Polar routes with SimA

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jackpilot
Site Admin
Posts: 1064
Joined: Sun Apr 25, 2004 9:19 am
Location: Montreal

Polar routes with SimA

Post by jackpilot »

P3D seems to have limitations as FS did.
Sim A did its job except a twisted magenta route close to the pole (88 N)

Details:
I planned a route from Thule (Greenland) to Alykel (Russia) over the pole.
Simbrief provided all data.
Imported into the FMS no prob.

All went well up to CYLT (Alert airport Canada) at 82 North. Shortly after the external view kept refreshing the same scenery

Image

SimA continued though to VNAV quietly
Approaching 88 North the magenta route was distorted and I had to resort to HDG.

Image

After reaching the tipping point where West turns East, and North lat decreases the scenery came back normal.

Image

Rest of the flight was uneventful and SimA did a very nice initial NDB approach to RWY 19 which I conducted manually (two NDBs in line so just keeping both blue pointers on top of each other.

Landed and parked in the grass in Russia.

Image

Worth trying, much more challenging than Montreal Boston :D
Jack
Full B737-800 DSTD/Sim-Avionics P3d4
ALL FDS & OEMs (+custom TQ)

Banananav
Posts: 92
Joined: Thu Oct 08, 2015 11:46 am
Location: 5nm West of RAF Cranwell

Post by Banananav »

It was obviously pondering that thorny problem “ if I am standing on the North Pole, which way is South ?�.

Regards

Chris
Chris Finn

Jetmax 737-800 & TQ
P3D 4.5 HotFix2
S-A 1.964
FSUIPC 5.152

jackpilot
Site Admin
Posts: 1064
Joined: Sun Apr 25, 2004 9:19 am
Location: Montreal

Post by jackpilot »

Good one !
Has more to do with something I missed about magnetic bearings.
May be a high '' authority'' could chime in...
Last edited by jackpilot on Wed Sep 19, 2018 9:03 am, edited 1 time in total.
Jack
Full B737-800 DSTD/Sim-Avionics P3d4
ALL FDS & OEMs (+custom TQ)

Banananav
Posts: 92
Joined: Thu Oct 08, 2015 11:46 am
Location: 5nm West of RAF Cranwell

Post by Banananav »

I just threw that one in for a laugh !
But it is essentially true.
As far as I can tell, FSX & P3D are lat/long based and therefore suffer from the same problem as any other LL based system does at high latitudes, that of meridian convergence which gives high rates of change of longitude and therefore true heading when passing near to the poles, if flying a great circle track.
Variation therefore also changes quickly.
Chris Finn

Jetmax 737-800 & TQ
P3D 4.5 HotFix2
S-A 1.964
FSUIPC 5.152

jackpilot
Site Admin
Posts: 1064
Joined: Sun Apr 25, 2004 9:19 am
Location: Montreal

Post by jackpilot »

Would be interesting to know how the Airlines do it...
Jack
Full B737-800 DSTD/Sim-Avionics P3d4
ALL FDS & OEMs (+custom TQ)

Banananav
Posts: 92
Joined: Thu Oct 08, 2015 11:46 am
Location: 5nm West of RAF Cranwell

Post by Banananav »

The simple answer is that the FMCs do it, using software certified for high latitude navigation.
LNAV generates Great Circle tracks between waypoints.
The MagVar database only works up to 76 deg North so the system uses True above this.
The Nav elements of the FMCs constantly calculate present position from a mix of the INUs and the GPSs and weights their inputs in favour of the most accurate ones, usually GPS.
As I navigated in the Doppler, gyro compass and Astro era I can’t add much more.
Rgds
Chris Finn

Jetmax 737-800 & TQ
P3D 4.5 HotFix2
S-A 1.964
FSUIPC 5.152

jackpilot
Site Admin
Posts: 1064
Joined: Sun Apr 25, 2004 9:19 am
Location: Montreal

Post by jackpilot »

The flightplan generated with Simbrief was basically a straight line and the magenta route on the ND was too.
It walloed a bit from 98 N to 92 on the downhill side (LNAV to HDG was necessary).
Entering close WPs could help ?
Maybe Mark has a comment

No big deal but it was a kick seeing the Russian coast appear after just a few hours.
ps (love your toast signature!)

Jack
Jack
Full B737-800 DSTD/Sim-Avionics P3d4
ALL FDS & OEMs (+custom TQ)

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