I am looking for an Installation Manual of those.
I have ST55x and ST-360 in my plane but there is a problem with communication between those units. AP doesn’t “see” the preselector, so ALT Capture doesn’t work.
I would like to recheck the wiring but don’t have the documentation.
Does this help:
Thank you very much!!
Another problem with this AP I have are some altitude fluctuations in ALT mode +- 20-30ft which is quite annoying. But sometimes everything is fine.
I checked the pitch trim and elevator cable tension and they are ok.
I suspect something in the electronics or the Absolute Press Transducer.
Normally when I fly in stabilised ALT mode – when I switch to VS – it should display “0” as I’m already in level flight.
However when the fluctuation starts, for example the aircraft starts to pitch up – when I press VS button – I see about “-5” hundred feet/min.
So the AP thinks – we are descending so it has to pitch up. Then after few seconds it realizes that it has already went too high and begins to pitch down.
I have an auto trim, which works fine. Tried to switch it off but doesn’t help.
Anybody experienced similar problems?
Are these fluctuations periodic?
I had this and a part of the solution was the replacement of most of the static pipework. It is possible something got pinched, or there was a crack.
The issue existed only in ALT mode.
I don’t know about STEC but I think King autopilots pick up the current VS value when VS is pressed.
Note that VS=0 will not hold altitude.
Yes they are periodic. Let say about 50% of flight time.
When I press VS button I think I read the current vs rate – as you described. Normally it is “0” but when the fluctuations come – I read different values – from minus 6 to plus 6 hundred feet/min when pressing VS.
VS=0 of course will not hold altitude. The plane very slowly drifts up or down but it generally helps to reduce variations.
Roughly what frequency?
More or less the same or a bit slower than on your video.
How easily can you arrange a static system leak test? I would do that first.
Then change any tubing where creepy crawlies might have crawled into and blocked it.
How easily can you arrange a static system leak test?
I will find out.
Do you think it could be also bad electrical connection between press transducer and the autopilot?
That I could easily check.