Why The Hell... (random rant)

In rec.aviation.piloting Mxsmanic wrote:
writes:

You are talking about a gyro compass.

No, I'm not.

Yes, you are.

A gyro compass is huge, expensive and heavy.

But there is none inside an inertial reference platform. An IRS uses laser
gyros.

They are still big, heavy, and expensive.

They can take hours to settle on a usable reading.

An IRS can find true north in a few minutes, depending on latitude.

An INS system can NOT find true north and requries an external input
to tell it where north is.

You are clueless.

An INS system has to be initialized with it's current position and just
tells you where you have moved relative to the starting position.

But it also finds true north on its own, without any need for external data.
It simply detects the rotation of the Earth, and that gives it an east-west
reference, to which true north is perpendicular.

No, INS can not find true north, only a gyro compass can find true
north.

A gyrocompass doesn't work at airplane speeds.

You have no idea what you are talking about.

Google for it. You'll be surprised.

Lets sum up reality versus your babbling ignorance:

Only a gyrocompass can find true north.

A gyrocompass won't work at all at airplane speeds and is problematic
at fast, modern ship speeds.

Because a gyrocompass uses the precession caused by the Earth's rotation
to find north and the Earth rotates so slowly, it can take several
hours for a gyrocompass to settle when first turned on.

An INS is a collection of gyros and accelerometers that sense movement.

An INS does not contain a gyrocompass.

An INS requires an external input to tell it where north is.

An INS has to be initialized to tell it it's current position.

Once an INS is initialized, it can tell you how far you have moved.

An INS has to be periodically updated with it's true position because
the gyros, including laser gyros, drift.

No GA aircraft and few transport aircraft have INS installed.

For how gyrocompasses work:

http://en.wikipedia.org/wiki/Gyrocompass

http://www.navis.gr/navaids/gyro.htm

http://tpub.com/content/administrati...s/14221_74.htm

For how INS works:

http://en.wikipedia.org/wiki/Inertial_guidance_system

--
Jim Pennino

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In rec.aviation.piloting wrote:
On Apr 5, 4:35 pm, wrote:
In rec.aviation.piloting DR wrote:

Mxsmanic wrote:

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.

LOL! My BS meter just went off scale! Declination? Lines of magnetic
_variation_ are plotted on VP charts and better than 0.5 degree accuracy
(except at local anomalies which are only noted in nautical charts as
far as I've seen so far). Declination in navigation is actually
something else but I'll let you googgle for it.

I can't think of any local anomaly that is both strong enough and large
enough to be anything other than a transitory "burble" at most to the
compass of an airplane in flight.


Yes, I agree, that is true of most but some are very big, the biggest
is in Kursk, Russia. If your autopilot is flying a magnetic heading
how fast would it respond if it flew over a common 6 degree anomaly?

It wouldn't; autopilots are linked to the heading indicator which
wouldn't care.

--
Jim Pennino

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In rec.aviation.piloting Mxsmanic wrote:
writes:

I can't think of any local anomaly that is both strong enough and large
enough to be anything other than a transitory "burble" at most to the
compass of an airplane in flight.

Try flying just outside Reno.

I have, have you?

Did I miss something?

--
Jim Pennino

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In rec.aviation.piloting Mxsmanic wrote:
Jose writes:

"It must be true - I found it on the internet"

I think you'll find that the more you research about the geomagnetic field,
the less reliable you find it to be for navigation.

I think you'll find that if you ever get an education, the less likely
you will be to babble nonsense like that.

--
Jim Pennino

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Kev wrote:
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


This seems too much to match the ICAO specified system accuracy
of +/- 5.2 degrees. The system accuracy includes transmitter
and receiver errors and the operative margin.

The VORs here are adjusted for an error of less than 1 degree
at the station, and a flight test is not passed if the error
exceeds 3 degrees (except on special terrain cases, which have
to be announced by NOTAMs).

--

Tauno Voipio
tauno voipio (at) iki fi

"Mxsmanic" wrote in message
...
writes:


INS is too big and expensive for GA aircraft.

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


Just how big is your desk????



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.


Then how can you be bothered by playing a sim????

"Mxsmanic" wrote in message
...
Ron Natalie writes:

This is makes you look pathetically
stupid and is the main reason that most people on this forum
are hostile to you.

I think that's a bit backwards. People who are stupid are likely to be
hostile.


Odd..you are clearly the poster child for stupidity, but you don't see
hostile.

"Mxsmanic" wrote in message
...
Jose writes:

"It must be true - I found it on the internet"

I think you'll find that the more you research about the geomagnetic
field,
the less reliable you find it to be for navigation.


That's OK, you can relax anyway. No matter how many hours you sim, you will
still find your desk in your bedroom.

wrote:
An INS does not contain a gyrocompass.

I thought I read somewhere that certain INS do have a gyrocompass, for
setting the initial positional reference.

The compass (compii??? :P ) in question was erected much faster than a
ship-borne model by being held at magnetic north by a mag compass while
it spun up (so the calibration time was only that to correct for local
variation, and not to find the entire harmonic of the Earth).

In any case, it was useless when actually flying, and the system only
used the accelerometers thereafter.

TheSmokingGnu

wrote:


Astro navigation, but it's still an angle away from a standard
vector. So different sciences are using the same word with different
meanings.

However, you're of course correct that for magnetic navigation,
declination and variation are the same thing.

http://www.ngdc.noaa.gov/seg/geomag/faqgeom.shtml

Kev


Thanks to you, farr1220, and Peter. I always wondered in the back of my
mind how the term declination came to mean variation. Now I'm ready to
navigate the outer space :-)