Stabilator – Hinge Brackets

Page 09-07

Hinges need to be attached to the spars with AN3-4A bolts going into nutplates. The nutplates are bit tricky. They are compressed slightly at the end of the thread, thus generating extra torque when you run the bolt first time. once the bolt passes the compressed area of the nutplate it goes much lighter.

The normal clamping torque for the AN3 bolt is about 25 in-lb.

I’ve measured the friction torque of the AN3 bolt going through the nutplate with quite a bit of Boelube on it. The result was around 9 in-lbs  +/- 2 in-lbs.

So I set my torque wrench to 35 in-lbs and tightened the bolts.

The installation of the hinges bushings turned to be interesting.

I made all the bushings about 22/32″ just in case I need to make them shorter. And it turned out that I had to, by about 1/64″

I put one in and tightened the bolt with the torque wrench set to 35 in-lbs (maybe 2-3 in-lbs tighter) and the bushing visibly shrunk and bulged. It became about 1/32 inch shorter and 1/64 inch thicker. Obviously the material of that aluminium tube is very soft. So I had to make another one and this time was much more gentle on the bolt.

Now I kinda understand why people often abandon the idea of using the torque wrench and tighten the bolts by the feel of the hand.