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  #11  
Old 06-16-2021, 06:23 PM
Bob Y Bob Y is offline
 
Join Date: Jul 2017
Location: Piedmont, SC
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The weight added will depend upon your starting vibration level. Yours was already relatively low to start with, thus not requiring as much counter weight.
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  #12  
Old 06-16-2021, 08:14 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Tonight, we just finished a friends RV-12 prop balance. See post #1 above. Started at 0.46 IPS and we added a single 14.96 gram weight at 4-1/4" radius to achieve 0.06 IPS. We flew the plane for about 45 minutes and noticed the improvement...
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 830

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #13  
Old 06-16-2021, 10:34 PM
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rcarsey rcarsey is offline
 
Join Date: Jul 2012
Location: North Brunswick, NJ
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Quote:
Originally Posted by Mike Howard View Post
I hope the scale is not wrong because it is the same one I use to weigh the carburetor floats and they came in at 6.7 grams for each pair.
Any thoughts?
I purchased this cheapo gram scale for $22 from Amazon. Since it was high-quality Chinese manufactured, I also purchased this $12 calibration weight set.

I have to say that for a $20 scale, it performed very well.. and for the extra $12, I have peace of mind that the scale is accurate (IIRC, it was +/- 0.002g or better every time I tested it). I'd recommend both of these as required tools when doing a balancing (0.001g resolution is definitely overkill. 0.1g is fine)
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  #14  
Old 06-17-2021, 05:26 AM
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dbhill916 dbhill916 is offline
 
Join Date: May 2013
Location: Westerville, OH
Posts: 181
Question IPS ?

Does anyone have an explanation for why vibration is expressed with units of velocity?
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  #15  
Old 06-17-2021, 05:41 AM
PCHunt PCHunt is offline
 
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Location: San Diego, CA
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I'm sure someone much more knowledgeable than I am will come along and set things straight, but here are my thoughts:

If something is vibrating (shaking) it has to start at zero, accelerate to whatever the max velocity is, then decelerate to zero, and then repeat many times per second.

I'm guessing that the velocity change, which is acceleration, has something to do with this. If there were no vibration, there would be no acceleration, and the result would be zero ips (inches per second).

What I DO know, is that the smaller the number, the better the result.

BTW, I don't think this takes into account any Torsional vibration, but I could be wrong.

What other unit of measurement would work?

I hereby reserve the right to delete this post later, if necessary!
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  #16  
Old 06-17-2021, 08:13 AM
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BobbyLucas BobbyLucas is offline
 
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Location: Belleville, MI
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Quote:
Originally Posted by dbhill916 View Post
Does anyone have an explanation for why vibration is expressed with units of velocity?
It's somewhat arbitrary. You could use velocity, acceleration, displacement, jerk, vibration dose value (VDV), furlongs per fortnight, etc. In my experience I would have expected acceleration units such as mm/s^2 in this application.

Piezoelectric accelerometers produce a voltage that is proportional to acceleration. The fft analyzer can integrate that to velocity, double-integrate it to displacement, or differentiate it to Jerk, etc. Software can further post-process the data into a human comfort metric such as VDV.

In the automotive industry we usually use velocity in mm/s for customer touch-points - seat track and steering wheel for example. This is because velocity correlates well to human perception in the frequency range of interest.

For source or transfer path measurements, such as engine vibration or engine mount frame attachment points, we might use acceleration.

If we want to estimate mount stiffness in-situ we might put accelerometers on both active and passive sides of the rubber and use displacement.

For transient events like engine start-up shake or shift quality we would use VDV.
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  #17  
Old 06-17-2021, 10:35 PM
RFSchaller RFSchaller is offline
 
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Location: Phoenix, AZ
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I always assumed it was the total distance travelled. That is, the peak to peak displacement times cycles per second.
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  #18  
Old 06-20-2021, 08:34 PM
ksouthar ksouthar is offline
 
Join Date: Apr 2005
Posts: 121
Default Prop Balance

I have balanced several. Did one today. 21 grams to get it to .04 IPS with the weight mounted to the backplate.

Do yourself a favor. Donít even bother to balance using weights under the spinner screws. The balance solution will change when you move the weight to the spinner backplate. You end up just doing it all over again. Take the time to drill holes and install #10 nut plates before hand. Put one at each screw location (10 total) leaving enough room to install an AN970 washer. The balance task will be fast and easy and you will end up using 2 or 3 of the holes.

I had balanced this prop earlier using weights under the spinner screws. The airplane owner decided to move the weight to the backplate. He did the calculations taking into account the difference in the arm and came up with the weight to make the same moment as the spinner mounted weights. We did a test run with the weights relocated. The recorded IPS was .26. This is more complicated than it seems. In the end, he ended up with holes in three locations.
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  #19  
Old 06-21-2021, 09:14 AM
seagull seagull is offline
 
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Location: Highland, CA
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You must have done something wrong with the calculation in the move or rotated the spinner etc. I have done many balances from Rotax to Lycoming. The move to the backplate or flywheel has never changed the ips more than .01.

I agree that having locations (nut plates) on the backplate would simplify the process but that is a lot of up front work to save a little time once a year.
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  #20  
Old 06-21-2021, 09:22 AM
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Piper J3 Piper J3 is offline
 
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Quote:
Originally Posted by seagull View Post
I agree that having locations (nut plates) on the backplate would simplify the process but that is a lot of up front work to save a little time once a year.
I don't think I'd trust nut plates with fast spinning weight. Better to ream hole for correct AN bolt and then split weights (washers) front and back of spinner plate. The washers will trap the aluminum backing plate and distribute load evenly and bolt will not move in reamed hole...
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 830

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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