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Magnetic Variations...

FlyingMasterChef

FlyingMasterChef

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Do these really matter in FS? Since the number is arbitrary, what effect could / would it have if it is not right, or rather very wrong?

The reason I ask... I have researched the mag variation for my NKL. As I know it changes over time. Starting with Airnav, I find that MANY airports have data that is 10-20-30 years old if you read the date of the data.

That being said, I found a site (I posted in another posting) that allows you to get updated information based on mathematical formulas for variations in different parts of the world. Thus, I come up with -2 for the current magvar for NKL. (FS has it as 0)

Interestingly, if you search all the airports around NKL, they all have different numbers. So NKL (stock info) is at 0 and airports around it just a few miles are anywhere from -3 to 4. I mean seriously... I checked in other parts of the country, and the same thing. One airport will be -1 and an airport 5 miles away will be 2. This is NOT possible.

Thus my question...does it really matter what the magvar is set to? I see people ask about showing the magvar for runways, airports, etc....but really, who cares as it doesn't seem to affect anything. Unless you are flying by charts, and apparently, they can't be right based on what I found in the FS world currently, the number can be anything, and you and AI will all find the airport and land just fine.

- Greg
 
Hi,

I guess as long as your are not using your magnetic compass to navigate you would not notice so much is the value is not correct.

Another area where you might notice is the runway numbering though. These are magnetic heading as well if I am correct (that is why they sometimes change due to the changing magnetic variation).
 
That is correct Arno...but I guess my point was more of does any of it really matter, as you can make the numbers (magvar) anything you feel like it. Apparently, that is what MS did.

And that being the case, there is not really any need (IMO) to display the current magnetic headings in ADE. As you just need to look at the magvar info in ADE for the airport you are at and then you can easily figure out any data you have to have.

As insane about being true to real world design work as I am being with my work, this just seems to be one of those things that really, means nothing. If MS didn't care enough to be even a little accurate, then it must not mean much.
 
Magnetic Variation makes a huge difference.

If you fly according to the true heading instead of the magnetic heading, you'll end up in the wrong place. If you set your runway headings without taking the variation into account, the runway(s) will not be properly oriented.
 
I realize that. But how many people actually fly only by the magnetic? AND, again, my point is just that MS apparently didn't care about them, because they are set all wrong at many airports. (I was just curious again, and out of 25 airports I looked at the magvar for in FSX, 23 were not correct according to fsnav NOR were they correct by taking into account current date/location. So where did MS get the data.... And, again, as stated above, airports within a 20 mile radius, have magvars all over the place.)

As for the design part...if you have a magvar of -2, can't you just look and take a wile guess as what the heading is? hehe

If it's added to ADE, won't phase me in the least. I was just wondering why it is important, when most people, especially if they are using this software, can apply simple math before they could ever click a button to figure it out.

Then again..... ;)

- Greg
 
SpectroPro said:
I realize that. But how many people actually fly only by the magnetic? AND, again, my point is just that MS apparently didn't care about them, because they are set all wrong at many airports. (I was just curious again, and out of 25 airports I looked at the magvar for in FSX, 23 were not correct according to fsnav NOR were they correct by taking into account current date/location. So where did MS get the data.... And, again, as stated above, airports within a 20 mile radius, have magvars all over the place.)

As for the design part...if you have a magvar of -2, can't you just look and take a wile guess as what the heading is? hehe

If it's added to ADE, won't phase me in the least. I was just wondering why it is important, when most people, especially if they are using this software, can apply simple math before they could ever click a button to figure it out.

Then again..... ;)

- Greg
Click to expand...

MagVar calculations are free in ADE ;)
 
Some more questions...

As I understand FSX or FS9 stores the world magnetic variation in a file magdec.bgl, which is basicly a C array or table with coordinates and the corresponding magvar.

How does FSX or FS9 use the magnetic variation based on the magdec.bgl? And why has every waypoint, navaid or airport an extra magvar field?

Is it possible to use the stock magdec.bgl for own purposes? Like to create new navaids with a magvar based on the stock magdec.bgl.

Is it possible to calculate a new magdec.bgl based on more current data. What would be the implications (runway headings etc)?

Many questions, but maybe someone can shed a light on this topic. :)

cu Stefan
 
teite said:
Some more questions...

As I understand FSX or FS9 stores the world magnetic variation in a file magdec.bgl, which is basicly a C array or table with coordinates and the corresponding magvar.

How does FSX or FS9 use the magnetic variation based on the magdec.bgl? And why has every waypoint, navaid or airport an extra magvar field?

Is it possible to use the stock magdec.bgl for own purposes? Like to create new navaids with a magvar based on the stock magdec.bgl.

Is it possible to calculate a new magdec.bgl based on more current data. What would be the implications (runway headings etc)?

Many questions, but maybe someone can shed a light on this topic. :)

cu Stefan
Click to expand...

The Magdec.bgl is where FS stores the variation from the zero Isongonic lines found around the world. The magdec.bgl is back dated to about year 2000-2002.

Navaid's and the various types of waypoints have the mag field but it does not do anything. We can only assume that FS in later versions would allow us to place the mag variation as a single value that would be honored but that was never coded.

ADE reads the magnetic degree for the ARP but again this does nothing and any value placed changes nothing. Many airports that are close together do not use the same mag variation in FS9/FSX XML which again we have to assume that FS had this on its list for future updates.

FS only codes a True heading for the runway and the magdec.bgl sets the variation which we have no control over. You cannot set the runway as per the magnetic variation since there is no attribute in the XML that reads this value.

In the ADE Approach Mode we will show the word Heading= which means you use the True Heading. If we show Magnetic heading= then you must use the Airplane heading as seen on the CDI gauge (calibrated to the wet compass). Approach code uses the True heading for runways and AI Plane course direction to a runway in the approach header. User Planes use the Magnetic heading as the course seen on the CDI since an actual Pilot is flying the plane.

The wet compass in FS does not lead/lag or dip based on the Magnetic deviation from the zero Isongonic line. Lead/Lag of a wet compass accelerates when the + - Isongonic line increases from zero in a bank turn. The dip (forward/backward) of a wet compass increases based on how fast you pitch the airplanes nose up or down. FS only codes the Wet Compass as a mag heading to calibrate the CDI gauge if you use the "D" keyboard key.

It would be very easy to make FS9/FSX too complicated for the average pilot to fly if they loaded single mag variations per every piece of data that uses them. That would also require a wet compass to work properly and lots of world mag deviation charts to be added to the FS NAV database.

Some in the past have tried to change the Magdec.bgl but then any airport value that is changed in that bgl requires a total rewrite of the entire approach code database. This is just one of the reasons MS/FS developers decided to use a fix mag variation (vs varible) for the entire world rather then allowing someone to tamper with one setting (like runway headings) which breaks the ATC system.

Remember, A runway number changes because an invisible magnetic deviation changed slightly from the zero Isogonic line or the zero line drifted slightly over a 50 year time. The true heading of a runway never changes since it is based on true north and not magnetic north (which moves back and forth). The only way we can change the Magnetic heading of a runway to coincide with the airport chart is to reposition the true runway heading which causes many unseen problems (gauges, AI Engine, approach code, Weather Engine, etc.).
 
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