REFLECTOR:S-Tec modifications

Chuck Jensen reflector@tvbf.org
Tue, 11 May 2004 11:29:19 -0400


An apparent advantage of the TruTrak Digiflight A/P is it allows a range of
value inputs during setup/programming to control roll and pitch (two
separate values) to dampen/kill loss of movement/oscillation issues.  In
short, this setup input takes the place of the variable resistors and wires
hanging around with S-TEC.  I would brag on how great the TruTrak flies but
I'm not there yet so I won't.  However, the TruTrak does seem to offer a $0,
0 hassle, solution to the oscillation problem.

Chuck

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Jack Sheehan
Sent: Tuesday, May 11, 2004 9:53 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:S-Tec modifications


Here is an update on the S-TEC autopilot roll oscillation problem I 
was having with the S-TEC 30.
Based on Mack's advice and after talking to Kenny at S-TEC I removed 
the Turn Coordinator and roll computer from the aircraft. S-TEC 
replaced the gain resistor with a variable resistor in each unit ( 
the size is different for each unit) I asked them to put the variable 
resistors on a 15 inch wire so that I could mount the resistors below 
the turn coordinator. The unit was returned with the variable 
resistor set at the factory setting. Yesterday I reinstalled the 
units and went for a flight test. I engaged the autopilot in the ST 
(wing leveler) mode and the oscillation (side to side) was as before. 
I have not mounted the variable resistors but just have them hanging 
from under the instrument panel. With the autopilot engaged and the 
side to side oscillation in progress I turned the roll resistor 
slowly counterclockwise until the oscillation stopped. I then engaged 
the altitude hold and the pitch oscillation was not as bad as roll 
but a similar adjustment has the pitch working fine.
I will fly for a while in different configurations to make sure all 
is OK. I don't think I will mount the resistors but probably just 
secure them under the instrument panel.
The S-TEC 30 I purchased from Velocity I installed with the 
assumption that it was a plug and play since I had specified the 
heading gyro etc. This is not the case as I am finding out. The 
wiring harness is set up for interfacing to the S-Tec gyro so there 
are other things such as jumper wires etc that need to be changed. I 
am still trying to understand that stuff but the oscillation problem 
has a solution.
I had a little bit of a problem with S-TEC concerning the cost of the 
modification. In talking with the technical folks it was " just send 
it in and we will fix it" . After the modifications were done they 
wanted to charge me and not cover it under warranty. My autopilot is 
a few years old but as far as I was concerned the date of 
installation has yet to occur because the installation is not 
complete until it works. They did after some discussion cover it at 
no charge. The proposed bill would have been $275. So if you have an 
STEC under warranty get that recognized up front.

Jack
N55XL
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