I've been preparing for a round-the-world trip.  Learning IFR, learning the intimate details of the planes to find out what I want to fly, etc.  The catch is, instead of going 'round the normal way I plan on taking a route which will bring me over the poles.

Anyway, in prep for the grand mission last night I decided to fly from extreme northern Siberia to Alaska via the North Pole using the magnetic compass.  I was curious as to how the compass would behave as I flew over the pole.  Well, it was an interesting trip that revealed some of the inner workings of FS9.

First off, while enroute and at the extreme upper end of the globe I noticed that I was no longer tracking a straight line over the ground.  The airplane appeared to be slewing sideways.  Apparently the world doesn't "wrap" over the pole the way you'd expect.  Instead there appears to be some sort of invisible barrier which prevents you from continuing north at the extreme top of the world (kinda like the 100,000 foot max altitude ceiling).  Fly North in to this barrier and you slew around the top of the world bumping up against it.

Once I "emerged" on the other side of the world (by skimming along the barrier) I found that the true north pole and the magnetic north pole are not in the same place (just like real life.  Impressive).  If I continued North (magnetic) while traveling South (true) I eventually came to the magnetic north pole.  And again something interesting happened.

I found that the compass respons smoothly to changes of direction.  Turn and the compass smoothly tracks your heading.  But it only updates itself relative to the magnetic north pole every 30 seconds or so.  As you approach and overfly the pole the compass doesn't smoothly adjust.  It skipps heading every time it updates.  The result is an odd ratcheting behavior in the compass.  By using time compression I found that this skip is not goverend by sim time, it's governed by real time.  Set time compression at 64x and the compass still skips every 30 seconds or so.

Interresting...  As for my round the world trip, that north pole slew thing will make it interesting, and it will be difficult navigating at the extreme lattitudes without the help of GPS or the map function.

Anyone know the distance around the world at its narrowest point?  I assume the trip around the world at the highest latitudes is shorter then it would be around the equator.

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Um somebody said the max lat is ±84° (-ish) It uses a Lambert Conformal Projection which is a cone touching at about 40 and 60° latitude and uses a Mercator projection for the equatorial area. There is no polar stereographic projections available for the poles so you can't go there as it is off the MSFS map.

Ian

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Thanks.  Your post snuk in before mine...

here's another way to do it
http://members.shaw.ca/wji/news.htm
bill

Maybe it's  cyclinder, wider round the middle and shallower at the edges, like a big bulge in a cylinder, kina hard to explain.

Earth's equatorial circumference*cos(max latitude)

therefore 40000 km*cos (84deg) = 4181 km = 2255.2 nm
If not that latitude do your own maths.

Ian

Hello John,
that is the modelled circumference nearly. Do you mean the polar circumference or the max/min latitudes?

I assume they use the WGS84 geoid.
http://www.wgs84.com/wgs84/wgs84.htm

Earth Data
Equatorial circumference - 40, 076.5 km (24, 902.4 miles)
Polar circumference - 40,008.6 km (24,860.2 miles)
Equatorial diameter - 12,756.34 km (7926.42 miles)
Polar diameter - 12,713.54 km (7899.83 miles)
Total surface area - 510,100,000 sq. km (196,950,000 sq. miles)
Volume - 1,083,230,000,000 cubic km (259,880,00,00 cubic miles)


Ian