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Prop Hub Static Balancing?

supik

Well Known Member
Do you guys do prop hub static balancing before dynamic balancing?

This is how my hub looks like from inside and it's throwing of when the engine is running. Found a bit of grease on both inner sides of the hub; the airplane has about 16hrs TT.

Lyc IO 540
Van's standard prop hub
Hartzell standard 2 blade CS

I'm just wondering whether I shouldn't start with static bal. first. If so, what's the recommended method / procedure?
 

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The hubs should come statically balanced from the factory, so doing it again probably isn't required. Put a dynamic balancer on it and if it starts at more than 1.0 IPS then it needs a static balance. If it starts under that you can probably balance it out on the plane. Check the installation/owners manual, I thought some grease was normal on brand new props. If that's all grease in the picture though, that seems a bit excessive.
 
I think what you are calling a "hub" is generally referred to as being a prop spinner.

Yes, the spinner gets dynamically balanced with the prop in the procedure.
 
Spinner static balance

Thank you all, yes my bad, it's the spinner.

Here is another pic with the grease visible. More or less the same amount can be found on the opposite side of the inner side of the spinner (not visible in picture).

There is lots of unevenly distributed epoxy where the spinner was separated from the form. (this is what you saw in the 1st picture)

I wanted to verify the static balance of the spinner but found videos for static balancing RC model spinners only.. Haven't found a good resource for static balancing real aircraft spinners.
 
Hi Igor, this looks very much like what my spinner looked like as well. I sanded it a little bit to make it smoother, but I didn't bother trying to balance it. I did a dynamic balance on the prop with the engine running using a dynavibe classic, and lots of instructions on the internet. The company that sells the dynavibe was also happy to answer questions. You probably have someone near you that has one or something similar.

Surprisingly my prop/spinner was very balanced, so it took very little effort to get it down into the "excellent" range.

I didn't get much grease leaking out of my Hartzell, perhaps just a little mist on the windscreen and on the cowl the first few hours of flight time.

There seems to be 3 different types of grease used in our Hartzell props, Aeroshell 5, Aeroshell 6, and Nyco GN3058.

https://hartzellprop.com/top-tips-for-airplane-propeller-lubrication/

Seems the Nyco is the best - I hope you have that. There are a lot of reports of Aeroshell 6 leaking. Unfortunately to change from 6 to Nyco, you have to essentially do an IRAN on the prop hub.
 
The hubs should come statically balanced from the factory, so doing it again probably isn't required. Put a dynamic balancer on it and if it starts at more than 1.0 IPS then it needs a static balance. If it starts under that you can probably balance it out on the plane. Check the installation/owners manual, I thought some grease was normal on brand new props. If that's all grease in the picture though, that seems a bit excessive.

When I see a reading of 1.0 IPS it’s time to regroup, usually something drastically out of wack and I won’t attempt a dynamic balance. A “normal” high vib is less than half that.

Balancing the spinner would be a waste of time.
 
When I see a reading of 1.0 IPS it’s time to regroup, usually something drastically out of wack and I won’t attempt a dynamic balance. A “normal” high vib is less than half that.

Balancing the spinner would be a waste of time.

Agreed, but I've been confronted before about not sticking strictly to manufacture recommendations. Dynavibe doesn't mention redoing the static balance until 1.0.
 

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Agreed, but I've been confronted before about not sticking strictly to manufacture recommendations. Dynavibe doesn't mention redoing the static balance until 1.0.

If an owner wants to confront me on my recommendations, it’s pretty simple for me… put it back together and send him down the road.
I prefer not to put my name in the logbook when I suspect something is wrong. (I’ve done this a number of times, most come back with a new or OH’d prop and thanked me).
I don’t let let the customer dictate what I do, and I don’t have a boss telling me what to do anymore either (except my wife).
 
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"What he said ...."

If an owner wants to confront me on my recommendations, it’s pretty simple for me… put it back together and send him down the road.
I prefer not to put my name in the logbook when I suspect something is wrong. (I’ve done this a number of times, most come back with a new or OH’d prop and thanked me).
I don’t let let the customer dictate what I do, and I don’t have a boss telling me what to do anymore either (except my wife).

I had a prop that CLEARLY not balanced (I think about 1.5 IPS!!!!!!!!).
Had the prop overhauled (Whirlwind) and STILL could not reach the expected numbers. Spoke with Whirlwind owner/chief engineer (?) and was told that there as a RARE chance of something not quite right with my hub (older version), so we had THAT replaced as well. Prop now smooth.

The point is that as Walt mentioned, if the numbers are high, there is something that NEEDS to be done. I for one did not want to sling a blade or two off in flight. Vibrations aside, that was my REAL motivation.

Your Mileage May Vary, but that is MY story. :)
 
Static vs Dynamic Balancing

Most propellers, especially those with a TCDS i.e. Hartzell, McCauley, will be static balanced on a static balancing arbor prior to leaving the MFR.

Most prop shops will check the static balance of the prop after an IRAN or overhaul.

This helps get the prop hub and blades into a known "in-plane" mass balance condition.

In plane axis is spanwise to the blade, out or plane is perpendicular to the spanwise axis of the blade.

Rotorcraft folks will know this the Vertical and Lateral axis.

Static balancing on an arbor typically does not include the spinner or mount plates / hardware.

The prop hub and blades are also typically checked for blade track and angles to ensure the blades / hub meet the static blade track and angle requirements for the prop.

Once the prop is reinstalled on the engine and run, it requires Dynamic balancing to take into affect the mass imbalance (aka vibration) caused by centrifugal forces.

Note - Dynamic balance of the prop only addresses "in plane" mass imbalance, if there is a out of plane vibration, adding weight will not solve it.

There are several items that can cause a perfectly static balanced prop to exceed the dynamic balance limits, which are "typically" 1.0 IPS.

If the crankshaft is bent or one blade is bent / out of track, it will cause the entire prop to "wobble" enough in the out of plane axis that it will be hard to dynamically balance, if not impossible.

Typically all the blades have the same chord and spanwise profiles, however if one blade has been repaired, it may produce more or less thrust than the other(s) and this will result in a out of plane vibration (aka a thrust imbalance) which cannot be dynamically balance with weight alone. Prop overhaul shops check this as part of an IRAN / Overhaul, so it shouldn't be an issue...unless Bubba had filed the heck out of one blade to remove a nick / gouge.

If the either the spinner or mount plates have excessive mass imbalance, it can create a situation where a perfectly static balanced prop cannot be dynamically balanced because the entire prop, spinner and mount plate assembly is spinning as a "total mass".


You can check the static balance of the spinner / mount plates using a bubble balancer and add / subtract weight as necessary to get a decent static balance before attempting dynamic balancing.
 
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