Why The Hell... (random rant)

On 04/04/07 10:40, EridanMan wrote:
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.

It's true that all the airplanes in which I've flown have had
compass cards, but that's not what they do. They provide the
deviation for the compass at various headings, which are due to
magnetic fields within the aircraft.


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





--
Mark Hansen, PP-ASEL, Instrument Airplane, USUA Ultralight Pilot
Cal Aggie Flying Farmers
Sacramento, CA

wrote in message
oups.com...

Anyone out there who (honestly) uses only his mag compass as his
primary navigation equipment, let's hear from you. And using the
whiskey compass to set the DG doesn't count - we're talking navigation
by charted heading and mag compass. Tried rolling out on and holding
an accurate heading using only your whiskey compass lately? Fun,
isn't it...That's why they invented the DG.


I use my magnetic compass as my primary navigation equipment. But only
because it's my only navigation equipment.

"Mxsmanic" wrote in message
...
Peter Dohm writes:

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.

It's already so inaccurate without interference that that's bad enough.
There
are plenty of spots on charts where the compass will be 6-8 degrees off
even
from the already irrgular declination over larger areas.

Anyway, if you push this concept to its limit, you should be able to
complete
a trip without an engine, since engines are not 100% reliable. Obviously,
that's not a practical reality, and at some point you have to recognize
that a
compass alone, no matter how reliable in the sense of always working to
some
extent, may simply not be enough to get you home.


What did you have for dinner last night, Welsh Rarebit????

Maxwell writes:

What did you have for dinner last night, Welsh Rarebit????

My point is that you have to strike a balance between assuming all equipment
will work perfectly and depending on that, and assuming that all equipment
will fail and trying to plan for that. In reality, chances are that all
equipment will work; and the chances of equipment failing diminish rapidly as
the number of simultaneous failures increases.

It's true that a compass always works--more or less, since compasses are so
finicky even when they are "working"--but I'm not sure that this is really
much of a practical help if nothing else works. All a compass can do is tell
you your direction of flight in a very approximate way. That isn't much use
for getting where you want to go. Charts help a lot, but you need more than a
compass to find out where you are on the chart, and if you don't know where
you are on a chart, a compass won't help.

Early ships navigated using a compass as one important instrument, but a
compass along was never good enough. It wasn't enough four hundred years ago,
and it's not enough now. If all you have is a compass, you're in deep
trouble.

You're actually better off with an accurate watch and a way to shoot the
stars. But even that is more of a theoretical method than a practical method
these days.

When people talk about how this old method or that old method is reliable,
they tend to forget how many people died in the days when these "reliable"
methods were the only ones available.

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

"Don Tuite" wrote in message
...

Under the heading of "Enquiring Minds Want to Know:

In defining an intersection, what's the maximum distance from a VOR
that's allowed?


I guess the simple answer is 135 miles.

The limiting factor is the minimum divergence angle. The minimum divergence
angle (smaller angle of the two crossing radials) is one degree per NM up to
45 miles, beyond 45 miles it's 1/2 degree per NM. Since the mimimum
divergence can't exceed 90 degrees, the furthest you can get is 135 miles.



Does an intersection in a GPS database represent the actual
intersection of VOR radials, or is it defined in LAT/LON terms?
(I.e., can there be two locations for an intersection, depending on
whether you're using VORs or GPS?


There can be many locations for a given fix. For example, a fix identified
by intersecting radials as well as radial/DME from either navaid. The exact
position varies with altitude and which navaid you choose to determinr
position.

In rec.aviation.piloting Mxsmanic wrote:
writes:

Where do you get a true north compass?

Aviation uses magnetic compasses less and less, and every other navigation
method works best with true north.

Total, utter, nonsense.

The use of magnetic north versus true north hasn't changed.

A sensor to find true north in an airplane in flight doesn't exist.

Your comment about magnetic south being unusable is just asinine.

Magnetic south isn't exactly the opposite of magnetic north on the Earth's
surface, so if one entity uses it, all must use it, or make constant
corrections to convert between the two. In fact, the failure of the line
between the poles to pass through the center of the planet introduces
additional complications into precise use of a compass. Not to mention the
many other factors that get in the way.

