Service Instruction: Installation of a propeller by usage of round-neck nut set for ROTAX® 912, 914, and 912 i (Series) Aircraft Engines

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ROA,

Out of interest;

Under what circumstance would a owner/builder/mechanic use a  "round-neck nut" in preference to a socket head / cap screw  & nut or hex nut / bolt ?😈

Hi Sean,

I see these inserts all the time and if I need to work on the gearbox I have to take them out. I've never had an issue taking them out or putting them back in.

Sean,

I was also thinking about the advantages and disadvantages of using these round neck nuts vs. the drive bushing with a hex nut behind it. My aircraft uses 8mm hex nuts (fiber type locknuts) behind the hub. I have a friend with the same SLSA aircraft that is a few years newer, and it uses the round-neck nuts.  We also both run Duc Helices Flash propellers with an approximate 2" spacer, so the bolts are about 6" long. 

On my aircraft, checking the torque is done at the hex nut behind the propeller hub, whereas on his aircraft it's done at the front of the prop since the round-next nuts are fixed in place.  In both cases, you need to pull the spinner so you can hold (or torque) the bolt.  I have the box end type crow's foot for reaching the nut behind the prop hub with a torque wrench, but it's easier checking the torque from the front bolt head, which you can only do if you have the round-neck nuts installed. On the other hand, I think torquing the nut itself is more accurate than torquing the bolt from the head side, especially with the longer bolts that will have a bit of a twist spring back. I think this is just a choice, and I don't see a big advantage wither way.