RUDDER TRIM

THE MAYBE MOD

Of all the various rental planes I've flown during the last 6 or 7 years, only a couple have had rudder trim.  Many people feel it's not even necessary, especially on a pusher like the Kolb.  Many others, however, including some who are Very Experienced in the type, have told me they'd be very interested in such a thing.  For myself, not having to hold right or left rudder in a climb, or especially during cruise, would be a major benefit.  I know I certainly appreciated it in the planes so equipped.   So, since it's easier to build it in during construction, here we go.  It seemed simplest to use a spring system, similar to the elevator trim that comes with the kit, rather than try to build & install in-flight adjustable trim tabs.  The question became - how to vary the tension on the rudder cables.  As so often happens, I noodled on this - off & on - for quite a while, trying to figure where to put how big of a spring, when it dawned on me..........use the existing springs.  Sounds simple, but it took a while.  The pics of the brackets, etc. are pretty much self explanatory.

It did take more spring tension than I expected to hold the lever in a selected notch, and I had to add a longitudinal brace under the floor to prevent flexing and eventual cracking.   Pivots for the tension arm are AN366F-1032 two lug anchor nuts, with the threads drilled out and polished.  Believe me, I did double check the numbers on those nuts.  One boo-boo like that was enuf.  I'm really not sure at this point which way I'll have to compensate, and how much.  With that in mind, I drilled one extra hole in the extension support, so that if necessary, I can switch springs quickly and easily.  It may also become necessary to reduce the amount of tension change per notch of adjustment.  We'll see.

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