Torque on prop

[DannyDot]

What is the torque value for a wooden prop on a C-85 engine?

Danny Deger

[crispy critter]

Re: Torque on prop

if you are using the original crush plates then it is the same as the recommended bolt torque for that size bolt.

[alwaysoar]

Re: Torque on prop

Go to the Sensenich site--it tells how and how much.

[DannyDot]

Re: Torque on prop

Go to the Sensenich site--it tells how and how much.

I found a great pdf on the Sensenich site on how to install a wooden propeller. The site recommends checking the bolt torque every 50 hours because the torque can change based on moisture content of the wood. I had never heard of this. Does anyone out there do this? If not every 50 hours, it sounds like a good thing to do during the annual.

Danny Deger

[VictorBravo]

Re: Torque on prop

Actually, any time you fly the plane from a very dry environment to a wet one or vice versa, you should check the torque. Wood props are living breathing things and need constant attention if you want to do it right. 50 hours is a good starting point.

[Guest]

Re: Torque on prop

Dan, do search on this forum on prop torque. Many post in the past and bottom line is the Sensenich site has data for FLANGED cranks. If you have a taper hub the data is not valid, longer story why, read the prior posts to get the gist. Dave.

p.s. If they updated their site for taper hub then I eat my words, too lazy to check now, historically it has been as I said.

[DannyDot]

Re: Torque on prop

Dan, do search on this forum on prop torque. Many post in the past and bottom line is the Sensenich site has data for FLANGED cranks. If you have a taper hub the data is not valid, longer story why, read the prior posts to get the gist. Dave.

p.s. If they updated their site for taper hub then I eat my words, too lazy to check now, historically it has been as I said.

Good catch. It looks like the document is on flanged cranks. I found an attachment in a previous thread that recommends turning the bolt a certain amount after it snugs out. Any comments out there on using this technique?

Danny Deger

[alwaysoar]

Re: Torque on prop

Call Sensenich. I did after all the posts about tapered cranks. Their tech support is very helpful and will tell you what to do with a tapered crank.

[Guest]

Re: Torque on prop

Good catch. It looks like the document is on flanged cranks. I found an attachment in a previous thread that recommends turning the bolt a certain amount after it snugs out. Any comments out there on using this technique?

Danny Deger

I think you may have found one that I posted, I like that scheme and have never had a problem with it. And have never had any signs of slippage. That table is from an old Sensenich document.

Be carefull of buying in to the torque range method. I swallowed that story 9 years ago and deformed a brand new taper hub. Didn't ruin it but a new taper hub is like gold and deforming it on the very first usage was upsetting.

It's related to the use of the filler bushings and their dimensions compared to the builting in bushing in the flanged crank. If the wood hub had the smaller holes (same size as bolt) the torque method might work. Problem is that with the large hole and a bushing that does not fill the hole space 100% and to the surface, the 3/16" thick metal hub plate it deformed as it is pulled into the annular hole (ie. the bushing is not flush with the prop's rear surface). So you can keep re-torqing and just keep deforming until finally the bushing contacts the metal hub. I don't like that scheme. But I am a nit-picker!

BTW- looks like I will be able to get 1280 lb gross weight. STC holder, ACO and my FSDO all seem to think it's ok. I think there is more than one approach to it but I'll use the most expensive which involves using the STC but it's also the most convenient. Your plane looks real nice.

Dave

[alwaysoar]

Re: Torque on prop

First, for his own satisfaction, I think Dannydot ought to call Sensenich tech support. I called and got different answers. Second, I sense from all his questions he is not an A&P, so he should not be doing any of this himself.

[Guest]

Re: Torque on prop

First, for his own satisfaction, I think Dannydot ought to call Sensenich tech support. I called and got different answers. Second, I sense from all his questions he is not an A&P, so he should not be doing any of this himself.

Agree, good points both of them.

As you have sensed I did not get answers I found satisfactory and have stated in the past if Sensenich thinks the flanged instructions apply to to the taper hub they need to write that way in the instructions. I'll stop my rant.

Please share the answers that you got. Sounds interesting

Dave.

[alwaysoar]

Re: Torque on prop

I called Sensenich when this thread first appeared because I have a tapered shaft with a hub installed and have been torqueing to their published specs. What I RECALL them saying is: They have not heard of distortion occuring to the hubs the way it was described in the thread. The bushings do no good. Snugging down while still in their installation instructions should not be done (They said, but I don't remember why or why that is in their instructions).

