Solving the Vibration Puzzle

Jun 22, 2012 No Comments by
Hello Paul,

I hope you might be able to offer some sage advice on a project that has me stumped. 
I just completed a Century Heli / Funkey MD-500D body as an OH-6 "Loach". 
For mechanics I'm using my flybarless Chaos 600 with MicroBeast that I've been flying
over a year and a half. I flew the scale body in primer several times prior to painting, and
everything seemed fine.  Now, when I attempt to fly it, the body
shudders so badly it tosses off the canopy (which is secured with
alignment pins and 4 pairs of 3/8" rare earth magnets).  I've checked
the mechanics over carefully and can't seem to track down the source of
the vibration.  I thought it might be a governor gain issue, so I
dropped that to low.  It'll fly without the tail, but when I add the
T-tail it's back to shaking off the canopy.
I've checked blade balance, replaced the main shaft and flown it again
on the stock landing gear.  It seems okay, but there is a touch of
vibration that I can't seem to completely eliminate.  It doesn't cause
a problem in pod & boom config, but when I add the scale body this minor
vibration propagates.
I would note that the mechanics are securely mounted in the body,
including cross braces in the doghouse, so damping should be sufficient.
Can you offer any tips or suggestions for tracking down the last of the
vibration?  I'm up against deadline, so I'm getting a little panicked.
Jim

 

First of all I’m forwarding your e-mail to Tony Iannucilli. He flies with me, and has several scale helicopters, and may be able to shed some light on your problem.
Hi Jim,

I’d say internal body support, blade balance all around, and head speed are the things I’d focus on.  You seem to have a handle on all of them, so I don’t think I can be of much help.

Securing the boom firmly is important, as you know.  The hard foam rings work, and also wedging some hard balsa worked for me on my Century Agusta A109.  It sounds like you’re satisfied you’ve done a good job with that, BUT, when you added the tail is when you have the problem, so double check it all.

We’ll get more into solving this vibration problem later, but for now let me know if you have any ideas that may be of help.

 

Paul Tradelius

About the author

A regular contributor to Model Airplane News, he is also the columnist for our “Rotor Speed” helicopter column. Paul has been flying RC helicopters since the early ‘80s and now enjoys all types of rotary machines, including scale and aerobatics, and he continues to experiment with modifications to improve performance.
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