GTN 750 VNAV function? (resolved)

[Deltaair1212 53]

So before people get mad that this question has already been “answered” I have looked at several posts in this forum in regards to this topic but there is really no “yes”, or “no”. It really has not been explained in a simple term. I ported over from F1 because they stopped updating their GTN. One thing that I loved about the F1 GTN is that I could shoot RNAV, and visual approaches that had a glide slope when weather got hairy. It was the one tool that made the GTN invaluable to me. Since making the move to RXP, I have found that the VNAV function is not working. At my base airport, the same visual approach that had a glideslope that I use just about every week no longer works with RXP. I see the litte glide slope bug inching its way down but even with my GS button active my aircraft doesn’t capture the GS. This is  concerning to me because why would a company go through the trouble of making such a realistic garmin unit if it doesn’t even capture glide slopes? No disrespect to the authors of the program but it’s a genuine question. I looked in the settings pop up menu and I do in fact have VNAV enabled so maybe I’m just missing something here? In real life if I had a $2 million dollar jet and I purchased a Garmin 750 suite for it just to find out my VNAV didn’t work, I’d personally fly my aircraft to the garmin headquarters (during clear skies of course being that my VNAV was INOP) and throw the unit through their lobby windows. But thank God this is just a sim right? 🙂 

[Deltaair1212 53]

UPDATE: I switched VNAV to VCALC and it somehow picked up the glideslope this time albeit not as smooth as I remember with F1…. It was quite violent even though I had it at 600fpm. I’ll keep toying with it to see if I can get it any smoother 

[RXP 2,338]

Hi,

The GTN fully binds to the autopilot but you have to make sure it is in a condition to do so:

- The device is set as the "Master Device" (there can be only 1 device controlling the A/P at a time)
- The device settings enable "Connect GPS to Autopilot" (otherwise it won't do anything)
- The simulator autopilot has valid HNAV and VNAV mode armed
- The device CDI mode is "GPS"
- The simulator nav/gps switch is "GPS"
 

What could go wrong? depending on the aircraft you might want to review the GTN settings "Connect CDI Mode to NAV/GPS Switch" and change the "Sync Mode". Some aircraft are using their own switch and are overriding others, in which case you'd use "GPS <-- SIM" and the aircraft switch instead of the GTN CDI button.

PS: VNAV/VCALC shouldn't have any incidence.

[Deltaair1212 53]

All of those are ticked on. But for some reason VNAV doesn’t work and VCALC does. VNAV worked automatically with F1 so it is puzzling. I’m not sure what’s going on I’m still flying the same aircraft which is the FSW Learjet 35A. Nothing has changed but my port over from F1 to RXP. And also “connect CDI mode to NAV/GPS switch” is greyed out so I cannot mess with that setting so I cannot change my sync mode. 

Edited December 28, 2021 by Deltaair1212

[RXP 2,338]

Are you actually talking about the pseudo ILS signal generated by the GTN for landing, or the vertical deviation enroute?

The former is fully supported, the latter requires a Garmin autopilot IRL and is therefore not implemented in the RXP GTN as a "generic" mode for any aircraft.

1 hour ago, Deltaair1212 said:

And also “connect CDI mode to NAV/GPS switch” is greyed out

Is there any chance you can post a screenshot of this?

[Deltaair1212 53]

28 minutes ago, RXP said:

Are you actually talking about the pseudo ILS signal generated by the GTN for landing, or the vertical deviation enroute?

The former is fully supported, the latter requires a Garmin autopilot IRL and is therefore not implemented in the RXP GTN as a "generic" mode for any aircraft.

Is there any chance you can post a screenshot of this?

With all due respect I do not recognize some of the terms you are using. All I know is that when I had the F1 GTN and I would shoot a RNAV or visual approach that had a glideslope, all I would have to press is the GS button in my Learjet and my autopilot would capture the glideslope bug and descend automatically. This was in GPS mode. But with RXP I cannot get this feature to work. If you’re telling me that in the name of accuracy that RXP does not include a functioning LNAV feature I can sort of appreciate it because it’s true to real life. But on the contrary, I found the LNAV feature very useful in the sim and would like it back. With WAAS and RNAV approaches becoming more accurate, many airports do not utilize ILS approaches especially the smaller airports. So a functioning LNAV to me is very critical. In my Learjet I would say out of all of these airports I fly into, only about 30% of them have an ILS. So is a functioning LNAV something that you can implement? I know it’s doable because like I stated I had it with F1. And I know a lot of people have been asking for it because I’ve sifted through the forums and just about every other question is about LNAV’s. 🙂

[RXP 2,338]

@Deltaair1212

Please allow me to repeat myself again:

2 hours ago, RXP said:

The GTN fully binds to the autopilot

This means both lateral and vertical guidance, the former always, the latter for LPV approaches.

