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Old 06-12-2018, 12:34 PM   #1 (permalink)
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Just got a set of RT690 blades and got to fly them over the weekend. After the flight when I land a the heli spools down, it shakes violently. I tried tightening blade grips and loosening them too, still does it. They fly fine in the air just shake on spool down.

Wondering if anybody else has had a issue or is it just my set?

Thanks, Jeff
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Old 06-12-2018, 08:53 PM   #2 (permalink)
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What heli?
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Old 06-13-2018, 10:16 AM   #3 (permalink)
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I did not say, because I do not think that it matters. The heli does not exhibit this behavior with other blades, just this set of Rotor Techs.
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Old 06-13-2018, 11:41 AM   #4 (permalink)
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Things to check. Static balance, dynamic balance, unequal grip tightness, and defects in the surface of the blade grip where it contacts the blade. If you use spacers, use a brand new set that has no surface blemishing, as that can grab a blade, or the grip, in the spooling up and down of a blade. You didn't mention the surface you were taking off from as that can have an impact if some of the above mentioned items are not within balance or equal tension. Hope this helps.

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Old 06-14-2018, 12:57 PM   #5 (permalink)
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I suggest that you put your previous blades back on and see if the dance goes away.
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Old 06-14-2018, 10:07 PM   #6 (permalink)
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Quote:
Originally Posted by kineticheli View Post
Just got a set of RT690 blades and got to fly them over the weekend. After the flight when I land a the heli spools down, it shakes violently. I tried tightening blade grips and loosening them too, still does it. They fly fine in the air just shake on spool down.

Wondering if anybody else has had a issue or is it just my set?

Thanks, Jeff
Quote:
Originally Posted by kineticheli View Post
I did not say, because I do not think that it matters. The heli does not exhibit this behavior with other blades, just this set of Rotor Techs.
It's about the whole heli not just the blades. Have you measured the blades' weight and test balanced them as well as check and compare CG of each?

I've had this experience before and it was due to resonance on the heli not the blades.
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Old 06-18-2018, 10:57 AM   #7 (permalink)
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Thanks for all the suggestions and help, but I wasn't looking to fix the problem. I was asking if any others have had issues with the Rotor Tech blades. Again, the heli flies great in the air, the shake is only on spool down. I did reduce by loosening the blades grips, but it is still there. I finlly just put a different set of blades on the heli and no issues at all.
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Old 06-23-2018, 03:34 PM   #8 (permalink)
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Some blades have an aggressive chord-wise CG where others don't. Blades with a chord-wise CG more towards the trailing edge will "cant" somewhat ahead of the blade hinge bolt. These blades can cause exaggerated ground resonance on spool down if you throw in too much negative pitch.
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Old 06-26-2018, 08:27 PM   #9 (permalink)
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I have flown many and various RT blades over the years and only had that issue once on a Century Swift heli. Tried some other blades and found it did the same. It proved to be an airframe / ground resonance that was cured by spreading the landing gear struts out another 2 cm.
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