Why are headings still magnetic?

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

"Grumman-581" writes:

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

Yes, but the ANS could recognize stars even from the taxiway in broad
daylight. I still don't know how it managed that.

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

Stubby writes:

A Blackbird would use less fuel if it didn't leak prior to take-off.

The leakage was trivial, and it rapidly warmed up enough to seal the
leaks.

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

Andrew Sarangan writes:

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

A combination of INS and GPS would work. It would be at least as
accurate as a compass.

This could be cross-checked against a magnetic heading internally as
long as the exact location of the geomagnetic poles are known.

An ANS could give you true heading even standing still.

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.

As soon as you move, GPS can give you a heading, and an INS can
maintain it for you.

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.

How you navigate with true headings is irrelevant here; the important
thing is that true headings never change.

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

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

Walt wrote
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.

Right! And at PanAm, we paid real big bucks for those 'low precession'
gyros. Actually they had an anti-precession controller into which one
would set the latitude as one progressed.

Bob Moore