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Date: Fri, 17 Feb 2006 00:22:28 -0500
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From: bob mackey <n103md@yahoo.com>
Subject: Prop Balancing
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A friend of mine here in San Jose just 
got the equipment and training to do 
dynamic balancing of propellors & engines. 

My O-320 with wood prop has been a bit rougher
since I rebuilt it last year, so I had Kregg
take a look. After a few minutes to align the 
sensors, we ran the engine and found 0.9 in/sec
peak velocities at 2100 RPM. 

Following the procedures, we added bolts and
washers to the Lycoming flywheel. Conveniently
the lycoming has 1/4" holes spaced every 30 
degrees around the flywheel rim. After two tries, 
we had the vibration down to 0.03 in/sec. 

A thirty-fold improvement in vibration 
looks nice on the computer display, but
the proof is in the flying. I might have
to start tapping the gauges again to keep 
them accurate. The panel, the rudder pedals, 
the canopy all feel smoother. It's much quieter
in flight. Now I realize that the vibration 
was probably causing the canopy seal to 
bounce around, letting wind noise in. 

All that out-of-balance rotating mass
was also putting more force on the engine's
main bearings. I suspect the engine may last
longer when balanced. 

Kregg also mentioned that Don Barnes had
talked with him about getting a group rate
to do a bunch of Lancairs all on one day. 
I suppose the idea would be to have a small 
fly in and balance our props while we're there. 
I'm sure it will be announced here. 

For anyone in the Bay Area or northern California, 
you can reach Kregg at
   kvictory2000 (AT) yahoo (dot) com

-bob mackey
 Lancair 235 / O-320 


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