CTE

[Keith Black]

Matt,

The negative CTE of Kevlar seems as though it would exaggerate the loosening and tightening of the cables. As the fuse shrinks the cables will lengthen and visa versa. 

How would this be better than metal cables?

Keith Black

  ----- Original Message ----- 
  From: Rcmaster199 at aol.com 
  To: discussion at nsrca.org 
  Sent: Tuesday, November 25, 2003 7:45 PM
  Subject: Re: CTE


  In a message dated 11/25/2003 1:12:08 PM Eastern Standard Time, geobet at gis.net writes:



    Subj:Re: CTE 
    Date:11/25/2003 1:12:08 PM Eastern Standard Time
    From:geobet at gis.net
    Reply-to:discussion at nsrca.org
    To:discussion at nsrca.org
    Sent from the Internet 



    Sorry to disagree here, but it would appear that the conclusion being drawn by the respondants is that the pushrod expansion and contraction is the major cause of the problem. Not so, in my experience! Going to pull-pull cables, whether they be steel or kevlar thread will not get rid of the elevator trim change under consideration here.The coefficient of thermal expansion between the cables, which is very small, and the balsa in the fuse, which is significantly greater(glass too) will generate a differential of sufficient magnitude that the "devil" will still attack you when you least expect it. 
    The best solution that I have observed is to put the servos in the stabs. Short of this, I have been using servos mounted just at the L.E. of the stab and using a very short pushrod(approx. 6"). My current thinking is that I will still mount the servo in the same area and go with cables.Very light and direct. As regards Kevlar, I currently have a pattern practise ship that I do almost all of my flying with that has kevlar on the rudder and it has two years of mucho sequences to it's credit with no apparent wear or abrasions to the thread. At this point in time I have still not acquired the necessary intestinal fortitude to use kevlar on the elevator. 
    Georgie Amir Neshati wrote: 

      Pull-pull will eliminate the trim change... Amir 




  Georgie,

  Don't fret it. I have used Kevlar every where in the tail without problems at all. 

  BTW Kevlar has a negative CTE, that is it gets shorter as temp increases. Kevlar cables actually get a little tighter in summer and looser in Winter, or opposite what you would expect. I have never had a set-up that retained it's trim as well 

  All, I still have a quantity of 40 pound test and 80 pound testTeflon coated Kevlar for sale. These are  the smallest profiles around, for all you discriminating modelers. The teflon coating eliminates the chafe on composite fuse sides. Contact me directly please

  Matt K 
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