[RESOLVED] EHSI Ground Track uses True bearings when Compass Rose uses Magnetic

[Ramsay]

Not sure if this is WIP or a bug that's made it into the wild'

 

The EHSI Ground Track Pointer and Digital Display use True bearings when Compass Rose, HUD, etc. are set to use Magnetic bearings.

 

The pointer and track therefore don't lineup with the real flight path and the EHSI is displaying a mix of True and magnetic bearings when the 'T' lubber line is 'off'

 

 

Tested in DCS 2.5.2.19641 Steam Open Beta

Edited July 20, 2018 by Ramsay
Picture was a little bigger than needed

[defeatist99]

Yeah this has been bothering me since the update.

[Shadow_1stVFW]

Bump. To be worked on in a future update.

 

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[Shrike88]

Can someone from Razbam please ackn. this as it's from July. Would like to see this addressed.

[Shadow_1stVFW]

I could have sworn this was correct for an update or two.

 

Though maybe I was just in the habit of switching to true headings. Either way, +1 to be addressed.

 

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[Shadow_1stVFW]

Bump

 

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[JaBoG32_Herby]

23.9.7

Ground Track (Digital Readout) and Ground Track Pointer

This pointer indicates the aircraft true ground track. On Radar and Night Attack aircraft ground track is also a digital readout. Trainer aircraft with H4.0 have a digital readout of ground track as well.

 

 

This is from the A1-AV8BB-NFM-000 manual making me believe, the described system behavior in game is as per design.

[Shadow_1stVFW]

23.9.7

Ground Track (Digital Readout) and Ground Track Pointer

This pointer indicates the aircraft true ground track. On Radar and Night Attack aircraft ground track is also a digital readout. Trainer aircraft with H4.0 have a digital readout of ground track as well.

 

 

This is from the A1-AV8BB-NFM-000 manual making me believe, the described system behavior in game is as per design.

Negative. "True ground track" does not mean down in degrees true. It means where the aircraft is actually flying. Meaning of I'm flying in no wind, and my jet isn't bent, I will be pointing 090* and tracking 090* both magnetic.

 

If I've got a stuff crosswind I could be pointing 090* and flying 085* both magnetic.

 

The point of this gets to homing vs tracking.

 

Watch this it explains it

 

 

 

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[JaBoG32_Herby]

Thank you very much, Sir, for the well meant advice and the link.

 

I have to disagree however, I’m afraid, since the video as well as your description illustrate the difference between Heading and Track, as you rightly noted.

 

In aviation terminology, “True” used in conjunction with a direction points out the difference to this direction in “Magnetic “, where, and I’m sure you’re familiar, the first is based on the geographical North pole while the latter is referencing to the Magnetic Pole with the difference in the positions between the two contributing (among other local magnetic factors) to the local magnetic variation.

 

This would explain, what the OP showed in the images he posted.

Referencing his EHSI to Magnetic Heading, the True Ground Track Pointer regards the magnetic variation, which is supposed to be 6° East.

 

What I have no explanation for, I admit, is, what the practical purpose of this feature could be on the battlefield.

[Ramsay]

This would explain, what the OP showed in the images he posted.

Referencing his EHSI to Magnetic Heading, the True Ground Track Pointer regards the magnetic variation, which is supposed to be 6° East.

 

What I have no explanation for, I admit, is, what the practical purpose of this feature could be on the battlefield.

 

The AV-8B is flying the same ground track in both pictures 120°M (125°T), the aircraft's direction does not change, when changing between modes.

 

You may argue that the AV-8B digital ground track displays 125°T in both EHSI magnetic/true modes.

 

However, with the EHSI set to display magnetic bearings, the ground track pointer points to 125°M (131°T), not 125°T

 

Personally, I believe 'true ground track' in the manual, when taken in context, means 'ground track' corrected for wind drift, etc., not TRUE bearing, as all the other bearings on the EHSI and HUD respect the lubber line - "T" = True bearings, "|" = Magnetic bearings

 

If it were otherwise, the numeric ground track bearing would have a 'T' postfix.

