[BillO]

Given the information here: https://wiki.tfes.org/Circumnavigation

And given these handsome representations here:
https://wiki.tfes.org/File:Map.png

And here:
https://wiki.tfes.org/File:Altmap.png

How is one of these gyroscopic heading indicators supposed to work? https://en.wikipedia.org/wiki/Heading_indicator

For example, if you traveled from east to west on line of latitude on either of those maps, the gyroscopic HI would indicate a continual change of direction, yet your magnetic compass would not.  This creates a paradox from contradiction.  As far as I can see the only ways to resolve this paradox are:

• Gyroscopes do not work
• Magnetic compasses do not work
• The earth s not flat

Which of these resolutions is most accurate?  Are there other ways to resolve the paradox?

Some resources to help with the discussion:
https://en.wikipedia.org/wiki/Gyroscope
https://en.wikipedia.org/wiki/Compass
https://wiki.tfes.org/The_Flat_Earth_Wiki

[BillO]

So, at this point 39 people have viewed this, and not one has any problem with the fact that Gyroscopic HI/DI will not work on the flat earth, yet in reality they work just fine?

I have heard Dave Murphy drone on endlessly about how he, quite mistakenly as a matter of fact, believes that a gyroscopic AI should not work on a spherical earth and proudly presents that as a definitive proof that the earth is not spherical.

Well, here is my attempt to resolve this paradox.  We all know gyroscopes and magnetic compasses work.  They have for hundreds of years in the case of gyroscopes and thousands of years in the case of magnetic compasses.  They have also worked in agreement, within the error of the magnet poles WRT the axial poles, in aircraft for decades and continue to do so.

The only sound and sensible conclusion one can come to is, the earth is not flat.

This document details how aircraft instrumentation works.  The discussion on gyroscopes starts on page 52.  Attitude Indicators (AI) begins on page 56.  Heading Indicators/Direction Indicators (HI/DI) are mentioned on page 58.

[edby]

So, at this point 39 people have viewed this, and not one is has any problem with the fact that Gyroscopic HI will not work on the flat earth, yet in reality they work just fine?

I have heard Dave Murphy drone on endlessly about how he, quite mistakenly as a matter of fact, believes that a gyroscopic AI should not work on a spherical earth and proudly presents that as a definitive proof that the earth is not spherical.

Well, here is my attempt to resolve this paradox.  We all know gyroscopes and magnetic compasses work.  They have for hundreds of years in the case of gyroscopes and thousands of years in the case of magnetic compasses.  They have also worked in agreement, within the error of the magnet poles WRT the axial poles, in aircraft for decades and continue to do so.

The only sound and sensible conclusion one can come to is, the earth is not flat.

This document details how aircraft instrumentation works.  The discussion on gyroscopes starts on page 52.  Attitude Indicators (AI) begins on page 56.  Heading Indicators/Direction Indicators (HI/DI) are mentioned on page 58.

A query on this from me, being a dumbo at mechanics generally. I understand (from playing with one age 10) that they maintain an absolutely constant orientation, so that e.g. if the gyroscope is pointing North, and I turn round 180 deg, it still points north (but changes its orientation to me by 180 deg).

Now if I travel full circle around a flat earth, I would expect to see the gyroscope rotate 360 deg relative to me, although it's really maintaining a constant orientation.

But why should it be any different on a globe earth? If I follow around on the same line of lat, that is.

On GE I would expect to see a change in tilt, though, given the earth is 'leaning'. Is that right?

[BillO]

I'm not sure I understand your question.  The gyroscopes in a HI/DI is oriented horizontally with their axis initially along the direction of flight and they have the same correcting mechanism that an AI has, so as you go around the earth they maintain that orientation.  However, the are free to rotate around the vertical axis (direction of gravity), and this is what gives the direction indication.

The lean of the earth should not bother it.

The key here is that on a flat earth it will be forced to show a continual change of direction even if flying 'straight' according to the compass.  Even around the equator.

[edby]

The key here is that on a flat earth it will be forced to show a continual change of direction even if flying 'straight' according to the compass.  Even around the equator.

Still not getting it, although I understand about the 'tilt' now. Assume the AE flat earth map, and assume the plane is flying along a line of lat. Then according to both GE and FE, the compass will (approximately) not change direction, because magnetic north in FE is in the same place as GE. And according to both, the gyro will indicate a change in direction, because both are travelling around the geographic North Pole.

Perhaps I am being stupid.

[BillO]

I think I get what you're getting at.

