I think the trim tab concept is to simplify installation.  If your control 
cables work fine and are adjusted properly, then one train of thinking is to 
not mess with those.  Adding small trim tabs is a simple thing to do without 
messing with your controls.  That said, most autopilots do work by installing 
along the control cables.  One system uses a bar often used at a horn, another 
sister ribs another cable to the control cable and the new one goes around the 
servo with a capstan.  Either is designed so you can override by manual control 
and they don't mess up your original control cables.  If something happens, 
like the loop comes off the capstan, the original controls still work fine.  I 
was going to build a KR, but changed to a Zenith CH-650 with full Dynon system 
and we have two servos for autopilot.  One of each kind.  The bar or rod type 
and the capstan type on elevator.  They've worked great for 2 years now.  The 
autopilot controls are built into each Dynon screen, just add servos and 
calibrate.  Dynon servos are about $750 each, total $1,500, which I think is a 
lot for servos, but the total is cheap for a full autopilot system.  Other 
brand servos can be used.

As for balancing a prop, I'm wondering maybe you balanced by weight, but is 
there a chance the twist is a bit different for each blade?  There is a dynamic 
prop balancer, and I know some in KR land have them as it was used at the 
Oregon gathering a few years ago.  Our EAA Chapter 84 in WA has one in the tool 
crib.  They cost $1,200 to $1,500 (for the cheap ones, shop type are $4k+).  
Having a shop do it is often about $400 to $500.  Our chapter charges $20 but 
it is only available to members and then only with supervision by a member with 
experience.  Belonging to a EAA Chapter with a good tool crib is very valuable, 
even after your build is complete.  We also have very high quality aircraft 
scales in our chapter, as well as swaging tools, a vinyl cutter, a 3D printer, 
and more.  We want to add a cable tensiometer as this is often a one time use 
when setting control cables in a build.  All these items are typically used 
only a few times during a build and generally not worth buying as an 
Jim McGauhey
Prez, EAA Chapter 84
Snohomish, WA

-----Original Message-----
From: Gary Sack <garys...@gmail.com> 
Sent: Thursday, May 14, 2020 11:52 PM
To: KRnet <krnet@list.krnet.org>
Subject: KR> Two questions

I've enjoyed the comments concerning the autopilot. My question is: could the 
servos drive springs attached to the control cables. This has been done in 
aircraft for pitch trim and works pretty well. Seems simpler and more 
aerodynamic than trim tabs that work opposite of the desired result. Either 
way, I am interested.
   Second question...a year ago I wrote about damaging my KR prop while hand 
starting. I have repaired the prop and statically balanced it, but it vibrates 
badly. Is there a simple way to dynamically balance a prop? Also does it matter 
how the prop is orientated to the throw of the crankshaft? I know the engine is 
fine because my spare prop runs smoothly.

   I took Richard's advice to mount a Subaru starter on my HAPI  engine. I had 
some problems getting the adapter plate just right, but my engine really cranks 
now. Thanks.

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