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Why Is Wind Measured In Degrees True?  
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Posted (1 year 5 months 3 weeks 4 days 4 hours ago) and read 3328 times:

Why is wind measured in degrees true when heading are generally always measured in degrees magnetic?

13 replies: All unread, jump to last
 
User currently offlineweb500sjc From United States of America, joined Sep 2009, 726 posts, RR: 0
Reply 1, posted (1 year 5 months 3 weeks 4 days 3 hours ago) and read 3310 times:

Ill take a stab...

the maps pilots plan their flights on are sectioned off by true cardinal directions (north, south, east, west), and since this is done it is easier for pilots to take their plotters and find the true course, and is therefore easier to use wind measured in degrees based off of true north.

Magnetic heading is used because for most of the history of flying, the quickest and most reliable way of finding ones heading was a magnetic compass.

Just to clarify Course is the direction one goes over the ground, and Heading is the way one points in the air or water.



Boiler Up!
User currently onlineMir From United States of America, joined Jan 2004, 21490 posts, RR: 56
Reply 2, posted (1 year 5 months 3 weeks 4 days 3 hours ago) and read 3283 times:

Quoting web500sjc (Reply 1):
the maps pilots plan their flights on are sectioned off by true cardinal directions (north, south, east, west), and since this is done it is easier for pilots to take their plotters and find the true course, and is therefore easier to use wind measured in degrees based off of true north.

It's not really easier, actually. Not harder either, just a different process. With the way things are now, you have to take your true course, apply the wind correction, then convert to magnetic. If the winds were in magnetic, you'd just covert your true course to magnetic first before applying the wind correction. Same result, just different order. Why they decided to do it that way I don't know, though it does make it easier to look at a map of the country and see which way the winds are really blowing in relation to the ground - in some areas the magnetic variation can lead to the numbers being 15-20 degrees off of the true values.

It should be noted, though, that this is only for winds aloft - METARs still report winds in magnetic values.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 3, posted (1 year 5 months 3 weeks 4 days 3 hours ago) and read 3282 times:

Thanks for the reply web500sjc
I see the logic in what you're saying, though the maps that i plan from have variation lines running through them so therefore enables you to see magnetic heading from them, so i can't see the advantage of having wind in degrees true?


User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 4, posted (1 year 5 months 3 weeks 4 days 3 hours ago) and read 3277 times:

Ya i see just a different order thanks Mir   

User currently offlineweb500sjc From United States of America, joined Sep 2009, 726 posts, RR: 0
Reply 5, posted (1 year 5 months 3 weeks 4 days 1 hour ago) and read 3231 times:

Quoting Novice (Reply 3):
I see the logic in what you're saying, though the maps that i plan from have variation lines running through them so therefore enables you to see magnetic heading from them, so i can't see the advantage of having wind in degrees true?

the variation lines do not point north, they just place a line upon which the difference between true north and magnetic north is known, and ascribe the known difference at that line.


Another point I had not brought forward, the magnetic north pole moves in relation to the true north pole, and so the maps would periodically change orientation so that magnetic north would still be at the top.



Boiler Up!
User currently onlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 6, posted (1 year 5 months 3 weeks 4 days 1 hour ago) and read 3230 times:

Quoting Mir (Reply 2):
It should be noted, though, that this is only for winds aloft - METARs still report winds in magnetic values.

The way an instructor explained it to me is that (in the US), the rule of thumb is that "printed" products measure in true, while "voice" stuff measures in magnetic. The METAR is related to the ATIS, thus "voice".

So the winds aloft forecast is in degrees true, while the wind check from the tower is magnetic.

Another way to look at it is that it makes sense to have METAR/ATIS in magnetic since runway headings are magnetic. You use this number when close to the airport only. However for route planning true is more practical since maps use true directions, and as Mir says variation can be quite large.

If everyone still navigated by compass, having magnetic wind directions in the forecast would make sense. But most people don't anymore except as a last resort.


By the way with GPS becoming the preferred method even in general aviation, will we someday see runways with true headings?

[Edited 2013-01-28 17:04:33]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 7, posted (1 year 5 months 3 weeks 3 days 23 hours ago) and read 3187 times:

Quoting Starlionblue (Reply 6):
If everyone still navigated by compass, having magnetic wind directions in the forecast would make sense. But most people don't anymore except as a last resort.

