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TID MC and HD readings: Magnetic vs True


Karon
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I'm putting together some stuff about the geometry. I noticed a while ago that the MC reading seemed a bit odd, but I did not bother much. I spent 5-6 hours trying to understand this problem, but I'm giving up. Plz help.

 

Issue: Magnetic Course displays True value rather than Magnetic.

 

I checked the NAVAIR 01−F14AAA−1, page 20-20. Two cases:

1- Own Aircraft;

2- Hooked Aircraft (other).

 

1- Own Aircraft.

According to NATOPS:

- if Own Aircraft is selected via TID, then the readings are magnetic;

- if Own AC is selected via CAP, then True values can be accessed by using the CAP functions: SPD → GS and Magnetic Course; HDG → TAS and True.

 

(Note: If quotes are not allowed feel free to remove them)

Quote

Normally, own−aircraft airspeed and magnetic heading are displayed on the TID. If own−aircraft data file is hooked using the TID cursor, heading will be magnetic. If OWN A/C pushbutton was selected (hooked) via the CAP, own−aircraft true heading, speed (groundspeed), altitude, or course can be displayed on the TID by depressing the appropriate prefix pushbutton.

[..]

Quote

Depressing the SPD pushbutton displays groundspeed and magnetic course. However, true airspeed and true heading are displayed when the HDG prefix push button is depressed.

 

Example:

test-tid-mc-spd-values-1.jpeg

 

Since in HDG the reading is "MH" I'd assume it's the Magnetic Heading so the value does not sound wrong (there is no wind in this scenario). It differs from the NATOPS, but it is not a big deal (You/HB said the TID we have is quite old).

 

2- Hooked Aircraft (other)

In this scenario I have a tanker flying dead ahead. My intention was practising a rejoin. MC reads 107, so BR would be 287. The problem is, I placed the aircraft to have its flight path fairly overlapping the F-14's, so it should have been the reciprocal of the F-14 itself, therefore 277→ 97 (close to 100), not 107.

 

Example:

test-tid-mc-spd-values-hooked-1.jpeg

 

I also added the TacView's pilot point of view to display the Mag HDG, and it matches what I expected.

After putting together these images I tested via LINK4A as well and the readings are the same.

 

The problem here is that if 107 is used, the reciprocal is ~285 and the resulting Target Aspect is 5L. If the correct (?) value of 100° is used, the reciprocal is 280, so Target Aspect is zero and the geometry is computed differently. If this works as intended it's not a problem, I just have to take into account the magvar manually every time, but it sounds to me a bit convoluted, having everything in Mag and then Magnetic Course as True. What am I missing? 🤔

 

Notes:

- DCS is fully repaired and updated;

- Mission: https://www.dropbox.com/s/avnkj03rouh3ar3/test_intercept3.miz?dl=0

- Tacview: https://www.dropbox.com/s/m6n2gnahjx7bi25/bugreport_Tacview-20210124-212440-DCS.zip.acmi?dl=0


Edited by Karon
Wrong Tacview link

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10 minutes ago, Alphabet_Ghost said:

BR is bearing to target so 0 .. no problem .

 

Thanks for your reply but, I'm sorry, I fail to get how the ATA should help me to understand why the Magnetic Course shows the True value rather than, well, the Magnetic (unless it's intended, of course).

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27分钟前,Karon说:

 

Thanks for your reply but, I'm sorry, I fail to get how the ATA should help me to understand why the Magnetic Course shows the True value rather than, well, the Magnetic (unless it's intended, of course).

test it , Very likely it's bug , vC is +9 in this case , no problem for own MC , INS has few bug for long times .


Edited by Alphabet_Ghost

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5 minutes ago, Alphabet_Ghost said:

test it , maybe bug , vC is +9 in this case , no problem for own MC , ins has few bug for long times .

VC is 650kts in this case, why +9?

I just spawned so INS should be fine. Moreover, Tacview and the F-10 map confirm the readings.

 

Own MC technically has a problem as well, but I guess it depends on which version of the avionics they implemented, just look at the quotes from the NATOPS.

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刚才,Karon说:

VC is 650kts in this case, why +9?

I just spawned so INS should be fine. Moreover, Tacview and the F-10 map confirm the readings.

