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04-03-2012 03:08 PM  9 years ago
Topic Vote0Post 1
helibeli

rrApprentice

wales.uk

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ground resonance
What would be the best method of proving/disproving that your undercarriage were causing ground resonance?
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04-03-2012 03:24 PM  9 years ago
Richardmid1

rrProfessor

Leeds, England

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Put some skid rubbers on that usually reduces it. Or take off/land on grass.

Are you seeing this on a FBL heli or FB?
60% of the time, it works every time!
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04-03-2012 03:50 PM  9 years ago
GetToDaChopper

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Las Vegas , NV

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for starters if whatever your not telling us about only happens when your heli is on the ground, put one check in the "ground resonance" "pro and con" "pro" column OR if it doesn't only happen on the ground put one check in the "con" column and that would be a good way to start, then proceed from there......

P.S. my god not another ground resonance thread, they always go soooo well.......
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04-03-2012 04:08 PM  9 years ago
helibeli

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wales.uk

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The heli has a flybar is 12Kg in weight,starts shaking as it gets light on skids and have to throttle down from that point before it self destructs.Does it on grass or a pile of old carpets.Head is balanced perfectly.I'm clean out of ideas.
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04-03-2012 04:17 PM  9 years ago
Heli 770

rrProfessor

USA.

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Are your Main Shaft bearings good?
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04-03-2012 04:25 PM  9 years ago
Richardmid1

rrProfessor

Leeds, England

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Are you sure the head is balanced? Flybar is balanced? Feathering shaft isn't bent? Blades not too tight?

Try getting to a higher or lower rpm before the skids go light.
60% of the time, it works every time!
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04-03-2012 04:30 PM  9 years ago
RaptorRob

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hamlin P.A.

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Not enough headspeed possibly, and check how tight your blade grips are... they shoud be just tight enough that you can turn the heli on its side and they just about dont flop and check to make sure by hand that they lead and lag smoothly (no tight spots)

make sure your blades are in track too you can spool up at zero pitch get on the ground (at a safe distance) and see
no babe i swear i sold my other heli to buy this one :)
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04-03-2012 05:03 PM  9 years ago
GMPheli

rrElite Veteran

W. Bridgewater, MA USA

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"Try getting to a higher or lower rpm before the skids go light."

+1

Ground resonance is caused by the frequency of the slightly imbalanced rotor head, matching the resonant frequency of the airframe/undercarriage/surface it is sitting on. If you change the headspeed that it is at when the resonance begins, you should be ok
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04-03-2012 05:43 PM  9 years ago
Gyronut

rrProfessor

Martinsville In.

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I've been in full scales a few times when thtere has been some resonance and its just a matter of powering through it quickly.

Same thing applies to our models.
Rick
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04-04-2012 12:44 AM  9 years ago
helibeli

rrApprentice

wales.uk

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Without main blades fitted i've taken the rpm to 1800 and it's perfectly smooth.New main shaft fitted,feathering shaft, different dampers, new rotor hub,bearings checked bought new 810 mah blades to check.Nothing has worked and i'm now clueless what to do.I've also tried 0 degree pitch all the way to check.The critical rpm seems to be 950rpm when the skids start jumping up and down rapidly.Up to 950 rpm it's smooth.
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04-04-2012 01:37 AM  9 years ago
Kaborkian

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Lafayette, LA USA

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Add a set of struts across the skids to stiffen them up and try again. Even something as simple as heavy rubber bands could be enough to help. Need to change the stiffness significantly and go from there.
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04-04-2012 01:41 PM  9 years ago
CX1

rrKey Veteran

Canada

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you could try balancing the head on a high point balancer,I'd bet it's off." Team Protoast "
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04-04-2012 02:00 PM  9 years ago
nightstalker3D

rrNovice

DB-FLA

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P.S. my god not another ground resonance thread, they always go soooo well.......
+1
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