Board index FlightGear Development Aircraft Cockpit development

Magnetic compass not indicating magnetic heading

Discussion about creating 2d and 3d cockpits.

Magnetic compass not indicating magnetic heading

Postby dg-505 » Sun Mar 01, 2020 12:38 am

Hello, i've encountered the following situation:

With a magnetic heading of 238 deg and a magnetic variation of -35 deg, it results in a true heading of 203 deg. (As shown on the HUD properly).
However the magnetic compass indicates a heading of 246, which obviously is a significant difference between the mag heading in /orientation/heading-magnetic-deg.

Image

In my research I didn't find any hint how "/instrumentation/magnetic-compass/indicated-heading-deg" is calculated and where the difference comes from (A deviation is not implemented in this aircraft)
In addition this difference seems to occur somewhat randomly for different aircraft.

So, can you please give me a hint what's the background of this behaviour?

Reproduce:
Aircraft: DHC-6
Location: CYIO, Runway 20T

Thank you very much in advance!

Kind regards
Jonathan
A mile of road will take you a mile, but a mile of runway will take you everywhere.

DHC-6 Twin Otter development
User avatar
dg-505
 
Posts: 660
Joined: Mon Jun 02, 2014 2:36 pm
Location: Bonn, Germany
Callsign: dg-505
Version: next
OS: Ubuntu 20.04.2 LTS

Re: Magnetic compass not indicating magnetic heading

Postby ludomotico » Sun Mar 01, 2020 1:31 am

I don't know if this is your case, I can't see if you are accelerating.

Magnetic compasses have acceleration error: https://www.boldmethod.com/blog/learn-t ... ass-works/

Image

The acceleration error is simulated in FlightGear source code: https://sourceforge.net/p/flightgear/fl ... s.cxx#l132
User avatar
ludomotico
 
Posts: 1176
Joined: Tue Apr 24, 2012 1:01 pm
Version: nightly
OS: Windows 10

Re: Magnetic compass not indicating magnetic heading

Postby xDraconian » Sun Mar 01, 2020 1:40 am

Acceleration error is a good guess, but I can see that the HUD shows the throttle is closed. I'm guessing the aircraft is on the ground.
xDraconian
 
Posts: 346
Joined: Sun Jan 21, 2018 5:53 am
Version: Git
OS: Linux Mint

Re: Magnetic compass not indicating magnetic heading

Postby dg-505 » Sun Mar 01, 2020 9:07 am

Yes, I'm aware of this behaviour when accelerating, but as xDraconian guessed correct, the compass is showing this offset directly after starting up FlightGear, when the compass has stopped moving, i.e. without the aircraft moving at all.

So there must be another reason, why the compass output is different from the correct mag heading.

Any further ideas? :wink:

Thanks
Jonathan
A mile of road will take you a mile, but a mile of runway will take you everywhere.

DHC-6 Twin Otter development
User avatar
dg-505
 
Posts: 660
Joined: Mon Jun 02, 2014 2:36 pm
Location: Bonn, Germany
Callsign: dg-505
Version: next
OS: Ubuntu 20.04.2 LTS


Return to Cockpit development

Who is online

Users browsing this forum: No registered users and 2 guests