A reason to avoid dynamic propeller balancing?

[Pasturepilot]

I reached out to a local group of pilots on Facebook to see if anyone had a contact for dynamic propeller balancing. Got several names and phone numbers... and one surprising reply. 

One opined that he would never do a dynamic balance on a counter weighted engine after it had more than a few hundred hours on it. 

I’m at 1100 hours on my engine.  I know it was dynamically balanced 20 years ago, when we had a guy hanging around our air show group and he’d balance everyone on the strip when he came out for a work day. Then, the prop got changed a few years back to eliminate the monster AD, and hasn’t been balanced since. I’ve since changed and shimmed the engine mounts, and had the prop off to change an alternator belt. My logic says now is the time for a balance job. 

Is this the one old wives’ tale that I missed somewhere along the way, or is there merit to his statement? I can see his logic... but it sounds a bit fuzzy to me. 

[RLCarter]

Did he give any reason why he wouldn’t balance a prop with more than a few hundred hrs?

[Pasturepilot]

He never did elaborate. 

[RLCarter]

Just now, Pasturepilot said:

He never did elaborate. 

Not sure how smoothing out the harmonics of anything could be bad. 

[N201MKTurbo]

The counterbalances on the crank are for torsional vibration. Balancing the prop, is for radial vibration. 

Although they will have some interaction, it will be minuscule.

I can’t imagine what engine time has to do with it.

 

[ArtVandelay]

Why not balance the prop if it’s needed?
I heard it can make things worst.

[Mooney in Oz]

2 hours ago, Pasturepilot said:

I can see his logic...

What can you see as his logic?

2 hours ago, ArtVandelay said:

I heard it can make things worst.

Why?

I've never heard of this before.

Maybe @Cody Stallings can help here.

[ArtVandelay]

Why?
I've never heard of this before.
Maybe [mention=9703]Cody Stallings[/mention] can help here.

I think it requires some expertise.

[jaylw314]

IIRC, the prop and motor are balanced at the factory, but there's no way to balance the prop/motor combination without doing dynamic balancing.  That being said, when I bought a new prop and had it dynamically balanced, it started at 0.05 IPS, so it's certainly not a predictable problem. FWIW, the guy went ahead and did two rounds to get it down to 0.02 IPS.  

[Hector]

Do you think your engine (not to mention your avionics, passengers, etc) will be happy with more or less vibration? Get your prop balanced. I do it every 2-3 years.


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[RobertGary1]

I wouldn’t bother with a prop balance. I have the counter weight engine. I got a prop balance once. Honestly I never could tell any difference. Unless you’re having an issue I wouldn’t worry about it.  Mooney doesn’t require it in the service manual. 
 

-Robert 

[RLCarter]

If you can feel the vibration is one thing, what you’ll never feel is a high frequency vibration 

[RobertGary1]

1 hour ago, RLCarter said:

If you can feel the vibration is one thing, what you’ll never feel is a high frequency vibration 

Might be a princess and the pea thing. I’ve never had issues on planes I didn’t balance. I guess if you’re tearing up mounts or cracking the frame it could be an issue but I’d expect an AD if that was happening. 
I do agree that with some set ups it makes for a smoother ride, just not with the a3b6 in my experience. 
 

-Robert 

[RLCarter]

1 hour ago, RobertGary1 said:

Might be a princess and the pea thing. I’ve never had issues on planes I didn’t balance. I guess if you’re tearing up mounts or cracking the frame it could be an issue but I’d expect an AD if that was happening. 
I do agree that with some set ups it makes for a smoother ride, just not with the a3b6 in my experience. 
 

-Robert 

My E has the no go 2000~2350 red arc.... I’ve heard that is do to the Hi-Freq vibration.... had my prop IRAN’d late last year and they did a static balance then, no dynamic...... seems smooth to me but no one in this area that does dynamic balancing, so might not ever know

[jaylw314]

2 hours ago, RobertGary1 said:

Might be a princess and the pea thing. I’ve never had issues on planes I didn’t balance. I guess if you’re tearing up mounts or cracking the frame it could be an issue but I’d expect an AD if that was happening. 
I do agree that with some set ups it makes for a smoother ride, just not with the a3b6 in my experience. 
 

-Robert 

I suspect it's the prop/motor combo that may be an issue.  For example, the factory Macauley had not been dynamically balanced after the rebuilt IO-360 A3B6 was installed in my plane, and the difference after dynamic balancing was tremendous.  Before, I could barely read my compass in cruise because of all the foam.  IPS went down from 0.4 to 0.05.   On the other hand, after installing the 2-blade Hartzell I had the experience above.

[carusoam]

+1 for inviting Cody to the discussion...

Some vibrations are not a seat of the pants sensation...

