Bolting Torque for the RV-12 Prop??

[MartySantic]

The Sensenich prop manual tells us to torque the AN5 prop bolts to 240-265 in/lbs (20-22 ft-lbs).

In Section 5.0 of the plans, Van's has provided typical torque values for AN bolts that we have used during the build. For the AN5, Van's tells us to torque it to 100-140 in/lbs.

Why is there such a large difference??

 

[MartySantic]

I spoke to a mechanical engineer at the nuclear plant I retired from and discussed the bolting torque that Sensenich specifies in their manual. He performs bolting calculations on a daily basis. He did not do a formal bolting calculation, but, rather a back of the hand calculation. He indicated the bolt torque specified by Sensenich takes the bolt close to the yield point, and, as such, is acceptable. The "typical" torque values that Van's has specified in Section 5.0 of the plans, take the bolts to approximately 50% of yield, again, acceptable.

Because you do not torque the prop bolts beyond the yield point, they can be re-used.

 

[az_gila]

That does say....

I spoke to a mechanical engineer at the nuclear plant I retired from and discussed the bolting torque that Sensenich specifies in their manual. He performs bolting calculations on a daily basis. He did not do a formal bolting calculation, but, rather a back of the hand calculation. He indicated the bolt torque specified by Sensenich takes the bolt close to the yield point, and, as such, is acceptable. The "typical" torque values that Van's has specified in Section 5.0 of the plans, take the bolts to approximately 50% of yield, again, acceptable.

Because you do not torque the prop bolts beyond the yield point, they can be re-used.

...that you need an accurate torque wrench for the job.

A "standard" automotive 1/2 drive one probably would not have the accuracy at that low level of torque.

 

[MartySantic]

A very good point. This application DOES demand a good quality and calibrated torque wrench. My wrench has been recently calibrated and is a 3/8" 0-600 in-lbs wrench, so I am about 50% of scale.