Nut Torque

Question:

Just finishing up the vert stab and trying to bolt the lower rudder hinge bracket on. How do I determine the correct torque. Initially I thought it would be as easy as checking the table on page 5-20 of the plans but then I started reading about “friction drag/prevailing torque” and now I’m not sure. Also I don’t see an MS21042-08 even listed in the table. I’ve attached pictures of the plans and chart.

I feel like I’m missing something and this shouldn’t be hard.

Thanks,
Bryan

Two steps.
1. Look up the torque for a number 8 screw (fine thread). Dry, no lubrication.
2. Measure the ‘running torque’. This is best done with a small ‘bending beam’ type of torque wrench, not the ‘click’ type. Put the bolt head in a vice and measure the torque it takes to keep the nut smoothly turning, with the locking part fully engaged. You want the running torque; the torque it takes to start turning is higher, which is why it’s hard to measure with a click type wrench.
Add up the torques from 1 and 2. That’s what you use to torque the parts together.
If you only have the click type torque wrench you can still make this measurement. You need to help start the nut turning with some pliers. Start with a low torque setting. It should click when you remove the pliers. Repeat over and over, each time increasing the torque setting. When it barely does not click, that’s your number.
Edit. I wrote it backwards! Fixed.
Edit 2. I think most builders just use the same drag torque for any given size and type nut. E.g., I use 5 inch-pounds for all standard fiber lock nuts on an AN3 bolt.
Edit 3 Many engine parts have different torque specs, either because they are more highly loaded, or coarse threads, or assembled with oil.

Found at https://st.hotrod.com/uploads/sites/21/2020/09/152-TABLE-torque-values-aircraft-bolts-and-nuts-in-shear.pdf: 12-15 in/lbs. Not sure why #8 is not listed in the RV manual since #8 screws are used throughout the RV kits. I found no listing for #6 or 4-40, but they would be less. I use #6 to attach my wingtips and 4-40 in a few locations for wire clamps. Tightening by feel has worked in those situations.

Kitplane Article: Torque wrench basics

https://www.kitplanes.com/torque-wrench-basics/