When trying to do an LPV with the autopilot in the default C172 the GS is not coupled when flying an LPV.

 

Yes I approached via the IAF at correct altitudes and thus captured from below and NAV/APR/GS was active on the autopilot. But it did not start the descend as expected.

 

Any ideas?

I've read your other posts on the C172. Did you manage to correct this since then?

I will look at the GS flag thing later. And then check again how the GS coupling to the AP is for RNAV approaches with vertical guidance.

Strange is that the VDI indicator is anyhow correct for it, so you can fly manually the descent with the VDI, but the AP does not seem to be coupled to the same signal as the VDI.

8 hours ago, PeterBremer said:

Strange is that the VDI indicator is anyhow correct for it, so you can fly manually the descent with the VDI, but the AP does not seem to be coupled to the same signal as the VDI.

deleted

Edited February 3, 20215 yr by Bert Pieke

Found it:

To fly an LPV with the autopilot GS mode in the default Cesssna 172 it is not enough to couple the GPS to the autopilot but you must also couple the GPS to the HSI although the default Cessna 172 does not have a HSI.

This is for me only a workaround, just in case I like to fly with the autopilot, because it has a major disadvantage: OBS mode of the GPS with the VOR1/OBS indicator does not work anymore, and as there is no HSI, there is also not an OBS dial of a HSI.
Using OBS mode is for example a standard operating procedure when flying circling approaches. That would make e.g. a circling after an autopilot coupled LPV not comply with that procedure in the default Cessna 172.

The GS INOP flag remains visible on the VOR1/OBS indicator, it is not removed when a valid Vertical Path from the GPS is received, even not when the GPS is coupled to the not existing HSI.

 

 

Edited February 13, 20215 yr by PeterBremer

Did you link by any chance GPS to VOR instead of HSI? Linked both?

2 hours ago, RXP said:

Did you link by any chance GPS to VOR instead of HSI? Linked both?

That is not possible, afaik, as soon as you indicate you couple the GPS to the HSI, the option to couple in to VOR1/OBS disappears.

But based on the behaviour of the needles when GPS coupled to the HSI, the VOR1/OBS needles still behave as expected. Except the OBS mode of the GPS is not controlled by the OBS dial of the VOR1/OBS anymore.

 

So, in summary for LPV:

• GPS coupled to VOR1/OBS:
  • CDI and VDI needles of VOR1/OBS work as expected. Handflying is possible.
  • OBS dial of VOR1/OBS does provide course information to GPS in OBS mode (used after the LPV for circling).
  • Lateral navigation works on AutoPilot.
  • Vertical navigation and detecting GS on AutoPilot itself does not work.
  • GS flag on VOR1/OBS is not removed on LPV vertical signal.
  • GS flag on VOR1/OBS is not removed when after switch on the test screen appears and no valid ILS is received.
• GPS coupled to not existing HSI:
  • CDI and VDI needles of VOR1/OBS work as expected. Handflying is possible.
  • OBS dial of VOR1/OBS  can not be used to provide course information to GPS in OBS mode (used after the LPV for circling)
  • Lateral navigation works on AutoPilot
  • Vertical navigation and detecting GS on AutoPilot itself does work.
  • GS flag on VOR1/OBS is not removed on LPV vertical signal.
  • GS flag on VOR1/OBS is not removed when after switch on the test screen appears and no valid ILS is received.

 

Edited February 13, 20215 yr by PeterBremer

Thank you for the condensed and comparative testing report!

I won't be able to help much about this over the weekend (14th 💘) but you might want to explore the following in the interim: I believe there are options in Plane Maker to "tie" some of the OBS and/or CRS selectors between VOR and HSI. It might be in this aircraft there is a setting you might want to enable or disable.

The GNS V2/GTN plugins are using the XP11 "override" datarefs only:

• When connecting to HSI, the plugin is overriding the set of GPS datarefs (these are driving the HSI when using "override_gps").
• When connecting to VOR, the plugin is overriding the set of NAV datarefs (and "override_nav#_needles").
• When linking OBS, it uses "hsi_obs_deg_mag" if "connect to HSI", otherwise it uses "nav#_obs_deg_mag" if "connect to VOR".

But in all cases, there is no direct control nor any override for the NAV and GS flags: XP11 is doing it on its own and I believe it is not honoring the flags properly when a plugin is using the "override_xxx" datarefs (bug).

I've already asked for direct control in the past but I believe I'll have to ask again.

2 hours ago, RXP said:

... I believe there are options in Plane Maker to "tie" some of the OBS and/or CRS selectors between VOR and HSI. It might be in this aircraft there is a setting you might want to enable or disable. ...

...

But in all cases, there is no direct control nor any override for the NAV and GS flags: XP11 is doing it on its own and I believe it is not honoring the flags properly when a plugin is using the "override_xxx" datarefs (bug).

I've already asked for direct control in the past but I believe I'll have to ask again.

I can not find any tie function for CRS/OBS in X-Plane. Nothing about HSI's or OBSs andyhow. 

For trying to do direct control of the GS flag (via LUA?) I installed datarefeditor first to see what to use. Will try that later.

The NAV flag works fine in both GPS and VLOC.

The GS flag does not in GPS mode, will try to find how to tie the RealityXP GPS to it.

The flag datarefs are officially not writable, so I can not control the flags directly.

The dataref RXP/radios/indicators/hsi_flag_glideslope_1 and _2 do the right thing but are for some reason not coupled to the flag of VOR1/OBS indicator. If that would be anyhow possible as there seems no way to set these via a dataref.

I am having pretty much the same problem. For two days now I have been shooting LPV approaches to see when the LPV works as it should and when it does not. Sometimes when on the LPV approach, I can make the GS flag disappear by cycling the CDI button. But other times that does not work. If I remember correctly, when I can get the GS flag to disappear, the plane starts down as it should when it should. If the flag stays put, so does the plane.

Was there ever a solution?

Alex