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Thread: Nord-Lock Washers with Wooden Prop

  1. #1

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    Nord-Lock Washers with Wooden Prop

    Can Nord-Lock washers be used for prop bolts on a wooden prop or must the bolts be lockwired?

  2. #2

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    Quote Originally Posted by ahramin View Post
    Can Nord-Lock washers be used for prop bolts on a wooden prop or must the bolts be lockwired?
    Since wood prop hubs can shrink when they dry out, a washer that depends on compression for anti-rotation would not be useful. Now, as it turns out, safety wire on wood props isn't all that useful either, since it does nothing to maintain compression but only prevents the bolts from turning.

    If you're using a wood prop, what you want (if you have a diameter bolt for which I've engineered a solution) is belleville washers. See:

    http://cozybuilders.org/Prop_Bolt_Be...her/index.html

    for more information. Feel free to contact me directly if you have any questions. But even with the bellevilles, safety wire is required. It might be interesting to try Nord-Locks in combination with bellevilles instead of safety wire - I'll have to think about that a bit more, but it should work as a safety wire replacement in that instance.

  3. #3

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    Very interesting Marc. Thank you.

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    Quote Originally Posted by Marc Zeitlin View Post
    Since wood prop hubs can shrink when they dry out, a washer that depends on compression for anti-rotation would not be useful. Now, as it turns out, safety wire on wood props isn't all that useful either, since it does nothing to maintain compression but only prevents the bolts from turning.
    While I agree that safety wire will not maintain compression on the bolts, it WILL prevent them from departing the aircraft.
    Mel, DAR since the Last Century, Specializing in Light-Sport and Experimental Aircraft.

  5. #5

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    Quote Originally Posted by melann View Post
    While I agree that safety wire will not maintain compression on the bolts, it WILL prevent them from departing the aircraft.
    Nope - didn't on my plane. See:

    http://cozybuilders.org/Oshkosh_Pres...ert_Center.pdf

    The safety wire will prevent the bolts from turning, but that's not worth diddly squat if the hub shrinks away from the crush plate and the hub loses compression. Prop starts moving back and forth on the drive flange, the bolts fatigue, and bam - gone.

  6. #6

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    Interesting report. I guess it glides well with no prop.....

    What is "static torque"? (from report: "only checked static torque")

    edit, I found from your other webpage that said loosen the prop bolts first, then retorque while rotating in motion. Is that procedure adequate in most cases?
    Last edited by Bill Berson; 01-30-2020 at 10:22 PM.

  7. #7

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    Quote Originally Posted by Bill Berson View Post
    Interesting report. I guess it glides well with no prop.....
    Better than with it windmilling, yeah. And smooth, too :-).

    Quote Originally Posted by Bill Berson View Post
    What is "static torque"? (from report: "only checked static torque")

    edit, I found from your other webpage that said loosen the prop bolts first, then retorque while rotating in motion. Is that procedure adequate in most cases?
    Yes. There are always inaccuracies in torque measurements, due to friction, surface finish, lubrication, interference fits, etc., but if the bolt isn't rotating while you're measuring the torque, you're pretty much guaranteed to get a very inaccurate number unless you've lubricated the hell out of the threads first. Which you can't do if the prop's been on the plane for 6 months to a year prior to the torque measurement :-).

  8. #8

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    Every oil change (4 months) I remove the bolts, clean and lubricate with beeswax, and reinstall. This is the only way I know of getting an somewhat accurate preload on prop bolts.

    It would be nice to use lock washers instead of lockwire to speed up the process.
    Last edited by ahramin; 02-01-2020 at 10:09 AM.

  9. #9

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    Quote Originally Posted by ahramin View Post
    Every oil change (4 months) I remove the bolts, clean and lubricate with beeswax, and reinstall. This is the only way I know of getting an somewhat accurate preload on prop bolts.
    And if you used Belleville washers, you wouldn't need to do this but once per year, at the Condition Inspection.

    Quote Originally Posted by ahramin View Post
    It would be nice to use lock washers instead of lockwire to speed up the process.
    You indicated that you read my response above - while it would be nice, without bellevilles the Nord-Locks would be WORSE than safety wire, as a loss of compression could also lead to bolt rotation - at least the safety wire doesn't allow that, for what it's worth (which is little).

  10. #10

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    Is this a case of the prop manufacter using "green" instead of seaoned wood? I have use two wooden props and never had any slack or slop when rechecking the torque on them. My Sensinich on the Cub is nicely varnihed and seems to be waterproof. I cant recall the spec ,but it is fairly low maybe 25lbs so you are not crushing the wood. I also have a metal hub with 4 wooden blades with metal sleeves threaded into the hub and doesn't seem to have problems. Dowty Rotol design.

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