Balance Master

[Av8r3400]

I’ve got about 5 hours on it now. Combined with a 72” 2-blade Luga prop. She is smooooooooth.

Even the dreaded 2500-3500 normal vibration is totally gone!

[jrthomas]

I guess maybe I'm just trying to improve something that ain't broken. Mine is very smooth thru the whole rpm range. I have a model 4/912ul with the Kiev 3 blade. Leaf has this and it seems like a good price compared to the price that others are asking. https://www.leadingedgeairfoils.com/propellers/balance-master/propeller-balance-master-6-hole-prop-black-anodized.html (I don't know why this won't highlight.)(Not sure if this is the right one since it doesn't say 912)
It's cheaper than the coolant cap that I recently ordered. My flyin buddy, also with a model 4/912, has a rough midrange. He has a Warp Drive prop. Lots of work, even new carburetors haven't completely cured the problem. I'm really trying to spend some of his money hoping it will cure his problem. I think I'd probably get one myself just to insure mine is as smooth as possible. Should help the gearbox live longer too.

[WWhunter]

Wow! That's half the price of what I have seen.

[Av8r3400]

... https://www.leadingedgeairfoils.com/propellers/balance-master/propeller-balance-master-6-hole-prop-black-anodized.html...

I do not believe this is the one for a 912. The photo may not be of the actual unit, but the center hole and slot proportions are not correct for a 912. All of the other sources for a 912 ring are between $150 and $200.

[avidflyer]

Looking at this $76 balance master, it says it fits the 75mm and 100 mm bolt pattern. The way I see it, this means it would fit on a rotax 2 stroke gearbox with the 1" boss in the center and it looks like the bolt slots are for an 8 mm (5/16") bolt. The real early 912s had a boss that measures about 1 5/16" and has 100mm bolt pattern, and the later 912s are about 1 3/4" boss with 101.6 mm bolt pattern. Long story short, I think Larry is correct. JImChuk

[efwd]

Hmmm. I used a Dynavibe to balance my prop. It worked and I may even swap to the balance master regardless. I seriously hope my $22k Rotax was balanced at the factory.

[jrevens]

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I flew for 1.5 hours on 1/16/20 with the Balance Master installed. The airplane didn't feel as smooth as before, but definitely smoothed out more after full throttle run-up. Today I installed my balancing equipment to get some real numbers. After warm-up, I advanced to 5000 rpm, took a vibration reading, then did the same thing at 4000, 3000 & 2000 rpm. I then went back up in 1000 rpm steps to 5000. I then removed the Balance Master and performed the same exercise again. I had previously dynamically balanced the assembly to 0.02 to 0.03 ips at full-throttle static of approximately 5100 rpm. Here are my results and observations -

With Balance Master - Starting at 5000 rpm - 0.04, 4000 - 0.04, 3000 - 0.12, 2000 - 0.02 Starting at 2000 - 0.03, 3000 - 0.07, 4000 - 0.03, 5000 - 0.10

Without BM - Starting at 5000 rpm - 0.02, 4000 - 0.02, 3000 - 0.01, 2000 - 0.02 Starting at 2000 - 0.02, 3000 - 0.02, 4000 - 0.03, 5000 - 0.03

I allowed time for things to "settle down" before each reading, and observed that with the BM it took a minimum of 30 sec. to 1 min. (sometimes considerably longer) to reach the best balance condition. There was no delay without the BM. I'm not certain why the spike at 5000 rpm when going from 4000 to 5000 with the BM as compared with starting at 5000. Hysteresis in the throttle cable when pushing as opposed to pulling on the throttle arm (I don't have the throttle springs) creating a little carb imbalance may be a factor, but I don't see the same thing without the BM.

So, my experience is smoother operation without the Balance Master, and much smoother during the transition "settling down" periods. I think that the Balance Master would potentially offer a good improvement/option for an out-of-balance condition if dynamic balancing was not easily accomplished, such as when a small "skull-cap" spinner is used on a Rotax. For me, there is no doubt that my situation is better with a good dynamic balance job alone. Your mileage may vary.

[Clark in AZ]

Very interesting. Thanks much for taking the time to do this and report the findings. Maybe some others will chime in with their findings.

Clark

[JoeRuscito]

Great report. Thanks John.

[Dave S]

John,

It's great to see some empirical data on this.