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Wooden Propellor Bolt Torque


Louie
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Looking for information regarding recommended bolt torque for a wooden propeller. Article in latest Sport Pilot says 11 to 14 ft. lbs. Also is there an adjustment in the setting when using lock nuts due to the resistance?

 

 

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Jabiru installation manual, available on Jab website, has torque details and they use nylock nuts. I'd have a look and tell you except my book is at home and I'm on Rocky at the moment!

 

 

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Jabiru installation manual, available on Jab website, has torque details and they use nylock nuts. I'd have a look and tell you except my book is at home and I'm on Rocky at the moment!

Jabiru Prop Manual says 6ft.lbs but I'm wondering if any difference because they use Belleville washers. Mine is wooden prop on jab 6 cyl jab. (Morgan Sierra and prop)

 

 

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I agree with the comment "not good to experiment"

 

Was talking with a maintainer who told me he had seen a prop catch on fire when it was not torqued correctly (loose), the individual engine produced pulses caused the prop to slip against the prop flange and that slipping produced heat which eventually caused ignition.

 

I recall that Jab say to retorque at fairly low intervals in the beginning of life of a new prop and thereafter at not huge intervals of time.... The washer arrangement as I understood allowed for some variations in humidity (translating to wood moisture content changes) that would of themselves be reason for a retorque otherwise.

 

Seems to me that a prop manufacturer that doesn't supply torque info and timelines/ event triggers against various aviation engines is unlikely, and if on a LSA aircraft the manufacturer of the aircraft is also unlikely to not have clear instructions on exactly that point.

 

If I was to tell you to use 9foot pounds......why would you accept my answer over that of the manufacturer(s) and even if you did accept it (and I suggest you don't) does it give you the authority to apply it?

 

Andy

 

 

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Thanks guys absolutely understand the importance of what you are saying and I don't ever second guess anything. I was intrigued to read quoted numbers in the article given that different mounting methods and situations apply. I will get a number from Garry.

 

 

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No one can give you an official answer but as a general comment you have to overcome any stiffness to apply the specified torque. If it required 4 ft/lbs to overcome the nylock nut resistance, that would be part of the consideration. Torqueing relates to a distance the thread winds depending on the pitch.. This compresses the wood and gives the desired clamping effect. You have the same consideration regarding oiled threads and non oiled threads, Sometimes you bottom the bolt or nut on the face and then move a specified number of degrees. This can be a safer way of getting a consistent result.. (In my view). Nev

 

 

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If it's a Jabiru engine and prop, use the beleville washers and the Jabiru recommended torque. A great deal of experimentation went into the development of that specification and nobody other than Jabiru has any proper idea of the reason why that is the correct and best solution to the specific engine and prop. There is WAY too much hangar gossip factor involved in varying from the manufacturer's specification - and ALL of that is personal opinion that is NOT backed by rigorous testing.

 

The Jabiru solution IS backed by rigorous testing. HOWEVER: ensure that the nylocs you use are AN items, not Bunnings OTS crap. And - make sure that the torque wrench you use is accurate, because the pre-load on the beleville washers has been very, very carefully calculated to provide the required friction co-efficient between the prop and the flange while having the compliance to accommodate variations in the moisture content of the prop wood in the range of expected conditions in Australia.

 

 

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Note I'm not advocating anything specific. Just explaining a few principles. Jabiru have a process and the figures to go with it. Stick to that..Wood changes size with moisture change. Long trips heat up the hub and dry it out. Wood props are a special problem in this regard. Nev

 

 

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Jabiru recommend 72"/lbs which equates to 6'/lbs, if you are re-torquing make sure you loosen the nuts first prior to setting the torque, if you are using nyloks they will need to be replaced as they are a one time use nut, torque wrenches have around 30% accuracy depending on the user, facthunter's comments above are the most accurate way of obtaining the most accurate torque.

 

 

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Never, in my time around aircraft, seen a wooden propeller installed without Belleville washers, (doesn't mean there aren't any) I believe that they accommodate propeller expansion and contraction with change of moisture content, never seen them installed with nylock nuts until my jabiru either, they always used to be castellated nuts and split pins.

 

 

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Torqueing them and pinning, or safety wiring (or tabwasher) has to be the go. Nylock complicates the whole process introducing an unknown factor. Critical at low torque settings. Check torque wrenches often. Some mechanics develop a very accurate feel but You can't use that in a QA situation where you sign something off as meeting a standard. Nev

 

 

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