Propeller vibration and adjustments

[SHIPCHIEF]

I've been experiencing a-lot of engine/propeller vibration on my Yak-55m since I bought it. I've added a 15 inch strip of electrical tape to the blade I thought would be the lightest, no apparent change. I've tracked the blades, not great, about 3/16". Not bad either. The counterweights of the V-530 (original) propeller seem to be on correctly. The blades have been rebuilt by Whirl Wind propeller, with nickel leading edges and fiberglass covering.
I recently gained access to a DynaVibe propeller balancer, and built a frame to mount the transducer and the optical pickup to the engine gear case.
I had placed the tape on the heavy blade! After many test runs, involving me running the engine and recording data from the balance computer, then cooling and shutting down the engine, then sliding off the back of the wing and adding another 15" piece of electrician's tape to Blade #2, then climbing back up the front of the wing to enter the cockpit and starting the test again....I achieved a somewhat satisfactory balance with 7 each, 15 inch pieces of electrician's tape on blade #2 near the 80% span.
Upon closer inspection, I realized that some previous person had painted the back of the #1 propeller blade, the paint was much thicker than the #2 blade. I borrowed the neighbor's electric palm sander and got to work sanding off this thick black paint.
Test runs were then made while removing strips of tape from the #2 bade, with 3 pieces remaining being about best.
after the test with all tape removed, I sanded the fresh Yak oil off both blades, and lightly primed and painted the heavy blade, then heavily primed and painted the light blade. We'll see how it balances out tomorrow...

[SHIPCHIEF]

This morning, I made sure the paint was dry on the propeller blades, then pushed the Yak outside, chained it to my tractor and started it up!
The vibrations were worse than before, but the DynaVibe indicated the other blade to be heavy. I had sprayed on too much paint! Out comes the sandpaper! After many sessions of sanding and testing, I got a reasonable reading of .15 ips @ 272 degrees, blade 1 being 0/360 degrees and blade 2 being 180 degrees. The readings went from about 190 to 215 degrees to 272 degrees as the vibration reduced from each sanding session, I figure 270 degrees for the heavy spot (half way between blades) is about as good as I can get. If I had a spinner, I could add weight to the back plate at the 90 degree position to gain that final bit of smoothness.
The original vibration was 1.15 ips @ 349 degrees, 1285 propeller RPM 1952 engine RPM. This is about 65% RPM, used for long range cruising.
Final vibration reading was .15 ips @ 272 degree, 1282 propeller RPM, (.658:1 reduction gear ratio)
vibration is now 13% of previous, or you could say it was 7.66 times worse before balancing.
I did test twice at 1470 prop RPM, 2234 engine RPM with similar vibration readings. this is 75% RPM, a higher power cruise setting. I flew the Ephrata contest at 2500, = 85% RPM, Max engine RPM is 2950.

[SHIPCHIEF]

This is the Dyna Vibe unit

monoplaneforum.jpg (116.68 KiB)

reading my first test after painting the back of the propeller blades. I had sprayed too much paint on the light blade, and had to sand most of it off.

[SHIPCHIEF]

I have flown the Yak 4 or 5 times sense the prop balance, all were those acro practice sessions, and all were quite acceptable concerning vibration.
A side note, I'm getting pretty good at landing this thing, but landings in the RV-8 I Built are suffering....