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Thread: Propeller Ballancing

  1. #1

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    Propeller Ballancing

    Thought that I would try and make things as smooth as possible by doing a Dynamic Prop Ballance. I am flying a 68 SC with a Lycon rebuilt O-320 (160) with about 630 Hrs on it. Borer 44/41. Many have said it was one of the smoothest Cubs they had flown in as it is, but I had planned to mount a new camera and wanted to take out all the vibration that I could. There was a little vibration in cruse (2350 - 2400), so I thought what the heck, just had an Annual in Oct. where I replaced a cracked spinner back plate, so figured now would be the time.

    Bottom Line, after changing some weight around on the propeller and adding a couple washers to the spinner, spinner (On-Off) four run ups - it vibrates worse. Not bad, just noticably worse. There is vibration in the Stick and Peddles that wasn't there before. The quick fix would be to (Put everything back the way it was), so here is the question.

    During static run-up, which was about 2370 RPM, is there any flexing going on with the prop that would cause the ballancer to give a unreliable reading? Say compared to Non-Static (flight mode) Still would like to get things as smooth as possible. I do understand that it is a Cub and should have some lee-way in my expectations.

  2. #2
    Dave Calkins's Avatar
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    Usually dynamic balancing is performed for a certain RPM. If all you can do is 2370 static, for instance, you might expect it to be not as good at 2550 RPM.

    Still, I'd expect better after a dynamic balance.

    I smell a rat, I think. Please let us know what you find. Thanks.

  3. #3
    180Marty's Avatar
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    Is it possible to take the weights off that were used to balance. Make sure you keep track of where they went and see what nothing is like.

  4. #4

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    Quote Originally Posted by Hood River 5 View Post
    Bottom Line, after changing some weight around on the propeller and adding a couple washers to the spinner, spinner (On-Off) four run ups - it vibrates worse. Not bad, just noticably worse. There is vibration in the Stick and Peddles that wasn't there before. The quick fix would be to (Put everything back the way it was), so here is the question.
    Not sure what kind of equipment you're using to take the measurements, but make sure you (your mech) are reading the clock angles correctly. The machine will most likely tell you where the vibe is, for example 6:34 @.22 IPS...then give you a different clock angle for the "solution", ie. 18 grams @ 12:26. Then you have to read the card correctly to make sure your not putting the weight in the wrong place.

    I have done this on the ground, and in-flight. IMO its better to do it in-flight just because you can take your time, and I think it gives the equipment a more real-world environment to measure...smooth air really helps too. I've taken a prop from .25IPS down to .01IPS in 2 flights. Also, i've tried taking measurements at different RPM's on the same flight and the vibe measurements all come really close to each other...I guess that means the machine is doing its job and reading the vibe correctly.

  5. #5

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    Thanks All, The balancing insturment is Microvib. We started at .5 and after 4 test runs was able to center by moving weights down to .02 tied down. The insturment says the weights were properly distributed, but a test flight told me we were still not right. The balance guy called Microvib and they sugested to make sure nothings touching somewhere then do what Helmetfire is saying (do the reading in the air). So sometime this next week we are going to give that a try. Will let you know.

    Dave were correct in that on take off, where the RPM is nearly 2600, you really notice the vibration after relocating some weight from where is was. It was obvious that the vibrations felt was from the inbalance of the propeller. Quick and could be felt in your hands and feet. Down around 2100 things smoothed out. The vibration I am tring to get rid of (smooth out) was right at 23 - 2400 RPM.

  6. #6
    Jim 4WF's Avatar
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    I think the flywheel is a stronger spot for weights and may save spinner parts.? Mine always seemed better after a ballance at all cruse RPMs. I try to only balance after 100 hr with clean plugs, leed check, timing checked and a good tight intake.

  7. #7

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    If I was convinced I had a prop vibration I'd have that prop to a prop shop for inspection, repair, and static balancing. In the couple of times I've done that my dynamic balancer couldn't improve on things. It's nice to have good prop shops in the local area.

