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Dynamic prop balancing

 
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pilot623(at)gmail.com
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PostPosted: Tue Jan 24, 2017 3:38 pm    Post subject: Dynamic prop balancing Reply with quote

I have always wanted to dynamically balance my props but never even static balanced them. I mentioned on this list that I’d like to see prop balancing discussed at our next Lawrence fly-in and a gracious and trusting reader offered to loan me his DynaVibe balancing system. The system requires mounting an accelerometer in vertical orientation near the front of the engine and an optical sensor pointing at the back of the prop or backplate, registering each pass of a reflective tape.

During my fire rebuild in 2009, I changed from an Ivo 3-blade inflight adjustable prop to an Airmaster 3-blade constant speed prop. The Airmaster came static balanced, evidenced by an AN3-4A bolt, area washer & AN365-1032A nut (9.5 grams <42.75 gram inches>) in the 240 position. The Airmaster backplate came with 3/16” holes drilled every 30 at 4.5” from center. I referenced the hole directly behind blade #1 as 0 and measured increasing degrees in the same direction as prop rotation.

The DynaVibe instructions suggested not changing any static balance weights. I ran the engine in the initial (static balanced) configuration at around 1840 rpm prop speed (~4,500 rpm engine speed) and registered the magnitude of vibration as 0.26 IPS (inches per second) at 196. According to what I’ve read, anything above 0.25 IPS is considered rough, down to 0.15 IPS is fair, 0.07 is good and 0.04 is excellent. The identified degrees is the heavy point. Since I didn’t want to remove weight (grind away metal) at the heavy point, I added weight 180 opposite the heavy point. Only having holes every 30, I chose to add 10 grams <45 gram inches> (AN3-4A bolt, area washer, #10 thin washer and nut) at 30.

Running in this configuration produced 0.06 IPS at 82. I added 1 gram (#10 thick washer) to the original static balance location (240), bringing the total mass balance at that location to 47.25 gram inches and ran the engine again, registering 0.02 IPS at 54. It was a windy day so I’ll verify the final reading in calmer conditions but I think that’s where it will stay.

I believe the DynaVibe balancing unit will be at Lawrence so maybe we can demonstrate the process on someone’s plane and remove a few vibes in the process.

Jim
N623JF


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