Your local prop shop is bothered because a traditional dynamic balance is dynamically balancing the propeller and crankshaft of the engine as a complete assembly.
They are correct in their thinking that that is not possible on a Rotax 912 because the relationship of the propeller to the engine crank shaft is always changing.
It can still be very beneficial though as has been proven 1000's of times.
The main reason is likely the same as comparing a simple bubble balance of a car wheel/tire to the result attained by spin balancing at high normal operating speed.
The main difference in the procedure is that they need to compensate the test settings on the equipment to reference the propeller RPM, not the engine RPM (what you see on the tach.).
I usually set 2000, because that is about the most you will see for static RPM running on the ground.
Any opinions expressed in this message are my own and not necessarily those of my employer.
RV-6A (aka "Junkyard Special ")
Last edited by rvbuilder2002 : 06-04-2018 at 08:58 AM.