Mag heading vs. true heading bug?

[GTFreeFlyer]

See screenshot. Aircraft is in unaccelerated flight. The mag compass in the top-right reads a MAGNETIC heading of approx. 305 and the title bar at bottom of screen shows a TRUE heading of 317. The mag. variation in this particular part of the map is close to -4.8 degrees (tested and also verified with mist's getNorthCorrection) so something is amiss.

 

Now, look at the compass gauge. It reads approx. 295. If I spin the adjustment knob, the needle rotates with the gauge. This gauge does not agree with the floating compass in the top-right.

 

Bug, or am I reading something wrong?

[iFoxRomeo]

From where do you expect a 1950s System to get true north/local variation from?

And actually magnetic north is still the reference in todays aviation.

 

Fox

 

p.s. Tip: "fast slave" the compass before takeoff

[Snake122]

He's not asking to reference off of true north, he's saying that the mag variation doesn't add up and on top of that the true heading reported by the info bar is 317°, the mag course on the compass says 305° and the variation is -4.8 degrees. Which should make the true course be ~310° since that's working backwards from the traditional "east is least, west is best" assuming mist reports a "-" as we would an East variation. Which map is this OP? Looks Caucasus so an East Variation would be around that there. If so, we would need to add that back to the magnetic number to get true since we normally work it the other way:

True course/heading +/-Variation = Magnetic +/-Deviation= Compass course/heading. Course ONLY matches heading in zero wind conditions.

So a few thoughts:

A. from the manual:

"Indicator readings will be incorrect if the airplane exceeds 85° of climb or dive or banks left or right more than 85°. Error in heading indication when the airplane is in an extreme bank or roll movement is an inherent characteristic of the gyro; however, it disappears when the airplane returns to straight and level flight. An additional error, however, will build up in the indication during turns. This is caused by centrifugal force which tends to swing the transmitter flux valve into the vertical component of the earth's magnetic field. The amount of error is proportional to time and duration of the turn. Therefore, errors will result in the indicator during turns, banks, or rolls. The fast slaving button may be actuated after the maneuvers are completed so as to correct the heading indication at the fastest possible rate"

 

B. Magnetic Deviation, not sure if DCS actually models this, I've seen a few deviation cards in aircraft but can't find one in the F-86 and I tend to think that they are more atmospheric on the the planes they are in than actual use.

 

C. The info bar at least is saying heading and if Eagle Dynamics is proper in their terminology, there will be a difference because a heading is the course corrected for wind drift (remember the back side of the E6B GTFreeFlyer?). So that would be saying that even though your compass course is 305°, your wind drift is causing a 317° ground track. Similar to a lot of GPS that you may have flown OP, if you have the DCS NS430 system you might use it to confirm.

Edited May 17, 2020 by Snake122

[randomTOTEN]

I'm not seeing this on my end. Sitting on RWY 08 Kutaisi (Instant Action) measure tool (map), aircraft info tab on the map, and the info bar all agree heading 074 (presume this is True). Kneeboard reports 6°E variation. Compass and DG both agree heading is 068°M. Same when I take off and turn to a 180°M heading and compare with the map.

 

Only thing I can observe is that OP's screen is in a 2,000FPM climb.. so this might not be entirely "unaccelerated." Or else some mod or something else going on.. not seeing this on my end though.

[iFoxRomeo]

See screenshot. Aircraft is in unaccelerated flight. The mag compass in the top-right reads a MAGNETIC heading of approx. 305 and the title bar at bottom of screen shows a TRUE heading of 317. The mag. variation in this particular part of the map is close to -4.8 degrees (tested and also verified with mist's getNorthCorrection) so something is amiss.

 

Now, look at the compass gauge. It reads approx. 295. If I spin the adjustment knob, the needle rotates with the gauge. This gauge does not agree with the floating compass in the top-right.

 

Bug, or am I reading something wrong?

Sorry, I misread your post. Disregard last transmission.

Did you check this behaviour on other aircraft?

 

 

Fox

[Art-J]

Keep in mind two facts:

a) F10 map (and probably the info bar) uses grid north and not true north;

b) "flat earth" projection of Caucasus map, with distances and bearings origin located in the middle of Crimean Pennisula - the further you go east and south from it, the more messed up bearings, variations etc. are.

 

I don't know how instruments in F-86 are programmed to work (I don't fly it very often), but the aircraft in DCS are all over the place as far as their reference implementation (true vs north) is concerned, so what OP noticed might be a bug, or a game limitation.

[Ramsay]

I don't know how instruments in F-86 are programmed to work (I don't fly it very often), but the aircraft in DCS are all over the place as far as their reference implementation (true vs north) is concerned, so what OP noticed might be a bug, or a game limitation.

 

Full module aircraft use Grid North as "True North" with respect to GPS and their internal logic. Magnetic compasses and similar instruments subtract the local magnetic variation to display the correct magnetic heading for the location/date.

 

FC3 aircraft don't model magnetic variation, so always display True north including their magnetic compass, HSI, etc.

 

I don't see the OP's F-86F issue when lined up on Batumi RWY 31 (305°T as measured on the F10 map) both compasses read approx. 298°M and an A-10C's CDU MV=6.4 E (21 June 2016).

 

Magnetic = True - MV = 305 - 6.4 = 298.6°M = ~298°M (rounded down)

 

 

It's possible the OP is seeing instrument error due to effects from the earth's magnetic field or gyro drift but I don't recall how detailed BST went with their modelling.

 

Tested in Open Beta 2.5.6.47404

Edited May 17, 2020 by Ramsay

[Ramsay]

Only thing I can observe is that OP's screen is in a 2,000FPM climb.. so this might not be entirely "unaccelerated."