Though most GA traffic navigate using the DI and that uses magnetic heading


User currently offlineSAAFNAV From South Africa, joined Mar 2010, 260 posts, RR: 0
Reply 8, posted (1 year 5 months 3 weeks 3 days 21 hours ago) and read 3162 times:

It comes from back then when people still plotted.

All your plotting is done using a protractor on a plotting sheet. You align that with the longitude lines, which all point to True North.
Then, using a Nav Log, you work out everything, from left to right, True Track, Wind Vector, Drift, Magnetic Variation, Deviation, and then you get Magnetic Heading.

If you had to plot using Magnetic Headings, everytime you put your protractor down, you would first have to find out the variation at your position, add or subtract from 360, align to Magnetic North and then plot your position or whatever. Obviously, this could lead to a lot of confusion, so it's far easier to just make on addition or subtraction afterwards.

Magnetic Winds are spoken on ATIS Recordings and by ATC for runways, since you land on magnetic. A wrong calculation in the critical phase could lead to unexpected crosswind components.

Erich



On-board Direction Consultant
User currently onlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 9, posted (1 year 5 months 3 weeks 3 days 16 hours ago) and read 3081 times:

Quoting Novice (Reply 7):
Quoting Starlionblue (Reply 6):
If everyone still navigated by compass, having magnetic wind directions in the forecast would make sense. But most people don't anymore except as a last resort.

Though most GA traffic navigate using the DI and that uses magnetic heading

I can only speak from my own experience, but if I needed to go anywhere beyond 10 minutes I flew with the GPS with pilotage as backup, DI as backup to that and whiskey compass as final backup. The DI was mostly useful for keeping track of things over a short distance (like holding a heading during a LOC approach). If (when) I turned the autopilot on I set it to follow the GPS.

In the G1000 planes I used the GPS 99.9% of the time, except when I had to do VOR/ILS/LOC approaches.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineglen From Switzerland, joined Jun 2005, 221 posts, RR: 2
Reply 10, posted (1 year 5 months 3 weeks 3 days 15 hours ago) and read 3063 times:

Quoting Mir (Reply 2):
It should be noted, though, that this is only for winds aloft - METARs still report winds in magnetic values.
Quoting Starlionblue (Reply 6):
The METAR is related to the ATIS, thus "voice".

That's not quite correct. Printed METAR (e.g. at the met office) are also in true values. Only ATC towers, ATIS and airport advisory service (real time reprts to flight crew) report wind as magnetic. See also this documentation (the only "official" publication I found in short time):
www.uscg.mil/auxiliary/missions/auxair/metar_taf.pdf



"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
User currently onlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 11, posted (1 year 5 months 3 weeks 3 days 15 hours ago) and read 3054 times:

Quoting glen (Reply 10):
That's not quite correct. Printed METAR (e.g. at the met office) are also in true values. Only ATC towers, ATIS and airport advisory service (real time reprts to flight crew) report wind as magnetic. See also this documentation (the only "official" publication I found in short time):
www.uscg.mil/auxiliary/missions/auxa...f.pdf

So there is a difference between ATIS and METAR values. Very interesting! Thx for info.

Also strengthens the "printed" vs "voice" rule.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSAAFNAV From South Africa, joined Mar 2010, 260 posts, RR: 0
Reply 12, posted (1 year 5 months 3 weeks 3 days 12 hours ago) and read 3013 times:

Quoting glen (Reply 10):

That's not quite correct. Printed METAR (e.g. at the met office) are also in true values. Only ATC towers, ATIS and airport advisory service (real time reprts to flight crew) report wind as magnetic. See also this documentation (the only "official" publication I found in short time):
www.uscg.mil/auxiliary/missions/auxair/metar_taf.pdf

True, forgot to point that out.



On-board Direction Consultant
User currently offlinepeterpuck From Canada, joined Jun 2004, 323 posts, RR: 3
Reply 13, posted (1 year 5 months 3 weeks 1 day 12 hours ago) and read 2737 times:

Simple way to remember it is "If you read it it's true"

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