Balancing a Whirlwind Prop
Thought I would follow up on my efforts to balance my 75" Whirlwind after P.Johnson reminded me that it's better to have the tape on the prop than the backing plate. I had come to that conclusion and had moved my DynaVibe reflective tape from my spinner backing plate to my blade but never followed up on my build log. Here are the takeaways from my balancing experience.
My first issue was that my results weren't repeatable. I would run up my prop with no weights and get a set of numbers for vibration. Then I would do the exact same thing 10 minutes later and get different numbers. As in not even in the same Zip code kind of different numbers. Thought it might be the backing plate flexing some so modified my mount for the tach so that it was now higher up, moved my reflective tape from the back plate to the blade and the numbers became relatively repeatable. The second thing I ran into was getting a set of numbers that said to put a half ounce weight at a position, running the engine again and the next set of numbers said to put another half ounce at another position around 120 degrees from the first. Run it a third time and get a whole new position for another half ounce that was within around 45 degrees of the first position. Was literally chasing my tail here. Sent DynaVibe my datasheet from my runs and asked for some help on what they thought might be the issue. To get the weight size, I was using the numbers in the instructions that said it took around 50gr for every ips. The DynaVibe guys (who were really helpful and got back to me right away with questions and suggestions) said that it looked to them like my prop was "very light" and that the 50gr number was a starting point for any number of different props. That the 50g number was probably a bit too heavy for the lighter, carbon fiber blades. I should try determining weight size using 30gr/ips. That was the ticket. Pulled all the aforementioned weights and started over. Was balanced to .02ips in three runs using a quarter oz weight and an eighth oz weight and was able to repeat the results a couple times over a couple days.
Hope this helps someone reading the instructions and thinking they are chasing their tails. Pics are of my modified install for the sensors.
Gary
DynaVibe Mod 1.JPGDynaVibe Mod 2.JPG
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Originally Posted by Delta Whisky
