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Propeller balancing


MooneyMitch

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No experience with a 3 blade, but a bunch of us from my local EAA chapter (1300 in Henderson, NV) pitched in to buy a dynamic prop balancer. Those of us that pitched in get free use of it for life - $50 for anyone else I think. One of the guys made a bracket that works for all of the Lycomings (360 series) that we've tried so far, and also one for the rotax guys.


My initial vibration level started off much higher than normal so I'm going to have my prop statically balanced before I do any more adjusting, but I was still able to cut my IPS (inches per second) by about 40 percent. Noticable at all RPMs.


Pics below are from a members RV7A, which was easier because he could but the weights on his starter ring. My spinner had to come off to add hardware. Didn't take pics of my own unfortunately.


 


Vid below explanes the process much better than I can in a paragraph:


http://www.rpxtech.com/rpxweb/Dynavibe.asp


 

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I'm having my 3 blade done on my 63 C right now.  The shop said there was a large improvement according to the machine, but they were at the limit of the weight they could add.  Still waiting for the fuel/manifold gauge overhaul, so haven't been able to test fly it yet to see if the difference is noticable.  I'll let you guys know next week when I fly it.

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I had my 3-blade balanced, although once we got started the tech indicated that it was already pretty good. As I recall, his initial reading showed the IPS number to be ~.1, which he said was pretty close to turboprop standards. But since I was paying him anyway he worked to get it down to .07 by adding a screw and washer set to the the bulkhead. It was a little disconcerting watching him drill into a perfectly good piece of metal but I just put my trust in his experience and so far all has worked out well.


BTW...no idea what "IPS" stands for but it's some measure of vibration.

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IPS is inches per second.  You are looking at acceleration to determine vibration.  The other way to measure vibration is to use proximity probes on the bearings which measure the displacement of the shaft that is turning with respect to the bearing.  Proximity probes are more expensive and require a port to be drilled and taped on the bearing with the probe inserted and carefully positioned within thousandths of an inch to the shaft not practical for us.  This process is generally used on large industrial equipment.


Side topic the EI G3 has the capability to mount an acceleration type vibration probe on the engine permanently.


 

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IPS stands for inches/second which technically is a velocity vector. A vector has magnitude and direction. In contrast to inches/ second ^2 (i.e. inches per second squared or per second x second) which is an acceleration unit. This velocity is the speed (magnitude) the prop reaches as it passes through (vector) the center of the range of its displacement as it rotates. Velocity is the quantity measured because it measures vibration independent of RPM. The perfectly dynamically balanced prop will have zero IPS or zero velocity through the center of the range of its displacement and 100% of its rotational velocity in the direction of rotation. In other words the velocity vector for displacement is zero in a perfectly dynamically balanced prop. We never of course attain this ideal level of zero IPS but they do come very close!

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OUrs was just balance by Walt Aronow in Dallas.  Top notch work.  200$.   Our IPS started at  0.395 and ended at 0.053.  Huge difference in noise, vibration, and harshness.  We just flew it back from Key West to Houston in 8 hours, and arrived fresh enough to go out that night.  The vibration and noise is a lot less at 2500 RPM now.  Worth it for sure  Walt@expaircraft.com   www.expaircraft.com

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  • 1 month later...

Quote: jrwilson

I'm having my 3 blade done on my 63 C right now.  The shop said there was a large improvement according to the machine, but they were at the limit of the weight they could add.  Still waiting for the fuel/manifold gauge overhaul, so haven't been able to test fly it yet to see if the difference is noticable.  I'll let you guys know next week when I fly it.

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when did you guys realize that you need to balance your prop? Gauges vibrating and not readable? Any indications you used? Or there is no way to tell unless I take it to the prop shop? I just generally accept that a piston engined airplane will vibrate like crazy. What I think is smooth enough may not be smooth however :)


 

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Quote: bd32322

when did you guys realize that you need to balance your prop? Gauges vibrating and not readable? Any indications you used? Or there is no way to tell unless I take it to the prop shop? I just generally accept that a piston engined airplane will vibrate like crazy. What I think is smooth enough may not be smooth however :)

 

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Quote: lamont337

If you have an Iphone and $5 to burn, there's an app that uses the phones internal accelerometer to record and plot vibrations.See link below. One of our guys set it on his dash to record the before and after results during flight. Surprisingly accurate and I can only assume you can find a similar app for android phones.

http://www.macworld.com/appguide/app.html?id=67886&expand=false

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Quote: bd32322

when did you guys realize that you need to balance your prop? Gauges vibrating and not readable? Any indications you used? Or there is no way to tell unless I take it to the prop shop? I just generally accept that a piston engined airplane will vibrate like crazy. What I think is smooth enough may not be smooth however :)

 

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Mitch: Thanks! But don't get too close or you'll see how bad the paint is faded...


bd32322: Wish I did, but I never actually used the app myself. I'll go ahead and add it though since I'm still curious. Unfortunately I don't think I'll be back in the air until at least the middle of next week.

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