More babbling nonsense.

The isogonic lines on a chart take care of all the problems of where
the actual north/south magnetic poles are.

As for constant corrections, the time period for corrections is measured
in years.

Early navigators used it because they had nothing better. Today there are
lots of things that are better.

Wrong again, bucko, there is nothing better for finding north in an
airplane in flight.

The only way to find magnetic north is a magnetic compass.

The only ways to find true north are celestial navigation and a true
gyro compass.

You can't use celestial navigation unless you have a clear sky, an
almanac, a precise clock, and the necessary instruments to measure
celestial angles and the training to be able to use it all.

You can't use a true gyro compass because they can take hours to
settle to a usefull reading, are enormous and heavy, and don't
work unless you are moving very slowly, i.e. at the speed of a
ship. They do not work if moving at airplane speeds and they
don't work without power.

GPS could be used to indirectly find either type of north, but it
doesn't work without power, which is an important concideration
when flying a real airplane without a pause button.

Inertial navigation requires an initial set up against something
else, constant updating measured in minutes, and again, power.


--
Jim Pennino

Remove .spam.sux to reply.

In rec.aviation.piloting EridanMan wrote:
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.

Umm, no, the compass card corrects for installation error in the
compass reading.

Isogonic lines on charts gives you the local difference between
true and magnetic north.

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?

Any inacurracy in VOR radial alignment with magnetic north will
be more than swamped out by the ambiguity in the winds aloft
forcast.

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?

Exactly.

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



--
Jim Pennino

Remove .spam.sux to reply.

In rec.aviation.piloting Mxsmanic wrote:
Ron Natalie writes:

No you are confused. Magnetic SOUTH is the exact opposite of magentic
north you fool. The fact that the MAGNETIC SOUTH POLE is not exactly
opposite the MAGNETIC NORTH POLE is a different issue.

I assumed that others would understand this, but I often get into trouble when
I assume others will understand things.

The fact that
the poles aren't aligned with the arbitrary "true" datum just means that
the variation equations aren't as simple as they might be.

They are more than just misaligned: they are not at opposite points in terms
of longitude and latitude, either. A line drawn between them does not
intersect the center of the Earth.

And it doesn't matter.

Really, like what?

GPS and inertial reference platforms, VORs, NDBs, you name it.

Compasses are still damned reliable compared to
anything else. Cheap too. The only thing that presumes to do better
perhaps is GPS. And it's easier to program that to deal with the
magnetic measurements than to try to force everybody else the other
way.

So how often do you fly using just your magnetic compass alone?

For some people, quite often, and for some others, all the time.

You do understand there are real, flying, airplanes with no electrical
system, don't you?

--
Jim Pennino

Remove .spam.sux to reply.

and all of our
aircraft have compass cards in them anyways for coverting between
Magnetic and True headings.

That's not what a compass card is for. The compass card corrects for
errors due to installation (such as the local field of the airplane).
Aeronautical charts have the information needed to convert between
magnetic and true.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

On Apr 4, 2:08 pm, wrote:
Anyone out there who (honestly) uses only his mag compass as his
primary navigation equipment, let's hear from you. And using the
whiskey compass to set the DG doesn't count - we're talking navigation
by charted heading and mag compass. Tried rolling out on and holding
an accurate heading using only your whiskey compass lately? Fun,
isn't it...That's why they invented the DG.

Yes, but we're talking about using magnetic course as the main
navigation theme. Setting the DG from the whiskey is just a part of
that overall theme.

Bottom line, if the mag compass was demoted to emergency heading
reference, we could accept the mag var problem and use true heading
for day to day use. Heck, most whiskey compasses swing as much as the
local variation inflight, anyway!

The arguments presented in this thread for using True North are
actually starting to override my own sense of historical inertia.
Your comment above is icing on the cake. Very interesting
discussion. Especially since, as you pointed out, it's just a math
problem, not a radical change.

Kev