Peter,

Your setup looks very nice but I agree with Red that having the servo horns offset behind the wheel and the rudder control horn exactly over the hinge line will cause increased tension in the cable opposite the side that is pulling. In other words, if you input right rudder as the surface deflects to the right the left cable will increase in tension over the right. This is very undesirable and if the offset is too much it *will* cause a flutter situation at high speeds when the cables begin fighting each other as one side deflects and the other side gets tighter thus pulling to the opposite side. I have a friend that snapped his stab twice when flutter occurred due to the control horns being in front of the hinge line (same effect as having the servo control arm behind the servo center line).

Your offset looks very minor so you may not experience any flutter, but I thought I'd warn you.

As to the distance between the control horns and the servo arm being the same, I've heard this too but believe it's a misnomer. I've experimented with this and I believe that different distances between the two will simply result in the end with the least distance separating the right and left having to move further, but I don't think there is any other adverse effect. Where this was useful for me was in the case of the elevator. It's better if our servos operate at near 100% throw between full up and full down so we have the max precision. My last elevator pull-pull setup only had the servo moving about 30%-50%. To increase this I used a smaller space between the cables at the servo and a larger one at the elevator. This meant that the servo had to move further to accomplish less throw at the elevator. As far as I can tell the the geometry works out because the distance one side moves is equal to the opposite side even if the other *end* is moving a different amount.

Here’s a great article on pull-pull geometry. I learned a lot from this web page: [link=http://members.cox.net/bdfelice/Ackerman/ackerman.htm]members.cox.net/bdfelice/Ackerman/ackerman.htm [/link]

KeithB