Best regards,

-a-

[alextstone]

Some vibrations are good 

 

[Hector]

I used to think my C was just normal. Then I had the prob balanced and was much happier with the new normal.


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[PT20J]

Dynamic balancing corrects the prop/spinner combination for a condition where the center of mass is not in line with with the center of rotation. Balancing may or may not produce a discernible improvement in perceived vibration, but it’s still a good idea as it may increase the life of accessories and other components.

An extreme example of a dynamically unbalanced propeller is ground resonance in a helicopter. An airplane propeller would not become this unbalanced (unless it lost part of a blade), but it is illustrative of how the propeller vibration transmits to the airframe.

 

Skip

[N201MKTurbo]

On 6/27/2020 at 8:29 PM, RLCarter said:

My E has the no go 2000~2350 red arc.... I’ve heard that is do to the Hi-Freq vibration.... had my prop IRAN’d late last year and they did a static balance then, no dynamic...... seems smooth to me but no one in this area that does dynamic balancing, so might not ever know

It is due to torsional vibration. I don’t think many people understand what that is. It is the prop speeding up and slowing down with respect to the crankshaft. This twists the crankshaft and can cause it to fail. It has to do with the moment of the propeller and the power pulses generated by the pistons along with the torsional compliance of the crankshaft. This sets up resonant modes that can be destructive. The red arc on the tach are there to keep you out of these resonant modes. 

BTW these torsional vibrations don’t shake your engine and you really cannot feel them.

[RobertGary1]

6 hours ago, N201MKTurbo said:

It is due to torsional vibration. I don’t think many people understand what that is. It is the prop speeding up and slowing down with respect to the crankshaft. This twists the crankshaft and can cause it to fail. It has to do with the moment of the propeller and the power pulses generated by the pistons along with the torsional compliance of the crankshaft. This sets up resonant modes that can be destructive. The red arc on the tach are there to keep you out of these resonant modes. 

BTW these torsional vibrations don’t shake your engine and you really cannot feel them.

Then why do different prop engine combinations have different red areas on the Mooney? My stc for my a3b6 has a whole table based on prop. 

 

-Robert 

[N201MKTurbo]

39 minutes ago, RobertGary1 said:

Then why do different prop engine combinations have different red areas on the Mooney? My stc for my a3b6 has a whole table based on prop. 

 

-Robert 

because different props have different moments. 

https://en.wikipedia.org/wiki/Moment_of_inertia

https://en.wikipedia.org/wiki/Torsional_vibration

 

[JimB]

On 6/27/2020 at 8:23 AM, Pasturepilot said:

I reached out to a local group of pilots on Facebook to see if anyone had a contact for dynamic propeller balancing. Got several names and phone numbers... and one surprising reply. 

One opined that he would never do a dynamic balance on a counter weighted engine after it had more than a few hundred hours on it. 

I’m at 1100 hours on my engine.  I know it was dynamically balanced 20 years ago, when we had a guy hanging around our air show group and he’d balance everyone on the strip when he came out for a work day. Then, the prop got changed a few years back to eliminate the monster AD, and hasn’t been balanced since. I’ve since changed and shimmed the engine mounts, and had the prop off to change an alternator belt. My logic says now is the time for a balance job. 

Is this the one old wives’ tale that I missed somewhere along the way, or is there merit to his statement? I can see his logic... but it sounds a bit fuzzy to me. 

I have the -A1A and just balanced my prop yesterday. Went from .21 to .06. Actually had it at .03 on the second run but it came up just a little after I installed the permanent weights. I "think" I could feel a mild vibration (mostly a buzz in the rudder pedals) before and she does seem smoother now. 

Is your 0-360 counter weighted? I thought the only engines with counter weights were the ones with a 6 in the suffix like the M20J engines. (IO-360-A1B6D or IO-360-A3B6D or IO-360-A3B6)

[steingar]

Only reason I can think of not is it costs money.

[Cody Stallings]

Anything that Spins needs to be balanced. Human body can’t feel certain vibrations, but your Crankshaft an everything aft can.

3 issues with Dynamic Balance.

1) Old Timers don’t wanna hear About it, it wasn’t available back in their day an everything worked fine. 
2) Viewed as a Gimmick, sorta like MMO Conversation. People think if they don’t feel a very pronounced difference in Vibration, then they were Had!!

3) An in my opinion only. A balance Machine in the hands of an Individual that isn’t properly trained, an equipment isn’t kept Calibrated is Dangerous.

A balance gone wrong can be detrimental to a Crankshaft, Dampeners, Avionics an the overall well being of the Rotating assembly. 
Not trying to throw stones at anyone at all

If you have the Ability to have your propeller balanced by a tech that is trained an uses equipment that’s not covered with dust, do it.

You won’t be disappointed.