Prop vibration - help needed

[mike mcs repair]

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Another idea would be put the prop on another plane and see what happens, as well as trying another like prop on your plane...

I like that,
might be quicker than finding another one of same type!

 

[skywagon8a]

so a prop shop rebuilt the prop, (incorrectly), balanced it, fixed it, rebalanced it and charged you to repair? or are they different shops? Who ever did the original work should be paying for the repair...

Another idea would be put the prop on another plane and see what happens, as well as trying another like prop on your plane...

I agree with aktango58. Also note that a properly balanced stock Sensenich 74" prop always has more vibration than a 82" McCauley but not to the extent that you describe. It certainly does seem that there is a problem with your Sensenich.

What did the mechanic do to correct the wow in the one blade? You did not say. Was it corrected or was it only that the blade angles were verified? That wow, if it is still there, could be the culprit. It would provide a different airflow between the two blades thus generating the vibration at one particular rpm.

 

[mvivion]

12/2 would be weird Mike. 8) I have seen more constant speeds clocked 12/6 than not. There is a Lycoming Service Instruction which calls out how the bushings are to be indexed. Would like to know why they are the way they are, if it is vibration, torsional loads etc. I will have to see if there is a pattern between counter weighted shafts or others.

The Lycoming service bulletin is the reason Aviat chose to re-index the prop on the Huskys. We checked with Lycoming, and it was an attempt to reduce felt vibration. No third or fourth order vibratory issues, just a "feels better" kind of thing. We found that by re-indexing them to "proper" indexing, then doing a good dynamic balance, we wound up with an engine we could hand prop AND that was smoother than with the prop at 12 and 6. Apparently, Lycoming assumes that most operators will not go to the trouble of dynamic balancing their rotating assembly. And, my experience is that seems to be true, so Lyc just chose the indexing that was smoothest out of the box. Since it's a SB, there is no requirement to abide by it under part 91.

And, again, this is a Lycoming O-360 deal for the most part....I doubt that "most" two bladed CS props are indexed 12/6. For example, all the Continentals out there on Cessnas.....

MTV

 

[Eddie Foy]

Was this ever resolved?

 

[DavePA11]

I had some vibration at higher RPM start after the cowling was barely touching one of the cylinders. Re-positioned the cowling off the front cylinder and fixed the vibration. Might want to check the cowling.