Hello,
I am a recent customer of the RXP GTN 750 solution and I must congratulate RXP team. 
My question concerne the VNAV feature. 
I have the Carenado H850XP (P3Dv4.4) that i customized for GTN and it works fine except i'm not able to operate the vertical guidance with GTN (VNAV).
The original Carenado H850XP is able to follow vertical guidance according to a flight plan if you turn on the VNAV button. I'm sure of that because i have used it many times.

In Reality XP GTN User's Manual, one can read :

Autopilot
The GTN is capable of precise course deviation and roll steering outputs that can be coupled to the simulator
autopilot so that IFR flight procedures may be flown automatically. It controls the simulator A/P system both
horizontally and vertically.

Maybe this problem is in connection with P3D 4.4 and maybe an update RTX is in progress about AP ...
Is there someone who could help me ?
Thanks in advance.

Edited December 28, 20187 yr by Livingston

Hi,

this is most likely due to the unconventional 'VNAV' mode in this aircraft: the default autopilot (FltSim) is not capable to provide vertical guidance from GPS sources, so every single vendor has his own trick. In this case the 'trick' could be their gauges driving the elevons directly.

Our GNS V2 and GTN are coupling vertically with the default autopilot, provided it is in APR mode, and I'd guess their VNAV mode is not arming the APR mode.

Our upcoming update is solving some issues in regard to autopilot, as well as it correctly implements automatic NAV->APR mode when AFMS settings are set to "GPS Selected" (as intended in the real world).

I have found that some, not all Carenado aircraft have  strange behaviors compared to default and other when it comes to AP behavior particularly  in regards to LPV or Vnav. I can't pinpoint it but I have found they don't always reliably capture Vnav GS on approaches. I look at the GS saying capture capture..NOPE. 🙂  Perhaps I'm doing something wrong with them but no issues with other model AP's. Again, I'm probably wrong..

 

OK and thanks for your quick replies.

Is your upcoming update planned shortly ?

For Adrian, take a look at this : 

 

Interesting discussion...

In the Hawker GTN retrofit, I disconnected the VNAV button on the autopilot, since it requires input from the Proline FMC.

@RXPJean-Luc, what kind of vertical guidance does the GTN provide to the autopilot during VNAV operation?

Does it require APR mode to be active?

If so, I could just have the VNAV button activate APR mode.. or the user could try activating APR mode directly, as a test..

Edited December 28, 20187 yr by Bert Pieke

@Livingston Any update release is a candidate for failure at the worst time, and we won't be able to be fully operational support-wise in between the 25th and the 1st, so we're polishing up the update code during that time. However should we find the update not disruptive potentially it might get there sooner.

@Bert Pieke The GTN and GNS V2 couple both axes, but we enable vertical only when APR mode is armed. However, there are cases we've identified during the work on the update which could potentially makes the code logic fail under some situations, especially with dual GPS panels. Furthermore, the next update will automatically handle NAV->APR mode at the FltSim autopilot mode level (which is 95% of FltSim aircraft as opposed to aircraft with custom-coded A/P controlling the surfaces directly). This NAV->APR function depends on the AFMS GPS Selected "Auto" setting. In "Prompt/Manual", the GTN and GNS V2 ask you to arm the mode manually first, which is cool!

Also for people wondering: the CDI mode change from GPS to VLOC is automatic by default but can be configured manually in the in-device settings (Settings/Aux pages).

Made one observation with Carenado. Cycling the CDI button and re-initiating APPR works for capturing vnav on approach.

3 hours ago, RXP said:

Furthermore, the next update will automatically handle NAV->APR mode at the FltSim autopilot mode level (which is 95% of FltSim aircraft as opposed to aircraft with custom-coded A/P controlling the surfaces directly). This NAV->APR function depends on the AFMS GPS Selected "Auto" setting. In "Prompt/Manual", the GTN and GNS V2 ask you to arm the mode manually first, which is cool!

Will be interesting to parse what all this means. 

Up until a year or so ago I took a series of right seat rides in a Cessna 310R equipped with a pair of GNS 430's. The keypress to go from NAV to APR was always just after the turn to the final approach course, which was often well before the outer marker, but still on the FAC. Much like the 430's I have used here from RXP.   Recently, as have many others here, I have been following a series of Youtube videos posted by Youtube member and pilot "310 Pilot"  https://www.youtube.com/channel/UCcBTQfcjYcSkYvO4kXM5-Bg/videos.  His 310 is set up with a pair of GNS's and on at least two occasions I noted that he keyed over to APR mode from NAV before his turn to the final approach course. And once well before that turn.

So what is real world accurate? Will this be modeled? Modeled by RXP? Or dependent on AP modeling by the simulator aircraft developers?  Any thoughts on RXP providing some accurately modeled autopilots?

So many variable in the sim AP. Then I go back forth between Xp and P3d and the same aircraft by the same Designer is different. 😉

@fppilot the way it works is the most simple and the most authentic: it will switch from NAV to APR exactly like the real GNS/GTN. It seems the moment it switches depends on the procedure, the altitude and a number of other parameters. Suffice to say it switches at the 'right time' so that you capture the GP signal (vertical equivalent to GS but for GPS source).

NB: it is different than with the legacy which triggers the switch in a certain way which is not entirely accurate to the real device, whereas with the GNS V2 and the GTN it is the same signal which would drive the A/P which we are listening to.