 

Own MC technically has a problem as well, but I guess it depends on which version of the avionics they implemented, just look at the quotes from the NATOPS.

hei vC is computed magnetic variation that use to caculate magnetic heading . You misunderstood what i'm talking about , TH is 287 and MH is 277 . magnetic variation is 9 , no problem for it .

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9 minutes ago, TheCamper said:

What is the mag var in this scenario? maybe this can be the problem?

I thought about it, I'm not sure why it would affect only one reading, but it's worth checking.

VC = 9 - 9.3

VM = 6.7

 

I forced the VM over VC, the MC switched to 108°. The F-14's HDG was unchanged.

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6分钟前,Karon说:

I thought about it, I'm not sure why it would affect only one reading, but it's worth checking.

VC = 9 - 9.3

VM = 6.7

 

I forced the VM over VC, the MC switched to 108°. The F-14's HDG was unchanged.

system us VC in INS mode and only use VM as follow , so it won't change Mag heading when operational in INS mode . image.png


Edited by Alphabet_Ghost

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4 minutes ago, Alphabet_Ghost said:

hei vC is computed magnetic variation that use to caculate magnetic heading . You misunderstood what i'm talking about , TH is 287 and MH is 277 . magnetic variation is 9 , no problem for it .

Ah sorry, I see what you mean, I thought you were talking about the closure, and I was a bit confused 🙂

 

Yes, that's correct, yet in theory incorrect (although again it may depend on the implementation HB used for the TID) as the TID in SPD should read 287 whereas it still reads 277.

The part that really buggers me though, is the MC of the hooked target.

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2分钟前,Karon说:

Ah sorry, I see what you mean, I thought you were talking about the closure, and I was a bit confused 🙂

 

Yes, that's correct, yet in theory incorrect (although again it may depend on the implementation HB used for the TID) as the TID in SPD should read 287 whereas it still reads 277.

The part that really buggers me though, is the MC of the hooked target.

no problem , i'm also meaing onw aircraft MC don't have any problem as it present 277(i don't know why it called MC , there may be other reasons but no drifferent in-game), yes MC of target very likely a bug .

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Just now, Alphabet_Ghost said:

system us VC in INS mode only use VM as follow , so it won't change Mag heading when operational in INS mode . image.png

 

Yes, I am well aware of that, I wrote a short study about the effects of the MagVar (included VC) over the INS, especially when re-aligning. In this case I used the second entry of the table you posted, I switched to AHRS and updated VM.

 

I think we are missing the point: I never said the magvar or the headings were incorrect, instead, that it seems to be a discrepancy between True and Magnetic in readings. It is either a bug or working as intended (although it sounds different from the NATOPS - if I'm not misunderstanding it) and I need to clarify that.

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Hi!

 

I have been trying to get my head around the problem here and I think I've succeeded.

 

Case 1: Own A/C. The indicated prefix on the TID always indicate what type of data is being presented, so if it says MH it is magnetic heading. When it shows true heading the prefix indication should be TH. As said in the Natops you need to hook own a/c via the CAP, pressing the own a/c message button and if you then select the HDG prefix the TID will show AS and TH. To go back you need to hook something and unhook it using the HCU and then if you press HDG it will again show AS and MH.

 

Case 2: There is indeed something odd going on here, the WCS is not capable of showing magnetic heading or course readouts for target tracks, it simply doesn't know the magnetic variation at any other location than own aircraft. What I think is happening is that the MC prefix indicator is bugged and should instead read CR which would then make the indicated number the target tracks true course. I need to verify this but if this is true it's indeed a bug and we need to make sure that it doesn't say MC but CR.

 

I hope I understood you correctly, feel free to ask me otherwise.

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Thanks for the reply mate!

 

Case I
I found the error I made: when you hook your aircraft, OWN AC is not deselected (unless something else was hooked). When I un-hooked my AC, I did not re-press OWN AC as it was selected already, so this part of the NATOPS drove me off.

Quote

If OWN A/C pushbutton was selected


By physically re-pressing the button it did work. My bad.

 

Case II
Ah! I did not think about the fact that the aircraft does not know the MagVar at the target's location. In fact, I went down the rabbit hole and tested other aircraft looking for what I was missing: besides the F-16C showing odd stuff (110°), F-15C, F-14 and F/A-18C showed the True Heading of the target (107°). Now that explains it, brilliant!
That being said, I guess the problem is just the label of the course that, as you said, it should not probably be 'MC'.

