MK Dual Elavator Bellcrank & Pushrod?

[Verne Koester]

Jerry,
The easiest way is to turn the MK unit into a pull-pull setup. Basically, it involves fabricating a horn that slips over and is glued and screwed to the existing horn (center one that's inside the fuse). Delrin or phenolic board about 3/32" - 1/8" thick is a good choice for the horn. The new horn can be screwed to one of the existing holes in the built-in horn plus one on the other side of center on the little stub that sticks out there. Ball links are a good choice on both ends. I learned about this from Mickey Losardo and if you've ever seen any plane fly from the Chicago area in recent years, it's a pretty safe bet that it has Mickey's setup.

The harmonic vibration forces that happen to a pushrod are serious. I once sold a plane to a friend that I had flown for a whole season without any problems. He changed the engine from a 1.4 FZ to a 1.4L. The difference in vibration was enough to set up a harmonic force so strong that it sheared off the splined output shaft on the servo. Others have reported similar problems. The pull-pull setup is easier to make than describe and eliminates any potential for problems from harmonic vibration. I realize this isn't quite the answer you were looking for, but it's a proven alternative to using a pushrod.

Verne

 
  ----- Original Message ----- 
  From: Jerry Wilson 
  To: discussion at nsrca.org 
  Sent: Wednesday, February 02, 2005 10:59 PM
  Subject: MK Dual Elavator Bellcrank & Pushrod?


  I've mounted the bellcrank and will use Central's carbon fiber push rod.  The pushrod length from servo to crank is about 28".  

   

  Is it necessary to install a support of the rod  halfway down the fuselage to prevent flexing.  And if so does anyone have a simple way of doing this inside a fiberglass fuselage?

   

  TIA

  Jerry

   
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