mdnanwelch7(at)hotmail.co
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 Posted: Thu Apr 09, 2009 4:19 am Post subject: Eliminating harmonics |
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Ted C
I have a couple of suggestions to try out C if you haven't already tried these.
First C get a few lengths of plastic tubing C and tape the ends securely near where you think harmonics are coming from C like the exhaust tip C near the prop hub C the motor mounts C etc. Place the other end inside the cabin C so you can listen to each one during a test.
Whatever it is that is generating the harmonic vibration C it will be loudest at the source.
Once you have the tubes secured C do a run up to the worst harmonic level C and listen to each hose. Usually (!) C the noise source is much louder in one hose. Just a thought.....
Next C to help identify the source C change something (very slight). If you think the prop is likely the culprit C try taping the entire leading edge of each blade with duct tape. It'll only be on for a few seconds C so I don't think it should hurt a thing!!
With three exact lengths of duct tape C place them on the leading edge of the blades C splitting the middle of the tape down the sharp edge of the blade. Do a worst case harmonic run-up C and see if things change (harmonics are better or worse). It's a good chance that the duct tape will change the prop blades enough to alter their effect at creating a harmonic resonance. The tape will change the blade's profile C balance (very slight!!) C and performance.
A quick run-up should give you an idea about whether or not the blades are the cause. Remove the tape.
Mike Welch
MkIII
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