Planes fly great circles, well on the GE they fly real great circles, but on the FE map, the great circles are the circles of latitude.  So on the FE, as you fly one of the great circles (around a latitude), the compass will not change, but the HI will, and not in any useful way.  Also, if you fly to keep your heading according to the heading indicator, the compass indication will change.  The only possible way to keep them in agreement is to fly directly south or north.

On the GE keeping the HI on the set heading means you will navigate a great circle.  Your compass heading won't change either (unless, of course, you fly directly over one or both of the magnetic poles)

In other words this:

Q. What about other types of navigational instruments?

A. Using a compass, gyrocompass, or looking at Polaris as a reference for Eastwards or Westwards travel will take the navigator in a broad circle around the North Pole.

Is just plain wrong.

[edby]

Planes fly great circles

Ah now I understand. Correct, the direction cannot change.

This is an argument against the bipolar map too, and any map which has curved lines of longitude. A plane flying due south along a line of longitude would maintain absolutely constant direction, whereas on the bipolar map, it would have to show a change of course.

[TomInAustin]

If I recall correctly, it has been years, the gyro compass has to be reset to the heading from the magnetic compass quite often in flight due to the rotation of the earth, something like every 15 minutes.  The more expensive ones have other sensors that compensate but the standard ones that have been in use for many decades need constant attention.  The reason for the gyro heading indicator is that the magnetic compass is only reliable during straight and level flight.

[BillO]

If I recall correctly, it has been years, the gyro compass has to be reset to the heading from the magnetic compass quite often in flight due to the rotation of the earth, something like every 15 minutes.  The more expensive ones have other sensors that compensate but the standard ones that have been in use for many decades need constant attention.  The reason for the gyro heading indicator is that the magnetic compass is only reliable during straight and level flight.

Yes.  It's due however to the fact that true north and magnetic north are not aligned.

[TomInAustin]

If I recall correctly, it has been years, the gyro compass has to be reset to the heading from the magnetic compass quite often in flight due to the rotation of the earth, something like every 15 minutes.  The more expensive ones have other sensors that compensate but the standard ones that have been in use for many decades need constant attention.  The reason for the gyro heading indicator is that the magnetic compass is only reliable during straight and level flight.

Yes.  It's due however to the fact that true north and magnetic north are not aligned.

That makes sense.  The last time i took flight instruction was in the 70's

[Tom Bishop]

What would be the gyroscope difference between traveling Eastwards in a circle 100 feet from the North Pole on a Flat Earth and a Round Earth?

[ICanScienceThat]

What would be the gyroscope difference between traveling Eastwards in a circle 100 feet from the North Pole on a Flat Earth and a Round Earth?

Tom, I think it would be a valuable exercise for you to do that calculation yourself. Try it 100 feet from the North Pole, and then try it again at the equator. Tell us what the differences are. We'll all learn something extremely valuable that way.

[BigGuyWhoKills]

What would be the gyroscope difference between traveling Eastwards in a circle 100 feet from the North Pole on a Flat Earth and a Round Earth?

Very little.  But I see the point you are trying to make.

Here's the rub: on a FE, as you travel due east, the gyroscope will appear to rotate/yaw clockwise, with no change in pitch.  On a RE, the same thing happens in the northern hemisphere, but with an amount of pitch varying based on your latitude.  But in the southern hemisphere, the gyroscope would appear to rotate/yaw counter-clockwise with similar pitch based on your latitude.  And at the equator, the gyroscope would only pitch.

[BillO]

What would be the gyroscope difference between traveling Eastwards in a circle 100 feet from the North Pole on a Flat Earth and a Round Earth?

As yes, the Just So Scenario^tm.

I believe this has already been answered.  However, you would be banking rather steeply and your HI would not be of interest let alone any use.  If we can keep discussions like this in scope of the items intended use, it would be helpful and more enlightening.

I think a more appropriate question would something like:  If it is a flat earth, what use is the HI and why is it a mandatory instrument for IFR flight?

[BigGuyWhoKills]

I think a more appropriate question would something like:  If it is a flat earth, what use is the HI and why is it a mandatory instrument for IFR flight?

It is mandatory for low visibility reasons that have nothing to do with the Earth being flat or round.  There are no shortage of stories where pilots "felt" like they were flying straight and level through clouds at night, but upon checking the AI, saw that they were nose down 15 degrees or more.

I like the line of reasoning where we compare the compass to a gyro in the northern and southern hemispheres, and at the equator.  Eastward flight would produce drastically different deviations in those 3 locations.  The most damning to FET being pitch.

[BillO]

That works too.

The point of my 'question' was, it would be utterly useless on a flat earth so would not even have been invented, let alone mandatory.