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HelicopterVario Sky Fox - Benzin - Evolution - Xtreme › benzin bell 47G vibration..help
05-31-2004 03:15 PM  13 years agoPost 1
mycolic

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UK

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I have just flown my vario benzin bell 47 G yesterday. It has a hell of a vibration on it with the two fuel tanks mounted on the top of the side rames vibrating like hell. The side frames I have are the 1st generation airstar ccpm frames, not the standard benzins. Could these be causeing the problem??? Also what about head speeed??? The set up is the standard trainer blades/gear ratio powered by a 22cc Zenoah G2D with 214/10 ml shaft.

Any help guys????

Thanks

Geoff

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06-01-2004 12:24 AM  13 years agoPost 2
S76GUY

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UpState, NY

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Need more info.
What type of vib? High/low freq, tail fins head etc.
What head do you have?
And what head speed?
Also check your throttle curve
And your needle settings.
I had a side to side shake and it was my throttle cure.

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06-01-2004 12:42 AM  13 years agoPost 3
Notar

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Taxachussetts

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If you have the standard gear ratio from a benzin trainer,and the stock blades, that is your problem
Joe

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06-01-2004 06:18 AM  13 years agoPost 4
Gstjohn

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Shreveport, LA

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your problem is in the mounting of the fuel tanks to the frame and also the mixture of your engine. Not the gear train and blade issue I know this because our gasser 47 does the same thing Joe. what you have to do is find the happy medium between your headspeed and the engine rpm on the high side needle of the carb. we run our 47 at about 1380, 1400 rpm and the tanks shake at a very minor high frequency. the tanks are going to shake because they are plastic mounted solidly to a metal frame from the under side. don't worry too much about it our does the same thing. if you have any more questions about this just let me know I can help you out!

Greg "G-Dog" St. John, Team Lowerheli.com, Optipower USA, VP/ Powermaster fuels, BK Servos

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06-01-2004 11:06 PM  13 years agoPost 5
RLO1

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Chandler, AZ

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Running rich will induce vibration. Most motors are set at 1 1/8 to 1 1/4 turns open on the high needle.

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06-02-2004 08:42 AM  13 years agoPost 6
mycolic

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UK

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Guys,

thanks for all your help.....

Joe....by any chance would your solution have been to buy new gears and 810 719 blades?????


thanks

Geoff

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06-04-2004 05:33 AM  13 years agoPost 7
DStJohn

rrApprentice

Ft. Collins, CO

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It will help some

On my Bell 47 I have run all 3 gear ratios that Vario has (87-23, 85-21, 90-18) using the #419 scale blades. I have the same setup as you with the Airstar CCPM sideframes (vertical servos). I had to build 2 plates to move the sideframes out to clear the servos. I have always had a shake in the tanks. My tanks are mounted on rubber grommets and they still shake. Yes you can minimize it by going to the 90-18 ratio (use the heavy clutch with this gear ratio) and then adjusting the mixture. Some days it is very minimal, some days it is terrible, you just never know.
I have checked the blades on my Koll Rotorpro, they are right on, the head is balanced perfectly. I personally believe that the shake is caused by moving the tanks out. If you are building a semi-scale, you may want to try running a brace diagonally from the tank mount to the 47 diagonal support tube. I suspect that this would reduce it greatly.

Oh by the way, my tanks were shaking when I flew this heli at Top Gun in 2002.

Dan St.John
East Coast Scale Helicopters Vario Field Rep

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