those of you who torqued any bolts from the head, did you incorporate the torque it takes to turn the bolt in the hole? I just measured 25 ft lbs to just turn the bolt in the hole, no nut. Does this mean when vans told me to torque to 40 ft lbs, head or nut, I am under torquing by 25 ft lbs?
Click to expand...

When you torque a fastener, you are indirectly stretching the shank by rotating the nut along the helix if the bolt threads. Really critical fasteners such as connecting rod bolts are routinely measured with a micrometer before and after torquing to measure the stretch or preload. Less critical bolts are merely tightened to a specified torque value. So, yes, you are right, the torque required to overcome the locknut friction on the threads, or the bolt friction in the hole should be added to the tightening torque.

Unfortunately, in spite of our best efforts and using calibrated tools, even perfect input torque can give us a +/-25-30% variation in preload.*

In the case of the wing spar bolts, as another poster stated, these bolts are loaded in shear, so while they should be torqued, they are nowhere near as critical as a tension bolt such as a connecting rod bolt.

*"An Introduction to the Design and Behavior of Bolted Joints" by Bickford.
 
Last edited:
You must log in or register to reply here.