Why The Hell... (random rant)

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


If the drift is sufficient ( 2 or 3 degrees, I forget the number; it's
in the AIM ) they are supposed to be recalibrated.

The uncertainty in the wind drift angle is usually a lot more than
that.

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.

The uncertainty in the wind correction angle is greater than the
total error in a VOR radial.

So you plan the flight given the winds aloft forcast, crank in a
wind correction angle, and come up with a heading.

The heading you wind up flying to keep the needle centered will
seldom be the heading on your planning sheet.

That's all I'm saying.

--
Jim Pennino

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Mxsmanic wrote:
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.



Tell that to Charlie Lindbergh.

Mxsmanic wrote:
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.



Tell that to Charlie Lindbergh.

In rec.aviation.piloting Mxsmanic wrote:
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.

If you want to go to and from true and magnetic, you need a chart to
get the local difference.

If you want to go somewhere in particular, you need a chart to find it.

If all you want to do is go in some particular direction until you
can see a recognizable landmark, all you need is a compass.


--
Jim Pennino

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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.

As an expert in Location based services and GPS, let me assure you
that depending solely on GPS for any form of navigation is a fools
errand that is going to get a lot of people killed one of these
days.

The system is a rube goldberg contraption with an instant-on kill
switch. Wait until someone launches a home-made GPS guided cruise
missile into Washington DC, watch them flick the switch, and see what
happens. Just hope it doesn't happen at night, and you're not in the
air at the time.

Documenting them doesn't really eliminate them.

It does make you aware of them, which is all you need.

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

It also requires constant, very expensive maintenance, a complex
receiver in good working order, and as I mentioned, can be turned off
at the push of a button. None of these are traits you want for you
primary navigation system.

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.

The simplest, fastest and most dependable (in VMC) way of finding true
north (or any form of navigation) is simple spatial awareness and
pilotage. A good chart, and a good eye.

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

Not at all... about the only modern navigation that requires a precise
clock is night over uninhabited terrain or over water.

Unless the airplane is a glider, you have power.

GPS have batteries, power isn't the issue. The problem (in my
experience) with GPS is that they're _SO_ good that people very
quickly delegate all of their navigational requirements to them,
letting their pilotage, dead reaconing, and other navigational skills
atrophy (in my humble experience at least). This is fine, until the
tremendously complex system finally fails (either intentionally or
otherwise). Either way, its not something I want to bet my life on.

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.

The whole idea of navigation is to know where you are in space at any
given time. Autonomy is irrelevant.

On Apr 4, 12:22 pm, "Steven P. McNicoll"
wrote:
"Kev" wrote in message

ups.com...
VORs are allowed to get +/- 6 degrees off. [..]
http://www.naco.faa.gov/index.asp?xml=naco/faq#q2h

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

Yeah, weird, eh? So I ran across this section of a site explaining
that it's often really a lot faster than that (2-25 years per degree).

http://www.geocities.com/magnetic_declination/#FACTORS

The "Local magnetic anomalies" section mentions the Ramapo area by me.

The "Where were/are/will be the magnetic poles? " talks about the
movement.

And the section about the "reversing Earth" theory is just plain
terrifying :-) (Not just reversal of the poles... but the entire
crust rotating upside down in a matter of days... ouch!!)

Kev

And the section about the "reversing Earth" theory is just plain
terrifying :-) (Not just reversal of the poles... but the entire
crust rotating upside down in a matter of days... ouch!!)

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

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

EridanMan wrote:



GPS have batteries, power isn't the issue. The problem (in my
experience) with GPS is that they're _SO_ good that people very
quickly delegate all of their navigational requirements to them,
letting their pilotage, dead reaconing, and other navigational skills
atrophy (in my humble experience at least). This is fine, until the
tremendously complex system finally fails (either intentionally or
otherwise). Either way, its not something I want to bet my life on.

The exact, word for word, arguments against VOR, NDB, four course
ranges, colored lights, etc. It goes on and on.

On Apr 4, 8:01 pm, Newps wrote:
EridanMan wrote:

GPS have batteries, power isn't the issue. The problem (in my
experience) with GPS is that they're _SO_ good that people very
quickly delegate all of their navigational requirements to them,
letting their pilotage, dead reaconing, and other navigational skills
atrophy (in my humble experience at least). This is fine, until the
tremendously complex system finally fails (either intentionally or
otherwise). Either way, its not something I want to bet my life on.

The exact, word for word, arguments against VOR, NDB, four course
ranges, colored lights, etc. It goes on and on.

I think I have to give you that point, set and match.

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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