Collar nuts for Whirlwind prop installation

Do the Kitfox supplied collar nuts get pulled into the Rotax prop flange while tightening/ torquing the prop bolts, or must they be pressed in first?

Torque pulls them flush.

Thanks Eddie, that is what I expected, but was a bit hesitant since the bolt torque doesn't seem particularly high.

Gary,


Regarding your comment that the torque does not seem to be particularly high, there is some engineering behind it.



Essentially the collar nuts take the shear forces; and, the bolts purpose is to keep the tension sufficient to hold everything together.


One little factoid about tightening bolts, in easy terms, is this - any of the tension within the bolt created by applying torque subtracts from the tensile strength of the bolt - for example, if a particular bolt has a tensile strength of 10,000 pounds and the torque applied to it puts 6,000 pounds of tension on the bolt, the bolt has 4,000 pounds of strength left.


The balancing act is using an amount of torque necessary to hold the parts together but no more than necessary to retain the maximum amount strength in the fastener.

Dave, maybe I don't understand exactly what you are saying, but I disagree somewhat. If you have a load that cycles from zero to 6000 lbs and you put in a bolt good for 10000 lbs (lets ignore safety factors for now) and torque it to 6000 lb clamp load, it can then hold up to 6000 lbs without stretching any farther, thus giving you zero fatigue cycles- good thing. If you load it up with 4000 more lbs (a total of 10,000) the bolt will begin to stretch more as the load exceeds 6000 lbs. The bolt is still good for the 10,000 lbs total but now you introduce fatigue cycles as the load exceeds the 6000 lb clamp load, and it will eventually fail as the fatigue limit is reached. Now here is where I disagree with you, if you torque the bolt to 10,000 lbs clamp load just to make sure, you haven't hurt anything even if the load never exceeds 6000 lbs. You will never get any fatigue cycles and the 10,000 lb clamp load on the bolt is still within its capabilities (ignoring safety factors as previously stated). In other words, there is no value in trying to torque a bolt to just barely above the expected load. Just torque it to the recommended value for that size and grade of bolt.

For a primer on the purpose of torquing bolts, read the article in this months Sport Aviation written by the Carpenters of Rainbow Aviation.

As to seating the "collar nuts" you need to seat them before torquing. You can do this with a bolt of the correct size and thread, not necessarily one of the prop bolts. Use a large flat washer and a tubular object (a large, deep socket will work to pull the collar nut into place and fully seated. Then instal the prop and torque to the appropriate specification.

If you are using a ground adjustable prop. You will need to do several rounds of torquing. Torque the blade clamping bolts, then the prop flange, the go back and check the clamping bolts... and back to the flange. Then safety wire. The front and back of the prop hub will loosen the initial torque as you tighten the others.

Ralph



Ralph