Edited February 9, 2019 by Ramsay

[Shadow_1stVFW]

 

What I have no explanation for, I admit, is, what the practical purpose of this feature could be on the battlefield.

 

Ok, so you're missing what I'm saying.

 

NATOPS manuals use specific terms for specific things. "True ground track" does not mean the same as "degrees true." "True ground track" means your "[actual] ground track" I will call your attention to the word track also. Which references the actual path over the ground. (Notice how track and tracking are used here)

 

What is the use for this?

 

Two simple examples:

"Blazer 222, turn left heading 270"

Here you turn until your magnetic heading is 270, regardless of your ground track. In this instance the control will make any corrections for cross track error. Such as in a precision approach radar approach, or under positive radar control.

 

"Blazer 222, proceed direct the Demming VORTAC"

In this instance the control wants you to track directly to the VORTAC, not home it, track it. While this can admittedly be done with magnetic headings and the needle, the ground track indicator gives you a direct indication of how to do that. In this case you place your ground track indicator directly underneath the tacan triangle on the EHSD.

 

Further, the system allows you to change the reference heading system in the press of two buttons, in which case all headings are displayed in true. What changes there is the heading on the compass, not your ground track.

 

Ask yourself, what is more useful information to the pilot, a conversion to degrees true, or his actual ground track?

 

The purpose of the video I linked was to show why you'd have both indications on the display.

 

I'm not asking if the system is incorrect. I know it's not. I can further explain should I need to.

 

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[Shadow_1stVFW]

The AV-8B is flying the same ground track in both pictures 120°M (125°T), the aircraft's direction does not change, when changing between modes.

 

 

 

You may argue that the AV-8B digital ground track displays 125°T in both EHSI magnetic/true modes.

 

 

 

However, with the EHSI set to display magnetic bearings, the ground track pointer points to 125°M i.e. magnetic, NOT 125°T

 

 

 

Personally, I believe 'true ground track' in the manual, when taken in context, means 'ground track' corrected for wind drift, etc., not TRUE bearing, as all the other bearings on the EHSI and HUD respect the lubber line - "T" = True bearings, "|" = Magnetic bearings

 

 

 

If it were otherwise, the numeric ground track bearing would have a 'T' postfix.

You are correct. It's displaying incorrectly.

 

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[JaBoG32_Herby]

@Shadow_1stVFW

I appreciate your effort to try and explain all those terms to me, but I think, you shouldn’t invest more of your time in doing that. I’m an active aviator for the last 27 years and I make a living out of flying airplanes for the last 23 years of my life. For that I’m quite familiar with the concept of headings and tracks and references based on true or magnetic directions.

 

The NATOPS manual I referenced to uses the term True Ground Track exactly the way it’s meant to be used, as an explanation for an indication that is based on the reference datum true north.

 

Ramsay posted two images, the first showing an EHSI with a Track indication to Batumi Tacan of 119° magnetic with a Ground Track Pointer and it’s associated Ground Track Digital Readout showing 125° true and the second showing the EHSI set to TRUE now indicating a true track of 125° to Batumi Tacan with the Pointer and the Readout still at 125° true.

 

I’m not sure, where you gentlemen see the bug.

 

The system does, what the Airplane Flight Manual describes.

It shows a True Ground Track. That it does this with the EHSI in either TRUE or Magnetic is self explanatory.

[Shadow_1stVFW]

@Shadow_1stVFW

I appreciate your effort to try and explain all those terms to me, but I think, you shouldn’t invest more of your time in doing that. I’m an active aviator for the last 27 years and I make a living out of flying airplanes for the last 23 years of my life. For that I’m quite familiar with the concept of headings and tracks and references based on true or magnetic directions.

 

The NATOPS manual I referenced to uses the term True Ground Track exactly the way it’s meant to be used, as an explanation for an indication that is based on the reference datum true north.

