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BAD VIBRATIONS from OS 120

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Old 07-02-2007, 06:21 AM
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BINGO4
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Default BAD VIBRATIONS from OS 120

Sure hope someone can help. I have an OS120 in an ARF I just finished putting together. (Goldenskies Rc Crossfire) When I started the motor everything seemed fine untill I slowed the motor to idle the whole plane started to shake something awfull. I change the prop (yes it is balanced) and changed the spinner but there is know change with the vibration when you speed up the motor everything seems ok. I had this motor an another plane with out any problems. What could be wrong.
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Old 07-02-2007, 06:32 AM
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Don M.
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Default RE: BAD VIBRATIONS from OS 120

Do you have the wings on ? Sounds like the low end maybe rich ? A very flexible mount ? Trying to idle it too low ?
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Old 07-02-2007, 08:52 AM
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Default RE: BAD VIBRATIONS from OS 120

Bingo, it could be a case of your Crossfire having a resonant frequency that matches the rpm of the 1.20 at your chosen idle speed (sympathetic vibration). This would explain why there was no problem with this engine in the other plane. Maybe you could bump up the idle speed a bit to escape this frequency.
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Old 07-02-2007, 11:30 AM
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Default RE: BAD VIBRATIONS from OS 120

Or beef up the model. Many times, modern aircraft have structures that are not really meant for high-power engines. Is the model intended for a 1.20-size four-stroke engine? If you've put an engine larger than recommended, then it's not the engine's fault, nor the airplane's.
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