I had the prop balanced and...

Discussion in 'Maintenance Bay' started by Morgan3820, Nov 17, 2017.

  1. Morgan3820

    Morgan3820 Cleared for Takeoff

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    The A&P said that it took 4 washers to balance the prop. He was kinda surprised that it took that many.
    What is your experience? Is four washers a lot?
     
  2. Bell206

    Bell206 Line Up and Wait

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    Morgan:
    Not near enough info to make a comment. What kind of washers? Was this the 1st time you checked the balance of your prop? Or, was it a regular follow up check? Same equipment or different equipment? Is this a constant speed prop? Was it serviced with grease prior to the check? Or is it a fixed pitch prop? Etc, Etc.

    It’s not so much the amount of washers but the weight they represent at the location they are installed, For example, 4 washers weighing 10 grams a piece installed 6 inches from the center of your prop shaft (starter ring gear) will have a lesser effect on balance than 4 identical washers installed at 10 inches from the prop shaft center (spinner back plate flange).

    So it all depends…
     
  3. Morgan3820

    Morgan3820 Cleared for Takeoff

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    Sorry... Arrow II, CS, three blade, 1st time. Other than that I have no other info.
     
  4. Bell206

    Bell206 Line Up and Wait

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    Morgan:
    Still not enough details. But here is some info for your benefit.

    If I recall, depending on the prop OEM and balance equipment mfg’r the maximum dynamic balance weight at any one point varies from approx 25g to 45g. This would equate to 6 AN970-3 washers up to 11 washers of the same size.

    The AN970-3 washer is a large fender-type with a 3/16th hole. These weight limits would also include the weight of the attachment hardware.

    If there is a need to add more weight at that same location for proper balance, most guidance allows splitting the weight between two adjoining locations. This increases the total effective balance weight to 50g to 90g, or a total of 12 to 22 washers split into two separate stacks.

    So if you have 4 AN970-3 washers installed at a single point that would amount to 16.4g which is below the max limit of most props.

    Whether those 4 washers are considered “a lot” I would defer to your mechanic. But for comparison, if your prop was fresh out of O/H or had a static balance performed, I would expect to see a lower dynamic weight amount depending on the condition of the remaining items like the spinner/backplate, engine mounts, etc. But each case is different.
     
    Last edited: Nov 18, 2017
  5. Morgan3820

    Morgan3820 Cleared for Takeoff

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    Thank you. Sorry I could not offer more info. But your response did give me some perspective.
     
  6. JAWS

    JAWS Line Up and Wait

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    Not long ago I installed two brand new Hartzell swept blade props and found the dynamic balance was something like 0.01 IPS each. I was very impressed - have never seen new props that good before.
     
  7. SEMOAV

    SEMOAV Pre-Flight

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    I dynamically balance a lot of props. I use an ACES 2020. One of the things that I have found is sometimes when the props are statically balanced the outer weights are 180 degrees off from where it needs to be. I have talked to several other mechanics who are afraid to remove the static weights or move them. I have found many times that moving these weights (depending on the prop) makes a huge difference and reduces the amount of additional weight needed. Just speaking from experience.
     
  8. N659HB

    N659HB Pattern Altitude

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    I'm thinking my prop needs balancing. :(

    Lots of vibration.
     
  9. SEMOAV

    SEMOAV Pre-Flight

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    It’s always a good idea to have it balanced. But there are many other things that can cause a vibration.
     
  10. Bell206

    Bell206 Line Up and Wait

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    SEM:
    You may want to review your references again on adjusting static weights for dynamic balancing. It's not so much fear or ability, but a Part 65 matter. Plus static balance is done for a different reason than dynamic balance.
     
    Last edited: Nov 27, 2017
  11. BigBadLou

    BigBadLou En-Route

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    Agreed.
    The mechanic should hand you a printout of the before and after vibration analysis. "4 washers" ain't cutting it if I am paying a 3rd of AMU for an hour of work.