Prop balancing using the DynaVib

[rv7charlie]

I've balanced several (Lyc) engines using our EAA chapter's Dynavibe. It's not a very 'smart' balancer, and it's somewhat tricky to interpret their directions. But once you get what they're trying to tell you straight in your head, it works just fine. If you don't have it straight, you'll chase your tail for quite a while.

For Scott: I've never used any of the smarter balancers, but it sounds as if the major difference is that the DV doesn't tell you how much weight to use; it just gives you the acceleration number and the angle. But once you've added a bit of known weight & re-run the balance test, it's not that hard to zero in on the correct weight.

I've never added weight to the outside of the spinner to do my initial balance. I just go straight to longer spinner attach screws and add any weight to those, inside the backplate nutplates. Regular nyloc nutplates have worked just fine for me. I've had one or two where I had to make a weight, due to a badly out of balance situation (prop, badly cut spinner, etc). I've also split weights between two screw locations, as mentioned earlier.

On using the ignition as the trigger: Seems iffy with mags, and a nightmare if you have any kind of variable advance ignition. The optical trigger will fire at exactly the same point every time, and you can duplicate that point by simply moving the prop until the LED lights.

Nosewheel, etc: The prop does bounce the plane around quite a bit (I've done both nose & taildraggers), and it does seem to have some effect on the DV's ability to give a stable reading. I wonder if that's why DV tells us to run 3 sequences before adding weight.

Weight location: I wonder if the whole 337 thing is driven by drilling extra holes in the spinner backplate (that *is* a bit of a mod, especially on a TC'd plane). As a FWIW, I know of at least one local RV that has the balance weights from a DV balance job mounted on the flywheel, using the existing holes. Obviously takes a bit more weight because they're on a smaller radius, but it seemed to work just fine on that plane.

Charlie

[rvbuilder2002]

Originally Posted by rv7charlie

For Scott: I've never used any of the smarter balancers, but it sounds as if the major difference is that the DV doesn't tell you how much weight to use; it just gives you the acceleration number and the angle. But once you've added a bit of known weight & re-run the balance test, it's not that hard to zero in on the correct weight.

Dynavibe has a more expensive model that does weight calcs for you.

[rv7charlie]

Good to know, but when we bought ours, there was only one model.

[DonFromTX]

Here is a link to my friends builder log, he and I are both trying to learn all about prop balance stuff. Any suggestions would be appreciated.
http://torstensrv-12.blogspot.com/

[waterboy2110]

Originally Posted by DonFromTX

Here is a link to my friends builder log, he and I are both trying to learn all about prop balance stuff. Any suggestions would be appreciated.
http://torstensrv-12.blogspot.com/

Download the manuals from DynaVib and ACES. Get a copy of the AC and ACES guide referenced in both manuals. The ACES system is more advanced for what looks like an extra hundred bucks and walks you through each step.

[philrisl]

I have owned a Dyna-Vibe Classic, an ACES Probalancer Sport and currently an ACES Probalancer. The Classic is accurate but does not do solutions. The other two do solutions which generally reduces the number of runs needed. As a rule a solutions balancer requires three runs. One initial run that tells where and how much weight. You can put a weight that is close to the indicated amt/location. As long as you accurately tell the balancer what was actually installed, the balancer will give an accurate amount after the second run. It will allow you to split the weights in two location and calculate the amount. The third run just verifies the final result. The biggest difference in the Probalancer over the Sport is the time of the run to get a reading. The Pro is much shorter time.
Hope this is understandable.

[jask]

[quote=philrisl;1230467]I have owned a Dyna-Vibe Classic, an ACES Probalancer Sport and currently an ACES Probalancer. The Classic is accurate but does not do solutions. The other two do solutions which generally reduces the number of runs needed. As a rule a solutions balancer requires three runs. One initial run that tells where and how much weight. You can put a weight that is close to the indicated amt/location. As long as you accurately tell the balancer what was actually installed, the balancer will give an accurate amount after the second run. It will allow you to split the weights in two location and calculate the amount. The third run just verifies the final result. The biggest difference in the Probalancer over the Sport is the time of the run to get a reading. The Pro is much shorter time.
Hope this is understandable.[/QUOT

I do agree that the Aces pro sport is probably the best information for the dollar spent. The Dynavibe just makes you do the calculations. For the initial weight used, just use the standard formula ((HP/10) +30) * ips. That is the correct weight in grams to be used if the weight is attached at the same distance from the center of the crankshaft as the piezo layer of the accelerometer is from the center of the crankshaft. If it is not the same, use an inverse ratio to modify the weight. Weight =( Calculated weight * Accelerometer dist) / attached weight distance.

You can also manually split weights using vector addition.