Dynamic Balance Question

[rcfaubion]

D-B last weekend with very noticeable improvement. We wound up adding about 80 grams of weight (a lot?) over three runs and and got very close to the "bullseye", this was done at my max static rpm of 2150. Is there a way to calculate or otherwise determine the change in balance at a cruise rpm of 2500-2600? Should a person "under shoot" the balance solution when static rpm is significantly less than cruise rpm, and if so by how much? I know there is no such thing as a stupid question but I may be pushing it!

Thanks

[Geico266]

What were the IPS readings before and after balancing?

I'm in the process of learning prop balancing, (I've only done two planes) but 80 grams sounds like a HUGE amount of weight. That is 2.8 OZs. A standard fender washer I use is 2 grams. When I balanced the -12 I only added 6 grams for final weight. When I balanced the RV-10 from .17 to .09 IPS I only used 9 grams. There was a weight already there, but I could not weight it.

To add that amount of weight you must have been way out of balance, and you should have the prop static balanced and start over. JMHO

[rcfaubion]

Larry, I agree with your thoughts and ending suggestion. That being said, what are your thoughts on balancing at a much lower static rpm (2150) than high cruise rpm (2500-2600), this is a fixed pitch wood-composite setup.

Thanks

[Geico266]

From what I've learned you should balance the prop at the RPM that you use that most in cruise, but if 2100 static is all you can get on the ground then that's all you can do, and the improvement should be very dramatic if he had to add 80 grams. Have you flown it yet?

For anyone who has not done this I highly recommend you get your airplane dynamically balanced ASAP. You will be amazed at how much vibration goes away. Less vibrations means more comfortable trips, less fatigue on the airframe and avionics, and less engine wear which equals longer TBO's.