    To Hood River 5, I have had a minor vibration in the past in my 180 and after a dynamic balance the vibration changed and became more noticeable. I can't say it was worse from any scientific perspective but it made my instrument panel vibrate and that was impossible to ignore. A prop overhaul fixed my issue. Turns out the hub needed attention, too. Granted, that was with a constant speed but the same shop tracked and balanced my 8242 Mac on the -12 and it was smooth as silk. I favor good prop maintenance over adding screws and washers to my spinner plate. Not there's anything wrong with dynamic balancing but clearly it has limitations.

  8. #8
    Sean007mi5's Avatar
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    do you think if you have an overhaul with juggs rods pins etc you need to redo dynamic balance? I am detecting new vibration in 2350 to 2450 range. makes the compass oil wavy.

  9. #9

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    Quote Originally Posted by Sean007mi5 View Post
    do you think if you have an overhaul with juggs rods pins etc you need to redo dynamic balance? I am detecting new vibration in 2350 to 2450 range. makes the compass oil wavy.
    Yes

  10. #10
    PerryB's Avatar
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    If the dynamic balance checks out as good but the vibe persists, pull the prop and turn it 180 degrees. I had a 2500 rpm and up vibe with a freshly balanced 82-41 Borer and the 180 flip cured it completely. Don't ask how, I can't explain it but I'd heard it in the past and thought it would be worth a try. It was!
    After Monday and Tuesday, even the calendar says WTF !

  11. #11
    Crash's Avatar
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    Is the prop indexed correctly on the prop flange? If it's not, you'll never be able to get it to run smooth.

    At shut down the prop should point at the 10 o'clock and 4 o'clock position. More technically speaking.... an O-320 is indexed one position counter clockwise of the flywheel "0" mark. An O-360 is indexed over the "0" mark.

    As a rule, I index the prop, fly it. Re-mount 180 degrees, fly it, then decide how it ran best. If needed, I then Dynamic balance.

    Take care,

    Crash
    "The fear of God is the beginning of wisdom". Psalm 111:10

  12. #12

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    I have been running a new sensenich 74DM on my 0-290 for maybe a 100 hours....it vibrates. I dropped it off at the prop shop today and they will check blades for equal pitch, track and balance. I flipped it 180 degrees, no difference.

    I have a Borer that is nice and smooth if mounted right. I reinstalled it and holy crap I thought for a second I had hung a valve on climbout. Landed flipped it 180 and almost smooth as butter.

    I asked the head prop dude at the shop and he had no idea...me neither.. Anyone???
    Steve

  13. #13
    Gordon Misch's Avatar
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    Flange AND prop both out of whack.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  14. #14
    hotrod180's Avatar
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    I put a freshly installed seaplane prop on my 180 a while back & it gave it the shakes.
    Flipped the prop 180 degrees and it was amazingly better.
    Doesn't make sense, just one of those things.
    Cessna Skywagon-- accept no substitute!

  15. #15
    Gordon Misch's Avatar
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    Compensating errors in one position, additive errors in the other.

    Gotta catch up with you at some of the flyins this year - didn't get to chat much at Cougar Mountain last year.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  16. #16
    Colorguns's Avatar
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    I had a 8245 overhauled prop I put on 0-360 at 2400 it had vibration, swapped 180 still. Later I found #2 cylinder had blow by and low compression , overhauled it and now smooth.
    Just a finding I had.
    Doug
    Likes skywagon8a liked this post

  17. #17
    mvivion's Avatar
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    One thing nobody's mentioned yet is that there are also vibrations that you can't necessarily feel. And some of those can be very destructive. That's one of the arguments for a good prop balance.

    MTV

  18. #18

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    We obviously balance to get rid of vibrations, Anyone who has never tried the "Balance Masters" product is missing out on a simple solution. Have 1 on my Acro plane and have several friends who have bought it and swear by it.
    Thanks skywagon8a, Bill.Brine thanked for this post

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