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JohnInReno 01-19-2020 04:23 PM

Need help with Dynavibe
I have access to a Dynavibe but I can't figure out how much weight to use. So far, it has gone from .32 IPS at 042 degrees to .16 IPS at 126 degrees but I seem to be chasing it with trial and error.

The engine is an IO-320 with a newly overauled whirlwind CS and was previously balanced with weights on the ring gear.

All I can find in the manual is, "A good starting poin is 0.50 grams / IPS."

Is there a spreadsheet to help?


jask 01-19-2020 05:06 PM

Check messages

JDA_BTR 01-19-2020 05:07 PM

The best way is to create a vector diagram and solve to bring the solution to zero.

Download the polar chart:

I'm looking for the paper that describes how to use it.

JDA_BTR 01-19-2020 05:15 PM

The paper that shows the vector math is:

The whole thing is interesting; but the applicable part of computation starts on page 10 with "Single Plane Balancing". It describes the vector math in detail.

You can make a vector plot with MATLAB or a perl script or an excel spreadsheet to solve it, but the paper plot may be easiest overall.

Aviaman 01-19-2020 05:16 PM

Need help with Dynavibe
I recently balanced my Cato prop with Dynavibe. I think you want to make the measurements at your normal cruise rpm. Like you, my measurements varied with rpm, both phase and and IPS. Use the phase reading at cruise rpm, and attach a weight, normally 180 from that angle, referenced to normal clockwise rotation of the prop, as seen from the cabin. Come as close as you can with the ring gear holes. Then experiment with other weight values. Does the first weight change improve things or get worse? If worse, go in the opposite direction (opposite weight change). It would be a lot of work, but you could straddle a phase angle with 2 nearest flywheel holes, and use differing weights to effectively give an intermediate weighted phase angle.

Running up to cruise rpm while on the ground without the cowl on will cause the CHTs to rise rapidly. Especially if you are using the averaging feature of Dynavibe which prolongs the run. If you can, it would be desirable to have a baffle of some kind that directs air downward through the cylinders. I had to let mine cool a while between runs, and shut down at 330 degrees max.
Maybe you can mount your sensors with the cowl on, a much better arrangement.

JDA_BTR 01-19-2020 05:21 PM

If you tell me what mass and location got you from the first reading to the second I'll run the math for you with a theoretical solution. Getting to less than 0.1 is doable with the math. Better than that is tough and a little trial/error.

If your prop has ever been dressed for nicks then a fine balance may not be possible. One plane on our field could not be better than 0.2 from this.

My IO390 driven RV14 is at 0.03 repeatably. Awesome to have the stick not vibrate at all.

Planecrazy232 01-19-2020 06:51 PM

What if your fixed pitch prop will only go to 2150rpm static and your cruise is 2450?

az_gila 01-19-2020 11:10 PM


Originally Posted by Planecrazy232 (Post 1401491)
What if your fixed pitch prop will only go to 2150rpm static and your cruise is 2450?

Then you are stuck with a reading at 2150 rpm.

A fact of life for FP props. :)

Bicyclops 01-20-2020 09:59 AM


Originally Posted by az_gila (Post 1401538)
Then you are stuck with a reading at 2150 rpm.

A fact of life for FP props. :)

Or figure a way to take the reading in flight.

Ed Holyoke

Aviaman 01-20-2020 12:16 PM

Need help with Dynavibe
I read the math article and more or less understand it. However it is confusing regarding some symbols which are sometimes not defined. Also it appears some inconsistencies exist where they divide mass, which is a scalar, by a vector, which makes no sense. Yes, you can divide a scalar by the magnitude of a vector, but not by a vector itself. Maybe they forgot to put the vector inside the vertical brackets to indicate magnitude. Or am I missing something? Item 6 on page 11 is one example, where the M’s seem to be mass (scalars) being divided by vectors without the magnitude brackets.

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