bpcw001

Question about GPS mode

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Hi,

I use a single GTN750 and the Milviz WXR config in the Lear 35. My question pertains to the behavior of VLOC  and GPS coupling with respect to the RMIs.

In VLOC mode, everything works as expected, i. e. HSI1 displays VOR1, HSI2 displays VOR2, and each RMI has VOR1/2 and NDB1/2.

In GPS mode, both HDI1/2 are coupled to GPS. Ok. But the VOR channels of the RMIs seem also blocked. NDBs are still picked up, but RMIs don‘t point to VORs any more.

Should it not be that only the HSI‘s are coupled to GPS, but the RMIs can still point to VORs?

Thanks

 

Edited by bpcw001

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NAV 1 can't be detected in GPS mode. Only NAV 2. So in GPS mode the larger green arrow in the RMI which is for NAV 2 will work for VOR's. And of course in VLOC all works.

This is because flight sim needs to borrow Nav 1 when in GPS mode.

Edited by Flysimware

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1 hour ago, bpcw001 said:

Should it not be that only the HSI‘s are coupled to GPS, but the RMIs can still point to VORs?

What you say above is correct in the real world. But as FSW explained above, in the sim when in GPS mode, the GPS 'signal' is used as a Nav1 replacement.

Al

Edited by ark

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Thanks for your replies.

I understand that the channel for VOR1 will be taken by GPS, but I will have to double check again if I can still see RMI VOR2 reacting properly with GPS mode on.

I had at least one flight where both VOR channels were INOP as soon as GPS mode was engaged.

Let‘s see ...

 

 

Edited by bpcw001

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Still: 

According to the logic that GPS takes VOR1, why is HSI2 also INOP? should it not display VOR2 with HSI1 coupled to GPS?

Is it intentional?

Sorry for pestering you with questions, but the Lear is so great I fly it every day and I just would like to understand.

Thanks

Edited by bpcw001

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hHi Flysimware,

I was speaking too soon.

On the ground, when switching from VLOC to GPS with no flight plan being followed, the system behaves as expected, i. e. RMIs will indicate VOR2.

However, when enroute with GPS coupled and on autopilot, VOR2 is dead on the RMIs.

Can be easily checked by switching autopilot to from NAV to HDG and going from GPS to VLOC mode. Immediately, a tuned VOR2 will indicate on the RMIs. As soon as GPS mode is engaged again, the RMI needles for VOR2 will turn to the six o clock position and stay pegged there.

Maybe something to look into after all. It appears that GPS grabs both VOR 1 and 2 channels when actually navigating a flight plan. Or is my GTN integration flawed?

 

btw: the same happens in VLOC mode if you put an ILS frequency into NAV1 via GTN. 

Try the following at an airport (works on the ground also):

Tune in two different, receivable VOR1 and VOR2 stations and put both RMI needles to VOR indication. Observe the correct indication.

Now, in the GTN, put a receivable ILS frequency into NAV1 standby and activate it. Observe BOTH VOR iindications on RMI are lost (needles go 6 o clock).

Switch NAV1 back to the VOR before and observe the   correct RMI indication being restored.

It appears that ILS or GPS NAV on VOR1 also block VOR2 being properly displayed. Interesting enough, the DME for VOR2 is still received.

Something seems not right here. Please advise.

 

 

 

Thanks for your help

Edited by bpcw001

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1 hour ago, bpcw001 said:

hHi Flysimware,

Can be easily checked by switching autopilot to from NAV to HDG and going from GPS to VLOC mode. Immediately, a tuned VOR2 will indicate on the RMIs. As soon as GPS mode is engaged again, the RMI needles for VOR2 will turn to the six o clock position and stay pegged there.

No, I can't replicate your experience. RMI needle 2 works as it should for me. No matter what I do with the AP or VLOC/GPS modes, it points to the VOR I have tuned in on NAV2 as long as the VOR is in range.

Regarding the HSIs. In VOLC, each HSI responds to its 'own' nav signal. In GPS mode, HSI1 responds to the GPS signal and HSI2 is basically inop.

