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Thread: Nord-Lock Washers with Wooden Prop

  1. #11

    Join Date
    Sep 2011
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    60
    I know that this thread is about wooden props/Nordlock washers, but for interest-- Sensinich sends Nordlocks with their composite props when you buy a new one. They not only claim a zero fail rate, they put it in writing. In 4 years mine have never lost torque spec. I don't know what their deal is for wood props.

  2. #12
    Dana's Avatar
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    Jul 2011
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    A new wood prop installation is supposed to be retorqued after the first hour, then after 25 hours, and every 50 hours thereafter. Torque on 3/8" bolts is 15-19 ft-lb. From the Sensenich installation instructions:

    The main factor that leads to the loss of propeller bolt torque is the variation of the wood hub thickness. The hub thickness will vary with (a) wood moisture content changes and (b) temperature changes. Even though your propeller has been sealed and painted, changes in wood moisture content will occur which can significantly change the thickness of the hub. A one percent (1%) change in the moisture content of a propeller (increase / decrease) will cause a 0.010” change in hub thickness. As the required compression for a typical 65 HP wood propeller is 0.021”, almost half of the required hub compression has now been lost. Moisture content changes are not immediate and can span several weeks or months, depending on many factors such as temperature, humidity, and operating schedules.
    Operating temperature changes have similar effects but are not as severe.

  3. #13

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    Oct 2011
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    WA
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    My variable pitch Hoffmann prop has fiber nuts. (1/2", I think.)
    I saw a charred wood prop that was loose.

  4. #14

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    Oct 2014
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    Tehachapi, CA
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    Quote Originally Posted by Dana View Post
    A new wood prop installation is supposed to be retorqued after the first hour, then after 25 hours, and every 50 hours thereafter...
    When I was researching for the belleville washer design, I found requirements from many wood prop MFG's that ranged (after the first retorquing or two) anywhere from every 10 hours (holy crap - that's all you'd spend your time doing) to the 50 hours you state. The most interesting one was Jabiru - they originally had a 25 hour retorque time, but after they went to belleville stacks on their prop bolts for their wooden props, they dropped the maintenance interval to once/year, no matter how many hours the plane flew.

    That's what I use for aircraft that use bellevilles - inspect/retorque at the CI only (or whenever the prop is removed and reinstalled, obviously).

  5. #15
    melann's Avatar
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    Jul 2019
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    One thing I haven't seen mentioned is seasonal issues. If you live in an area where seasons change from extremely wet to extremely dry, then you should retorque a wood prop when these changes occur. I don't mean to imply every time it rains, but at the beginning and end of such seasons.
    Mel, DAR since the Last Century, Specializing in Light-Sport and Experimental Aircraft.

  6. #16
    Airmutt's Avatar
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    Jan 2018
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    NW. Atlanta GA
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    Not just seasonal but a big swing in temperature; obviously warm to cold where the wood can contract. Note to self......Probably not a bad idea to record the temp and RH with each retorque. Just thinking out loud.
    Dave Shaw
    EAA 67180 Lifetime
    Learn to Build, Build to Fly, Fly for Fun

  7. #17
    melann's Avatar
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    Jul 2019
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    Quote Originally Posted by Airmutt View Post
    Not just seasonal but a big swing in temperature; obviously warm to cold where the wood can contract. Note to self......Probably not a bad idea to record the temp and RH with each retorque. Just thinking out loud.
    Not a bad idea.
    Mel, DAR since the Last Century, Specializing in Light-Sport and Experimental Aircraft.

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