Propeller Woes

[Forrest Barber]

Re: Propeller Woes

That "big hole" has to be filled with an aluminum bushing when using a flange shaft wood prop on a tapered shaft. Where or where are the good mechanics in this world.
YES I know that the NEW Sensenich factory has torque values , BUT older charts showing 1/2 or 5/8 turn of the nut after going "snug" is the method I still use. Figure out the pitch of the thread and THINK. DO NOT deform the beautiful new props by over torquing them. bye

[Guest]

Re: Propeller Woes

Hi Richard, what you describe sounds like what happened to me about 7 years ago.

Sensenich was telling me to torque to something like 175 in lbs, my memory may be off, but what they said was the same as on their sheet.

As I did that I could see my brand new taper shaft hub getting warped. It annoyed me as I had two new hubs that I have been saving for a long time and used one with my new wood prop.

I noticed a few things that convinced me not to use their torque table but to use their deformation table instead. The deformation table specs something like .53 nut rotations after contact with the wood.

The table they had at that time (1998) was for flanged hubs and mine is not flanged but taper shaft.

The old props made for a taper hub had a 3/8" hole in the back so the back of the prop made conatact with the hub directly adjacent to the bolt.

My prop had big holes in the back as it was made for a flanged hub so torque on the bolt is not pulling directly against the wood but against air space.

The above statement is true even when using the spacers because the spacers are shorter than the hole is deep.
So the bolt is deforming the hub by pulling the back of the hub into that big hole. ie. the hub is working as a circular plate (about 7/8" dia) with point load at the center rather than a direct compression onto a wood surface.

I used the deformation table and have had no problems at all.

My new hub is not so like new because of this but at least it will not get any worse.

If I understand what is happening to you correctly I would suggest that you look into using the deformation table too.

Hope this is useful, Dave.

The spacers I refer to are those aluminum bushings that Sensenich sells, sorry for any confusion with any other device. I call them spacers. Probably not the best term. Dave.

[Guest]

Re: Propeller Woes

I looked at the Sensenich site to see if they still have what I call the "deformation table".

They no longer have it on their site so I scanned it off of the Sensenich 1997 torque instruction sheet for wood props.

The proper name for it is "Optimum wood propeller installation hub compression method", I like my name for it better.

It should be attached.

Dave.

[alwaysoar]

Re: Propeller Woes

Where did you get the deformation table? I torque mine to 175 up to 200 which is within the limits sensenich sets. You think this is too much? If it's not torqued properly, then it will wobble and the holes will get elongated. Don't the spacers you insert in the big holes serve to bush the hole rather than to give more surface contact to the hub?

[Guest]

Re: Propeller Woes

Where did you get the deformation table? I torque mine to 175 up to 200 which is within the limits Sensenich sets. You think this is too much? If it's not torqued properly, then it will wobble and the holes will get elongated. Don't the spacers you insert in the big holes serve to bush the hole rather than to give more surface contact to the hub?

The table was included in Sensenich's 1997 torques instructions. I have them but only scanned the table. It seems to be the main thing that is different from the new intructions on their site.

I think 175 -200 ip is probably ok if you have a prop with a 3/8" hole in the back and front. But many of us do not but rather have those big holes.

But the Sensenich instruction are for a flanged crank. Do you have one? I do not I have a taper shaft and hub. When I say hub I refer to the metal hub.

I agree, the aluminum bushings work as you say. I was told that by Sensenich too. They are shorter than the hole and do not provide surface area because they are shorther than the hole is deep, they bush the hole to quote you. I tried to get longer ones that did give more area but Sensenich would not go along with that.

Since the aluminum bushings provide no contact area then if you keep tightening the bolt you will keep pulling the hub "into" the big hole. What I mean by "into" is that the area of the hub at the bolt hole will be out of plane with the rest of the hub, ie. a high spot. That's happening because without a surface on the prop adjacent to the bolt and bolt hole the hub right next to the bolt hole is not being compressed against the wood but is being bent into the big hole. The guys who suggested putting a dowel in th eprop's big hole and then drilling had the best idea,(and I assume one would make the dowel flush with the surface so you get more surface area). Long time ago they made two wood prop configurations, one with big holes for flanged cranks and one with the small holes for taper shafts.

Sorry for being so wordy.

Bottom line for me is that I don't think torquing the bolts is applicable because the effect of the big hole on the hub has not been considered in the torque value calculation. One would have to model the hub as a circular plate with center load as a first step towards avoiding damage to prop and HUB.

So my opinion is don't torque but rather use the deformation table instead. It too is not entirely accurate but the method of turning the bolt N revolutions after intial contact has an end. The torque method as I experienced it is nearly endless and the only noticable result was a deformed metal hub.

My opinion is that we have all this confusion because Sensenich publishes a spec for a flanged crank installation but not for a taper shaft. If the two use the same installation procedures then Sensenich should re-label the instruction for flanged (integral ... ) and taper shaft. But they don't and they have had 10 years or more to do it. Hmm...


Hope this helps, remember, free advice is worth 4 times what you paid for it!

Dave.

[Forrest Barber]

Re: Propeller Woes

yes the bushings are slightly shorter, tapered off on the ends too. BUT if you use the "deformation table" the wood will compress before any metal hub will pull in ( in my experience). We never "retorque" unless moving from here to an extremely dry part of the country. I do remove the prop from the hub about each three years and reinstall after checking the hub area. The best of course is to use a prop without the big holes on a taper shaft...those bushings are used on metal props too....The Franklin 113 HP on the L-6 was the one with only four bolts & AND THAT had to be retightened a lot...It would burn the wood when loose. good night folks....