Jim Fackler came out to hangar Tango-4 at El Monte airport to perform a dynamic prop balance on the Cherokee 140. Most props are balanced off of the airplane and that's just fine and dandy. But if you perform a dynamic balance with the prop on the airplane and spinning, you can balance it to include all the rotating parts.
Jim hooked his sensors up to N6794J and then attached his Vibrex 2000. He had Ron run the engine up (I think it was 1000 rpm, then 1500 rpm, then 2000 rpm) and then analyzed the results.
He added a small weight to the outside of the spinner (temporarily) and then ran the engine again. The computer told him what needed to be done, and then he added some more weight in another area. When he was done, the balance was within 0.02!
Jim then took the spinner off the prop to mount the weights on the inside...only to discover that the prop's bulkhead (backing plate, some call it...or dam, others call it) was cracked! Rats! Now the airplane is grounded until we can get another one. Several attempts ended with the part being shipped from the east coast, arrival in 3 days (since we paid the extra 50 bucks).
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