Also note there is no switch to switch the AP between NAV1 and NAV2. The way the AP operation has been coded, the AP 'follows' NAV1 is there is a valid NAV1 signal in VLOC, or it follows the GPS in GPS mode. The AP will 'follow' NAV2 in VLOC mode if the is a valid NAV2 signal AND if there is NOT a valid NAV1 signal of any 'type' (VLOC or GPS). So as far as the AP is concerned, NAV1 (VLOC or GPS) dominates.

Hope this helps explain things a bit,

Al

 

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1 hour ago, ark said:

No, I can't replicate your experience. RMI needle 2 works as it should for me. No matter what I do with the AP or VLOC/GPS modes, it points to the VOR I have tuned in on NAV2 as long as the VOR is in range.

Regarding the HSIs. In VOLC, each HSI responds to its 'own' nav signal. In GPS mode, HSI1 responds to the GPS signal and HSI2 is basically inop.

Also note there is no switch to switch the AP between NAV1 and NAV2. The way the AP operation has been coded, the AP 'follows' NAV1 is there is a valid NAV1 signal in VLOC, or it follows the GPS in GPS mode. The AP will 'follow' NAV2 in VLOC mode if the is a valid NAV2 signal AND if there is NOT a valid NAV1 signal of any 'type' (VLOC or GPS). So as far as the AP is concerned, NAV1 (VLOC or GPS) dominates.

Hope this helps explain things a bit,

Al

 

Have you tried with an ILS frequency in NAV1 ?

Edited by bpcw001

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10 minutes ago, bpcw001 said:

Have you tried with an ILS frequency in NAV1 ?

Have I tried what with an ILS freq in NAV1?

Al

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25 minutes ago, ark said:

Have I tried what with an ILS freq in NAV1?

Al

yep. switching to an ILS frequency in NAV1 instead of having just a VOR tuned in there.

However, playing around with the described situation, it seems not always reproducible.

Will do a full reinstall and see if it gets fixed, 

If you cannot reproduce my observations then it must be something particular to my system.

 

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1 hour ago, bpcw001 said:

yep. switching to an ILS frequency in NAV1 instead of having just a VOR tuned in there.

However, playing around with the described situation, it seems not always reproducible.

Will do a full reinstall and see if it gets fixed, 

If you cannot reproduce my observations then it must be something particular to my system.

 

You still didn't explain exactly what you are looking at with the ILS freq in Nav1. It would also be helpful to know what sim you are using. I am using P3Dv4.4.

I will assume you are looking at the RMI needles when an ILS freq is tuned into NAV1. Here is what I see in that case if in GPS mode. The NAV1 RMI needle is off in the 6 o'clock position as it should be. RMI needle 2 points to an in-range VOR if the VOR freq is in NAV2. If an ILS freq is in NAV2, RMI2 incorrectly points to the localizer. This, of course, is with the RMI set up for NAV and not ADF signals.

However, if the above experiment is conducted in VLOC mode, RMI needle 2 goes to the off position whether a nearby VOR or localizer is tuned into NAV2. It should point to the VOR when that freq is tuned in. I think this is a bug that crept into some code designed to fix another bug!  There has been a long standing bug in the sims such that if an ILS or LOC signal is tuned in, the RMI needles will point to the localizer location (airport), which is not correct. FSW has added some special code to fix this bug in the Falcon 50 so that the RMI needles will be off if an ILS or LOC is tuned in. So what I think may have happened in the Lear35 fix is that both RMI needles have been turned off if NAV1 is tuned to an ILS frequency when in VLOC. I will let FSW know about the bugs in the Lear.

All seems to work correctly in the Falcon 50. I think the next update of the Lear will have the same fix as the Falcon 50

Also, if you are using P3Dv4.4, you might try using the F-35 as your default flight or a/c if not already doing so. For reasons I can't explain, a number of us have found that switching to the F-35 as a default flight, so it is loaded before the Lear35 or Falcon 50, has cleared up some strange problems -- such as AP lights flashing, switches not working, etc. Very strange.

Al

 

Edited by ark

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Hi Al,

thanks for your explanations. Makes sense.

However, I experimented a bit more and found the following:

The VOR2 needlle on them RMI is INOP with AP on and a flight plan being followed in GPS mode in case the GTN VNAV is enabled.