 

Ramsay posted two images, the first showing an EHSI with a Track indication to Batumi Tacan of 119° magnetic with a Ground Track Pointer and it’s associated Ground Track Digital Readout showing 125° true and the second showing the EHSI set to TRUE now indicating a true track of 125° to Batumi Tacan with the Pointer and the Readout still at 125° true.

 

I’m not sure, where you gentlemen see the bug.

 

The system does, what the Airplane Flight Manual describes.

It shows a True Ground Track. That it does this with the EHSI in either TRUE or Magnetic is self explanatory.

 

I hear you, you are mistaken on how you think this works.

 

I'll let the manual speak then.

 

23.9.34 TRUE Pushbutton (TAV--8B with H4.0 and Radar and Night Attack Aircraft)

When selected the system uses true heading to compute the orientation of the compass rose, aircraft symbol, ground

track pointer, map heading and bearing to waypoint, offset or TACAN station. The selection of true or magnetic also

affects the display of TACAN, waypoint, and markpoint offset bearing, targetpoint terminal heading and pattern

heading, and radar BRAA (bearing, range, altitude, aspect) and cursor data block displays. A T legend appears in

place of lubber line and also a Tappears above heading display onHUDto indicate true heading display.WhenTRUE

legend is boxed true heading is enabled, else magnetic heading is enabled. Selection of TRUE is NOT independent

for each MAPM. Selecting TRUE on any MAPM affects all displays.

 

23.9.26 EHSI Pushbutton (TAV--8B with H4.0 and Radar and Night Attack Aircraft)

Selecting map menu (MAPM) on the centered or decentered EHSD display, any DATA display, or the EWM (with

H4.0) display enables the EHSI pushbutton legend. Selection of EHSI is independent for eachMAPM. Pressing this

pushbutton on the Center, Decenter, or EW MAPM enables display of the compass rose, lubber line and T legend,

ground track pointer, waypoint and waypoint offset, TACAN and TACAN offset and target (with H4.0) bearing

pointers on the Center, Decenter and EWpage. Pressing this pushbutton on the WYPT or TCNDataMAPMenables

display of the compass rose, lubber line and T legend, and aircraft symbol on the WYPT and TCN Data pages.

Pressing this pushbutton on the A/C DataMAPMenables display of the compass rose, and lubber line and T legend

on the A/C Data pages. When enabled the EHSI legend is boxed.

 

23.9.7 Ground Track (Digital Readout) and Ground Track Pointer

This pointer indicates the aircraft true ground track. On Radar and Night Attack aircraft ground track is also a digital

readout. Trainer aircraft with H4.0 have a digital readout of ground track as well.

 

 

Works the same way as this: Should be familiar to you.

 

[JaBoG32_Herby]

Well, sir, I certainly understand, what you’re up to. And as I’ve mentioned in my initial remarks, I’m not sure how to make good use of a track pointer that is referenced to true north while my compass rose is referenced to magnetic north.

But we might agree that user comfort is not the point here.

 

You show us the function of the TRUE Push button in 23.9.34.

This paragraph describes the change of compass reference from magnetic to true.

Here you seem to accept the fact that, in the context of this manual, True used in conjunction with a direction indication is meant to be as opposed to magnetic while you decline the same concept in 23.9.7 for a True Track?

Well, I’m sure you see my point.

 

As a side note for the image you’ve picked from the NATOPS manual, it shows an EHSD presentation for a Day Attack Harrier.

 

And another side note for the CDI tutorial, it is your interpretation of how the Ground Track Pointer should work. The manual nowhere mentions that on this aircraft the Track Pointer is used to show the Aircraft Track in degrees magnetic.

Edited February 10, 2019 by JaBoG32_Herby

[Ramsay]

I’m an active aviator for the last 27 years and I make a living out of flying airplanes for the last 23 years of my life. For that I’m quite familiar with the concept of headings and tracks and references based on true or magnetic directions.

...

Ramsay posted two images, the first showing an EHSI with a Track indication to Batumi Tacan of 119° magnetic with a Ground Track Pointer and it’s associated Ground Track Digital Readout showing 125° true

 

This is where you (and the module) are in error - in the first image, the Ground Track Pointer is pointing to 125° magnetic on the compass rose i.e. 131° true.

