S-Tec System 50 nav mode adjustment

@wigglyamp or @GarryIAE might know. Not sure if they are still here though.

I don’t know if I have sent you what manuals I have, Przemek. I can’t see a “50” installation manual among them.

Przemek wrote:

I found only maitenance manual with roll center callibration but nothing regarding sensivity etc.

Other problem is that my unit is too sensitive for altitude change. On altitude hold mode happen that its waving.

There is no field adjustment for nav tracking sensitivity and generally they’re pretty poor (We have the System 20 in our PA28 and it’s not great in this mode). If you have a GPS then get a roll-steering adaptor installed as that works really well.

For an S-Tec pitch axis, it’s not uncommon to have porpoising. Check the pitch system for any friction in bearings/pulleys or incorrect control cable tensions. A servo motor that requires a higher voltage to get moving will also cause the same problem. Occasionally it can be water in the static system to the altitude transducer but this is much less common.

Przemek – check your email. I am told by a US installer that there is no IM for the Stec50; just a generic wiring diagram. I have emailed it to you.

Peter wrote:

I am told by a US installer that there is no IM for the Stec50; just a generic wiring diagram

This isn’t correct. There are specific installation manuals for each STC along with airframe-specific mechanical drawings. Only the wiring diagrams are generic across all platforms that use a particular system. What airframe is this for?

He told me the mechanical drawings come with the STC but there is no specific IM detailing the wiring and any electronic config. I have put that generic manual here.

Each S-Tec STC has a specific install manual which details the airframe-specific parts list and gives instructions for installation and set-up including clutch slip settings for the servos. It will have something like ST-711 on the front cover (this is the one we have for our PA28).

There is no electronic configuration or gain setting required other than setting up for a specific heading source. Normally the programmer comes from S-Tec pre-set for the heading system that was specified on order, but future changes (such as removing a DG and adding an H.S.I or EFIS) can be accomplished in the field by changing some resistors on the interface board.

Fascinating how different STEC is from the King stuff. On say a KFC225, all the control loop parameters are adjustable, albeit only via a config file on a diskette which was very tightly controlled and only some dealers could get it. I never managed to get the one for the TB20 although I do have one for some Piper. OTOH STEC for STCs for almost everything imaginable, while King only got a few. But then King produced autopilots which didn’t oscillate…

There are control loop gain settings developed during certification testing and these will be addressed by the specific part number of the programmer. It’s just that there’s no field adjustment of any of these.
The only field adjustment that can be made other than configuration for alternate heading sources, is the roll null (compensating for a slightly offset turn co-ordinator signal) which if not addressed will cause the aircraft to fly slightly to one side of a Nav track.