If I disable VNAV in the GTN 750, VOR2 will indicate on the RMIs as expected, no matter if GPS mode or not. 

Can you reproduce this behavior?

 

btw: I am on P3D v4.4, no issues otherwise so far. I always load thr Lear starting from a shutdown Piper Cub.

 

Edited by bpcw001

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46 minutes ago, bpcw001 said:

Hi Al,

thanks for your explanations. Makes sense.

However, I experimented a bit more and found the following:

The VOR2 needlle on them RMI is INOP with AP on and a flight plan being followed in GPS mode in case the GTN VNAV is enabled.

If I disable VNAV in the GTN 750, VOR2 will indicate on the RMIs as expected, no matter if GPS mode or not. 

Can you reproduce this behavior?

 

btw: I am on P3D v4.4, no issues otherwise so far. I always load thr Lear starting from a shutdown Piper Cub.

 

No, the RMI needle for NAV2 seems to work in GPS and AP mode whether or not VNAV is active (tested with flight plan on the ground, didn't actually fly it). It is hard to see why the GPS VNAV would impact the RMI. I have not seen any other posts with similar problems (yet) which makes me think it may be your setup rather than something generic with the Lear.

For what it's worth, if you look near the end of this thread https://www.avsim.com/forums/topic/549794-fuel-control-in-lear/?tab=comments#comment-3968429

you will see one example of where switching from using the Piper Cub to the F-35 as the default a/c solved a weird switch problem in the Lear. As I said, very strange.

Al

 

 

Edited by ark

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19 minutes ago, ark said:

No, the RMI needle for NAV2 seems to work in GPS and AP mode whether or not VNAV is active (tested with flight plan on the ground, didn't actually fly it). It is hard to see why the GPS VNAV would impact the RMI. I have not seen any other posts with similar problems (yet) which makes me think it may be your setup rather than something generic with the Lear.

For what it's worth, if you look near the end of this thread https://www.avsim.com/forums/topic/549794-fuel-control-in-lear/?tab=comments#comment-3968429

you will see one example of where switching from using the Piper Cub to the F-35 as the default a/c solved a weird switch problem in the Lear. As I said, very strange.

Al

 

 

You cannot reproduce this on the ground. That‘s what caught me too.

You need to do a flight with a flight plan with alt constraints, typically in a prselected arrival/approach procedure, and wait for GTN VNAV to become active, which will be a couple of mins after takeoff. As soon as you see the VDEV indicator appear on the left side of HSI1, VOR2 indication will be gone.

 

Will try to use the F35 as a starting point.

Edited by bpcw001

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OK. started now with the default P3D v4.4 F35.

 

All the same. 

Could you try the following, doesn't even require to make a flight.

 

Load the Lear35. Use the Hangar Panel and turn everything off using the "All systems off"  option.

Place yourself at threshold runway 25 at EDDS. Power up the Lear. Batteries, Inverters, and Avionics master. Let everything come up, especially the GTN 750. 

Have the GTN in VLOC mode.

Tune 116.85 into VOR2 (STG VOR). Observe correct indication in RMIs vor VOR2.

Now, in the GTN, put in 109.90 as active NAV1 frequency.

You should get vertical indicators on HSI1 since 109.90 is the ILS for EDDS RWY 25.

What are the RMI needles now showing for VOR2?

 

As far as I can see the pattern now, the problem on my system narrows down to the following: as soon as there is any kind of vertical guidance involved on the VOR1 channel, either from an ILS glideslope or from GTN's VNAV, I lose the VOR2 channel.

 

Thoughts?

Edited by bpcw001

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1 hour ago, bpcw001 said:

OK. started now with the default P3D v4.4 F35.

 

All the same. 

Could you try the following, doesn't even require to make a flight.

 

Load the Lear35. Use the Hangar Panel and turn everything off using the "All systems off"  option.

Place yourself at threshold runway 25 at EDDS. Power up the Lear. Batteries, Inverters, and Avionics master. Let everything come up, especially the GTN 750. 

Have the GTN in VLOC mode.

