[NSRCA-discussion] Metal Servo Arms

[Earl Haury]

Bob

I've no direct info regarding soft mounts on the big gassers. It's my understanding that they were used by some TOC competitors. I've been told that some engine manufacturers advise that using a soft mount will void the warranty. Also, that using a soft mount results in broken cranks. Others claim that the big composite airframes are designed to absorb the vibes and don't need a soft mount. My guess is that just adding a soft mount in the radial mounting scheme may not work well - but this is a mounting problem and not a mount problem. 

Earl
  ----- Original Message ----- 
  From: Bob Richards 
  To: NSRCA Mailing List 
  Sent: Saturday, September 01, 2007 8:18 AM
  Subject: Re: [NSRCA-discussion] Metal Servo Arms


  Earl,

  You are right about soft mounts. One thing I don't understand is why soft mounts have not made much progress in the larger 50cc+ size planes. 

  Bob R.


  Earl Haury <ejhaury at comcast.net> wrote:
    Bob

    I agree - in reality servo arm / spline strength is pretty much of a mute point for pattern. I did the tests after a friend broke an 8411 shaft on a big gasser, and some heli friends claimed the Al arms stripped the spines from nylon servo shafts. Takes excessive force to do either. 

    Recall changing a clevis to a ball link on a Rossi carb arm - arm broke on the first flight, a doubled arm broke on the next - back to a clevis and never broke another. Vibratory forces aren't understood by most - but experience is a great teacher.

    Somewhere I've some DSA data gathered with mini-accelerometers mounted on aileron servo mounts, firewalls, etc. One look at those data with and without a soft mount will make one a believer in soft mounts!

    Earl



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