Autopilot Steering in Holding Pattern

[Bob Denny 2]

I'm sorry but on Avsim searching returns a flood of irrelevant matches (or I am too stupid to figure out how to search within just this section)?

Anyway, what do I need to do for the autopilot on the Bell 429 (which is actually the X-Trident Bell 412 autopilot) to follow a GTN 750 holding pattern? In other respects the autopilot flies the procedures from the 750 flight plans. However on arrival at a holding fix, it simply keeps flying straight. If I switch to HDG mode and manually steer it around the hold, the 759 happily reports the turnpoints, and flips the to-from arrow when passing abeam the  holding fix after the turn to outbound. It  just won't steer the ship through the autopilot. Is there something that the aircraft author needs to do? Or is there something I can do? I've played around with the RXP settings but I've just managed to break other functionalith ha ha.

[Bert Pieke 7,585]

Have you got the latest real Garmin GTN 750 Pilot's Guide?

I believe it covers that.

[Bob Denny 2]

I do ... Pilot's Guide, GTN 725/750 - SSV 6.60 / Revision R / Mar 2019 / 190-01007-03 ... but I don't find info here except in a few places it says "roll steering is provided to aircraft with compatible autopilots" for example Section 6.5.

 

Edited November 16, 2020 by Bob Denny

[Bert Pieke 7,585]

 

https://vansairforce.com/community/showthread.php?t=132952

https://flightlevelsonline.com/2019/garmin-tips-tricks-flying-the-hold-going-beyond-the-racetrack/

Edited November 16, 2020 by Bert Pieke

[Bert Pieke 7,585]

BTW... for a simple hold as part of an approach..

This is what I fly often:

Take off from KTPA, and select RNAV 01L via PIE.

Fly at 2000 ft in GPS NAV mode.

Before FITPA, the autopilot will fly a hold without you doing anything..

Edited November 16, 2020 by Bert Pieke

[Bob Denny 2]

Interesting. What is your aircraft and autopilot type?

[Bert Pieke 7,585]

I am flying in P3D... but any GTN 750 equipped aircraft will fly it..

[Bob Denny 2]

OK, I will look farther. Everything else works, but I believe the AFCS runs off the ADI/HSI deviation and course (or heading depending on the mode) bug. I don't believe it is listening to steering directly from the GTN 750. 

Edited November 19, 2020 by Bob Denny

[Bert Pieke 7,585]

26 minutes ago, Bob Denny said:

I don't believe it is listening to steering directly from the GTN 750. 

That may depend on the airplane.. In simple GA aircraft, the HSI course needs to be set and adjusted by hand.  The autopilot in NAV mode will still fly the GTN course, regardless.

[RXP 2,338]

On 11/19/2020 at 4:12 PM, Bob Denny said:

I don't believe it is listening to steering directly from the GTN 750. 

In X-Plane it is really simple: we do use override_fd and then override the flight director. This requires the GTN being the master device, and of course you Connect GPS to Autopilot for this to work. However it is also relying on the currently set A/P mode inside XP11. This is not the autopilot mode whatever your aircraft is showing (some are just faking it), it is the actual internal autopilot state within XP11.

It also appears some aircraft aren't triggerring the XP11 autopilot commands in a way which would make the GTN read back the correct state from the XP11 dataref and this might be the case with a custom helicopter autopilot. I'm yet to determine whether this is a bug in XP11 or a problem with the aircraft LUA code, but for example IIRC you need to set the PA28 autopilot to OMNI (not NAV) and HDG ON.

[Bob Denny 2]

@RXP thank you! This could be useful but I'd like a bit more depth. I assume that override_fd is a DataRef which, when set to true/1 allows you to take control of the FD deviation needles? Assuming the AP uses that as its steering input this ought to work. I have the GTN set as Master, and Connect GPS to Autopilot. How can I determine the "internal autopilot state within XP11"? I'd like to know how that relates to the mode(s) in the 412/429 AFCS. I have some leverage with the AFCS developer at X-Trident as I helped him get the skid/slip indicator into a real-world state a few years ago and I talk with him regularly. It would be fun to get GPS steering into the AFCS to work. Not essential though. Overall it's quite usable now.

[RXP 2,338]

On 12/1/2020 at 6:59 PM, Bob Denny said:

It would be fun to get GPS steering into the AFCS to work. Not essential though. Overall it's quite usable now.

You can also directly use the GTN own datarefs which are exposing this kind of data for others to consume and use. In this case, you could for example have the AFCS directly command the XP11 A/P and read the F/D commands from the GTN, provided you disable GTN A/P coupling.

[Florian-K 0]

On 11/22/2020 at 10:10 PM, RXP said:

In X-Plane it is really simple: we do use override_fd and then override the flight director. This requires the GTN being the master device, and of course you Connect GPS to Autopilot for this to work. However it is also relying on the currently set A/P mode inside XP11. This is not the autopilot mode whatever your aircraft is showing (some are just faking it), it is the actual internal autopilot state within XP11.

It also appears some aircraft aren't triggerring the XP11 autopilot commands in a way which would make the GTN read back the correct state from the XP11 dataref and this might be the case with a custom helicopter autopilot. I'm yet to determine whether this is a bug in XP11 or a problem with the aircraft LUA code, but for example IIRC you need to set the PA28 autopilot to OMNI (not NAV) and HDG ON.

I do have this problem partially. I have set the GTN as Master with Connect GPS to autopilot enabled. I'm using X-Plane's default KAP 140 implementation, all plane specific scripts regarding the autopilot have been disabled. When switching the autopilot to NAV mode, everything works as expected. The plane will follow the ILS when the GTN is set to VLOC and will follow the gps flight plan including holds and LPV approaches. 

But if I instead set the autopilot to HDG mode and activate GPSS in X-Plane (via Dataref sim/cockpit2/autopilot/heading_is_gpss) to simulate how the KAP would work in combination with the GPSS provided by a Garmin GTN + Aspen 1000 combination then everything works like a charm except for holds. I assume that this is due to the fact that the RXP plugin just sends the waypoints of the flight plan to XP but isn't otherwise involved in the GPSS part. And therefore XP will just follow that flight plan to the next fix instead of going into a hold. I assume that this could also be a problem with DME arcs (I haven't tested those yet as there are no arcs procedures in the area I currently fly). So in order to work properly, the GTN plugin would probably just have to enter a few extra waypoints to the flight plan if a hold is activated. This would also mean that we could see the hold on a PFD that depicts the active flight plan.

Other than this, both the RXP GTN and GNS are really great as a easy and cheap solution for real world pilots to get really proficient with the Garmin navigators! 

Best regards

Florian

[412guy 0]

Hi Bob,

Wondering if you ever found a solution to the XTrident 429 not flying the hold headings cued by the GTN? I'm trying to solve the same issue with the XTrident412: the aircraft just following the slewed CRS bar (as commanded by the GTN) but ignoring the GTN sector entry or hold headings. You mentioned you have some relationship with the XTrident developer? FWIW the RXP GTN flies the holds and sector entries perfectly with the base XPlane11 S76 so it's something in the XTrident model, so hopefully that info helps in their troubleshooting.