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The value of dynamic propeller balancing

MSFT-1

Well Known Member
A couple weeks ago I did a write-up on my trip to Hartzell Propeller in Piqua, OH. After Hartzell did the necessary repair, they asked if I wanted the propeller dynamically balanced. The cost was about $250 and the mechanic that worked on my plane said it was well worth the money.

I had them do it.

Basically they use a piece of test equipment and a set of sensors to figure out where on the spinner bulkhead to add weight. Before balancing they did a run-up test for about 1 minute and determined that my prop was at 1.7 IPS (whatever that means). They added a small weight in the proper location and redid the test and then proclaimed that I was now at .45 IPS. They seemed very pleased with this.

The whole process took about an hour.

I wondered if I would even notice the difference.

It is AMAZING how much smoother the airplane feels. I could tell the difference immediately. Without a doubt, this was money very well spent. I guess it makes sense that it would be a big difference since there is a big hunk of metal out there turning at 2300 RPMs. Feeling (flying) is believing.

Bruce
N297NW
RV-8
 
I had mine done a week ago at Ohio University airport (UNI). On my log book it says the propellers is balanced to .14 IPPS (should it be IPS?) using Chadwick Helmuth Balancer. The AP who did it told me the initial reading was 5. They charge $150 for the service.

Ted
------------------------------------------

T.C. Chang

http://tc1234c.googlepages.com/
RV-9A, Lycoming (ECI) O320-D2A, 160 hp, Carb, Dual Mag, Sensenich FP
GRT dual DU H1, TT DigiFlight II VSGV, 183 hr Hobbs
 
The Chadwick manual " The Smooth Propeller " calls out for a balance to be at .2 or better to be considered balanced, if the propeller started at 1.7 that is really high, when i do balances on reciprocating engine they normally start at the .5 to .8 range and i can always acheive at least a .2 and most times i can get .1. The good thing about balancing is that even if you do not feel it the rest of the airplane can, baffling and other items that crack due to wear from vibrations have a longer life after balancing.
 
Worth it!

Prop balancing is indeed worthwhile just as balancing your engine or any reciprocating assembly is. In fact when you do a dynamic prop balance you're really balancing the engine/prop assembly.

Our EAA chapter has a state-of-the-art computer prop balancer program that has been a huge success. Check our web site for info, but especially interesting is the log of jobs we done found on a link toward the bottom of the page, or by clicking here. I encourage any of you who are active with your local chapters or builders groups to consider it and would be happy to speak with you on the details. The DSS MicroVib II system was around $6,000, but I think you could make it work by charging members $100 and have it paid for with 60 jobs. We paid for it when we merged the Home Wing treasury into our local chapter so we only charge a $20 fee for consumable parts (bolts & tape) and repair reserve.

Lastly, if you are considering paying someone to do a balance job make sure they have decent equipment and capable operators. For many years Chadwick Helmuth made the only balancer around and frankly the results achievable with it were questionable. Seems Honeywell bought CH and they now make computerized equipment, but if you see an old balancer with needles instead of a digital readout walk away. I know we have balanced at least a half dozen props that were already balanced by a shop with the older CH gear (and even some newer gear) and the error we measured was not good. In all cases we have been able to improve the error by at least 50% (half the error) and usually considerably more.
 
randylervold said:
...but especially interesting is the log of jobs we done found on a link toward the bottom of the page, or by clicking here.
A quick look at the data suggests that all of the five most popular RV prop makes (not model specific!) can be balanced well. Of the 60 props balanced, 59 of them were able to get below 0.1 IPS (the only one over was a Champ with a FP Sensenich). This also suggests that there is no large difference with respect to props before balancing, with the possible exception of the WW.

Prop Before After
Sensenich 0.238 0.031
Hartzell 0.228 0.015
Catto 0.200 0.017
MT 0.251 0.022
WW 0.530 0.020
 
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Errors in my original post

When I wrote the original post, I was quoting my numbers from memory (obviously a flawed memory). I pulled out my paperwork from Hartzell and here are the numbers they recorded:

Pre balancing: 0.173
First run: 0.084
Second run: 0.045

These numbers seem much more inline with what other people have reported here.

Bruce
N297NW
RV-8
 
Did it go any faster at 2700 RPM?

Smoother means very little to me if it is smooth enough to start with.

