Why The Hell... (random rant)

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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In rec.aviation.piloting Mxsmanic wrote:
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.

You are talking about a gyro compass.

A gyro compass is huge, expensive and heavy.

They can take hours to settle on a usable reading.

They don't work if they are moving much faster than a slow ship, and not
at all at aircraft speeds.

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.

Wrap some smarts around it with a built in map and it shows you where
you are.

Since real gyros in the real world precess, you have to update the
calculated position to the true position on a regular basis.

You have no idea what you are talking about.


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.

Theoretically you could do that, but no such thing is available for GA
aircraft.

INS is too big and expensive for GA aircraft.

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

You don't fly anything, ever.

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.

You don't fly anything. You sit on your ass and watch a computer monitor.

Lots of real airplanes don't have electrical systems.


--
Jim Pennino

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writes:

You are talking about a gyro compass.

No, I'm not.

A gyro compass is huge, expensive and heavy.

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

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 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.

You have no idea what you are talking about.

Google for it. You'll be surprised.

--
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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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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

In rec.aviation.piloting TheSmokingGnu wrote:
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.

Well, if you forced it to magnetic north on turn on, it would be
statistically faster than some random position, but still takes
a long time to settle; the Earth doesn't rotate that fast.

What a gyrocompass actually seeks is alignment of it's axis with the
axis of the Earth's rotation, so you would also have to throw in
a latitude initializer to do much good.

That's not saying no one ever tried to build such a thing, but the
laws of physics that make it work make it impractical for airplanes.

Plus, the initialization for INS has to set the position AND which
way is north.


--
Jim Pennino

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writes:

They are still big, heavy, and expensive.

Laser gyros are not big or heavy, although they are usually expensive.

I'll skip the rest of your post, as there are more anomalies than I care to
address.

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

They are still big, heavy, and expensive.

Laser gyros are not big or heavy, although they are usually expensive.

I'll skip the rest of your post, as there are more anomalies than I care
to
address.

Then why wonder about real flying dip****, it certainly does the same.

In rec.aviation.piloting Mxsmanic wrote:
writes:

They are still big, heavy, and expensive.

Laser gyros are not big or heavy, although they are usually expensive.

I'll skip the rest of your post, as there are more anomalies than I care to
address.

Or in other words, you don't know what the hell you are talking about
and don't want to learn what an ignorant fool you are.

--
Jim Pennino

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On Apr 4, 10:23 pm, Mxsmanic wrote:

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

You don't fly big aircraft. You don't flyany aircraft. The closest
you come is playing with an entry-level simulator game.

there's a lower
threshold below which I don't bother.

Lower threshold? Playing with MSFS is a first baby step into
aviation--there is nothing lower. And your upper threshold excludes
anything actually capable of flight.