View Full Version : causes of vibration?

09-11-2010, 05:21 PM
I have a hawk sport that I just put a brand new os 37 in today and flew for the first time. It fired right up but I see the heli has a lot of vibration. Is there a checklist I can run through to check the causes? any suggestions on where to start?

09-12-2010, 03:07 PM
this is just some of them ....


There are only a few systems that can cause a "low speed" shake. (5 - 30Hz) Low speed shakes are the most scarey kind because the thing looks like it might explode or resembles a paint shaker.

Nonbalanced rotorblades
Nontracked rotorblades
Blade grips that are not exactly spaced from the head the same, or have slop in them alowing the blade grips to shift laterally more than .5mm.
A flybar who's paddles are not exactly the same distance out from the center when the paddles are screwed in the same number of turns.
A bent flybar or spindle.
A bent main shaft. Unfortunately the only way to tell if it's bent is to remove it and roll it on glass.
A damaged head.
Excesive slop in the mixing arms possibly.
A set of blades that don't have matched CGs (debatable) Matching the CG is different than just balancing.
Warn out rubber dampeners.
Training gear can amplify a otherwise harmles imbalance into a scarey violent shake. You can usually cure this by running a different head speed and or changing the length of the training gear and how securely or loosely they're fastened to the landing struts.

There are also only a limited number of things that can cause a "high freq shake." (100-300 Hz) High frequency vibrations are most evident by a hum sound comming from the canopy, blurred stabelizer fins, and or foamy fuel in the main tank.

Engine vibrations or bent crank shaft.
Damaged or unbalanced clutch or clutch bell.
Cooling fan not balanced.
Bent start shaft.
Resonating tail drive shaft.
Tail blades unbalanced or not tracking.
Tail mast or hub bent.
Damaged pinions or gears.