Posted Monday, March 13, 2023 @ 08:26 AM  

Like Collin I have always understood that with wooden props, which can expand and contract with the change of season, they should be loosened and re-torqued three or four times a year to compensate.

But it's interesting too about your torque value of 18 foot pounds for a 7mm bolt.
My RF3 is a different animal to a Vivat and my prop is a Hoffmann, a wooden prop but again a different animal to one from Props Inc.
My prop bolts are 8mm and until a few years ago I had always used a torque value of 24.5 N/m, equivalent to 18 foot pounds, as stated in the old L-666 based flight manual. From slight crushing visible on the prop hub I'd often thought that too much, but who was I to counter the flight manual?

However with the Hoffmann the data plate on the prop itself states that for 8mm bolts the torque value should be from 15 - 17 N/m, that's equivalent to 11 - 12.5 foot pounds! That data plate has these values for different sizes of bolts:-
I'd have kinda expected that torque for 7mm bolts would lie somewhere between that for 6mm and 8mm but then again I've always assumed that with a wooden prop the concern would be crushing of the prop hub, not the tensile strength of the bolt, so probably my expectation is meaningless. So I'm not saying you should do this, just that the torque value of 18 foot pounds seems high to me. Does your prop hub show any evidence of crushing?

In my own case the step down from 24.5 to 15 N/m, -40%, was huge! (When first fitted I used the lower value of 15N/m on the basis that the new prop would have come from a climate controlled condition at manufacture to my climatically very variable hangar in Scotland where expansion would be likely.) That worked fine and I've never varied it. My Hoffmann has suffered no crushing of the hub nor departure in flight so I take it Hoffmann know what they are about. Does Props Inc state what the torque value should be?

Posted Tuesday, March 14, 2023 @ 04:55 AM  

I know it's in the manual for MT-propellers, Hoffman propellers used to have it and i think it's stated in the manual for our hercules propeller on our RF4.

I have until now not heard of a propeller departing from the engine like it did for you Bob but i am very glad that everything went ok .

As a flight instructor i am curious to know how the area around your airfield looks like, in Europe (at least in Sweden) we teach to not do a 180 in case of emergency below 300 feet AGL if anything happens during take-off, if you are below 300 we teach our students to land straight ahead at the best possible location in the direction of the runway +-10 to 15 degrees.
I guess that the american instructons may differ and that it may depend on how the location looks?