John Barrett wrote:
I'm interested to know about any experiences with Tru Trak and yaw damper in
the IVP.  Is there a need to add auto trim?  I seem to recall reports that
without the yaw damper the aircraft gets a little unstable longitudinally,
but can the yaw damper solve the problem on its own?  

John,

I have an IV-P with a TISO 550 Continental, winglets and a two-axis TruTrak
SVGS autopilot that's fed from a Chelton Sport system. I have not found the
yaw to be a problem at all, and deleted the TruTrak yaw damper from my
original plan based on the recommendation of other builders. For my money,
invest elsewhere in your toy... Ditto for the auto trim. My SVGS indicates
when the aircraft is out of (pitch only) trim. This is easy to see and
correct with a blip of the trim switch during a normal instrument scan. The
trim changes very little in cruise flight; it's mainly a function of
airspeed, so you'll need to monitor it a bit more closely during climbs,
descents and power changes, but again for my money, invest elsewhere.
Aileron and rudder trim on my airplane stay in the center with two
exceptions: I use aileron trim to correct for fuel mis-management--more than
a 10 gallon imbalance between the wings, and rudder trim to manage yaw
during power changes. The rudder trim change required is significant between
high power settings at low speed (climbs) and cruise. Not so significant for
high speed descent when the power is reduced, but perhaps a blip or two.

Last item: I spent some time and effort building a "dual speed" pitch trim
system into my airplane. Had a minor wiring problem that kept it from
working during the initial test flights, so I just disabled it. I like the
trim system as it is now; wish I'd not wasted the time with the dual speed
system...

Bob

PS: I understand that the turbine-powered airplane is significantly
different, although this is second-hand to me. The above may not apply at
all to the IV-PT airplanes.