Bob Axsom
 
I balance props here in Northwest AL. and the worst one so far was a Yak at 1.5 ips. which sets off an alert on my system and I got that one down to .04. I believe that a balanced prop keeps parts from vibrating off your airplane and also relieves stress on your prop hub, engine mounts and airframe. With a balance you can also look at spectrum and waveform analysis and see what shape yor alternator bearings are in and look at your power pulses to see how balanced your cylinders are. Get your prop balanced your plane will love you for it.
 
raddatz said:
With a balance you can also look at spectrum and waveform analysis and see what shape yor alternator bearings are in and look at your power pulses to see how balanced your cylinders are. Get your prop balanced your plane will love you for it.
Interesting, I also have prop balancing equipment (ACES 2015) but I am curious how you detect alternator bearing problems. Can you elaborate (with graphs, etc.)?
 
Indigo said:
The Chadwick manual " The Smooth Propeller " calls out for a balance to be at .2 or better to be considered balanced, if the propeller started at 1.7 that is really high, when i do balances on reciprocating engine they normally start at the .5 to .8 range and i can always acheive at least a .2 and most times i can get .1. The good thing about balancing is that even if you do not feel it the rest of the airplane can, baffling and other items that crack due to wear from vibrations have a longer life after balancing.


The reason Chadwick came up with the .2 Inches per second "Good" is becuase this was the "noise floor" of the equipment....they could not tell if the vibration level was much lower.

Modern digital equipment can go much lower... repeatably.

.1 is over 5 times higher than my post balance average. I have taken even some .04 IPS under .005 IPS the results are like comparing 80 grit sandpaper to 1200 Wet & Dry.
 
Smooth is an adjective that describes words...

A analogy...

What is your cholesterol level? What is your blood pressure? Just because you feel ok does not mean you have a great chance of keeling over tomorrow...

How about having someone hook up some calibrated test equipment and showing real numbers what the vibration health of your engine/prop/airframe....you will even get an idea if an how it can be improved....

Vibration damage to an airframe, wiring, electrical circuit is CUMULATIVE...you can never remove the workhardening effects of vibration without a serious amount of cash and time.

Best regards,

Jim
 
If you know the rotational frequency and have an accelerometer mounted at the correct position you can see the vibration amplitude of the item in question...Raddatz uses the DSS MicroVib II equipment and the MicroBase Pro software. The complete history of the balance procedure, spectrum and waveform plots are downloaded to a computer and processed the MicroBase Pro software. Machine rotational speed identification files are attached to the specific spectrum plots...peaks are ID'd with the rotational speed of the component....simple equipment with few separate items speeds can plotted as well as much more complex items like PT6 engines (and special reports generated for the MORE program for one example)

I have samples of these reports on my website www.aviationvibes.com from a 6 cylinder Continental ....note these forms make great "health records" for future and fleet type comparisons...and great logbook entries!

Best regards,

Jim
 
No feel

I fly both an Air Tractor with a 110" Hartzell and my RV with a three-bladed Catto. An A@P friend balanced both airplanes and I can assure you, Bob, that you cannot feel high frequency vibrations that are cumulatively destructive. My PT-6 in the 'Tractor always "felt" smooth until I saw the IPS during balancing.....big improvement and this engine has almost 8000 hours on it and is still strong and smooth. The RV picked up a noticeable, albeit small, increase in max cruise RPM's. I'm definitely a believer......it started with a Ford 427 balanced in my kit Cobra-long time ago ;)

Regards,
Pierre
 
Prop Balancing

There are basically 3 units of measure in vibration: acceleration (G's) Velocity (IPS) and displacement (Mils PP).

Typical displacement readings are found on large rotating equipment and recorded with a non contacting proximity (eddy current) probe. As the target material moves closer to or farther away from the probe, the output voltage changes. Readings are in distance of movement and usually mils (.001") from peak to peak of the sine wave.

Velocity is measured with a velocity transducer which is nothing more than a magnet suspended inside a coil by a spring. As the mounting base vibrates the magnet moves up and down generating a voltage. This is read as a distance of movement over a given period of time hence inches per second (IPS) and usually read in IPS peak which is from the center of the sine wave to either the upper or lower peak of the sine wave. Anything over .5 inches per second is considered to be rough. Velocity transducers are prone to mounting error, resonance, fatigue and are typically found in the low to mid frequency applications.

