DCS Gaming

[Solved!] Tripped on a Bug (True vs Magnetic readings)

An apparently marginal bug, ended up causing quite a headache…

Update: Mysteries solved!

In the discussion on ED’s forum, Naquaii from Heatblur solved the two dilemmas:

  1. the conundrum is the OWN AC pushbutton in the CAP, as it tends to be the default selection when any element is un-hooked. Although selected, it has to be pressed again, then in works as NATOPS suggested. My error was not pressing it again because it was already selected;
  2. the MC representation instead looks like a bug, although a very interesting one. The explanation is simple:

    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

    Considering the current MC as the True Course, makes the value coherent with the other aircraft. The problem therefore appears to be the label: rather than saying “MC” for Magnetic Course, it should be “CR” (or something else) for the True Course.

    The fact that the Magnetic values are missing (I assume Magnetic Heading will have the same fate – I’m happy to be proven wrong!) and we have to rely on True values, means the Magnetic Variation will always have to computed, either in the form of the F-14 BDHI reading “turned True”, or by removing it from the BH.

At the end of the day, I learned a couple of new things, so I’m quite happy. I have recorded a new Demo where I took into account the MagVar and it worked quite well (besides when the parts where I’m piloting ¯\_(ツ)_/¯ ). It should be available on YouTube in a couple of days.

I recorded three short videos about the modern intercept geometry, aiming to quickly demonstrate how to use what was discussed in Part IV (Gameplans) and Part V (Displacement Turn, Counterturn, Timeline) to satisfy (or getting close to) the goal of having 40,000ft at 10nm, prior turning towards the target’s RQ (rear-quarter).

I put together the first one very quickly, it is available already, and I spent more time on the second and the third. As I was reviewing the TacView tracks for the second and the third, I noticed that there was something odd with the displayed value of the Magnetic Course. It seems that the displayed value is actually the True Course, causing a lot of confusion when it comes to the geometry. Consider that 5° at 50nm equals to 25,000 ft of Lateral Separation and, on top of the errors induced by the approximations, it can really end up creating a quite substantial error.

This short article is just to make you aware of the possible problem, although there is always the chance that I am doing something wrong.

Long story short, quoting NATOPS:

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.

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.

I opened a thread in Eagle Dynamics’ forum, you can read it here.
This is the chapter of the manual describing the behaviour of the CAP.

Quick Recap

I see two possibilities:

  1. It is working as intended (HB says they implemented a quite old version of the TID);
  2. MC displays the wrong value.

What does the Bug say?

Out of curiosity, I duplicated the F-14 in the mission editor and used it to verify what other aircraft “say”:

  • F/A-18C;
  • F-15C;
  • F-16C.

This is what the avionics say:


Although LOMAC/FC level, the F-15C can help to understand the situation (besides, I’d love to have an F-15A in DCS).

From the attack display we have that the target is flying at GS 299 (matches), Heading 107° (matches True HDG). The F-15C is flying 287° (since the target is dead ahead), matching the value of the True Heading.
The F-15’s manual does not specify whether the Headings are True or Mag.

This is the HUD of the F-15 (did it always look that bad?), showing heading 287°.


Another Navy aircraft, the Bug is definitely the most complete and complex module so far, along the Veteran A-10C.

The radar gives us 280° for the F/A-18C’s heading (I verified that True was not selected), matching the Magnetic Course, and 107° as the heading of the target. This value matches the True heading, not the Magnetic. That reading is described by the manual as the “Flight Heading of the L&S Target”, Chuck, in his guide, calls it the “Target Ground Track”.

This is how the radar looks like when True Heading is selected.


I played the F-16 a lot back in the original, slide-show simulator, Falcon 4.0.
The HUD shows Heading 280°, matching the Magnetic pals.

The attack display instead shows… 110°.

Both the manual and Chuck concurs in having such value defined as the “Ground track”. I’m not sure why it diverts from the value seen so far (MagVar?).

Recap of the Values


Magnetic Heading: 101° (from an F-14 overlapped, verified by means of F10 ruler and TacView)
True Heading: 107° (from info bar and TacView)
Aircraft Own HDG M/T? TGT HDG M/T?
F-14B SPD [3] ► 278°
HDG [8] ► 278°
but ≠ NATOPS
SPD [3] ► 107°
HDG [8] ► 107°
but ≠ NATOPS
F-15C 287° True 107° True
F/A-18C 280° Magnetic (default) 107° True
F-16C 280° Magnetic (default) 110° True?


I’m still not sure what to do about the videos I recorded: one is public already, I will add a note to it rather than taking it down. I will probably dump the others are record them from scratch.

At the end of the day, it does not really matter if a value displayed is True or Magnetic, but it is important that such value reflects what the display is supposed to show.
Going forward, as an ad interim solution, recalculating the target’s course or heading by means compensating for the MagVar, should help to offset the problem (the value can be obtained by means of the CAP).

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