Why are headings still magnetic?

Mxsmanic wrote:
The SR-71 navigated by finding stars in the sky
[...]
(although it could not see them through cloud cover).

I thought the SR-71 flew above all the clouds.

Roy Smith writes:

I thought the SR-71 flew above all the clouds.

It did, but the aircraft's ANS would take a preliminary fix even as it
taxied out to the runway, if the sky was clear.

--
Transpose mxsmanic and gmail to reach me by e-mail.

"Roy Smith" wrote in message
...
I thought the SR-71 flew above all the clouds.

And high enough that the sky was dark even when the sun was out -- at least
from the photos that I've seen published...

Mxsmanic wrote:
Like AM radio, magnetic headings are still with us, even though
navigation in general has advanced by leaps and bounds. When will
true headings be used? The magnetic poles are in continuous motion;
the rotational poles are stable.

Eventually, the magnetic poles will move so far that every station and
aircraft everywhere will have to be recalibrated to account for it,
and all charts will have to be changed. And the poles occasionally
reverse, which would also be somewhat of a disaster for
magnetically-based aviation.


So what instrument would you suggest we use for true headings? GPS does
not give you true heading; it can only give a true course. You can't
reliably use a GPS for verifying your runway heading. GPS headings only
work when you are in motion. Remember the Comair accident? I suspect
such accidents will increase if we switch to GPS based true headings.

Your suggestion will only work if we install gigantic beacons at the
true poles which everyone can navigate by. At present mother nature has
given us such a beacon, albeit a less than perfect one.

Andrew Sarangan wrote
So what instrument would you suggest we use for true headings?

Airliners have had 'true heading' available from their INS for
many years.

GPS does not give you true heading; it can only give a true course.

But isn't it 'true course' that I really want to fly? That line
that I drew on the chart? No more correcting for wind, variation
or deviation, just plot and fly true course. Someday it will happen.

Bob Moore

Bob,

But isn't it 'true course' that I really want to fly? That line
that I drew on the chart?


Actually, no, I'm flying the magnetic course line my GPS just drew on
its moving map display ;-)

--
Thomas Borchert (EDDH)

Thomas Borchert wrote
Actually, no, I'm flying the magnetic course line my GPS just drew on
its moving map display ;-)

Hmmmm....seems as if that really started out computed as 'true course'
to which the GPS added the local variation. :-)

Bob

Bob Moore wrote:
Andrew Sarangan wrote
So what instrument would you suggest we use for true headings?

Airliners have had 'true heading' available from their INS for
many years.

GPS does not give you true heading; it can only give a true course.

But isn't it 'true course' that I really want to fly? That line
that I drew on the chart? No more correcting for wind, variation
or deviation, just plot and fly true course. Someday it will happen.


Actually, I have never worried about accounting for wind correction,
variation or deviation. I plot the course on a computer, estimate a
heading and then during flight I fiddle with the heading until the
ground track agrees with the plotted course. It makes very little
difference whether the plotted course was in true or magnetic. If there
is an absolute reference for your system, either one should work the
same. With magnetic, we have the compass as the absolute reference.
With true direction, it is not that easy. I don't know enough about INS
systems or how they are used as an absolute reference, but those are
not within the reach of most GA pilots. So, I still don't agree that
navigation systems have advanced to the point where we can abandon the
magnetic based instruments.

Andrew Sarangan wrote
So, I still don't agree that navigation systems have
advanced to the point where we can abandon the
magnetic based instruments.

Hmmmm....I wonder how we used to navigate 'over-the-pole'
back before INS? Hint....Grid Navigation, an unslaved
DG referenced to true north.

Bob Moore

Bob Moore wrote:
Andrew Sarangan wrote
So, I still don't agree that navigation systems have
advanced to the point where we can abandon the
magnetic based instruments.

Hmmmm....I wonder how we used to navigate 'over-the-pole'
back before INS? Hint....Grid Navigation, an unslaved
DG referenced to true north.

Bob Moore

Way back when I was a navigator on a KC-135 using Grid Navigation we
referenced the DG to Grid North, not True North. Big difference between
the two, although I think I know what you're hinting at.

And, I remember taking a celestial shot every 15-30 minutes or so to
check for gyro precession. That would be hard to do in the Warrior I'm
flying nowadays. :)

--Walt Weaver
Bozeman, Montana