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HSI/HUD showing Wrong heading!


MikeMikeJuliet

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Hello,

 

upon looking some things up I've come to the conclusion that the A-10C HSI / HUD heading tape shows incorrectly

 

Manual states that both HSI and the HUD should show Magnetic heading. We can be certain that the backup compass shows magnetic.

 

My case is on Caucasus, Batumi approach. The Mission Editor shows the ILS localizer on heading 126. By comparing the direction of the shown ILS arrow with the ruler you can indeed see the same heading. On the in-game F-10 map you can compare the ruler to the Lat/Long lines. When positioned to north the heading says 354 near Batumi. This is correct given the 6 degree eastern magnetic variation. If I line up perfectly on the final approach course with my A-10C, the ruler shows a heading of 126. This is all fine and well. With eastern magnetic variation, the magnetic heading compared to true should be less, which is true in this case.

 

However!

 

In cockpit however both HSI and the HUD heading tape show exactly heading 120. The backup compass shows exactly heading 126 (I assume no compass error is modeled in DCS). This means that the HSI and HUD heading tape actually doesn't show any meaningful direction. True heading is 132, magnetic heading is 126 and the HSI and HUD shows 120.

 

This doesn't seem like a problem only because of the old "2D" caucasus, there seems to be correction on the HSI, which is *A) wrongly in place and B) done in the wrong direction anyway.

 

 

Regards,

MikeMikeJuliet


Edited by MikeMikeJuliet
Changed "declination" to read: "variation" to avoid confusion. Bottom line still stands.

DCS Finland | SF squadron

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Fly an FC3 aircraft and you will get different results. This is a bug that has existed since before DCS World was released.

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Fly an FC3 aircraft and you will get different results. This is a bug that has existed since before DCS World was released.

 

Negative.

 

I just tested on the Batumi approach: F-15, Su-27, Su-25T, TF-51, Harrier, L-39C, MiG-21 and the A-10A all show a magnetic heading of 126 on both HSI and magnetic backup compass (if installed) on the approach course.

 

 

Only the Hawk (in addition to the A-10C HSI) shows a heading of 120 on both HSI and the backup compass.

 

 

Regards,

MikeMikeJuliet


Edited by MikeMikeJuliet
Formulated my post better.

DCS Finland | SF squadron

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R U talking about the A-10 or the Hawk? The MH/TH issue is really dubious due to the DCS flat world model. I assume that you are talking about deviation, not declination.

 

https://forums.eagle.ru/showthread.php?t=171274

 

https://forums.eagle.ru/showthread.php?t=104140&page=3

 

No I'm talking specifically about magnetic declination, i.e. the difference of magnetic north compared to true north.

 

Now I am aware that the current Caucasus has some accuracy issues on this because of the flat-earth projection, but that only becomes an issue on the edges of the map, and does not create more difference than 1 or 2 degrees on the map.

 

What I'm talking about here is that:

1 - The HSI of the A-10C shows incorrect values. Firstly, the manual clearly states the heading should show magnetic, which it does not.

2 - The A-10C HSI doesn't even show true, because the True heading on Batumi in particular (ILS) is 126 plus 6 degrees! Not minus! On the HSI the A-10C HSI shows 120 degrees (backup compass shows correct 126). If it showed True north (which would still be wrong, see #1) it would show a heading of 132.

 

 

The point about Hawk was just a curious point that I reported separately on the Hawk subforums as well. All other aircraft I've tested so far show correct magnetic heading of 126 on Batumi.

 

Regards,

MikeMikeJuliet

DCS Finland | SF squadron

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According to the 2 links I posted that's not the case...

 

(btw, in aviation you usually only use the terms deviation/variation) https://www.pprune.org/archive/index.php/t-279910.html

 

Pardon. English is not my native. In finnish it is called "eranto" which translates to declination. My mistake.

 

Bottom line is, I'm talking about the difference between Mag and True on Caucasus (even though the True there is more akin to Grid north due to the nature of the map projection).

 

EDIT: Strange though. Is started to look into the differences, and all sources I'm able to find at the moment declare quite the opposite. I will further investigate.

 

EDIT2: Can't find my ATPL material... call it even and let's use Variation as a median? After all, approach charts use the term "Mag Var."


Edited by MikeMikeJuliet
I'm a doofus.

DCS Finland | SF squadron

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Pardon. English is not my native. In finnish it is called "eranto" which translates to declination. My mistake.

 

Bottom line is, I'm talking about the difference between Mag and True on Caucasus (even though the True there is more akin to Grid north due to the nature of the map projection).

 

EDIT: Strange though. Is started to look into the differences, and all sources I'm able to find at the moment declare quite the opposite. I will further investigate.

 

EDIT2: Can't find my ATPL material... call it even and let's use Variation as a median? After all, approach charts use the term "Mag Var."

 

Sometimes the langague can play tricks :). There is actually magnetic declination as well the deviation. Both are important and well known by sailors. The declination comes from the earth magnetic field variance while the deviation is caused by the nearby metalic objects. In other words the deviation can vary from a compass to a compass and between vehicles in which it is installed.

Deviation however is generally canceled by callibrating the compas so in DCS we should be concerned only with the decliatination.

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Yeah, I've been looking way too much into the issue in the past hours. Now let us pass the semantics and get to the bottom of this!

