S-Tec 20 issues

Eric Brunelle

Eric Brunelle

Pre-takeoff checklist
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Jun 26, 2018
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244
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KPYM
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Ericb
Hello All - Yesterday my S-Tec 20 started behaving badly. I set the heading bug and shortly after, my Archer turned left away from the bug. I changed the imput to my 430, and the AP started wandering back and forth a few degrees - always over correcting. It put me in a gentle side to side sway - OK for slow dancing, but no fun in the air. The steering control knob seems to work OK. Hopefully more tests tomorrow if the weather holds. Any ideas?
Thanks, EricB
 
The STEC uses the gyro in the Turn & Bank for stability, usually. My guess would be that your T&B is failing.
 
First off, I've found S-TEC (or whatever they call themselves these days) phone support to be pretty good if you have questions like these.

Note, manual or not, you're not supposed to be working on autopilots as a non-AP PERIOD.
 
Eric Brunelle said:
I have one - got it from a guy on the Piper Forum. PM me your email and I will send it to you.
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flyingron said:
First off, I've found S-TEC (or whatever they call themselves these days) phone support to be pretty good if you have questions like these.

Note, manual or not, you're not supposed to be working on autopilots as a non-AP PERIOD.
Click to expand...
How about an avionics IA???
 
flyingron said:
Note, manual or not, you're not supposed to be working on autopilots as a non-AP PERIOD.
Click to expand...

How about experimental? Database updates? Dusting and cleaning the exterior case?
 
Do you have something better to do than be a forum troll? The Archer Is **NOT** an experimental.
 
When I bought my plane its Century IIB over corrected and produced a side to side sway. I was advised that the roll (actually the only) servo could be sticky and requiring to much torque to start and reverse motion. That extra torque would cause it to overshoot the desired heading and over correct. The first try at a solution was to exercise the servo full left and then full right about 30 times using the manual control knob (in an effort to smooth out its motion). That worked for me. I exercise it a few times every runup and its been working properly for 7 years.

I recognize that they are different autopilots, but both use roll servos and could, I expect, share the same cause for similar symptoms.
 
I'm going to try that. If that doesn't do it, then over to the avionics shop. I'm not messing with any of the innerds.

It's actually been a good experience - not having the AP available. I think we can become too dependent on them, and that can erode the IFR skills.
 
bkspero said:
When I bought my plane its Century IIB over corrected and produced a side to side sway. I was advised that the roll (actually the only) servo could be sticky and requiring to much torque to start and reverse motion. That extra torque would cause it to overshoot the desired heading and over correct. The first try at a solution was to exercise the servo full left and then full right about 30 times using the manual control knob (in an effort to smooth out its motion). That worked for me. I exercise it a few times every runup and its been working properly for 7 years.

I recognize that they are different autopilots, but both use roll servos and could, I expect, share the same cause for similar symptoms.
Click to expand...
Good tip. We have an S-Tec that is overshooting. I will give that a try.
 
Eric Brunelle said:
I'm going to try that. If that doesn't do it, then over to the avionics shop. I'm not messing with any of the innerds.

It's actually been a good experience - not having the AP available. I think we can become too dependent on them, and that can erode the IFR skills.
Click to expand...
 
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