Acceleration is typically measured with an accelerometer which is a peizio electric crystal system that measures rate of change or "G's" and is usually used for high frequency applications. Industry standards for acceleration readings are usually in RMS or .707 x peak. Accelerometers are very tough, able to withstand high temperatures, have a very high mounting resonance and are relatively inexpensive compared to the other tranducers. Most of the data collectors will integrate the output of the accel to IPS for balancing applications.

The first step in dynamic balancing is to make sure that imbalance is causing the vibration problem and not something else. There are several things to look for if imbalance is in fact all or most of your vibration: 1) It should increase (or decrease) as a function of speed. 2) If you have a 2 channel system and mount the accelerometers 90 degrees of rotation apart the the vibration peaks should be 90 degrees, +-15 degrees out of phase.....or 270 degrees out of phase depending on direction of rotation. 3) 80% of the vibration energy is at 1 times rotation speed (1x).

Once you have the voltage signal (amplitude vs time) most data collectors will run a FFT to convert to an amplitude vs frequency spectrum which is where you can diagnose most vibration problems. Imbalance, assembly error, alignment, gear problems will all be syncronous, i.e. at multiples of running speed, 1x, 2x, et. Rolling element bearing problems are always non-syncronous for example .564x, 2.456x

Anytime you can reduce vibration you are making everything work better, last longer AND creating less pilot fatigue. If some of you guys are getting down below .1 IPS that is great. Most balance techs will keep making runs until they reach the resolution of their gear or they are chasing the remaining imbalance around with no reduction in amplitude which most likely means the remaining vibration is not a result of imbalance.
 
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It's part science and part ART

Not all equip is the same and more over not all technicians and techniques are the same. The test should be done under power with the blades off the stop (constant speed prop) with the cowl installed. This is hard to do on the ground. Still there is judgment in how you do the test, where you put the accelerometers, interpret the data and apply the weights.

You will notice a dynamic balance if its done properly and you had dynamic imbalance prior. I found it took three iterations and two technicians to get it right. When the sweet spot was found it was noticeable.

As far as vibration don't forget the engine mounts and things that hang off the engine and touch the airframe, baffles, control cables, houses all can transfer some buzz to the cockpit. We are almost sitting on the engine with just a piece of sheet metal between us. The engine mount is hanging off brackets mounted to structure that is right at our feet and elbow. The engine has its own vibs, and the prop has its own vibes as well. Its the total system that you try to optimize, but if the engine is out of balance dynamically or power produced by the cylinders are not even, than all the balance in the world on the prop can not totally cancel that out. Like wise if the prop blades are not tracking or at the same pitch, balance wts. can do only so much. VALUE? Look its a tune-up not a miracle. If you have severe vibs than start looking around for other issues. I highly recommend LORD CORP engine isolation mounts verses other brands. I found just witching to the LORD Corp solved most of my vib issues and the dynamic balance was the cherry on top.
 
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When I wrote the original post, I was quoting my numbers from memory (obviously a flawed memory). I pulled out my paperwork from Hartzell and here are the numbers they recorded:

Pre balancing: 0.173
First run: 0.084
Second run: 0.045

These numbers seem much more inline with what other people have reported here.

Bruce
N297NW
RV-8

And most of the .045 is probably engine vibration, which they can't do much about.
I had mine balanced recently and it came in at .016 at 2100 rpm. That's with a 3 blade MT which is little smoother than 2 blade props. The .045 your guy achieved with a Lycoming is excellent.
 
Does any body know who offers this service to balance props in the Missouri area. Im based at 8WC

Chris RV 8 N627CS

Call the local FBO and they will have a few leads for you. Most all bigger FBO's have access to a balancer. If not we have a guy here in Crete, NE KCEK that does them for $150.

$250 was a rip off.
 
Prop Balancing

1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***
4. Sometimes engine mounts are the problem. This is mostly noticeable during rpm acceleration or deceleration.
5. Do not unbalance the propeller to balance the engine.

*** Propeller clocking on the crankshaft is IMPORTANT. Wrong clocking can be the cause of bad vibration.

Hartzell and McCaully make sure your prop can be install I only one clocking. Follow their lead.
Kent
 
could you be more specific?

