GTN750 suspends for hold but AP ignores

[412guy 0]

Hi All,

I am using RXP GTN750 with XTrident's Bell 412. When I load a hold at an entry waypoint for a GPS approach the GTN acts exactly as per the real-world aircraft, displaying the hold and sector entry. Unlike the real aircraft though, once at the entry waypoint the XTrident 412 turns to intercepts track to the IAF rather than fly the sector entry and hold. The RXP product appears to be commanding correctly, but the XTrident 412 appears to be following steering commands from elsewhere.

I am somewhat computer illiterate, but can stooge through configuration files with clear guidance. I have managed to get the GTN working as it should for all other aspects (that I've experienced so far) but not to suspend and hold. From some searching it appears others have experienced this but I can't find a resolution. I got the impression from one post that while the RXP product was displaying correctly somehow the default Xplane model GPS was providing steering commands to the AP, and that suspending the GTN didn't suspend the base aircraft model GPS. Strange thing is I previously had this running on a Mac Windows partition (have now bought and installed on a dedicated PC) and I'm 99% certain I could fly holds previously. 

I'm hoping this is a simple configuration change that someone has seen before and can help me with. My RXP GTN settings are currently as follows:

Master Device -Yes

Connect GPS to Autopilot -Yes

 Connect GPS to HSI (pilot) -Yes

Connect HSI/CRS (auto slew) -Yes

Connect HSI/OBS (course in) -Yes

Connect GPS to VOR -No

Connect CDI mode to NAV/GPS switch -Yes. Sync mode GPS to Sim

A quick check now shows it is following the default aircraft 530, which isn't suspending the IAP when entered in the GTN, so seems to be a communication issue between the two. Any help appreciated!

 

 

 

[RXP 2,338]

Hi,

I'm sorry for the delay.

There could be multiple reasons but the first one I'd think of is this aircraft could be using a custom autopilot which isn't handling this kind of situation.

Probably one way to cross-check the nature of the problem would be:

- try the same route with a simple stock aircraft, not a 3rd party helicopter, and compare how the A/P steering is behaving.

- it there is a stock X-Plane helicopter with A/P support (I honestly don't know), then maybe trying with one instead.

Overall, the RXP GPS is using the "override_gps" dataref when in GPS mode and it is the Master Device. When enabling this dataref, the underlying stock GPS is supposed to stop functioning and stop steering. However SUSP mode is a special case which might need special care at the 3rd party aircraft autopilot code in order to work as it is expected, and in this case, the RXP GTN ouputs the necessary data, but I can't know whether the 3rd party aircraft custom code is using it. I'll be pleased to assist any 3rd party dev if they inquire.

[412guy 0]

Hi RXP,

Sorry for the delay my end also.

I've just tried flying with the default Cessna 172 and the S76 (helicopter) the GTN works perfectly suspending and flying the hold coupled.I noted the default settings in the GTN settings menu and tried these with the XTrident 412, but no joy.

Interestingly the 412 suspends the IAP and takes up the heading for the inbound track for the hold over the suspended waypoint. It just doesn't make a turn onto downwind, as per the native plane aircraft. It just flies off into the sunset on the inbound track heading. The GTN commands the turn but the 412 doesn't follow.

I don't know if that gives you, or anyone else with the computing "smarts", enough info to identify what is different in the set up of the XTrident412 and the default xplane11 aircraft and their GTN interface. It's almost as though the "Master Device" option is being ignored by the XTrident412.

 

 

[412guy 0]

Just tried a teardrop entry and as soon as the course bar slewed to the inbound the XTrident 412 turned to follow it. So it seems it is following the CRS bar rather than the GTN commands, if that helps.

 

[RXP 2,338]

It just means the XTrident 412 autopilot is doing it own logic somehow regardless of the value of some of the actual XP11 datarefs, and it seems to be following the XP11 flight plan waypoints instead of the GPS data maybe. If this is the case, you might want to enable the RXP GTN setting: " Auto-Update Simulator GPS Waypoints" which will override the default flight plan system waypoints and this might be helping. (NB: this might be not fully working with "procedure turns" or otherwise "complex" legs because the default flight plan system - the FMS data - is basically only a series of waypoints with straight legs between them).

[412guy 0]

Tried "Auto-Update Simulator GPS Waypoints": no change.

Tried "Use Simulator GPS Commands": again no change. Approach remains suspended arriving at the waypoint and the XTrident 412 turn to CRS bar heading and flies off into the sunset.

Definitely a coding difference between this model and the xplane default aircraft as they behave correctly. Is it one to try and pass to the XTrident412 development team?

[RXP 2,338]

I believe it is something you might want to document and report indeed. If they need any assistance I'll be pleased to help.