I missed that detail, IIRC the F-86F's back up (magnetic) compass sticks when under acceleration, so shouldn't / can't be relied on until in level unaccelerated flight.

[Snake122]

Full module aircraft use Grid North as "True North" with respect to GPS and their internal logic. Magnetic compasses and similar instruments subtract the local magnetic variation to display the correct magnetic heading for the location/date.

 

FC3 aircraft don't model magnetic variation, so always display True north including their magnetic compass, HSI, etc.

 

I don't see the OP's F-86F issue when lined up on Batumi RWY 31 (305°T as measured on the F10 map) both compasses read approx. 298°M and an A-10C's CDU MV=6.4 E (21 June 2016).

 

Magnetic = True - MV = 305 - 6.4 = 298.6°M = ~298°M (rounded down)

 

 

It's possible the OP is seeing instrument error due to effects from the earth's magnetic field or gyro drift but I don't recall how detailed BST went with their modelling.

 

Tested in Open Beta 2.5.6.47404

Also OP is discussing the large difference between the True heading (according to info bar) vs magnetic course(compass)

The mag compass in the top-right reads a MAGNETIC heading of approx. 305 and the title bar at bottom of screen shows a TRUE heading of 317.

My italics added because a mag compass does not show heading, it shows course. Headings in this sense technically are courses corrected for wind correction angles.

 

To remove it from DCS for a moment in case it's being really weird and doing the variation to the opposite way, factored with real life's Batumi is currently 5 degrees east variation, the true heading of the runway 31 would be 311 since it has a reported mag variation of 5 (306° magnetic + 5 variation since you are working backwards to true its now East is best, west is least) and runway heading at least in most ICAO countries are given in magnetic.

 

So my theory if DCS is modeling closer to real life, OPs compass reads a course of 305°, adding back in the 5-6ish degree east variation since we are working in reverse from normal, OP would have true course of 311ish. If DCS info bar is showing what it calls a "heading" (maybe more properly a track, using the NS430 and seeing if this matches the TRK with wind would possible confirm this) of 317° true, he would need a Wind Correction Angle of 6 degrees.

Interesting that DCS is reporting the true of Batumi 305° instead of 311°, Also DCS ARR/DEP chart report a 306 degrees for the runway final course, and a variation of 6°E in 210 which should make the runway have a 312°T if they were following aviation standards and reporting the runway in magnetic, but the airport diagram shows 300°M and 306°T. But as ART-J said there are some other things going on there.

 

Other theories if in DCS that "heading" = course:

magnetic deviation (but doubt that is modeled)

compass is not stabilized

 

Agree that the 295 gyro heading is most likely due to drift and needs re-slaved. See quote from DCS F-86 manual from previous post.

Edited May 18, 2020 by Snake122

[Ramsay]

To remove it from DCS for a moment in case it's being really weird and doing the variation to the opposite way, factored with real life's Batumi is currently 5 degrees east variation, the true heading of the runway 31 would be 311 since it has a reported mag variation of 5 (306° magnetic + 5 variation since you are working backwards to true its now East is best, west is least) and runway heading at least in most ICAO countries are given in magnetic.

 

I'm aware that RL runway numbering uses magnetic bearings as a basis for their numbering.

 

The Caucasus map was originally designed to work with Lomac & FC aircraft that don't model Magnetic Variation, as a result ED aligned the runway headings with the game grid that the FC aircraft also used for their magnetic compass, etc. and used their RL runway numbers (where they existed).

 

Later the Lomac Caucasus map and systems evolved to Black Shark 1, DCS: A-10C and DSC World but retained a lot of ED's legacy code, assets, etc.

 

When ED implemented more advance systems modelling that took magnetic variation into account, they used the fixed grid to be "True" as it is constant, and a MV database/model to take position and date into account when modelling magnetic instruments.

 

So my theory if DCS is modeling closer to real life, OPs compass reads a course of 305°, adding back in the 5-6ish degree east variation since we are working in reverse from normal, OP would have true course of 311ish.

 

Unfortunately your theory is inconsistent with other modules (some of which can switch between Mag and True) i.e. L-39, A-10C, F/A-18C, AV-8B, F-16C, etc.

 

In "DCS World\Doc\Charts" you will find that

 

• DCS_VAD_Charts_A10C.pdf --> lists Batuni RWY 31 as 300°M

(Page 3 - The magnetic variation contained in the DCS A-10C module was taken on the maps with a tolerance of ± 1°.)

 

• DCS_VAD_Charts_FC3.pdf --> lists Batuni RWY 31 as 306°T

(Page 3 - All tracks are given to true north with a tolerance of ± 1°.)

 

If DCS info bar is showing what it calls a "heading" (maybe more properly a track, using the NS430 and seeing if this matches the TRK with wind would possible confirm this) of 317° true, he would need a Wind Correction Angle of 6 degrees.

 

The NS430 is bugged on Caucasus map and calls what would be a True bearing in other full modules magnetic i.e. it shows Batumi RWY 31 as 304°M and switching the NS430's units to True it reads 311°T. AFAIK the NS430 True/Magnetic reading is only bugged for the Caucasus map and reads correctly in Nevada (I don't recall checking the PG as the NS430 has performance issue on it).

 

Interesting that DCS is reporting the true of Batumi 305° instead of 311°, Also DCS ARR/DEP chart report a 306 degrees for the runway final course, and a variation of 6°E in 210 which should make the runway have a 312°T if they were following aviation standards and reporting the runway in magnetic, but the airport diagram shows 300°M and 306°T.

 

You can't use the NS430 at face value as it's bugged, you need to be aware that it's Magnetic headings on the Caucasus map are really True headings and match the F10 map, etc.

 

As previously explained, the DCS Caucasus map's runway numbers do not follow aviation standards.