 

Edited February 10, 2019 by Ramsay
Add picture

[Shadow_1stVFW]

 

You show us the function of the TRUE Push button in 23.9.34.

This paragraph describes the change of compass reference from magnetic to true.

Here you seem to accept the fact that, in the context of this manual, True used in conjunction with a direction indication is meant to be as opposed to magnetic while you decline the same concept in 23.9.7 for a True Track?

Well, I’m sure you see my point.

 

 

Your ground track does not change whether it is referenced in true or magnetic headings. You are going towards where you are going (batumi tacan in the picture). The only thing that changes is the heading on a compass.

 

Ramsay said that picture is taken with no wind, his ground track is not pointing to the tacan. So the ground track indicator is not indicating his ground track. That's the problem.

 

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[JaBoG32_Herby]

Ramsay, I’ll make one last attempt.

 

The method to calculate a true bearing (TB) is to take the magnetic bearing (MB) and add the magnetic variation (MV) to it.

 

TB = MB + MV

 

For your example I suppose, since you seemed to be tracking perfectly towards Batumi Tacan, your magnetic heading to be 119° and without any wind your magnetic track to be 119° as well.

The magnetic variation at your present position in game is 6° East. The convention is to express easterly variations as positive and westerly variations as negative.

 

For the above given formula we would get 119° + 6° = 125°.

 

With that 125° is your True Ground Track.

 

Now we look at your image and we realize that Ground Track Pointer as well as the Ground Track Digital Readout indicate 125°.

 

This is what the manual says:

This pointer indicates the aircraft true ground track.

 

Whether your compass rose is oriented to true or magnetic is irrelevant. It doesn’t change the value for your True Track.

 

So, to summarize the above: we were able to calculate the expected True Ground Track to be 125°.

We were able to confirm the Ground Track Pointer as well as the Ground Track Digital Readout to show 125°.

And we were able to derive from the appropriate AFM that the Pointer and the Readout present the Pilot with a True Track.

 

I’m not sure how much more it needs to acknowledge that this is in fact not a bug but a system feature.

 

However, I rest my case here. There’s nothing more to be said about this.

[dahlgren]

Paragraph 23.9.34 in the manual says that the ground track should change between magnetic and true depending on the OSB selection "TRUE".

This leads me to believe that the current behaviour is incorrect. And it makes no sense to have ground track pointing in the wrong direction on the EHSD.

[tom_19d]

Bump: Any chance for acknowledgement on this one?

[UncleZam]

I was also baffled why the ground track points roughly 25 degrees off of the correct course in Nevada. After some testing I found out following:

 

1. Ground track works correcly when EHSI is in TRUE mode (also accounts for the wind drift).

2. When EHSI is switched to magnetic, the compass rose (in EHSI and HUD) react correctly by subtracting 12 degrees (magnetic deviation in Neavada) to get new values. However the ground track value is added 12 degrees instead of subtracting! This results in ground track value, which is 2x12=24 degrees wrong (you can see this both graphically and in digitals in EHSI display).

 

TL;DR: It is a bug: When calculating magnetic ground track direction from the true (as in true bearing) ground track direction, the magnetic deviation should be subtracted not added like it is done currently.

Edited July 31, 2020 by Unclezam

[audax]

Thank you for testing this! I almost thought that I was suddenly too dumb to read an HSI.

[Swift.]

There have been some changes to the EHSD it seems, but this bug is still present.

[Shrike88]

And will be shelved and collect dust with the other outstanding navigation EHSD Bugs

[Ramsay]

Ground Track Digits still use TRUE when EHSI set to use MAGNETIC after latest patch

 

First of all I must thank Razbam for fixing the Ground Track pointer when the EHSI is set to use magnetic bearings.

 

Unfortunately the Ground Track Digits still use TRUE when EHSI set to use MAGNETIC.

 

 

As I'm not sure if this is WIP or something that's been missed, I'll report it here.

 

Tested in Open Beta 2.5.6.55363 on final to Batumi.