the good and the bad news...

 

The bad : it's out of sync with present values around the World. You can easily track the Mag Decl at a location by going to this NOAA's site

 

In X-Plane10 we need updated values. You can use X-Plane's DataRef Editor / Viewer plugin to check it "on-the-fly". Select the specific dataref by writing magnetic_variation (should be magnetic_declination) in the lower left corner of the plugin window when enabled in X-Plane10.

 

The good: Austin is aware of it and might change the way it is calculated after 10.20 get's released. It can be table based or calculated by a series expansion. Hervé Sors, well know for his excellent MSFS information and applications site has implemented it, and mantains an updated FSX navaids and magvar database, and he is willing to help with X-Plane too!!!!

 

Also good is knowing that X-Plane no longer uses the same magvar value for a whole tile, like in version 8... There were sudden jumps when you crossed tiles with bigger variations and were flying on autopilot...

 

This would contribute to the consistency of any future updates to X-Plane10's navaids database, which must be consistent with magnetic variation...

Shouldn't the title be variation? Declination is different

Shouldn't the title be variation? Declination is different

 

Well, declination is the correct designation because it refers to the present value for a given date/place, while variation is usualy defined in secular terms... The magnetic declination varies according to a magnetic variation model. Both the variation and the declination can be obtained from the NOAA site above :-)

ahh ok. In aviation I thought that declination was the difference between real magnetic heading and the magnetic heading of the compass due to electrical and airframe interference. This is why we do compass swings

Hmmm... Down this part of the world there is compass deviation (from the airframe and whatnot) and magnetic variation from the magnetic field not lining up with true north. Where does the declination term come from? I'm curious because I haven't heard that before. As you say, it seems to be synonymous with variation.

 

Mike

- Magnetic declination is the difference between magnetic North and Geographical/Geoid North. It can be East or West, and in terms of X-Plane system, and many others, this reads as positive / negative.

- Magnetic variation is the "variation" of magnetic declination with date. At the above mentioned NOAA site, given a date and a place defined by it's Lat / Lon, the corresponding magnetic declination is computed, as well as it's "precession", such as in:

 

Declination = 2° 21' W changing by 0° 7' E/year

 

informing that present declination is 2º 21' West and preceeding at 0º 7' per year

 

- Finally there are all sorts of errors / interferences that affect compasses mounted in aircraft, and that's why that correction table exists next to them :-) Anyway, even corrected for those errors / bias, it will be magnetic and not true.

 

True values are also those reported my the meteorological sources for aviation. Wind direction is allways TRUE ( The meteo man allways says the truth ... )

Deviation. Thats the term not declination. Thanks Mike. Sorry jcomm, I got the terms mixed up :(

 

Rgds

Craig

Sorry jcomm, I got the terms mixed up

 

No problem! I had them mixed as well before starting to find out more about this interesting subject :-)

Just to toss in some 'worms'... the magdec for a given region does not necessarily apply for navaids/procedures.

 

I'll let that simmer a bit and then pop back in later to explain. :wink: