Prop Balance... "Feels Good to me!" (I hear this quite often)!

[Walt]

Thought this was interesting as Stephen "Christo" was in the neighborhood to get some work done at "Glo Custom" paint and asked me if I had time to check his prop balance. Steve seemed convinced it was really smooth and probably wouldn't need anything but wanted to check it just the same... just to be positive. I told him that if it didn't need any balance adjustment I would run the check and vib survey for half price so that pushed him over the edge and he said ok lets do it. He seemed a little reluctant to want to spend the money (don't know why, his next stop was Vegas so he was going to lose it anyway ) but his curiosity to see where it was was just to compelliing.

Well as you can see below it was over twice the limit (.403 IPS) when we checked it

A couple of runs later we had him running nice and smooth at .021 IPS



Below is the Vibration survey, engine was built well (Lyc Thunderbolt) and the counter balanced crank is obvious by the low 2.5 and 3.5 harmonics.



I might add that Steve's machine is a sweet ride with great workmanship, (and I was drooling over the IO-390).

[jartlip]

Does anybody do prop balancing in South Florida?

[AX-O]

Walt,
I hear the same thing every time I do a balance job too. ?Feel pretty smooth to me?, ?I am not going to be able to tell a difference?, ?is it really worth it?

Most people call me on the radio as soon as they lift off and start their journey home. Telling me how the bottom of the panel is not shaking or they can read their GPS without holding it, the plane sounds different etc, etc. It is definitely worth it.

By the way, nice equipment.

[Brantel]

Walt,

I had mine checked back this time last year and I was told it was so low that there was nothing that could be done.

My engine is a FP and at 2500+ rpm it is smooth as butter but around 2400 I have a pretty good vibration.

Of course during balancing, I could only get about 2200 static.

Is this typical of what I can expect or is there a better balance out there for me to find?

[Walt]

Originally Posted by Brantel

Walt,

I had mine checked back this time last year and I was told it was so low that there was nothing that could be done.

My engine is a FP and at 2500+ rpm it is smooth as butter but around 2400 I have a pretty good vibration.

Of course during balancing, I could only get about 2200 static.

Is this typical of what I can expect or is there a better balance out there for me to find?

Well this is a tough question to answer. Do you know what the vibs were when they checked it? The upper "limit" is generally considered to be .2 IPS before balance and .1 IPS after balance (McCauley recommends .07 as the upper limit after balance). Some folks who balance (like some prop shops I know) will tell you it's as good as it can be if it's below .2 IPS which we all know isn't true

I have generally seen very little difference above 2200 rpm and in fact it "usually" improves up higher. So I balance most FP props at 21-2200 and constant speeds around 23-2400 (only because they can get there and most folks cruise in that range).

The nice thing about the MicroVib is the spectrum analysis fuction which looks at the 150-15000 cpm vibrations. For example I can easily see a cylinder thats not doing its job by looking at the crankshaft half order (.5) vibration. Pistons and rods that are mismatched will typically exhibit high 2.5 and 3.5 vibrations.

Have I answered your question.... probably not, but my point is without good numbers and good equipment to measure the vibration it it's impossible to say what the problem is.

[Brantel]

Walt,

The final was 0.08 ips after the balance and only slightly worse before. The tool used did not seem to be as sophisticated as yours.

[Walt]

Here is some troubleshooting info from the McCauley manual on tracking down vibrations.. some things for you to look at (obviously some of these things do not apply to an RV but the theory is still the same):

VIBRATION TROUBLESHOOTING
Troubleshooting vibration problems can be very challenging and time consuming. Most digital dynamic equipment can also be used to track down vibration problems. The digital dynamic balancing equipment can display the amplitude and frequency of the vibration, which will help determine the vibration source. While vibration problems are occasionally caused by the propeller, they are usually caused by other things. Below is a list of other possible sources of vibration:
1. Engine
2. Worn, old, cracked or loose engine mounts
3. Cracked or loose engine mount structure
4. Cracked or broken spinner bulkheads
5. Loose or improperly mounted engine cowlings
6. Loose cowl flaps
7. Loose landing gear doors
8. Out of balance elevators
9. Loose control yokes
10. Exhaust stack touching engine cowling
11. Component in engine compartment that is touching engine cowling

I would also add check the prop and spinner are tracking true and is properly torqued.

[Walt]

Originally Posted by Brantel

Walt,

The final was 0.08 ips after the balance and only slightly worse before. The tool used did not seem to be as sophisticated as yours.

That is certainly not an excessive number and at face value I would not suspect that would be the cause of the vibration you're feeling. I'd love to work on it with you next time you get down to TX

[Bavafa]

Walt,
Being on the subject of prop balancing and my recent experience helping a friend balancing his prop on a Subi with not so great luck...

What is the typical way of balancing a prop, just front or front and rear? To be more specific, I had mine done little over 2 years ago and the guy that did it had a two probe type balancer, front and back. He ran a few test to get a good average between the two as oppose to just getting the front side smooth.

I am still trying to understand his numbers as the hand written report says, 0 IPS front and .06IPS in the back but the computer printed report is slightly different.

Also how often do we really need to balance them?

[Geico266]

Thanks Walt for reminding everyone the importance of dynamic balancing. The results are stunning.