 

 

An update on the previous observations!

A-10C magnetic backup compass does read the same as the HSI.

 

I've now tested All my available aircraft on Batumi by spawning "Take-off from runway" which gives the runway 31. All other aircraft except the A-10C and the Hawk give the heading of 306 (as suggested by ME, F-10 map and all available charts DCS or real life). I will further investigate on other airfields.

DCS Finland | SF squadron

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All other aircraft except the A-10C and the Hawk give the heading of 306 (as suggested by ME, F-10 map and all available charts DCS or real life). I will further investigate on other airfields.

 

The ME and F10 map show True headings, the magnetic declination in the Caucasus theater is +6°, so magnetic readings will be 6° less than measured in the ME/F10 map.

 

Although this diagram is for Nevada, the principle is the same:

 

attachment.php?attachmentid=172869&stc=1&d=1511909125

 

FC3 aircraft match the F10 map while the instruments/systems of full DCS modules are able to take magnetic declination into account.

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The ME and F10 map show True headings, the magnetic declination in the Caucasus theater is +6°, so magnetic readings will be 6° less than measured in the ME/F10 map.

 

Although this diagram is for Nevada, the principle is the same:

 

attachment.php?attachmentid=172869&stc=1&d=1511909125

 

FC3 aircraft match the F10 map while the instruments/systems of full DCS modules are able to take magnetic declination into account.

 

I know this. Problem is, the full fidelity aircraft apparently don't take this into account. The Headings are exactly the same on All FC-3 aircraft, L-39C and ZA, Harrier, TF-51, Su-25T and MiG-21 (those I own).

 

The only modules I own that seem to follow this are the A-10C and the Hawk. All others show exactly the headings shown on the ME/F-10 map. A couple of squad mates tested the same with the MiG-15.

 

 

 

 

 

I digress, we hade a long chat about this on our squadron discord and came to the conclusion that DCS modules don't follow the same rules between each other. i.e two modules claim to use magnetic headings, but show different values separated by variation amout. Also, neither true nor mag refers to the Lat-long coordinates.

 

Now I don't mind if the data on DCS doesn't show exactly the real world values, so long as the same error is applied to all modules.

 

 

Case closed. DCS is borkeh.

DCS Finland | SF squadron

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I know this. Problem is, the full fidelity aircraft apparently don't take this into account. The Headings are exactly the same on All FC-3 aircraft, L-39C and ZA, Harrier, TF-51, Su-25T and MiG-21 (those I own).

• The L-39C and ZA RMI uses True bearings, AFAIK this is by design and because the RSBN ground stations are aligned with True north. You should find the cockpit standby magnetic reads 6° less than the RMI.

 

• The early access Harrier displays True bearings (this is signified by the 'T' above the heading tape). IRL it can display both but the MFCD menu option isn't functional yet.

 

• Su-25T has FC3 level systems modelling, so displays ME/F10 map (true) bearings.

 

• I'm surprised the compass in the TF-51 matches True bearings as it's based off the P-51D but as I haven't flown any navigation exercises in it, can't confirm it does or doesn't.

 

• IIRC the MiG-21 flew to Magnetic bearings last time I flew her but it's been a while since I used her for serious navigation as I usually use the L-39 for that type of exercise. It's also possible it's changed since the L-39 came out.

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• The L-39C and ZA RMI uses True bearings, AFAIK this is by design and because the RSBN ground stations are aligned with True north. You should find the cockpit standby magnetic reads 6° less than the RMI.

 

• The early access Harrier displays True bearings (this is signified by the 'T' above the heading tape). IRL it can display both but the MFCD menu option isn't functional yet.

 

• Su-25T has FC3 level systems modelling, so displays ME/F10 map (true) bearings.

 

• I'm surprised the compass in the TF-51 matches True bearings as it's based off the P-51D but as I haven't flown any navigation exercises in it, can't confirm it does or doesn't.

 

• IIRC the MiG-21 flew to Magnetic bearings last time I flew her but it's been a while since I used her for serious navigation as I usually use the L-39 for that type of exercise. It's also possible it's changed since the L-39 came out.

 

I tested the L-39 on both versions, and it showed the same bearing on both compasses (HSI and backup). All those aircraft also show the exact same headings. What complicates things is that I just checked the MiG-21 manual, and it claims the headings are in magnetic... so how are they the same headings as the L-39 and Harrier if those are supposed to be True?

 

I did all the tests I reported here today, so it's not like this is old info. Current Stable version 1.5.8

DCS Finland | SF squadron

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The whole True North in Caucasus is wrong.

it shows straight up on the map as True North while in real life you should be able to track the ruler along the latitude line and that is True North.

You will therefor not have the correct correlation between True on magnetic on Caucasus map and it will become more off the further east you go.

 

So in reality this means the the DCS universe is not spherical in the way the earth is.


Edited by Bravo
Found same error in 2.2
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The whole True North in Caucasus is wrong.

it shows straight up on the map as True North while in real life you should be able to track the ruler along the latitude line and that is True North.

You will therefor not have the correct correlation between True on magnetic on Caucasus map and it will become more off the further east you go.

 

So in reality this means the the DCS universe is not spherical in the way the earth is.

 

Yep, I've figured in the past 48 hours. As I've said, case closed. My brain hurts.

DCS Finland | SF squadron

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