Safety Wire on Ultra-Prop

Discussion in '2-Stroke Aircaft Engines' started by Tuneturkey, Jan 14, 2020.

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  1. Jan 14, 2020 #1

    Tuneturkey

    Tuneturkey

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    The Rotax 503 prop hub has 6 threaded holes for 5/16" prop bolts. Should locking nuts be used behind the hub , or should castle nuts be used with holes on the bolts for safety wire?
    Thanks
     
  2. Jan 14, 2020 #2

    Dana

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    I've never seen safety wire or locknuts or anything on a Rotax powered ultralight. Never saw a prop come loose, either.

    Be careful though, they're probably 8mm, not 5/16".
     
  3. Jan 14, 2020 #3

    Tuneturkey

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    Hi Pops, you are up early. Ultra-prop hubs has slots, "8mm or 5/16" wide". Ivorptop says not safety wire, not loctite, no Ny-loc or castle nuts. Nothing to prevent re-torquing, regularly.
    Still working on my weight/bal problem!
     
  4. Jan 14, 2020 #4

    Victor Bravo

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    I understand about not wanting to pu t anything in there which would dissuade somebody from regular re-torquing. So how about an internal star lockwasher, or Nord-Lock? Nothing in the way of you putting a wrench on it every morning, but still something to slow down the loosening.
     
  5. Jan 14, 2020 #5

    Dan Thomas

    Dan Thomas

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    [​IMG]
    This is how it's done on real airplanes. Drilled-head bolts.
     
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  6. Jan 14, 2020 #6

    Victor Bravo

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    But 2-stroke engines have vibration and TV issues that are different than "real" airplanes. There may be a valid reason why they are always trying to encourage you to re-torque the prop bolts on a 2-stroke?
     
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  7. Jan 14, 2020 #7

    Dan Thomas

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    Perhaps, but constantly checking the torque on the bolts on a wooden prop can gradually crush it. The prop hub will expand and contract with atmospheric moisture changes, and if you retorque the bolts when it's dry you'll turn them in a little. When the prop expands again it gets crushed a little. Standard practice with wooden props on Conts/Lycs is to check them yearly, at annual time.

    Someone on an ultralight forum might know more about that. The makers of ultralight props would certainly have better advice than I can give.
     
  8. Jan 15, 2020 #8

    lr27

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    I seem to recall Mark Zeitlin doing some successful experiments with Belleville washers and a wooden prop.
     
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  9. Jan 15, 2020 #9

    pwood66889

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    I read an EAA pub article on bolts recently. It took me a while to get my head around "Clamping Action" and "Keeping it from coming off all together." What the article did was differentiate the two.
    What caught my attention was the "Vibration Proof" vs "Nut type" per below:
    Rel. Vib Perf,Description,AN number,(notes)
    100,Elastic Stop Nut,364 (shear/narrow),365 (tension/wide)
    53,All Metal beam type lock nut,363,
    38,Castle w/Spring Pin,310 (tension/wide),320 (shear/narrow)
    19,All Metal distorted type lock nut,,
    18,Castle w/Lock Wire,310,320
    8,Castle w/Cotter Pin,310,320
    5,Plain w/Spring Lock Washer,315 (tension/wide),316 (shear/narrow)
    1,Plain w/Toothed Lock Washer,315,316
    1,Plain Nut,315,316
    Why did I spend so much time learning to lock wine in A&P school if it only rates an 18 when an Elastic Stop Nut was a hundred?
    Short answer: The torque setting is kept longer in the stop nuts because the nylon absorbs the vibrations and the nut doesn't work loose.
    Yet lock wire keeps the nut/bolt together even if slightly loosened due to vibration.
    Thus IMHO, the higher vibration is countered by using nyloks and checking torque. Lower vibe rates can be lockwired. YMMV, of course.
    BTW, Dan, I'm not too thrilled about the angles of 2 of the wires in the above photo. Such may not have been acceptable when I worked on US Army helicopters.
    And wooden props introduce another issue, Ir27. As Dan noted, they expand and contract due to moisture in the air.
    Percy
     
  10. Jan 15, 2020 #10

    bifft

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    Everything I've ever read/heard on wooden props is to torque at seasonal changes. I've been doing it every two months or so.
     
  11. Jan 15, 2020 #11

    Dan Thomas

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    Yes. I got that picture off the 'net. I always ran the wire around to the next hole to get a positive pull in the clockwise direction on the bolt head. And pulled the wire tight. When it comes to lockwiring you'll often see installations that are nearly useless at preventing rotation. I've found it done backwards a few times, and inadvertently did it myself more than once.
     
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  12. Jan 15, 2020 #12

    Hot Wings

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    I'd seen this before - didn't associate the name attached to the work until now. Here is the web page:

    http://www.cozybuilders.org/Prop_Bolt_Bellville_Washer/
     
  13. Jan 16, 2020 #13

    Dana

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    Note, though, that the belleville washer thing only maintains the proper clamping pressure without having to retorque periodically; the bolts still need to be safety wired.
     
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  14. Jan 16, 2020 #14

    Marc Zeitlin

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    Also interesting is that with Belleville washers, the safety wire is actually accomplishing something. Craig Catto (who now ships bellevilles with every prop, to my understanding) has done experiments showing that even if safety wire is installed well on prop bolt heads, it's possible for the bolt head to turn up to 60 degrees (one flat), which is MORE than enough to lose almost all if not all compression on a non-belleville install wood core hub propeller. So with the ability of the prop hub to shrink out from under the compression, and the ability to turn the head substantially even with safety wire, the SW isn't doing a whole hell of a lot unless bellevilles are installed.

    On my plane, with 1/2" prop bolts, it takes about 60 - 90 degrees of bolt rotation to get to the 30 ft-lb of torque my Hertzler prop requires. WITH the correctly installed bellevilles (per my instructions - not just any bellevilles you find at McMaster-Carr or Grainger - this is an ENGINEERED solution), it takes about 3 full rotations (1080 degrees of rotation) to get to 30 ft-lb. So as long as the safety wire doesn't fall off, it'll keep the bellevilles doing their job :).
     
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  15. Jan 17, 2020 #15

    lr27

    lr27

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    I suspect that, with Belleville washers, you could determine the clamping force by measuring deflection, without having to move or re-torque anything. I don't recall if this was in the article, and for all I know it's a flawed idea.
     
  16. Jan 17, 2020 #16

    Marc Zeitlin

    Marc Zeitlin

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    My original goal was to be able to tighten the bolts just by counting the # of turns (or partial turns) of the prop bolt - I figured that while not everyone knows how to use a torque wrench correctly, most of us can count. That turned out to have a lot of variability in it due to confounding factors. So then I went to measured washer deflection, and that was better, but pretty hard to do, and also had a few confounding factors that made it somewhat inaccurate.

    So I gave up and currently just recommend making the prop bolt somewhat longer to account for the belleville washers, ensure that they're oriented correctly per the instructions, and then tighten per the prop MFG's torque specification. This is still WAY better than not using bellevilles, even with the inaccuracies in tightening per a torque specification, and it keeps the process the same as when you're not using bellevilles, so at least everyone is already familiar with doing it.
     
  17. Jan 18, 2020 #17

    lr27

    lr27

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    Further thought:
    If it's ok, with Bellevilles, to have the bolts turn as much as 30 degrees from optimal, you could have a little plate with 6 hex shaped holes for the bolt heads and some kind of clip or clamp or screw to hold it in place. No safety wire required.
     

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