autopilot s-tec

[Rick Gardner]

I have a 1976 P model with the STEC 55X autpilot with the altitude and vertical speed pre-select option. My previous airplane was a C206 with the KAP 140 with the same features. The difference between the two is night and day. Please bear in mind I am not a big King fan but.... The KAP 140 flew like it was on rails and the STEC is a very expensive dog. I have had the rigging checked and ALL the hardware for the 55X has been to STEC at least once. in lateral mode it blows through radials, localizers and GPS tracks like a drunken sailor and takes 2-3 cycles before it can finally capture the lateral course. Vertical mode is the same, it porpoises and half the time I cannot use the altitude hold portion because it makes the family sick. If you are lucky enough to be intercepting a course AND altitude at the same time then it is like being at 6 Flags - all over the sky.

The latest "fix" from the STEC camp is that the servos need to be cleaned because dirt causes the autpilot to have to increase startup voltages to overcome the resistance which then causes over-compensation. I think they may actuall be onto something because when I set the vertical speed to 0 the porpoising stops but it does not remain on altitude. They say that when you use the vertical speed mode that the auopilot uses higher voltages. Has anyone had a similar experience?