[NSRCA-discussion] Rudder pull-pull

[Lance Van Nostrand]

You all are so fast on this stuff that by the time I read the post the thread is old.

Ackerman exists if the rudder has control horns (as opposed to a wheel, which is very hard to build into a rudder).  The only ideal way to have constant tension is to use a symmetrical servo arm that is offset from its pivot (servo screw) the same amount as the rudder control horn attachment point.  This will work every time and is simple, however with a 1" thick rudder post and two 3/4" control horns you will need a 2.5" servo arm (1.25" each side of center) and the servo throw will only be equal to your rudder throw (maybe about 30 degrees) which gives you poor mechanical advantage and poor use of your servo.  If you use a shorter servo arm and more servo throw the cables will go slack.  The round servo wheel is a compromise by offsetting this slack tendency and letting you get more servo throw.  It's not a perfect match but it can be very close.

Anyone that can do the math on this and present a complete answer can get a recommendation to advance from a shade tree aerodynamicist to an apprentice.

--Lance

  ----- Original Message ----- 
  From: John Pavlick 
  To: General pattern discussion 
  Sent: Friday, May 09, 2008 9:02 AM
  Subject: Re: [NSRCA-discussion] Rudder pull-pull


  Chris,
   The only benefit that I know of is that you don't have to deal with the Ackerman angle like you do with arms / horns. The cable is always the same distance from the hinge center no matter what the angle is.

  John Pavlick
  http://www.idseng.com
    ----- Original Message ----- 
    From: chris moon 
    To: nsrca-discussion at lists.nsrca.org 
    Sent: Friday, May 09, 2008 9:13 AM
    Subject: [NSRCA-discussion] Rudder pull-pull


    Can someone explain the benefits (real or otherwise) of the pull-pull 
    wheel type rudder servo arm vs. a regular servo arm? Is there some real 
    benefit, or is it bling?
    Thanks

    Chris



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