I was re-reading the Sky Ranch Engineering Manual looking up
the gyro loads from a prop to calculate the gyro loads
on Tracy's psru plate and I found  this quote on page
390.

"You CANNOT dynamically balance second order vibrations
since they are caused by reciprocating and not rotating
masses."    Period no if ands or buts!!!!!

Take that Vance :-)

Great book and I highly recommend it for every one. Great chapter
on motor mounts and how to design them for low vibration transmissibility.
The author agrees with me on this subject :-)

The book is a huge bargain at about $25. (916) 421 7672
Sacramento Calif. in case they have changed the area code.
 
Paul Lamar
 
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