Date: Tue, 29 Feb 2000 22:36:29 -0600
Reply-To: John Rodgers <inua@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@HIWAAY.NET>
Subject: Re: Precision Navigation compass
Content-Type: text/plain; charset=us-ascii
Aeronautical maps are oriented to True North, with degrees of Magnetic Variation
printed on the chart as either easterly or westerly.. This allows the navigator
to make compass/navigation corrections. Alabama is pretty close to the "Zero"
or"0" degrees magnetic variation line, whereas Alaska ----if memory serves.. is
something on the order of 15 degrees west.
Pilots navigate by flying a course related to true notrh, and a compass heading
which is adjusted for magnetic variation in the earth and magnetic deviation
(compass displacement due to ferrous metals and induced electrical fields with
in the airplane.).
If a pilot flies a true course and a true heading of 360 degrees, with a 15
degree westerly variation and a 5 degree easterly deviation , he must first turn
his airplane so the compass reads 15 degrees west of true north or 345 degrees,
then add back 5 degrees of easterly deviation, at which time his compass heading
will read 350 degrees. That will keep him on a true course of 360 degrees. Now
if you want to add in the angular vector of the wind......and the airspeed of
the airplane and the calculated ground speed of the airplane..........!!!!!!
Well that's another story.
I think most other navigational maps are oriented to true north as well. If I
recall correctly the true north pole points at the North Star. I can't remember
if the earths axis is around True north or around the magnetic North. I do
remember they are not in the same place. As a matter of fact the magnetic pole
moves a bit each year tracing the perimeter of a circle at the top of the world.
John Rodgers
"88GL Driver
Greg wrote:
> Do you Know if maps use magnetic North or true North?
>
> ----- Original Message -----
> From: Mark McCulley <transporter99@HOTMAIL.COM>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Tuesday, February 29, 2000 1:39 PM
> Subject: Re: Precision Navigation compass
>
> > Not sure exactly what you mean by "adjust compass deviation". You first
> > calibrate the compass by putting it in CAL mode and driving in two
> complete
> > circles. You can then set the declination according to your location and
> > display true north (as opposed to magnetic north). I don't know any
> accuracy
> > specs but I'm sure this instrument works better than your typical auto
> > compass. The compass can detect when it's off (because of an adjacent
> metal
> > semi, bridge superstructure, etc.) and displays the word "Distortion". The
> > display shows degrees as well as direction (N, ENE, NE, etc.). The
> altimeter
> > shows only elevation, not barometric pressure. For accuracy you must
> > calibrate it at a known elevation (like all altimeters except GPS).
> >
> > MM
> >
> >
> > >From: David Beierl <dbeierl@IBM.NET>
> > >Looks pretty cool -- how do you adjust the compass deviation and how
> close
> > >can you get it (to my mind, +/- 15 degrees is not too bad for an
> automotive
> > >compass, but +/- 5 would be really nice)? How sensitive is the
> > >altimeter? How do you set it? Will it show barometric pressure as well?
> > >
> > >david
> > >David Beierl - Providence, RI
> > > http://pws.prserv.net/synergy/Vanagon/
> > >'84 Westy "Dutiful Passage"
> > >'85 GL "Poor Relation"
> >
> > ______________________________________________________
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> >
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