After static balance If vibration occurs, the engine is the problem.
Are you saying that the normal power pulses are the problem, the power pulses are unequal, or that something is wrong internally in the engine?
 
rebalance after changing engine mounts?

I highly recommend LORD CORP engine isolation mounts verses other brands.
Should the engine be re-balanced after changing engine mounts? I have Barry mounts and have been thinking of changing to Lord.
 
1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***
4. Sometimes engine mounts are the problem. This is mostly noticeable during rpm acceleration or deceleration.
5. Do not unbalance the propeller to balance the engine.

*** Propeller clocking on the crankshaft is IMPORTANT. Wrong clocking can be the cause of bad vibration.

Hartzell and McCaully make sure your prop can be install I only one clocking. Follow their lead.
Kent

Hmm, then why do you suppose all the major prop and engine manufactures recommend Dynamic prop balancing?
 
Static vs Dynamic balance

1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***

This would be true if the prop/spinner were truly 2 dimensional. i.e. Infinitely thin. In 3-dimensional rotating objects, dynamic balance is also important.

Imagine replacing the prop with a perfectly statically balanced wheel a few inches thick. Then attach a lead weight to the outboard aft rim of the wheel and an identical weight to the outboard forward rim of the wheel 180 degrees out from the aft weight. Because the weights are 180 degrees apart the wheel will still be statically balanced but the moment arm about the axis of rotation introduced by the weights will result in a wobble/vibration when the wheel spins.
 
Should the engine be re-balanced after changing engine mounts? I have Barry mounts and have been thinking of changing to Lord.

gmcjetpilot has not been on the forum for years.

And "No" would be the answer. True engine balance is independent of the mounts. There are a lot of cyclic forces generated in the engine that are inherent to its design configuration and not addressable with a weight rotating on the crank.
 
prop balancing

There is a lot of info going around about prop balancing. There are a few facts you need to know about this endeavor.

1. Propellers are balanced at the factory or the OH facility. The balance specs that the OH shop or factory is tight enough that it will be balanced when you put it on your airplane. If it is not then you had better start looking for engine problems.

2. Do not use your propeller to balance your engine. OK, you can do that if you are using a fixed pitch propeller, and probably get by with it. But if you use your propeller to balance your engine and you are using a variable pitch propeller then you are flirting with disaster.

I had a customer bring his Aeromatic propeller to me with a complaint that it was out of balance. He also brought an aluminum disc, about 9" diameter that had a stack of fender washers bolted to one side. The washers weighed about 4.2 oz. He said that it took this disc with the washers bolted on to balance the propeller.

I put his prop on my static balance stand, without the balance disc and I found the propeller balance to be in spec but on the edge of the spec. I then pulled the blades and found 5 of the 15 screws broken in one of the blades. So, even with 5 broken screws that balance still met the spec.

I say again, you can get by using a fixed pitch prop to balance an engine unbalance, TO A DEGREE. Because the mass of "beef" holding the blades onto a fixed pitch prop is virtually indestructible. So you can usually get by with such an atrocity but if you do that with a variable pitch prop you are flirting with disaster.

Another thing: Clocking your prop on the engine is important. You can get a nice out of balance vibration by wrong clocking on the crank shaft. You will notice that Hartzell and McCauly makes it so that you can put the prop on an engine only one way, or 180 deg. That is for a reason, especially on four cylinder engines. That is important!

Poor engine mount rubbers can be a cause of vibration. This show up during rpm acceleration more than during constant rpm.

When a propeller leaves the factory or an OH shot it IS IN BALANCE. If some dynamic balance guy starts tacking weight on it the warrantee should be immediately voided.
 
I'd be curious to know where you get your info.

Both Hartzell and McCauley (among others) recommend dynamic balancing in their FAA approved manuals.

From the Hartzell Manual
Dynamic balance is recommended to reduce
vibrations that may be caused by a rotating system
(propeller and engine) imbalance. Dynamic
balancing can help prolong the life of the propeller,
engine, airframe, and avionics.

McCauley Manual
McCauley endorses dynamic balance on propellers installed on piston and turbine powered aircraft.
 
Even though they call it dynamic prop balancing, you aren't using the prop to balance the engine. Usually you are using weights on the ring gear to balance the engine. Also, as the prop wears, and especially as it is dressed, it will lose its balance, in which case a dynamic balance balances the engine and the prop.
 
