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Retorque those wood props and composite props with wood cores

McFly

McFly

Well Known Member
I retorqued my Catto prop last night as part of the condition inspection and was surprised that it was approx 30 ft lbs. It should be 40 ft lbs. The last time I torgued was in Spring or early summer and it was spot on. In my mind I was just going through the motions but man, I am glad I did this.

Will the prop ever get over torqued as wood shrinks and swells?

Other finds during my first inspection (117 hours)
-Mag timing off by 2-3 degrees.
-One jam nut on the elevator push rod was loose
-Exhaust hangers were a tad loose on left side
-Tires need to be replaced. I could have gotten a lot more life if I had switched them a few months back, the wear is on the outside. Live and learn.
 
This fall I went to the Rough River canard fly-in and noticed several EZ's that had stacked belleville washers under the heads of the prop bolts. Belleville washers are designed to maintain a torque setting. Apparently they have cracked the code on how to maintain constant torque with wood props.
 
rocketbob said:
This fall I went to the Rough River canard fly-in and noticed several EZ's that had stacked belleville washers under the heads of the prop bolts. Belleville washers are designed to maintain a torque setting. Apparently they have cracked the code on how to maintain constant torque with wood props.
Click to expand...

Marc Zeitlin at http://www.cozybuilders.org/ developed the belleville washer system for a prop. He is a heck of an engineer and was working for Scaled last time I saw him which was at OSH.

I'm sure he will share any info on this system if contacted.
 
Yes, you should recheck wood prop bolt torque on a regular basis. A lot depends on climate, but there are other factors.

I assume that Catto prop has a maple core. Note to others; don't use 40 ft-lbs if you have yellow birch, mahogany, or any other wood with a lower "crush perpendicular to grain" value. Yellow birch on an SAE2 is about 16.5 ft-lbs, mahogany even less.

Re the the sudden popularity of belleville washers on canards, one of the lead dogs lost his prop a while back, so he got serious in pursuit of the belleville washer idea. Actual credit goes to the late Vance Jaqua and our own Paul Lipps (as in the Elippse propeller). Vance's kids still maintain his webpage, click on "propeller" in the left menu:

http://www.geocities.com/vjaqua/

A little-considered footnote to the propeller loss on the subject canard; the builder had a carbon fiber spinner backplate inserted between prop and extension. If the carbon is fully encapsulated in the epoxy matrix, the frictional contact is between aluminum and epoxy, with a coefficient of friction around 0.5 or 0.6. No problem so far.

However, the builder sanded the backplate for surface flatness. If he sanded enough to expose the carbon, the carbon-to-aluminum CoF would be much less, perhaps as low as 0.1. Static Cof is always higher than dynamic; once it started slipping Cof would drop further. Frictional heating would have softened the epoxy matrix, reducing clamp pressure. Bolt failure would have soon followed. That's my analysis anyway; your mileage may vary.
 
I also retorgued my Catto yesterday as part of the annual and had exactly the same results--most bolts down to about 30 ft lb. I have heard that this stabilizes after a couple of retorques. I didn't find any loose jam nets, but did find a loose exhaust hangar. Also one missing baffle screw. Not much else. Very happy at how everything came out. Finished today except for now having to wait for the new front fork.

Bob Kelly
 
I retorque mine at each oil change. I also retorqued in in Florida on a recent trip from Colorado then two or three weeks later after I returned. So mine is done several times a year.
 
As far as the canard that lost a prop in the desert, did he come from the humid east coast? If so, how long was he in the drier climate out west and did he retorque during that time?
 
I think he is pretty much desert-based, although the airplane gets around.
 
Ron Lee said:
As far as the canard that lost a prop in the desert, did he come from the humid east coast? If so, how long was he in the drier climate out west and did he retorque during that time?
Click to expand...

That was Marc and the airplane had been in California for some time.
 
Geico266 said:
Says my prop needs to be torqued to 16-19 foot pounds.
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Funny but my Catto is to be torqued to 35 ft-lbs. To each their own.

I re-torque my prop every three months, regardless if it needs it or not.

So as not confuse people, Catto puts a label on each prop hub with the proper torque spec. Mine is smaller than most 68" diameter by 64" pitch.
 
I assume it is due the different wood used. According to Sensenich a 3/8" prop bolts gets 16-19 foot pounds of torque. According to Sterba 15-18 foot pounds is good.
 
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Geico266 said:
I assume it is due the different wood used. According to Sensenich a 3/8" prop bolts gets 16-19 foot pounds of torque.
Click to expand...
That could be the reason. Catto uses maple for his cores, what does Sesenich use?

PS. My O-290 uses 3/8" bolts.
 
The type of wood isn't the only factor for torque specs. the number of laminations is also a factor. The older Warnke props had so many laminations, the torque was limited by the maximum torque for the bolt itself. With these props, there was almost as much glue as wood.
 
N941WR said:
That could be the reason. Catto uses maple for his cores, what does Sesenich use?
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I dunno, I have a Sterba. Sterba says 15-18 foot pounds for a AN-6 (3/8" bolt). I posted the Sensenich link becuase it seems to give a lot of good info and this thread was the closest thing I could find in a search.

I have been chasing down a vibration and was able to get some of it by re-torquing the prop bolts. Every little bit helps.
 
N941WR said:
Funny but my Catto is to be torqued to 35 ft-lbs. To each their own.

I re-torque my prop every three months, regardless if it needs it or not.

So as not confuse people, Catto puts a label on each prop hub with the proper torque spec. Mine is smaller than most 68" diameter by 64" pitch.
Click to expand...

Mel said:
The type of wood isn't the only factor for torque specs. the number of laminations is also a factor. The older Warnke props had so many laminations, the torque was limited by the maximum torque for the bolt itself. With these props, there was almost as much glue as wood.
Click to expand...

I agree with Mel. The fasteners are also part of the equation.

A problem I see with the previous post is that if I remember correctly (I don't have a chart in front of me) the max torque for a standard 3/8" AN bolt is 19 ft lbs. The torque for a 7/16" is a little higher, but still way under 35. I wonder why Catto would be recommending such a high torque?
 
Probably talking about 180hp with 1/2" bolts.

rvbuilder2002 said:
I agree with Mel. The fasteners are also part of the equation.

I wonder why Catto would be recommending such a high torque?
Click to expand...

He may be referring to 1/2" bolts. That's what mine uses. 1/2" bolts should be used on anything over 160hp.
 
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Okay, since I found the torque for the bolts to be 19 foot pounds on my Sterba prop w/ 3/8" bolts, where do I find the torque value of the locking nuts to add to that value? Also, should I add something for torquing the bolt and not the nut? I can't get to the nut very easy so I torque the head of the bolt. Does it matter?
 
Wood prop torque info

Here is a photo of the sticker on my MT wood core fixed pitch. I think the wood is Beech. I don't know if Maple is harder. I also have an old Pacesetter (Maple). Their data sheet says torque bolts to 25 foot pounds. No mention of bolt size but they do suggest a bolt torque pattern.



Sensenich wood propellers are Maple. They have a detailed document that explains torque value, how to torque, self locking nuts, etc. Try the link below to open the complete four page document. Lots of good info for wood prop users.

http://www.sensenichprop.com/sen_html/aircraft_cet/install/cf-a.pdf
 
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