 

Thanks Naquaii, I owe you a pint!

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55 minutes ago, Karon said:

Thanks for the reply mate!

 

Case I
I found the error I made: when you hook your aircraft, OWN AC is not deselected (unless something else was hooked). When I un-hooked my AC, I did not re-press OWN AC as it was selected already, so this part of the NATOPS drove me off.


By physically re-pressing the button it did work. My bad.

 

Case II
Ah! I did not think about the fact that the aircraft does not know the MagVar at the target's location. In fact, I went down the rabbit hole and tested other aircraft looking for what I was missing: besides the F-16C showing odd stuff (110°), F-15C, F-14 and F/A-18C showed the True Heading of the target (107°). Now that explains it, brilliant!
That being said, I guess the problem is just the label of the course that, as you said, it should not probably be 'MC'.

 

Thanks Naquaii, I owe you a pint!

 

No worries mate, tbh I should probably have caught this earlier, just haven't thought about it. In regards to the own aircraft I think you might as well treat all hooks except when you press the cap button as TID hooks, the complicating thing is that the TID always reverts to own aircraft when you unhook stuff and that is also counted as a TID hook.

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Ok, we had a look and it does indeed look like we've had a bug for some time that no-one found until now! Somewhere down the line the WCS was changed to show MC and MH for own aircraft instead of TH and CR (true course). The TH still being able with selection of own aircraft via CAP. This change when implemented seems to also have changed CR to MH for tracks in some mysterious way.

 

After checking myself I've verified that while saying MH both in the default alternating display and CAP -> SPD the TID does indeed display target true course while still indicating MH. So it already works correctly as CR would be the only thing the WCS can figure out using the AWG-9, it has no idea about track magnetic deviation or actual track heading, instead it uses the track updates to calculate course which will then be true course.

 

So tl:dr, the fix will be that we change MH to read CR instead for tracks and I think this will be in the next major patch. But until then the value is still correct as long as you remember that for tracks it isn't MH but CR even if it says MH.


Edited by Naquaii
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On 1/30/2021 at 4:48 AM, Naquaii said:

Ok, we had a look and it does indeed look like we've had a bug for some time that no-one found until now! Somewhere down the line the WCS was changed to show MC and MH for own aircraft instead of TH and CR (true course). The TH still being able with selection of own aircraft via CAP. This change when implemented seems to also have changed CR to MH for tracks in some mysterious way.

 

After checking myself I've verified that while saying MH both in the default alternating display and CAP -> SPD the TID does indeed display target true course while still indicating MH. So it already works correctly as CR would be the only thing the WCS can figure out using the AWG-9, it has no idea about track magnetic deviation or actual track heading, instead it uses the track updates to calculate course which will then be true course.

 

So tl:dr, the fix will be that we change MH to read CR instead for tracks and I think this will be in the next major patch. But until then the value is still correct as long as you remember that for tracks it isn't MH but CR even if it says MH.

 

Before you do that just making sure, do you know that in Caucacus map that the TH and MH are inverted? It was supposably cause by the map being a legacy map from the flanker series

 

Make sure you confirm if the TH and MH are correct on other map before making the change ( haven't had the time to test on other maps)

Just m


Edited by ustio
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1 hour ago, ustio said:

Before you do that just making sure, do you know that in Caucacus map that the TH and MH are inverted? It was supposably cause by the map being a legacy map from the flanker series

 

Make sure you confirm if the TH and MH are correct on other map before making the change ( haven't had the time to test on other maps)

Just m

 

 

This change is literally just changing a prefix, i.e. naming of what is displayed. No change in the actual values. And as a radar cannot calculate anything other than a tracks true heading this needs to change in any case.

 

If mh and th are inverted for all aircraft that is something on EDs side with the Caucasus map, not something for us to change. Thus far I haven't seen any reports that this is exists or is an F-14 specific issue.

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6 hours ago, Naquaii said:

 

This change is literally just changing a prefix, i.e. naming of what is displayed. No change in the actual values. And as a radar cannot calculate anything other than a tracks true heading this needs to change in any case.

 

If mh and th are inverted for all aircraft that is something on EDs side with the Caucasus map, not something for us to change. Thus far I haven't seen any reports that this is exists or is an F-14 specific issue.

Yeah thats why i'm qsking to check on other to see it checks up. Unfortunately i'm not in my pc right now so i cant test

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