Why The Hell... (random rant)

On Apr 4, 2:32 am, Tauno Voipio wrote:
EridanMan wrote:
Why in gods name are VOR's Mag heading based?

It's a nuisance for maintenance, but it frees
the pilot from calculating the variation at
the operative time. Just to off-load the pilot.

A good answer. Same for winds in flight, etc. Everything is based on
the magnetic to make it easier for the pilot. At least, the pilot of
old. If we had 100% reliable aids in the plane, then I suppose you
could argue for just following the red line on the electronic map, and
never even know what course you're taking ;-)

I know, ideally, that means that you can sync your DG and your VOR
indicator to fly to a waypoint... except that most VOR's around here
have long since fallen behind Magnetic drift... so - now, not only do
you have to flightplan in True Heading, convert to Mag Heading to get
your vectors, THEN you have to get the corrective factor for each of
the VOR's your using for navigation and note that as well? huh?

If they are off the mag variation, it is
mis-maintenance, and the VOR should be
marked defective or taken off-line.

VORs are allowed to get +/- 6 degrees off. Seems a lot, but it's
only a handful of miles off-course over most VORs' ranges. Anyway,
see:

http://www.naco.faa.gov/index.asp?xml=naco/faq#q2h

Kev

Acturally, it's a fairly good question. The answer is tradition.
When the only real navaid one had was a mag compass, it made sense to
reference everything to mag north and accept the need for correcting
for variation. But there was an exception - when navigating in the
polar regions, mag headings are useless, so grid was invented - which
overlaid an arbitrary grid on the map and navigation was done by
setting the DG to the arbitrary grid "north". Works just fine. Now
with GPS and INS, the only reason for converting all headings to mag
is tradition. It really would make more sense to use true headings,
and save the variation drill for emergencies (which navigation purely
via whiskey compass is, usually!).

I personally trust my two independent GPS's as much as my mag
compass. If GPS goes down, or my electrics and batteries all fail,
then it really wouldn't be a huge problem to take up an initial
approximate heading on a mag compass, look up the local variation, and
apply it.

Would be simple to have DGs slaved to true north automatically, given
a GPS or Inertial platform. And if you are flying "retro", then you
could always do the math in reverse!

Maybe in the future...(yeah, along with FM hi-fi comm radios, too)

Kirk

"Tauno Voipio" wrote in message
...

It's a nuisance for maintenance, but it frees
the pilot from calculating the variation at
the operative time. Just to off-load the pilot.


That would be true if VORs were set to local magnetic variation. They
rarely are.



If they are off the mag variation, it is
mis-maintenance, and the VOR should be
marked defective or taken off-line.


That doesn't happen until they differ by 6 degrees with local variation.

"Kev" wrote in message
ups.com...

VORs are allowed to get +/- 6 degrees off. Seems a lot, but it's
only a handful of miles off-course over most VORs' ranges. Anyway,
see:

http://www.naco.faa.gov/index.asp?xml=naco/faq#q2h


"The magnetic variation of the earth changes at a rate of 50.27 seconds of
arc per year." That seems a bit low to me. At that rate six degrees of
change would take 430 years.

"Ron Natalie" wrote in message
m...

So that they line up with the compass. All in-flight
navigation is magnetic based.


But VOR radials rarely line up with the compass. Most haven't been adjusted
for changes in local magnetic variation in decades.

"Ron Natalie" wrote in message
m...

Huh? What does the wind have to do with VOR's. If the needle is
centered, you're within the tolerance of the VOR. The tolerance
is primarily 4-6 degrees. This keeps you inside the airway at
moderate distances from the VORs.


What about at more than moderate distances from the VOR? At 40 miles from
the VOR 6 degrees is 4 miles.

I personally trust my two independent GPS's as much as my mag
compass. If GPS goes down, or my electrics and batteries all fail,
then it really wouldn't be a huge problem to take up an initial
approximate heading on a mag compass, look up the local variation, and
apply it.

Would be simple to have DGs slaved to true north automatically, given
a GPS or Inertial platform. And if you are flying "retro", then you
could always do the math in reverse!

Maybe in the future...(yeah, along with FM hi-fi comm radios, too)

Kirk

Some of you guys are a *lot* more trusting than I am. I was really hoping
for some of the current airmen to say this, but most have only nibbled
around the edges--so here goes:

The magnetic compass has exactly one thing in its favor, and that is just
plain old Brute Reliability.

It requires no power from the aircraft's systems, it is not subject to
happenstance or whim concerning any transmitting stations, and wide spread
interference with (the) signal is unimaginable.

Learn to love it, because it is here to stay!

Peter

On Apr 4, 5:23 am, "Steven P. McNicoll"
wrote:
"EridanMan" wrote in message

oups.com...



Why in gods name are VOR's Mag heading based?

Tradition.

Best answer I've heard yet

What I'm not 100% convinced of is the necessity of keeping the VOR's
aligned with your compass. A compass is a perfectly valid
navigational tool with or without VOR alignment, and all of our
aircraft have compass cards in them anyways for coverting between
Magnetic and True headings.

Seems to me using the same conversion factor for Magnetic Heading to
VOR Radial as we do for Magnetic Heading to True is no more
complicated (and in fact less so) then worrying about particular
magnetic offsets for each station?

Either way its pretty much a moot point - because yes - we fly to keep
the needle centered, period. Again then - why go to the expense and
trouble of re-aligning all the VOR's and re-numbering the Victor
airways every few years? Just align everything true-north and don't
touch it again?

Note - this was a semi-inebriated, pedantic rant, I just thought it
might stimulate some good discussion

If you are following a VOR radial, you can ignore wind altogether
and just point the nose in whatever direction keeps the needle
centered.

Of course, this would work regardless of what the VOR was centered
on, why not just center it on true north and not worry about having to
update it (and all the Victor numbering) every few years?