Why The Hell... (random rant)

Mxsmanic wrote:
writes:


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


GPS finds true north. And, just incidentally, you can find true north by
looking at the sky. ANS will do that, and people can do it, too.


Not all planes have GPSes. In fact, most don't. Many of the haldheld
units fail. The failure rate for compasses is quite low. The FAA is
not likely to revise its requorements for a compass any time soon.
Thus, the reliance on magnetic north.


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


Documenting them doesn't really eliminate them.


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


GPS is better, and more accurate, to name just one.

Not really. It is unreliable. Its signals can be disrupted - rendering
them useless. I don;t want my only source of reference taken away at
anyone's whim.



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


You can find true north by looking at the sky, or with GPS, or with ANS
(automated looking at the sky), or with an INS. The latter usually has to be
on the ground, although some systems support align-in-motion with a longer
setup time.


Not likely in most GA planes on most flights. Usually one is busy
flying and has no time for that stuff. Not possible on cloudy days.


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 need a precise clock to do just about any navigation. The need for the
rest is debatable, depending on how resourceful you are.


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.


Unless the airplane is a glider, you have power.

Bull****. Can you say piper cub (to name one counter example)
There is no need for electric power in a plane.



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


One third correct: it requires power, but engines provide power. It doesn't
have to be set up against anything else to find true north. It doesn't need
to be constantly updated; the whole idea is to be fairly autonomous.


Not in the real world. On a computer maybe...

compass is still the best, most reliable way to find north. (true or
magnetic)

On Apr 4, 5:57 pm, "flynrider via AviationKB.com" u32749@uwe wrote:
I was reading Lindbergh's book about his transatlantic flight and at one
point, both his whiskey compass and Earth Inductor Compass were just wobbling
around uselessly. Eventually, they both started working again on their own,
but he was guessing at his heading for nearly an hour.

I can relate. I have a video that I took on a cross country flight, of my
mag compass doing rapid 360s. It lasted about 5 min. and there were no
magnetic anomolies listed on the chart in that area. There were also no UFO
sightings reported that day :-))

There are lots of old iron mines around my area, and pilots sometimes
comment about their compasses going screwy for a minute or so
(assuming they noticed at all). The early settlers thought the woods
were haunted at first because of this effect... until they figured out
it meant money ;-)

Kev

Tim writes:

Not all planes have GPSes. In fact, most don't.

That depends on what category of aircraft you're looking at.

Many of the haldheld units fail.

How many? I've never seen one fail, although I'm sure it happens
occasionally. They don't even have any moving parts.

The failure rate for compasses is quite low.

So is their accuracy, even when they are functioning perfectly.

Not really. It is unreliable. Its signals can be disrupted - rendering
them useless.

Magnetic bearings are constantly disrupted, everywhere on Earth.

I don;t want my only source of reference taken away at
anyone's whim.

But a compass cannot give you the information that a GPS gives you. It can
hardly tell you anything at all.

Bull****. Can you say piper cub (to name one counter example)
There is no need for electric power in a plane.

You have an engine turning. That's power. And it can fail, just like
electrical power.

Not in the real world. On a computer maybe...

Even in the real world. The purpose of INS is to have a way of navigating
without any external references; it's a very advanced and accurate
implementation of dead reckoning.

compass is still the best, most reliable way to find north.

It's useless for truth north unless you have a chart _and_ you know where you
are. Even for magnetic north, it can be substantially off. And just knowing
which way is north doesn't help you much, anyway.

--
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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

I agree with the first part of your statement, that the whiskey compass is
well suited as the on board reference and cross check for other instruments.
That's actually the point I was trying to make, but I didn't carry the
logical argument far enough.

Hopefully, I will only ever have to use the whiskey compass alone as a
navigation aid for pilotage in VMC. If however, after I resume flying, I am
ever caught in IMC with only a whiskey compass; I hope that I can recall the
advice of one of the instructors here, possibly Mr. Campbell, on an earlier
thread--that the whiskey compass is least unstable when heading or turning
to the south when in the northern hemisphere.

Peter

Nomen Nescio writes:

The category that has wings and goes up in the sky.

You mean like a 747-400? It has two GPS receivers, three IRUs, two VORs and
two ADFs. One rarely falls back upon the magnetic compass.

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In rec.aviation.piloting Mxsmanic wrote:
writes:

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

And for still others, never.

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

Yes, but none that I'd want to fly, any more than I'd want to cross the
Pacific in a log raft.

Since you will never actually fly anything, no one cares what you
want.

--
Jim Pennino

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In rec.aviation.piloting Mxsmanic wrote:
writes:

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

GPS finds true north. And, just incidentally, you can find true north by
looking at the sky. ANS will do that, and people can do it, too.

Utter nonsense; you have no clue.

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

Documenting them doesn't really eliminate them.

It doesn't matter, you go by the chart.

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

GPS is better, and more accurate, to name just one.

Utter nonsense; you have no clue.

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

You can find true north by looking at the sky, or with GPS, or with ANS
(automated looking at the sky), or with an INS. The latter usually has to be
on the ground, although some systems support align-in-motion with a longer
setup time.

Utter nonsense; you have no clue.

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 need a precise clock to do just about any navigation. The need for the
rest is debatable, depending on how resourceful you are.

Utter nonsense; you have no clue.

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.

Unless the airplane is a glider, you have power.

Utter nonsense; you have no clue.

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

One third correct: it requires power, but engines provide power. It doesn't
have to be set up against anything else to find true north. It doesn't need
to be constantly updated; the whole idea is to be fairly autonomous.

Utter nonsense; you have no clue.


--
Jim Pennino

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In rec.aviation.piloting Mxsmanic wrote:
writes:

You got a true north compass in your airplane?

Both GPS and inertial navigation platforms can easily determine true north.
In fact, they work with true north, and must apply an unpredictable conversion
factor to true north to get current and local magnetic north.

No, they can't.

INS has to be initialized from something known and updated because
gyros in the real world precess.

GPS can tell you which direction you are going, but can not tell you
where the nose of the airplane is pointing.

INS is too big and expensive for GA aircraft.

Not all real airplanes have electrical systems.

--
Jim Pennino

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writes:

It doesn't matter, you go by the chart.

So you need a chart, which means that a compass alone isn't much use.

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writes:

INS has to be initialized from something known and updated because
gyros in the real world precess.

No, not for true north. An INS determines true north by sensing the rotation
of the Earth. It doesn't require any data input to do this.

GPS can tell you which direction you are going, but can not tell you
where the nose of the airplane is pointing.

If you are moving, it can tell you your ground track. If you have more than
one receiver on different parts of the aircraft, you can also determine which
way the nose is pointing.

INS is too big and expensive for GA aircraft.

That's one reason why I often like to fly big aircraft.

Not all real airplanes have electrical systems.

True, and some are powered by rubber bands as well, but there's a lower
threshold below which I don't bother.

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