Elevator Trim

I borrowed this idea from the GlasAir aircraft and my Piper Toamahawk.  I'm using the MAC trim servo out of the old elevator to move a shaft fore and aft which pulls on a set of springs to bias the elevator push rod fore and aft.  While this trim system does work, it doesn't work particularly well and is still in need of some refinement and tuning.

2007 update- While this elevator trim does work, it doesn't work well and I do not recommend using this method. - Jeff
The issue is that the aerodynamic loads against the springs change with speed.  Full nose up trim was inadequate and full nose down trim would let it trim for cruise, but could never be flown hands off as the nose would contantly wander up and down with significant altitude and speed variations.  Converting to a trim tab with the new tail made for a hands off cruiser.