I'm a fan of prop balancing too - But of course it all depends on how in or out of balance you are in the first place.

Here's a tip - If you have an Iphone have a look for "vibration" apps on the apple store. I used one before and after on my Pitts / MT balance job and the results were quite plain to see in the app.

I'm sure others may be able to share results and you could make an informed decision about how in or out of balance you were before deciding to have the work done.
 
I wouldn't think there would be any question on the benefits of dynamic balancing a prop. Car tires used to be static balanced and that was found to be inadequate so everyone "spin balances" them anymore since it result in much less vibration.

A typical mid-size SUV with 19 inch wheels has a wheel RPM of about 850 rpm at 70 mph and yet the improvement with dynamic balancing is very noticeable. Imagine the difference at 2200-2700 rpm like we turn our props:D
 
There's more to balancing a prop than just balancing a prop. Consider this process as diagnostic as well. I've been balancing prop for a long time (using ACES) and I've actually found other problems while attempting to balance. On a few occasions during balancing I've found props that had internal problems, one was a brand new Hartzell. The IPS would shift locations on the run ups. These props were sent to prop shops and were fixed then balanced. I once found static weights 180 degs off (the right amount just placed on the opposite side), low cylinders, etc.
People think they are balancing just their prop, but they aren't. Every rotating part on your engine is affecting the total balance. Consider just the flywheel being off tiny bit, the prop being off a tiny bit, the spinner, on and on. Sometimes they work in your favor and sometimes not. The prop by far being the largest mass is where the final balance takes place. The accelerometer is placed as close to the prop as practical during run ups. But a perfectly static balanced prop most likely will not produce a well balanced engine - prop combo.
 
"There's more to balancing a prop than just balancing a prop."

Thank you FasGlas!

Clocking your prop:

My plane was a player in the certification of the Hartzell 2 blade BA airfoil for the 550 Continental engine. 1st run was with the prop clocked 'normally'; second run had the prop re-clocked 60deg.

The second run was noticeably smoother, so the final version of the prop (to be fitted to the 550) has this 60deg clocking built in.

If I can recall correctly, this re-clocking started with Mooney when they decided to put the 200HP IO-360 in their planes, and the setup vibrated.

Way back in the stone age, when we would get a run-out metal Sensenich 0-360FP prop and grind and twist on it to make it work on our RVs, we also tried that clocking process - sometimes it did not make any difference; sometimes it did. So we went with the smoother position.

Carry on!
Mark
 
Piper Warriors with 160 hp... prop set at 12-6. 150 hp set 10-4

OK...why? 12/6 or 10/4 relative to what, exactly? Cylinders X and Y at TDC, or BDC, or something else? And what's different between two 4-cylinder engines that would have an effect on the prop clocking like this?

Etc.?
 
Good To Know

Cruise up to SW Wisconsin and I’ll do it! I have a Dynavibe GX3 and if works great!

I'm in Stoughton and have been looking for someone who can balance my prop. When the snow melts and I can fly again I'll be in touch. Please send private message with your contact.

PS, I have a friend in Middleton who also wanted his Starduster prop balanced.
 
Not all equip is the same and more over not all technicians and techniques are the same. The test should be done under power with the blades off the stop (constant speed prop) with the cowl installed.

"Off the stop". Does this mean prop to be pulled back as in coarse pitch?
Thanks
 
Helicopter AP/IA

Lost my regular AP/IA to full time work. Spent summer of 2020 on the ground trying to get a mechanic.

New AP/IA works on all the local Medvac helicopters.

Almost any helicopter mechanic can balance your prop.

Easy to see the difference. Spinner could be seen spinning in flight, now it looks like paint that is not moving/spinning.

Mine started out at 1.2ips, now .04. That after three runs lasting a total of about 20-minutes. Start/Stop/add weight.

Smooth as silk. Great investment for $200 total.

Mike
 
Not all equip is the same and more over not all technicians and techniques are the same. The test should be done under power with the blades off the stop (constant speed prop) with the cowl installed.

"Off the stop". Does this mean prop to be pulled back as in coarse pitch?
Thanks

I've heard this before but if the blades are not tracking correctly or blade angles are not the same, it will cause an aerodynamic imbalance which cannot be 'fixed' by balancing. If blade tracing is out of limits balancing is generally not possible.
 
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