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  #1  
Old 02-14-2020, 01:49 PM
jask jask is online now
 
Join Date: Feb 2018
Location: Ramona, CA
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Default Prop balancing

I had the opportunity to watch a professional balance an 0320 this week. He was using the honeywell vibrex which shows a full frequency of vibrations. It was interesting that it showed a strong vibration over 3 times the prop speed. He said it was probably the alternator which did measure over 3 times the speed of the prop. The owner then commented that he had replaced a broken alternator bracket last year.
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  #2  
Old 02-14-2020, 03:24 PM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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I use a MicroVib II and do a spectrum analysis with each balance. I forget exactly but the alt rate is about 3.8 if I remember correctly.

Dug up some old plots I had hosted, here's an example of a 2 blade prop, pretty normal to have a 'spike' at the 2 blade rate, a 3 blade will typically have a 3 order rate spike. You can see the alt rate in the plot



Here's a 3 blade on an RV12 and you can see the 3 order spike, the Rotax also has some other accessory drive speeds you can see.



Here's a typical polar plot of the balance:

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Last edited by Walt : 02-14-2020 at 03:33 PM.
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  #3  
Old 02-14-2020, 09:20 PM
jask jask is online now
 
Join Date: Feb 2018
Location: Ramona, CA
Posts: 156
Default Prop balancing

It's interesting that the out of balance alternator cracked the bracket but since the frequency is high, lt was not a annoying vibration.
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Free prop balancing for Vans owners
(I am not in the business of prop balancing, just as a courtesy to meet other owners.)
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