Chapter 17: Roll and Pitch Trim


I won't be installing the trim systems shown in the plans.  Instead, I'm going to use the Hanka roll trim system shown below and a modified version of the Davenport pitch trim system for the canard pitch trim.  The plans system is simple and it works well, but I don't particularly care for those high-tensioned springs. If one spring breaks, you immediately get full and opposite control input.  The Hanka and Davenport trim systems have benign failure modes.  If the trim springs break, they essentially disconnect themselves and don't cause any sudden control inputs.  Besides, I spent the bucks for those nice Infinity Stick Grips and I want to be capable of electrically adjusting the pitch/roll trim with my thumb on that nice coolie hat.


Step 1:  Roll Trim

The roll trim system is comprised of a horsehoe spring made from composite layups.  One end gets attached to the CS125 tie-rod at the firewall.  The other end is moved back and forth with an actuator.  This particular approach uses a Ray Allen servo. 



Step 2:  Pitch Trim

The pitch trim system is comprised of what is essentially a flat leaf spring made from 10-12 layers of UNI and BID.  One end is wrapped around the canard torque tube and the other end is moved fore and aft by a linear actuator or a mechanical lever.  I credit this approach to Bob Davenport of Long-EZ fame, but it actually started with the Velocity.  There are many variants of this approach. 


I'm toying with the idea of combining a manual lever with a smaller model of the linear actuator used for the landing brake.  In certified airplanes, the pilot is supposed to be able to use pitch trim as a backup to fly the airplane if the yoke fails for some reason.  If we lost the stick in the Cozy we could simply lean over and use the co-pilot's stick.  I'm sure this is a half-baked idea at best.  I predict I'll forego the manual lever and terminate the end of the linear actuator to the instrument panel.  I do like the trim position indicator though!



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