Dynamic Prop Balance

I rented a Dynavibe Classic from Viking Aircraft Engines for $200. With a few Kitplanes Articles (Propeller Balancing & Good Vibes) and some video help – it looked like something I could handle myself. My buddy Alan also needed to do his RV-4, so we made it a team effort. The process is actually dirt simple. The system is three components. First, you have the optical sensor that is used to track the propeller RPM through a reflective sticker on one of the prop blades. There are some constraints here regarding hub distance vs RPM vs sticker size. But again, read the chart and you’re good to go. The second component is an accelerometer. This device will measure the vibration produced. And lastly you have the control unit that allows you to get the outputs of your testing. Both the optical sensor and accelerometer bold directly to the engine. Make sure the optical sensor has a good line of sight to the master blade (the one with the sticker), and make sure the accelerometer is positioned perpendicular to the plane of travel for the cylinders (straight up and down works well for our horizontally opposed Lycomings) and as far forward as possible. Now decide on your target RPM. Your best options are cruise or take off RPMs. I chose to balance at 2500 RPM. Now run up your plane, average out the values, and see where you are at.

Run one for me showed a value of 0.21 IPS at 352°, which as starting points go, is pretty good! Now, here is the only thing that you have to keep straight in your head. First, the degrees given is where the HEAVY side is. In other words, to balance the system you need to add 180° from the value given. Second. The degrees stated are from the master prop (one with the sticker) IN THE DIRECTION OF TRAVEL. If you remember DIRECTION OF TRAVEL – its easy to remember what way you are looking both from the back or the front of the prop!

Adding weight with the standard Lycoming flywheel is easy. There are a number of holes all the way around, that enable the easy addition of weight. It took a couple more runs to fine tune. The second run gave a value of 0.16 IPS @ 121°. Basically we had a little too much weight, and were slightly off on the location. Run three, we moved that bolt one location over in the direction of the light side and got a value of 0.07 IPS @ 92°. Now we just removed a little weight and the final run gave a value of 0.01 IPS @ 146°. Anything under 0.07 is considered excellent, and 0.01 is awesome! Very happy with the results.

My buddy Curtis stopped by the hangar as we finished doing the balance to tell us “Oh, I have a DynaVibe classic you could have used for free!” Thanks Curtis for the timely announcement! 😀

We also balanced the wooden fixed pitch prop on Alan’s RV-4. As we had already done my prop, we were quite quick in doing his. His values started out at 0.61 IPS 29°.  After 3 runs, and three bolts, we arrived at a 0.05 IPS @ 216 degrees. I was not able to notice a difference between my 0.21 and 0.01 – but unlike Alan I am not yet attuned to the vibrations and sounds of my engine. I speculated that Alan would be able to feel a difference between 0.61 and 0.05. Sure enough he said on the taxi back to his hangar he could notice a definite reduction in vibration. I’m curious to hear his flight observations!

About Peter

plbarrett.com | Certified Flight Instructor (Single & Multi-Engine, Instrument, and Advanced Ground) | Commercial Helicopter

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