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
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.
Eddie Forward
Flying
SS7, 912iS, Garmin G3X
IMG_1368.jpgIMG_1386.jpgIMG_1370.jpgIMG_1385.jpg
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.
Last edited by jrevens; 01-18-2020 at 10:32 PM.
John Evens
Arvada, CO
Kitfox SS7 N27JE
EAA Lifetime
Chap. 43 honorary Lifetime
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
Great report. Thanks John.
John,
It's great to see some empirical data on this.
Dave S
Kitfox 7 Trigear (Flying since 2009)
912ULS Warp Drive
St Paul, MN
Was wondering what the consensus was on the Balance Master. It looks like some had good results and others marginal results. I will be putting my prop on soon (Airmaster, Whirl Wind blades) on a Rotax 912iS. The question is: do I Dynamic balance with a Dyna-vibe or put on a Balance Master and call it good? Help me decide!
Joe
Joe on the NR prop I got better results with balance master. Others have got better results with a dynamic balance. Dynamic balancing is mostly science and partially an art form. If you have never dynamic balanced a prop and will be doing it by yourself, I say just run the balance master. Maybe John will sell you his?
Dustin Dickerson
Building 7ss STI x 2
Oratex
29" shock monster
EP912STI 155hp
Garmin
N33TF......FLYING!
N53TF......FLYING!
With the early dynamic balance equipment that was available 30 years ago, i.e. from Chadwick-Helmuth, there was some “art” involved in my experience. With modern technology, not so much. I don’t have any Dyna-Vibe experience, but with my 20 year old ACES machine it’s all science. I’ve given my Balance Master to a friend to try on his Mod. IV. If he doesn’t like it I’d be happy to sell it.
John Evens
Arvada, CO
Kitfox SS7 N27JE
EAA Lifetime
Chap. 43 honorary Lifetime