Prop balancing

[tx_swordguy]

I have a sonex with a jabiru 3300 and a solid aluminum spinner. In trying to balance the prop i am running into trouble getting the initial balance done. I am getting .8 ips at 2650 rpm which translated to about 40 grams Needed on the light side. I was able to get 37 grams By using a much longer bolt and many washers. It ended up making it feel worse and actually showed it 1.08 ips at close to the same location after the longer bolt test run. I went all back to stock and changed the prop location on the hub by 60 degrees. I got exactly the same reading after prop reclocking ( .8 ips at 300 degrees before and after the reclocking) .I did not change the spinner to prop setting just changed it on the prop hub by 60 degrees. This leads me to believe that heavy spinner is heavy on one side. My question is what is the possibility of drilling lightening holes on the heavy side of the spinner? I was intending to drill maybe 2, 3/8” fairly deep holes around the prop bolt hole needing to be lightened. Trying to add 40 grams to the light side did not go well and that was quite a bit of weight to try and get on that bolt. I ended up with about 8 washers on the front and about 10 on the back with 1/2” extra bolt. Any help would be appreciated. I am using a dynavibe classic rented from viking engines.
Mark

[tx_swordguy]

Read and re read and i believe i see where i messed up in my measurements. I was about 90 degrees off due to where my optical sensor was placed. My question above still stands can i drill the spinner to remove weight or is that going to weaken the crush properties of the spinner

[peter anson]

Hi Mark. You could drill the spinner but it’s a terrible way to balance a prop. The spinner is probably the one thing that is in close to perfect balance. Once drilled, it only matches one prop and one orientation. The small Sonex spinner makes it a tricky thing to add balance weights but you can add washers on 2 or even 3 bolts to achieve the same thing. I used a couple of different size AN970 washers as balance weights, drilling out the smaller ones to suit the bolt size. AN970 are large OD, sometimes called mudguard washers or penny washers, although that last name probably only makes sense in countries that used to have large diameter pennies.

Peter

[jerryhain]

I have ended up balancing props on the Stemme motorglider way more often than I expected. The easiest way to keep track of what you’re doing is use the provided circular graph and mark your direction and ips after every run on it. Try using half or less of the weight you think is needed and you can watch it move closer to the center. The stemme props are very lightweight and I normally get them balanced to .03 IPS, Anything less than .09 is acceptable.

[garyb]

Hi Mark
I have been having similar issues and I found that the solid spinner was not centering nicely on the prop, so I have removed it and vibes went from 0.7 to 0.18 IPS and with a couple washers I get it to 0.01 IPS. I will make a bush for the spinner so it can center on the prop. You could also try loosening the prop bolts and tapping the spinner over to the light side and re-torque.
Regards
Gary

[DCASonex]

Two comments:

First, I have the same prop balancer. works great, but very easy to misinterpret the instructions on add weights in wrong direction.

Second, I purchased one of Sonex lighter weight spinners when they came out with those some years ago. The machining was off center, and I returned it. Mark the spinner on what your balancer says is the heavy side, then rotate it 180 degrees and check again. If no difference, leave the spinner alone.

The other advise posted is also very good. To get enough weight on mine without an longer bolts, used a couple of washers that were large enough diameter that had to trim off part of one side. Not sure how you mounted your sensor, but machined a clamp bracket for my 3300 that holds both the accelerometer and the photo-eye over the nose of the crankcase.. No need to remove any bolts from the engine. (Next project is to make bracket to balance the flywheel at other end of the engine.

David A

[tx_swordguy]

I got it balanced down to .08 at cruise rpm so i am happy with that. However i had to add a LOT of weight. I was at .8 ips unbalanced . I know when you have a solid spinner weighing pounds, 50+ grams may not seem too much. I had to put 20 or so washers on one longer bolt and 12 or so on another. Would rather not have 2 extra long bolts sticking out the front of the spinner but it did get the vibration greatly reduced. Trying to think about it logically, even with the added weight, when it is in rotation it will actually be better on the bearings. My thinking is because the lateral movement should be greatly reduced. I also balanced my biplane with an o320 much easier with just 2 or three 1/4 inch bolts maybe 25 grams total.

[Zack]

Could you use washers made out of something more dense, like tungsten?

[BRS]

Is your transducer perpendicular to the connecting rods (up and down) and centered over the crank? It could be picking up engine unbalance as well as prop. This will help.