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Counter sink or dimple the wing rear spar flange?

K

Kato's 8

Well Known Member
Good afternoon!
I wonder if anyone has dimpled the rear wing spar flange or countersunk like I did? I read afterwards that one should dimple the .040 flange and then follow up with light countersink since its hard to get a good dimple with that thick. Anyway, I countersunk it and now wonder if that's ok? Has anyone done this and called Van's for advice? Thanks for any input..

Also, I checked the torque on the AN3 tank to spar z brackets and it seems the factory employees in Phillipines torque them to 60"lbs instead of 20-25. Should I loosen them? 25 inchLbs sure does not feel very tight to me. I feel huge urge to tighten just a bit tighter.
thanks everyone!

Bill
 
Bolt Torque

Before you give in to the urge to tighten the AN3 bolts consult Table 7-1 in AC43.13. For a 10-32 thread the following torques (lb-in) are recommended:

Torque limits---Shear Bolts||||||||Torque Limits--Maximum Allowable
Tension Nuts---Shear Nuts|||||||Tension Nuts----Shear Nuts
---AN365-------AN364-----------AN365----------AN364

--20-25 lb-in----12-15 lb-in-------40 lb-in---------25 lb-in

Stress in Bolt----Stress in bolt----Stress in Bolt---Stress in Bolt
-40,000---------24,000 psi------90,000 psi-------54,000 psi

Note especially the third column: 40 lb-in torque on a tension type nut produces 90,000 psi of stress in the bolt. You do not want to exceed this.

Also keep in mind that the Z-bracket nuts are platenuts which probably do not have as high a torque rating as a shear or tension nut. The 60 lb-in of torque you measured may be misleading since loosening torque sometimes exceeds tightening torque.

To satisfy yourself that the above torque ratings are limits, make yourself a test article with a representative bolt, nut, and platenut, and gradually tighten with your torque wrench till failure. I think you'll find Table 7-1 is a good one to follow.
 
terrye said:
Before you give in to the urge to tighten the AN3 bolts consult Table 7-1 in AC43.13. For a 10-32 thread the following torques (lb-in) are recommended:

Torque limits---Shear Bolts||||||||Torque Limits--Maximum Allowable
Tension Nuts---Shear Nuts|||||||Tension Nuts----Shear Nuts
---AN365-------AN364-----------AN365----------AN364

--20-25 lb-in----12-15 lb-in-------40 lb-in---------25 lb-in

Stress in Bolt----Stress in bolt----Stress in Bolt---Stress in Bolt
-40,000---------24,000 psi------90,000 psi-------54,000 psi

Note especially the third column: 40 lb-in torque on a tension type nut produces 90,000 psi of stress in the bolt. You do not want to exceed this.



Also keep in mind that the Z-bracket nuts are platenuts which probably do not have as high a torque rating as a shear or tension nut. The 60 lb-in of torque you measured may be misleading since loosening torque sometimes exceeds tightening torque.

To satisfy yourself that the above torque ratings are limits, make yourself a test article with a representative bolt, nut, and platenut, and gradually tighten with your torque wrench till failure. I think you'll find Table 7-1 is a good one to follow.
Click to expand...

Thankyou for the information. I do have that circular and also the handbook. I just need some reassurance I guess. I just feel that the AN3's don't "feel" very tight and that maybe my torque wrench isnt accurate at the bottom range. But, I do torque to whats called for and torque seal it. Now on the other hand, the AN4's feel tight to me. And then all the hardware tightened down on QB wings are tighter than whats called for. You mentioned the loosen factor, so I tried setting the wrench 5 inch lbs higher and slowy tried to tighten. The bolt did not turn at all before it signaled. So set it another 5 inch lbs, etc.. until it moved at the 60 inch lb mark again. Now I wonder if I should leave them alone or de-torque them. Will the nut plates be ok now that the have been over torqued. Would I be better off leaving it alone?
Thanks for your help BTW
Bill
 
Torques

The problem with "feel" is that it isn't calibrated to anything. Without a torque wrench, even experienced mechanics tend to overtighten bolts under 1/2" and undertighten bolts over 1/2".

So the first thing to check is that your torque wrench is calibrated (I'm guilty of not doing this). Then use the torque wrench and the appropriate torque tables. Check the notes on the tables. Table 7-1 says "The following torque values are derived from oil free cadmium plated threads". If you use Never Sieze, or a thread locker, you need to find a table that accounts for this.

As far as checking the loosening torque, this is sometimes a factor if the bolt head imbeds into the part, or if there is corrosion, but for the most part, the loosening torque should be very close to the tightening torque. Regarding the platenuts, the Mil Spec says 125,000 psi ultimate and this is similar to the AN3 bolts and AN365 nuts, so as far as the material goes, they can be treated the same. However, many platenuts are coated with a dry film lubricant, which as noted above changes the torque value.

I would suggest you check with Van's regarding the apparent overtightening of the QB bolts.
 
AN3 nuts are easily tightened to spec with a torque SCREWDRIVER (with socket attachment of course). The torque is much less than you would think/feel.
 
One more thing

to keep in mind when torquing is to measure the friction drag torque due to the self locking features of a locknut. This drag torque should be added to the recommended torque for the fastener. For example, for an AN3 nylock nut, the drag torque is normally 5-7 in-lbs, so the final torque should be 26-31 in-lbs.

This comes from AC43.13 7-40d.

Just one more thing to keep in mind.

-Chris
 
terrye said:
The problem with "feel" is that it isn't calibrated to anything. Without a torque wrench, even experienced mechanics tend to overtighten bolts under 1/2" and undertighten bolts over 1/2".

So the first thing to check is that your torque wrench is calibrated (I'm guilty of not doing this). Then use the torque wrench and the appropriate torque tables. Check the notes on the tables. Table 7-1 says "The following torque values are derived from oil free cadmium plated threads". If you use Never Sieze, or a thread locker, you need to find a table that accounts for this.

As far as checking the loosening torque, this is sometimes a factor if the bolt head imbeds into the part, or if there is corrosion, but for the most part, the loosening torque should be very close to the tightening torque. Regarding the platenuts, the Mil Spec says 125,000 psi ultimate and this is similar to the AN3 bolts and AN365 nuts, so as far as the material goes, they can be treated the same. However, many platenuts are coated with a dry film lubricant, which as noted above changes the torque value.

I would suggest you check with Van's regarding the apparent overtightening of the QB bolts.
Click to expand...

Thankyou, I think I will double check with our good friends at Van's on the over tightened hardware.. I need to find an easy way to check calibration too. Lots of things to remember and do...
 
CMW said:
to keep in mind when torquing is to measure the friction drag torque due to the self locking features of a locknut. This drag torque should be added to the recommended torque for the fastener. For example, for an AN3 nylock nut, the drag torque is normally 5-7 in-lbs, so the final torque should be 26-31 in-lbs.

This comes from AC43.13 7-40d.

Just one more thing to keep in mind.

-Chris
Click to expand...

I'll check that out Chris, Thanks!
 
Just a quick note. Icalled Van's on the countersinking of the rear spar issue and they said it was ok if it wasnt over done. Most people tend to over countersink but iff the rivit sits flush to a little proud it should be fine. That was good news for me since I tend to do under countersinking anyway. The other wing Used the "beast". My pneumatic squeezer had no problem dimpleing the rear spar flange. I wouldnt even try to do a "touch up" counter sink in the dimple as called out in the instructions.
 
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