Dynamic Prop Balancing - Yes? No?

[bigmo]

I'll start off by saying I don't have any problems...well...with my Mooney

F model with a low hour engine and low hour  two blade prop (both around 500 hours). Penn overhaul and is smooth at all RPMs - and yet I have maybe 4-5 other IO-360's to compare with. As a fairly recent buyer, I combed through every log entry since the 2009 overhaul. It has not been dynamically balanced.

There's a traveling guy that swings through the area annually and it's $350 I think - might be $300 if there are a handful at the same airfield. Our local Facebook group has several folks that claim "it's the best ever"... Trying to see if that's just a comment to validate spending $350 or it REALLY IS the best ever.

I'll claim total ignorance that I don't really know what symptoms would cause me to say to myself - it's time for a dynamic balance. 

[Joshua Blackh4t]

My understanding of balancing is they set up the machine, run the engine, get a reading, add weight as necessary and then repeat until correct.

If yours is all ok and you decided to do it, it might be cheaper because the first reading will be within tolerance.

So that would be my first question: is it a flat rate or hourly.

If he's coming out anyway to do a bunch of others, it might be a simple fee and it might make it better. I was told by a mechanic to get it done every 500 hrs, but that was in an area with mainly dirt runways

[Rick Junkin]

Yes, it's well worth it.

Now having said that, everything is relative. You said your engine runs smooth, as compared to a number of other engines you've flown behind. My engine had the slightest vibration that I could feel, and dynamic balancing made it go away. But the other benefit is the improvement on reducing mechanical stress in your engine/prop combination. Less vibration yields less stress and less wear throughout the airplane, even vibration you can't feel in the cockpit. The best time to start that benefit is early in an engine's life, where yours is.

The balancing process is pretty simple, and the setup takes more time than the measurements. An accelerometer and optical sensor are attached to your engine to measure engine vibration and prop position, and an indexing reflector is applied to the back of one blade of your prop. You run the engine up to a nominal cruise RPM and the computer calculates vibration in inches per second, and also calculates how much and where to apply offsetting/balancing weight (bolts/washers/nuts in varying combinations) on your flywheel to reduce the vibration. Stop the engine, apply the weights, and repeat until you're happy with the results.

Here's a good introduction to dynamic balancing from Jeff Simon. 

 

[bigmo]

Thanks @Rick Junkin / this is great info.

[EricJ]

Mine started out pretty well balanced, so while the result was noticeable, it wasn't huge.   Others see larger and more noticeable results.

The guy that did mine said that some Mooneys are a pain because the long spinner backplates don't allow easy placement of the balance weight.   I have a Hartzell Top Prop so the  backplate is flat and the flywheel more easily accessible.   So, depending on how the technician wants to apply the balance weight, that may or may not be an issue.

Whether it makes a big difference or not will depend on how far out of balance your aircraft is to start with.

 

[MikeOH]

If you have a PowerFlow exhaust, I believe the ICA requires a periodic prop balance to maintain warranty:

 

[DCarlton]

Mine was checked when a new spinner backplate was installed.  It was within spec.  First time I’ve had ever had it checked.  

[47U]

2 hours ago, EricJ said:

So, depending on how the technician wants to apply the balance weight, that may or may not be an issue.

There are approved areas to add weight to the backplate and unapproved ways.  Make sure your tech knows what’s what.  

There are a number of cracked backplate threads on MooneySpace.  Dynamic prop balancing can be beneficial, but caution is advised.

[EricJ]

9 hours ago, 47U said:

There are approved areas to add weight to the backplate and unapproved ways.  Make sure your tech knows what’s what.  

There are a number of cracked backplate threads on MooneySpace.  Dynamic prop balancing can be beneficial, but caution is advised.

In this case the issue was ease of access to the flywheel so that the weights could be mounted on the flywheel.    Some backplates make this difficult, apparently.

[FlyingDude]

15 hours ago, Rick Junkin said:

The balancing process is pretty simple,

Everything is simple, if you know how to. I've been doing prop balancing since I got my A&P and there are some nuances to it. I can say that it's not on par with an engine rebuild, but it's not as straightforward as changing tires (though that can hurt you if you're not careful). If you are not careful, you can easily get lost in some rabbit hole chasing IPSs. No Alice waiting for you in chains, though. 

[Jsno]

I just balanced mine today.  I bought an assortment of bolts and washers.  Turned out I only had to add 1 AN960 washer to a prop spinner screw.  1 Ounce.  Didn’t need to remove the spinner.  It has a fresh O/H on the prop and engine so I guess I did a good job on the engine.  When I picked up the prop at the prop shop, I was told to that a dynamic balance would be needed to ensure the prop had no issues.  Was able to find a balancer that a guy let me borrow so it was free.