| Prior to my trip back to Calgary I wanted to get rid of a nasty vibration. My last A&P actually made the balance worse and now that I see the results I think it was 180 degrees out of phase. At 2300 rpm I had a nasty shake.
At Oshkosh I bought the simple Dynavibe unit from Spruce on sale. Short story is I wasted a day misreading the procedure. In essence, you measure "in the direction of prop direction" and I was moving the prop in that direction to get the balance position. However, once that was understood, I was able to get my prop dialed in from 0.63 to 0.03 in fast order. It would not be hard to go further with a miniature weight change but I wanted to fly.
These are photos of the setup. If you ever decide to do this, it is easy on the Legacy. You can mount everything on the inside of the cowl which allows the runs to be made with cowls on. It also means leaving all the cables in place when changing weights. I used temporary weights on the spinner exterior to narrow things down form 0.63 to 0.16 which took 4 large washers and about 16g net added weight on the spinner. At that point, it only took two small washers (the type that are used to fasten the spinner) to bring it down to 0.03. The final changes are very very sensitive. By moving the last weights from one spinner screw to another you can easily home in on the exact spot for final weight.
That final weight was permanently installed on the spinner back and the final weight was adjusted for the gram-inches between the final radius and the temporary spinner radius. It worked out darn close. The Dynavibe is not a feature rich machine but it does work well. I had no problems. You must guess at the initial test weights but it only takes a few quick runs to dial things in. It provides IPS at X degrees. Simple. I made some brackets with spare parts sitting in the hangar. I taped the cables to the airframe using 3M blue painter tape which held during runup but pulled off clean. I coiled the wires on top of the cowl so I could remove the cowl without disconnecting all the cables each time. Big time saver. When my final weight was installed on the spinner back plate I did a final run to verify the results and then removed all the gear.
The resulting 2000 miles back to Calgary was a big improvement. Whereas I could not really cruise at 2300 before, it was now quite smooth. I would recommend the procedure to anyone who wants to check out their balance or verify an existing balance weight or remove a vibration. I would note that the weights installed by Hartzell on the hub underneath the spinner are NOT changed or tampered with.
You can play the slideshow here
Paul Legacy Calgary |