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Question on Flightplan indication and VOR Radials

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The magenta line is irrelevant.

 

With the ND in heading up mode, the RMI indicates QDM (magnetic bearing from the aircraft to the VOR or NDB).

 

If you are established on a steady track inbound to the beacon, the white track line (which indicates the aircraft's current magnetic track) and the RMI *must* overlay each other.

 

If they do not then you *cannot* be on track to the station: the RMI needle would be falling away one way or the other.

 

The discussion about magvar is interesting, and explains why a particular track may result in flying a different radial if you display the raw data VOR CDI, but it is irrelevant to the operation of the RMI pointer.


Simon Kelsey

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The magenta line is irrelevant.

With the ND in heading up mode, the RMI indicates QDM (magnetic bearing from the aircraft to the VOR or NDB).

If you are established on a steady track inbound to the beacon, the white track line (which indicates the aircraft's current magnetic track) and the RMI *must* overlay each other.

If they do not then you *cannot* be on track to the station: the RMI needle would be falling away one way or the other.

The discussion about magvar is interesting, and explains why a particular track may result in flying a different radial if you display the raw data VOR CDI, but it is irrelevant to the operation of the RMI pointer.

+1

 

This is no longer a discussion about comparing the raw data to the fmc data. It is now a a matter of basics and principles.

 

On your next flight, tune and check the vortacs as you approach them. You may notice, as I did, one or more of the following:

- unable to manually tune a VORTAC's frequency, despite the queen having automatically tuned the same freq.

- the manually tuned VORTAC's alphanumeric ident differs between whats on the ND and what's shown on the NAVRAD page of the CDU.

- the aforementioned split/*partial split between raw data and fmc data.

 

*I say partial because, the fmc computed radial line SHOULD match it's equally computed waypoint, but instead, it matches the raw data. Which shows something is amiss.


Brian Nellis

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Emi,

 

My only thought is that you are very close to the station (like, practically overhead). With that in mind, I'm not sure I'd be paying too much attention to the needles at that range -- they become hyper-sensitive and the RMI starts doing weird things.

 

What's it like when you're a bit further, say 10-20nm, away from the VOR?

That's what I would say. You're so close to it. I'm not sure FSX deals with the "cone of silence" as in real life.


Chris Anders

PMDG 737NGX, 747, 777, DC-6; A2A 172, 182, Comanche, Cherokee, Texan, Constellation.

MSFS since version 3.0!

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Good conversation. I think everyone is misunderstanding what I mean. The ADF and VOR work on different RF principles. Yes you are right in that the the VOR needle does point to the magnetic bearing to the station. The nav signals from the nav radio are also sent to the RMI VOR indicator and since VOR theory and ADF theory are completely diffent on how the azimuth signals are generated. Actually the ADF is a relatively dumb instrument in that it just points to the station. The compass card is slaved to the magnetic heading, the ADF needle is tuned to the ADF reciever which gets RF from the Loop/Sense ADF antenna, and the VOR is tuned to the radial information from the nav radio. The RMI makes the VOR seem like it acts as an ADF to give a different way of looking at VOR data.

 

Yes...if you are tracking to the station (directly) then yes the VOR and track will line up. What I'm saying is the RMI VOR needle is sensing radial info from the nav radio in affect always centered. So if I'm flying due North and am east of the VOR the VOR needle head will point to 270 which means I'm crossing the 090 radial from the VOR. If at the same time I have the HSI set to NAV 1 and CDI set to 090 or 270 then the needle is centered and just the TO/FROM flag will be different.

 

I think the way the RMI is explained can mask the fact of how the two signals work. I think we are all thinking the same thing but getting hung up on bearing. With the RMI I no longer need to figure out the magnetic bearing to an ADF from my relative bearing sincethe ADF needle is overlaid on a slaved compass card. Also using the VOR needle and DME makes flying a manual DME arc a lot easier. No more twisting and turning of the OBS along an arc!

 

 

Steve Aull


Steve Aull

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I guess your comments aren't particularly aimed at me, as I understand what you're saying and have a working knowledge of Radio Theory, and, it is rather not applicable to the presented fault.

 

To Chris and yourself - It is never good practice to take data samples from just one point. It is far better to take them from multiple points and analyse that data.

 

In VXV's case, I tried at 40nm dme, 20dme and overhead at approx 3k/5k/10k ft agl. Always within LOS. I applied the same basic methods to the other 5 VORTAC's that I tried (not sure how ADF came into the subject). Only one behaved the way I expected it to.

 

My results were as stated in my previous posts.


Brian Nellis

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I guess your comments aren't particularly aimed at me, as I understand what you're saying and have a working knowledge of Radio Theory, and, it is rather not applicable to the presented fault.

 

To Chris and yourself - It is never good practice to take data samples from just one point. It is far better to take them from multiple points and analyse that data.

 

In VXV's case, I tried at 40nm dme, 20dme and overhead at approx 3k/5k/10k ft agl. Always within LOS. I applied the same basic methods to the other 5 VORTAC's that I tried (not sure how ADF came into the subject). Only one behaved the way I expected it to.

