Autopilot tracking

[Bert Pieke]

The STEC autopilot is supposed to be a very smooth autopilot, but I am seeing it hunting around on an approach..

HI TRK mode on final.

RNAV approach guided by an RXP GNS530, and the lateral direction oscillates +-20 degrees without any damping.

Not sure what I can try, but this is not the way an autopilot should be following the localizer..

[Scott - A2A]

Bert,

The STEC-30 us a very simple autopilot. We have one in our Comanche, and it's always wandering left, right, left, right, etc. Are you speaking from experience using the STEC-30 or a similar autopilot?

Scott.

[Bert Pieke]

No I am not, simply from a flightsimming background...

Wandering a bit, fine, but you are overdoing it, when you allow it to wander by 20 degrees either side.

Please have another look at this!

[some1 - A2A]

Yes, 20 is too much and hasn't been experienced during the beta.

Does it happen on ILS too, or LPV only?

[Bert Pieke]

Will try..

[gulredrel]

Had a nice and steady approach using ILS and initially catching localizer more than 10 nm out.

[Bert Pieke]

I can confirm that ILS hold works nicely on my system also.

However, I cannot get the autopilot to follow a GPS course with the RXP GNS steering the autopilot.

I start off on the initial leg of the GPS course in Hi Trk mode. This is OK until the first turn...

The autopilot overshoots the turn, and then attempts to recover by intercepting the course with a 90 degree
closure angle which leads to another overshoot and so on.. It never recovers.

In heading mode, the autopilot reacts swiftly and decisively, but in Hi Trk mode, it reacts late, and then seems
to forget about closure angles and damping..

I have flown with the RXP Stec 30 quite a bit, and it would follow a GPS course without difficulties..

[some1 - A2A]

The autopilot will not follow GPS route. It can't intercept the next route segment properly, just like it can't intercept VOR radial if you are far away from it. It should work to some extent if the route segments don't change course more than several degrees, but it definitely won't make sharp turns.

Now if we had this little toy installed, that would be a different story: http://www.avionicswest.net/articles/gpss.htm

[Jigsaw]

Did you follow the intercept instructions from the autopilot manual? If I understood them correctly you need to intercept the radial/localizer manually via the heading bug. Only when you are established on the correct course should you engage the Hi Trk mode. The problem you are seeing might be the result of trying to intercept the beam automatically, with the Hi Trk mode engaged right off the bat.

[Bert Pieke]

If this autopilot is not capable of following a GPS course in NAV (Hi Trk) mode, which would surprise me, yes , then I need
to steer the autopilot in Heading mode... lets see what the powers that be decide..

[gavink42]

If this autopilot is not capable of following a GPS course in NAV (Hi Trk) mode, which would surprise me, yes , then I need
to steer the autopilot in Heading mode... lets see what the powers that be decide..

That's exactly what I do in my real-world 180C that has the STEC-40. I have to anticipate the turn to the final heading, and use the heading bug to turn onto it. Once established, I can go into approach mode and it tracks nicely. The A2A PA280 STEC-30 performs identically to my -40, other than the user-facing interface.

- Gavin

[Bert Pieke]

OK - I understand...

The Stec-30 can track a straight GPS course segment, but it cannot turn to the next segment without the pilot reverting to heading mode, for the turn.

That will take some getting used to.. but if that is the real world behavior, I better practice it