My feeling in general is that there are some highly experienced and qualified individuals, you included, who have used techniques for a myriad of issues that less qualified individuals should try only at their own risk. In all these things I am very reluctant to second guess the manufacturers or do something that is not approved (eg epoxy brake linings). When I am confused or want clarification I call the manufacturer. I have always gotten great consideration. What tech support told me in this instance is that what I should do is what I have been doing, except I'll remove the bushings the next time if remove the prop.

[DannyDot]

Re: Torque on prop

I called Sensenich when this thread first appeared because I have a tapered shaft with a hub installed and have been torqueing to their published specs. What I RECALL them saying is: They have not heard of distortion occuring to the hubs the way it was described in the thread. The bushings do no good. Snugging down while still in their installation instructions should not be done (They said, but I don't remember why or why that is in their instructions).

My feeling in general is that there are some highly experienced and qualified individuals, you included, who have used techniques for a myriad of issues that less qualified individuals should try only at their own risk. In all these things I am very reluctant to second guess the manufacturers or do something that is not approved (eg epoxy brake linings). When I am confused or want clarification I call the manufacturer. I have always gotten great consideration. What tech support told me in this instance is that what I should do is what I have been doing, except I'll remove the bushings the next time if remove the prop.

Good advice. I plan to call Sensenich on the prop installation technique and have my A&P rivet the brake linings in. I don't believe in going against recommended manufator proceedures. The epoxy on the brakes is a good example. Maybe it is OK, but if it is not, it could ruin your whole day. I just retired from NASA and the two shuttle accidents were due in large part from NASA accepting a vehicle that was not behaving as it was manufactured to behave. In one case NASA accepted o-ring blow by and the other NASA accepted foam shedding. Just because it was OK once or twice, it doesn't mean it will always be OK. Epoxying brake lining could be a similar trap.

I am surprised prop installation is not as well understood as it could be. I am not the first person to need to torque a wooden prop on a C-85 engine Thanks all for the information given. I will pass it all to my A&P.

Danny Deger

[Ragwing nut]

Re: Torque on prop

Taper flanges will distort with enough force, usually caused by over torquing the bolts. Taper hubs are not as robust as a flange crank. Wood props work in the same manner as a cork gasket. Torque it to one spec today, come back tommorrow and it will be loose. Every time you torque it, the fibers compress until you run out of threads or compress the material until it won't yield any more.

Another thing to consider when torquing any wood proper is maintaining blade track. What ever the value is you want to bring it to the lowest value and then tighten as needed to track the propeller. You also want to ALWAYS store the propeller in a horizontal position. A wood propeller retains moisture and if store vertically, you will be wondering why you have a bad vibration when you go fly after a rainstorm the previous day.

I have a 2 page sheet that goes out with all my propellers. Above and beyond that sheet, you should check the torque after each major seasonal climate change.

Mike

[Guest]

Re: Torque on prop

When I contacted Senenich they told me that I MUST install the bushings, so I purchased bushings from them and from installed same using the torque spec.

Which is diffrent than the answer Alwaysoar recalls.

The issue is that you can get different answer from time to time. That's not good.

The published manufacturers instructions are for a flanged crank. Any intructions for a taper hub are by word of mouth as far as I know.

The primary maintenance inspector (PMI) I deal with at the FSDO says make STC holders and manufactures write it down and send it to you. They will tell one story on the phone and then later when something goes wrong you will not be able to hold them to that story they will have another that covers their butt.

I have had this experience with other mfgs. too. They tell you something on the phone, then ask to have a copy sent of the drawing or letter... and you never get so you are hanging out there on your own because you acted on what they said. It's very difficult to reference that "what they said" data in a log or 337.

In fact based on the PMIs advice I would say that we have no approved manfucters instructions for taper hub since the only published ones are for flanged crank.

I am trying not to rant. I think there is a very good lesson in this that that goes beyond prop hubs I would like to bring out while not ranting.

It is that we should get manufacturers to give approved written instructions rather than phone chat. Even though we had a discussion on the phone that is not documented and I would not call that approved manufacturers instructions, I suspect FAA would not either.

For example, if the prop flies off my plane are they going to say I had bushings in when I should not have and that was the cause? Or the other way around. Make a similar example with epoxy brake linings and so on.

BTW- After using the torque spec I actually sent them a letter and sketch describing the deformation problem I had and a solution to it, I called them to follow up discuss it too. They blew me off. They have heard this before.

Hope this had some value.

Dave.