 

My results were as stated in my previous posts.

No it wasn't aimed at you. I was just trying to explain the RMI when it comes to raw signals. :)

 

Steve Aull


Steve Aull

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Emi,

 

You were absolutely right and I was absolutely wrong.

 

I just flew the same route segment in PSX. (I did not fly the entire flight from Germany... I  just took off from Philadelphia and flew direct BKW then VXV.) I tried to duplicate your upper winds exactly. Not sure what your altitude was - I flew at FL360.

 

Anyway, here is a shot of the PSX ND

 

nd.jpg

 

I was a few miles closer to VXV, but the rest of the conditions are the same. Indeed, the magenta track overlays the VOR pointer and tuned VOR symbol.

 

Now, the VOR RMI pointer is offset to the left, just as it was in the PMDG ND. This is because your aircraft was set up with the Nav Display in HDG up mode, so you see the nose-right wind correction the aircraft is maintaining to track to the VOR - but the important point is that the VOR symbol, magenta course line and RMI pointer all correspond, as you (correctly) maintain they should.

 

Another option is to set your ND to show TRK up, instead of HDG up, in which case everything would line up directly under the white triangle at the top of the ND. In TRK UP, you will not see any wind correction angle. I  believe TRK UP is the more common option in R/W 747 operations. It is very easy to select one or the other in the PSX aircraft menu. I believe this is also selectable in one of the PMDG FMS options menus - but not certain. I shall check after posting this. 

 

It almost appears that the PMDG ND in your original screen shot is mixing both modes. The RMI pointer is responding as it would in HDG up mode ( where there will be an offset left or right with a crosswind), while the magenta course line, and VOR symbol appear to be responding as they would in TRK UP mode, (where they always appear directly under the heading index). If that is the root cause of the problem, it may be relatively easy for PMDG to fix. It would explain why the RMI pointer is not pointing at the VOR symbol.

 

The other issue is the QDM. in your shot, the position shows the aircraft on the 052 degree radial. In the PSX shot, it shows the aircraft on the 057 radial - (a 4 degree difference). I believe that PMDG and other add-ons extract the positions of VORs ADFs and other ground navaids from the default FSX/P3D scenery - which as others have pointed out is quite out of date in terms of having accurate magnetic variation data for individual navaids - though developers such as Herve Sors do offer updates which can improve the default navaid data.


Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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A follow up to my post above. I just did a quick experiment that anyone can duplicate to see if they get the same result with the Queen. I positioned the aircraft directly on the threshold of runway 26 at KABQ (Albuquerque NM). I powered up the aircraft, aligned the IRUs, and programmed a route, departing runway 26, going to the ABQ VOR. I tuned the VOR (113.2) on both NAV radios.

 

I know from real world experience, having lived in Albuquerque, and having flown out of this airport, that the ABQ VOR is located directly on the extended centerline of runway 26, about 10 nm west.

 

The magenta line on the ND was correctly drawn to the VOR waypoint on a heading of 261 degrees, matching the extended runway centerline, but when I enabled the VOR pointer on the ND, it was pointing about 4 degrees to the left of the VOR symbol on the ND, very much like Emi's in-flight screenshot inbound to VXV.

 

I checked the relative positions of the runway and VOR in Flightsim Commander, (extracted directly from the P3D scenery database), and the VOR position was exactly correct. This would appear to confirm that there is a bug in the RMI pointer logic in the Queen's Nav Display.

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Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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Jim, kindly read the previous posts. The experiments have been done and problem isolated. The PMDG VOR System is likely to be faulty. End of story.


Brian Nellis

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Thanks Jim, I'll take that as the final confirmation that, as Brian says, PMDGs VOR system is indeed faulty.

 

Let's now await PMDGs response to my query.


Greetings from the 737 flightdeck!

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Jim, kindly read the previous posts. The experiments have been done and problem isolated. The PMDG VOR System is likely to be faulty. End of story.

I agree. I did want to give a specific ground-based example with a VOR in a known fixed location in relation to a specific runway threshold, as it is easily repeatable by anyone, and takes out the variables of the aircraft being in flight, with different upper winds at different times which could affect aircraft heading. As you know, PMDG always insists on as much empirical data as possible with bug reports.


Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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Let's now await PMDGs response to my query.

Did you make a query?  Direct communication with PMDG is at PMDG Product Support where you create a support account and submit a ticket.


Dan Downs KCRP

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Did you make a query?  Direct communication with PMDG is at PMDG Product Support where you create a support account and submit a ticket.

 

Yes sir, of course I did :)

I opened a ticket the moment we agreed here that this is not a mistake in my reading of the instruments, but actually something in the plane itself.

At the moment the status is that the issue has been forwarded to the developers in charge and they are going to investigate this after we ruled out a few other ideas they first had by mail.

It's being looked into as we speak.


Greetings from the 737 flightdeck!

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