Day 1 - I decided to have the prop dynamically balanced the other day because I've heard from many it's a good thing to do. I was at the shop when it was being done and in fact I was controlling the RPM in the cockpit for the initial testing on day 1.
We measured the prop in "inches per second" or IPS across three different RPM ranges -- 2300, 2400, and 2500. My prop came in at an astonishing 2.5 IPS! Somewhere in the .4 IPS range is considered acceptable and typically after a dynamic balance it is much lower. The A&P figured there may be a problem with his sensor so he replaced it with another calibrated unit. There was no difference.
We proceeded to pull the spinner and he found that one of the blades had 138 grams of weight associated with it. Off the cuff he said he'd never seen that much weight added like that. Given this, he recommended that I have it static balanced by his shop. So they pulled it yesterday and today he ended up with over half of the weight removed from that blade for the new static balance! When he moved to dynamically balance it registered .50 IPS (remember what it was initially @ 2.5 IPS). Once he was finished with the balance it came in at .04 IPS.
This was my first experience with any of this and I must say the plane certainly didn't vibrate like one would think from a 2.5 IPS movement in the propeller. Three different highly competent pilots have flown in her and none of them noticed any crazy vibrations.
Day 3 - So I picked her up yesterday...The dynamic propeller balancing on my Comanche is astonishing. I cannot believe how smooth everything it is now. As reported earlier, there was no discernible vibration to speak of. It's like a sewing machine now
I obviously didn't know what I was missing before.As a result of the dynamic balance:
1. I actually have zero static weight (sorry, you'll have to look at the picture as I don't know the technical name of this location): http://1drv.ms/1ksDxc7
2. Instead, I have 26 grams of weight (dynamic) added to the inside of the propeller hub (where the nose cone mounts to).
The conclusion I've drawn is while it's possible to balance a propeller off of the plane (static) it's really the combination of the propeller and the engine that you want balanced together. Originally, neither of my balances were correct -the static nor the dynamic but yet nothing seemed out of the ordinary as the owner/operator.
One final thing I will add. In flying her back from Lancaster, PA to the Washington DC area/SFRA she seemed faster. I had to keep her slowed down due turbulence and down low due to Class B and VFR flight. I soon will wring her out and report one way or another on this.
What experiences do you all have with your props both statically and dynamically balancing props? Have you ever heard of such a wild initial results like mine?
All the best,
Pat Arnold
