REFLECTOR: TR: Autopilot servos

[John Tvedte]

Terry,

When it is the proper time to do more AP testing, it would be interesting to know how your GNS480 controls things - do you get the same altitude issues/heading issues?

Do you know what version of software your Trutrak is at?

Trutrak has had software issues with Chelton, currently TruTrak 2.24 is the version "working".

Chelton has also had heading issues, in their case it was traced to a wiring/documentation problem, where the GPS signal fed to the AP was directly wired, rather than via the Chelton - so no magnetic variation was being sent to the AP.

How are those repairs moving along?

John
________________________________________
From: reflector-bounces at tvbf.org [reflector-bounces at tvbf.org] On Behalf Of Terry Miles [terrence_miles at hotmail.com]
Sent: Wednesday, March 26, 2008 8:33 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: TR:  Autopilot servos

Gilles...and others

I'm outta town at a Penn State faculty awards ceremony, but I can and will
contribute what I can to this is asked.  I do not have BM stuff, but I am in
phase one fly off and soon as I get my repairs done.  About that, I can say
a contributing factor to my gear up landing was monkeying around with
autopilot issues when I should have been more "fly the airplane" orientated
in Jan of this year particularly when below 2500 AGL.

I have a TruTrak autopilot going into and out of a Grand Rapids EFIS.  I had
aileron cable issues with the factory, and had drilled so many holes in my
aileron bell cranks getting it all to fit and operate that I had to buy a
new set of bell cranks.  My roll servo is in the eng compartment.  Room to
do things and mount things was a challenge.  I sent my TT back to TT for
some software update that they needed to do when they found out I was a
Velocity.  Also the GRT EFIS has some manner of gain settings that can be
tweaked within their setup routines.  All I can say is that after several
attempts with the new a/p software/firmware it is still not holding a
heading or an altitude.

Due to my inattention to flying I am dropping any emphasis on autopilot fine
tuning until I take somebody else up with me, and a voice recorder as well
so I can deduce for my own needs and to TruTrak a good squawk profile of
what it's doing (or not doing).

I have slop in my cable too that is not me.  It is in the system design.
There is also potentially too much friction for the default torque and throw
parameters of the TruTrak - GRT EFIS combo that is probably manufacturer
preset to address RV market needs which ain't us.

If you are not there yet, take the time to decide how and where to mount
your roll servo and who to buy an autopilot from.

Terry Miles