May I suggest the following:

- Can you please post the content of the RXP log files? (see user's manual for file path)

- Can you also try with a stock aircraft in order to cross check whether it is aircraft related or gauge related?

 

[Deltaair1212 53]

On 12/28/2021 at 12:37 PM, RXP said:

@Deltaair1212

Please allow me to repeat myself again:

This means both lateral and vertical guidance, the former always, the latter for LPV approaches.

May I suggest the following:

- Can you please post the content of the RXP log files? (see user's manual for file path)

- Can you also try with a stock aircraft in order to cross check whether it is aircraft related or gauge related?

 

Hello I looked for the log files but I did not find them per the instructions they are not in my documents. Also I tried to fly a RNAV approach and a LPV approach with the GTN 750 and both times my aircraft never caught the glideslope even though I was at the correct altitude per the charts provided for both instances. I really would like to get this unit working properly. Nothing seems out of the ordinary in the settings so I’m not sure what’s going on. I did uninstall and reinstall both the unit and the garmin trainer. I verified both are updated to the latest and greatest. So I’m stumped. But I do not have any log files because those three that I need are there but are not “logs” they have no info in them at all so I have nothing to give you. 

[Bert Pieke 7,585]

4 hours ago, Deltaair1212 said:

Also I tried to fly a RNAV approach and a LPV approach with the GTN 750 and both times my aircraft never caught the glideslope even though I was at the correct altitude per the charts provided for both instances.

Having flown with the RXP GTN for years, I can testify that RNAV LPV approaches work correctly.

Could you provide the airport/approach that you tried?  Do you have the GTN in any other aircraft?

The F1 unit had an unrealistic enroute VNAV function that may have led you to procedures that do not reflect real world operation.

I do not know about the Lear specifically, but @ark would have an opinion on that. Hopefully he can jump in.

Edited December 30, 2021 by Bert Pieke

[Deltaair1212 53]

37 minutes ago, Bert Pieke said:

Having flown with the RXP GTN for years, I can testify that RNAV LPV approaches work correctly.

Could you provide the airport/approach that you tried?  Do you have the GTN in any other aircraft?

The F1 unit had an unrealistic enroute VNAV function that may have led you to procedures that do not reflect real world operation.

I do not know about the Lear specifically, but @ark would have an opinion on that. Hopefully he can jump in.

I am currently in Cahoots with Ark via email. I suspect this may be the issue that RXP is more realistic and therefore I am having placebo effects thinking it’s suppose to work a certain way. But I can testify Ark had me fly an approach where he can catch the GS but I can’t so that actually could be a problem…. 

[Deltaair1212 53]

what happened was the RNAV called for 5000ft until a fix where the glideslope starts the descent. Well I was at 5000ft AGL and had the correct altimeter. the GS bug actually did come alive but when it did it was already at the bottom of the sight glass meaning I had overshot the GS. But I was at the correct altitude so that was a head scratcher. Another time I was coming into KTNP on the RNAV LP+V approach which I have flown probably over 200 times. Literally. I always go direct to WISIR 6000ft and then from there the GS comes alive and will start my lears descent. Well with RXP the GS never did come alive at all. I was at 6000 at WISIR like normal. So this GTN is giving me quite the headache. I just want it to work. They say glass is suppose to relieve stress in the cockpit… but this GTN is the reason I’m now taking aleeve for my head lol! 

[Deltaair1212 53]

If the author of this program wants to share screen my computer and fly a RNAV approach himself he is more than welcome to so he can see exactly what I’m talking about. 

Edited December 30, 2021 by Deltaair1212

[Bert Pieke 7,585]

55 minutes ago, Deltaair1212 said:

Another time I was coming into KTNP on the RNAV LP+V approach which I have flown probably over 200 times. Literally. I always go direct to WISIR 6000ft and then from there the GS comes alive and will start my lears descent.

At 6000 ft you are not intercepting the RNAV glidepath.. that is an enroute descent, I would think.

[Deltaair1212 53]

Just now, Bert Pieke said:

At 6000 ft you are not intercepting the RNAV glidepath.. that is an enroute descent, I would think.

What does that mean? 

[Bert Pieke 7,585]

5 minutes ago, Deltaair1212 said:

What does that mean? 

I have not flown it... but the approach plate shows a glidepath intercept at 3800 feet.

I'll try it and see what I find.

Edited December 30, 2021 by Bert Pieke