Tune 116.85 into VOR2 (STG VOR). Observe correct indication in RMIs vor VOR2.

Now, in the GTN, put in 109.90 as active NAV1 frequency.

You should get vertical indicators on HSI1 since 109.90 is the ILS for EDDS RWY 25.

What are the RMI needles now showing for VOR2?

 

As far as I can see the pattern now, the problem on my system narrows down to the following: as soon as there is any kind of vertical guidance involved on the VOR1 channel, either from an ILS glideslope or from GTN's VNAV, I lose the VOR2 channel.

 

Thoughts?

Dave,

First, to do this test you need to put your a/c on runway 07.  Since the VOR is directly behind the threshold of runway 25 and on the runway center line, the RMI will point to the 6 o'clock position whether it is actually pointing to the VOR or is in its off position. 

I first tried the test with the Falcon 50 since I know the RMI code was updated to deal with localizers, etc, as mentioned above. RMI needle two pointed to the VOR (the 12 o'clock position since the a/c was on runway 07) both with and without freq 109.9 in Nav1, and in both the VLOC and GPS modes. So, all good.

As I mentioned above, I know the Lear has a bug in its RMI code as far as dealing with a localizer signal is concerned (and what other problems this bug could be causing I don't know). So I was not surprised the second RMI needle did not work correctly in this EDDS test under VLOC. It correctly pointed to the 12 o'clock position when there was no localizer signal tuned in on Nav 1, but went to the off position when there was a localizer signal tuned in on Nav1. So I think the bug is that BOTH RMI needles are getting 'turned off' when a localizer signal is tuned into Nav1 instead of just the first RMI needle getting turned off. Again, what other issues this bug could be causing I don't know, so I suggest you just ignore all RMI problems until FSW puts out the next Lear update.

Al

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Hi Al,

OK, then. So there is an issue with localizers in the Lear 35, and VOR2 not indicating correctly in this scenario is expected. 

So we have at least clarified that this is not a peculiarity of my system. So far so good.

I suppose the GPS LNAV/VNAV guidance will also internally be handled on the LOC/GS channels, and hence the same behavior concerning VOR2 shows in that case.

Good to hear that this does not occur in the Falcon. However, I would of course be interested if (and when) the fixed RMI code from the Falcon will make it to the Lear someday.

So, I think we're finally through with this one.

I'd like to thank you Al for your patience and for bearing with me through all this. Great forum!

 

BTW: I put the aircraft at the holding point of RWY25 in EDDS which is perpedicular to the runway, so the STG VOR would indicate at 9 o'clock on the RMI. Putting the aircraft straight on RWY25 would have been, as you correctly suggested, pointless since STG would indicate 6 o'clock in both RMI operational and INOP cases.

 

Edited by bpcw001

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6 hours ago, bpcw001 said:

Hi Al,

OK, then. So there is an issue with localizers in the Lear 35, and VOR2 not indicating correctly in this scenario is expected. 

So we have at least clarified that this is not a peculiarity of my system. So far so good.

Good to hear that this does not occur in the Falcon. However, I would of course be interested if (and when) the fixed RMI code from the Falcon will make it to the Lear someday.

 

 

Dave,

The code for the Lear's RMI is in the interior model file, which is a complied file so I can't see it with a text editor to see what is going on. However, I did talk with FSW and we both think there is a typo of some type in that code. FSW confirmed the intent is to update the Lear's RMI code with the same type of code as in the Falcon 50 once the update for the Falcon 50 is done in a few weeks. Hopefully the RMI errors you are having that I could not reproduce will go away with the updated code.

Al

 

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1 hour ago, ark said:

Dave,

The code for the Lear's RMI is in the interior model file, which is a complied file so I can't see it with a text editor to see what is going on. However, I did talk with FSW and we both think there is a typo of some type in that code. FSW confirmed the intent is to update the Lear's RMI code with the same type of code as in the Falcon 50 once the update for the Falcon 50 is done in a few weeks. Hopefully the RMI errors you are having that I could not reproduce will go away with the updated code.

Al

 

Cool. Thanks!

Fortunately, RMI issue is minor and definitely does not spoil my enjoyment of the Lear.

Outstanding support and communication with your customers!

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