[Dean Pichon]

On Friday, I taxied my -4 to the local FBO to have a long overdue prop balance (my first). We instrumented the engine, replaced the cowl, and tied down the tail (really tight).

I ran the engine to 2300rpm and held it there for 20-30 seconds. The Dyna Vibe showed 0.06ips. The mechanic could see no reason to try to improve this. I believe I read some posts indicating that improvements on values below 0.1ips would not likely be noticeable. We removed the transducer, replaced the cowl and I flew my "new balanced" propeller.

I can't decide whether I am happy my propeller has been reasonably well balanced all along and just didn't appreciate my good fortune, or I am disapointed that I did not get to "feel" the big improvements so many have described.

Regards,

 

[N91CZ]

How low is good enough

Dean,
While it is certainly possible to get lower with the Dynavibe (I typically get down to .02 in just a few iterations), your mechanic is probably correct. The vibration you feel contains many more contributors than just the prop.
I did a vibration survey a while back with an accelerometer on a structural member in the center of the plane. 1/2 order and 2nd order contributions far outweighed the prop. The propeller contribution was actually visible in the data 0.015 ips at the prop frequency. The Dynavibe was right on saying 0.02. The magnitude of the 1/2 and 2nd order contributions greatly overshadow the prop. Take a look at slide 13, vel vs. freq.
Prop is 0.015.
1/2 order is 0.165
http://www.n91cz.net/Vibration/Vibration_Summary.pdf