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General RC Heli Discussion Discuss general topics on rotary wing aircraft, including construction, Servo's, Gryo's and Stabilizer discussions. Heli Pro Shop

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Old 05-06-2006, 10:05 PM   #1
Gene Reimer
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I am new in flying helis, just purchased a Century Hawk Pro with a OS37 for the engine. I have training gear on it. When I increase power/pitch and the unit nicely lifts off the ground and then with in a coulpe of second the complete unit starts to shack. Any ideas what could be the problem? Could it be the training gear?

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Old 05-06-2006, 10:12 PM   #2
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Hi Gene,

The traning gear can cause a resonance at certian rpm's. Do you know anyone with a tach who can measure the head speed for you?

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Old 05-07-2006, 07:35 AM   #3
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As Colin infers, the excitation frequency generated by your rotor head is corresponding with the natural frequency of your training gear at the speed you are running the head. Training gear is often an issue because it is constructed on long cantilevered sticks whose natural frequency will be quite low and whose vibration is almost completely undamped. Here are just a few choices for altering the dynamics to reduce the vibration problem:

- change head speed higher or lower to avoid exciting the training gear resonant frequency

- change the stiffness of the connection between the heli main frame and the landing gear/training gear to change the training gear resonant frequency

- change length of the training gear sticks, the masses at the ends of the training gear sticks, or the diameter of the training gear sticks to change the training gear resonant frequency

- add damping to the system to reduce the amplitude at resonance (more difficult!)

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